Micronutrient Requirements of Children Ages 4 to 13 Years

Introduction

The period of childhood between ages 4 and 13 years is characterized by continued physical growth and rapid cognitive, emotional, and social development (1, 2). Many children, especially girls, undergo their pubertal growth spurt between ages 4 and 13. This period of childhood precedes adolescence — the transitional stage of development between childhood and adulthood. Due to increased growth and metabolism, the nutritional requirements of children are higher in proportion to body weight compared with adults (1, 3). Good nutrition throughout childhood is important not only to support normal growth and cognitive development but also to establish healthy eating patterns that are associated with decreased risk of chronic conditions and diseases in adulthood, including obesity, type 2 diabetes, cardiovascular disease, metabolic syndrome, and osteoporosis.

Inadequate intake of nutrients can impair growth and development in children. This article discusses micronutrient (vitamins and nutritionally essential minerals) requirements of children ages 4 to 13 years. The Food and Nutrition Board (FNB) of the Institute of Medicine establishes dietary reference intakes (DRIs) for each micronutrient; these reference values should be used to plan and assess dietary intakes in healthy people (4, 5). The DRIs include the estimated average requirement (EAR), the recommended dietary allowance (RDA), the adequate intake (AI), and the tolerable upper intake level (UL). The RDA, which is the average daily dietary intake level of a nutrient sufficient to meet the requirements of almost all (97.5%) healthy individuals in a specific life stage and gender group, should be used in the planning of diets for individuals (6). An AI recommendation is set when an RDA cannot be determined. In children, these intake recommendations are based on data regarding average micronutrient intakes of children and also on certain criteria for micronutrient adequacy. However, because of limited data, many of the micronutrient intake recommendations for children are extrapolated from recommendations for adults using a formula that accounts for metabolic body weight and growth (3). Metabolic body weight is determined by calculating the 0.75 power of body mass (body mass^0.75) (7). To account for growth, the equation used to derive an RDA or AI involves an age group-specific growth factor (3). The FNB establishes separate dietary intake recommendations for children between the ages of 4 to 8 years and those between the ages of 9 and 13 years (see Ages 4 to 8 Years and Ages 9 to 13 Years).

Micronutrient Needs of Children Ages 4 to 8 Years

For each micronutrient, the FNB sets an RDA or AI for children ages 4 to 8 years; these micronutrient intake recommendations do not differ with gender for this age group. Table 1 lists the RDA for each micronutrient. As mentioned above, the RDA should be used in the planning of diets for individuals. A few select micronutrient requirements for children are discussed below.

Micronutrient Needs of Children Ages 9 to 13 Years

For each micronutrient, the FNB sets an RDA or AI for children ages 9 to 13 years; these recommendations are gender specific to account for the unique nutritional needs of boys and girls as they undergo puberty. Table 2 lists the RDA for each micronutrient by gender. The RDA should be used in the planning of diets for individuals. A more detailed discussion of the requirements of certain micronutrients for children can be found below.

Vitamins

Vitamin A

Vitamin A is a fat-soluble vitamin that is essential for growth and development, normal vision, the expression of selected genes, and immunity (see the article on Vitamin A). Vitamin A deficiency is a major public health problem worldwide. It is the leading preventable cause of blindness among children in developing nations (8). The earliest evidence of vitamin A deficiency is impaired dark adaptation or night blindness. Mild vitamin A deficiency may result in Bitot’s spots, which are changes in the conjunctiva (the mucous membrane that lines the eyelids and the outer surface of the eye). Severe or prolonged vitamin A deficiency causes a condition called xerophthalmia (dry eye), characterized by changes in the cells of the cornea (clear covering of the eye) that ultimately result in corneal ulcers, scarring, and blindness (9, 10).

Vitamin A deficiency also places children at a heightened risk for infectious disease; in fact, vitamin A deficiency can be considered a nutritionally acquired immunodeficiency disorder (11). Even children who are only mildly deficient in vitamin A have a higher incidence of respiratory disease and diarrhea, as well as a higher rate of mortality from infectious disease, compared to children who consume sufficient vitamin A (12). Vitamin A supplementation in children has been found to decrease both the severity and incidence of deaths related to diarrhea and measles in developing countries, where vitamin A deficiency is common (13). The onset of infection reduces blood retinol (preformed vitamin A) levels very rapidly. This phenomenon is generally believed to be related to decreased synthesis of retinol binding protein (RBP) by the liver. In this manner, infection stimulates a vicious cycle, because inadequate vitamin A nutritional status is related to increased severity and likelihood of death from infectious disease (14).

The RDA for vitamin A is based on the amount needed to ensure adequate stores (four months) of vitamin A in the body to support normal reproductive function, immune function, vitamin A-dependent gene expression, and vision (15). Vitamin A intake recommendations for children were derived by extrapolating the recommendation for adults using metabolic body weight, accounting for growth. The RDA for children ages 4 to 8 years is 400 μg/day of Retinol Activity Equivalents (RAE), which is 1,333 international units (IU); the RDA for both boys and girls ages 9 to 13 years is 600 μg/day of RAE, which is equivalent to 2,000 IU. For information on vitamin A content in foods, see the article on Vitamin A.

Vitamin B₁₂

Vitamin B₁₂ is needed for two sorts of reactions in the human body. One is transmethylation (methyl transfer between two molecules) that leads to the synthesis of the amino acid methionine from homocysteine. Methionine, in turn, is required for the synthesis of S-adenosylmethionine, a methyl group donor used in many biological methylation reactions, such as the methylation of sites within DNA and RNA (16). The second sort of reaction is isomerization (rearrangement of a molecule). Vitamin B₁₂ acts as a coenzyme for methylmalonyl-CoA mutase to convert methylmalonyl-CoA to succinyl-CoA, an important step for the metabolism of proteins and lipids. Both transmethylation and isomerization reactions are essential for the metabolism of components of the myelin sheath of nerve cells and for the metabolism of neurotransmitters. Accordingly, vitamin B₁₂ deficiency damages the myelin sheath covering cranial, spinal, and peripheral nerves, resulting in neurological damage (17, 18). The myelin sheath is the insulating layer of tissue made up of lipids and proteins that surrounds nerve fibers. This sheath acts as a conduit in an electrical system, allowing rapid and efficient transmission of nerve impulses (19). In some cases, neurologic symptoms caused by vitamin B₁₂ deficiency can be reversed by vitamin treatment (18), but reversibility seems to be dependent upon the duration of the associated neurologic complications (20).

Although myelination primarily occurs during fetal development and early infancy, it continues through childhood, adolescence, and stages of early adulthood (21, 22). Because of the role of vitamin B₁₂ in myelination and other metabolic processes, it is important for children to meet dietary intake recommendations. The RDA of vitamin B₁₂ for children ages 4 to 8 years is 1.2 μg/day, and the RDA for boys and girls ages 9 to 13 years is 1.8 μg/day. This vitamin is naturally present only in animal products, such as meat, poultry, fish (including shellfish), and to a lesser extent in milk, but it is not generally present in plant products or yeast (9). Thus, children who have vegan diets need supplemental vitamin B₁₂ or need adequate intake from fortified foods.

Vitamin C

Vitamin C has a number of important roles during growth and development, including being required for the synthesis of collagen, carnitine, and neurotransmitters (23). Vitamin C is also a highly effective antioxidant and is important for immunity (see the article on Immunity). Further, vitamin C strongly enhances the absorption of non heme iron by reducing dietary ferric iron (Fe³⁺) to ferrous iron (Fe²⁺) and forming an absorbable, iron-ascorbic acid complex. Specifically, iron absorption is 2- to 3-fold higher with co-ingestion of 25 to 75 mg of vitamin C (24). This has special relevance to child health, considering the fact that iron deficiency is the most common nutrient deficiency in the world (see Iron below). Vitamin C intake recommendations for children are extrapolated from recommendations for adults based on relative body weight. The RDA for children ages 4 to 8 years is 25 mg/day, and the RDA for boys and girls ages 9 to 13 years is 45 mg/day (25). For information on food sources, see the article on Vitamin C.

Vitamin D

Vitamin D is a fat-soluble vitamin that is essential for maintaining normal calcium metabolism and is thus necessary for bone health. Severe vitamin D deficiency in infants and children results in the failure of bone to mineralize, leading to a condition known as rickets. Rapidly growing bones are most severely affected by rickets. The growth plates of bones continue to enlarge, but in the absence of adequate mineralization, weight-bearing limbs (arms and legs) become bowed. In severe cases of vitamin D deficiency, low serum calcium levels (hypocalcemia) may induce seizures. Although fortification of foods has led to complacency regarding vitamin D deficiency, nutritional rickets is still being reported in the United States and other nations (26-33).

In the US, fortified foods are a major contributor to dietary vitamin D intake, especially in children, because only a few foods naturally contain vitamin D (see the article on Vitamin D). In the US, milk is voluntarily fortified with 400 IU (10 μg) of vitamin D per quart (946 mL) (34), and other foods may be fortified with varying concentrations of vitamin D. According to a recent report regarding the American food supply, nearly all milk, about 75% of ready-to-eat breakfast cereals, around 50% of milk substitutes, about 25% of yogurts, and 8-14% of juices, cheeses, and spreads are fortified with vitamin D (35). Although not required by the US FDA to be listed on the Nutrition Facts food label, some packaged foods, particularly cereals, include the amount of vitamin D in one serving as the percentage of the Daily Value (DV). The DV is 400 IU, but the RDA for children ages 4 to 8 years and for boys and girls ages 9 to 13 years is 600 IU/day. In Canada, vitamin D fortification of milk and margarine is mandatory, with milk containing 35-45 IU per 100 mL (331-426 IU per quart) and margarine containing 530 IU per 100 grams (34), but vitamin D fortification of foods is less common in European nations (36). In addition to diet, vitamin D can be endogenously synthesized in the skin upon exposure to ultraviolet-B radiation from sunlight; however, sunscreens effectively block synthesis of vitamin D in skin (see the article on Vitamin D).

When setting the RDA for vitamin D, the FNB assumed minimal sun exposure, even though sun exposure could provide most people with their entire vitamin D requirement. For US children to meet the RDA of 600 IU/day (15 μg/day), about 6 cups of milk would need to be consumed each day. Analysis of data from the National Health and Nutrition Examination Survey (NHANES) 2005-2006 found that average total vitamin D intakes (from diet and supplements combined) in US children of ages 4 to 8 were 9.3 μg/day (372 IU/day) for boys and 7.9 μg/day (316 IU/day) for girls (37). Even though the analysis found that 43% of boys and 34% of girls in this age group took supplements containing vitamin D (37), their average total daily intakes were well below the current RDA of 600 IU/day (15 μg/day). Total daily vitamin D intakes were even lower for chilren aged 9 to 13 years (boys, 7.5 μg or 300 IU/day; girls, 7.7 μg or 308 IU/day). Sun exposure can substantially affect body vitamin D levels, and measuring 25-hydroxyvitamin D — the major circulating form of vitamin D — is a useful indicator of vitamin D status. It is assumed that a dietary intake of 600 IU/day results in a serum 25-hydroxyvitamin D level of 50 nmol/L (20 ng/mL), which the FNB considers as the cut-point for vitamin D adequacy (38). However, higher serum 25-hydroxyvitamin D serum levels may benefit health; thus, the Linus Pauling Institute recommends that children ages 4 to 13 years should have a daily intake of 600 to 1,000 IU (15 to 25 μg) of vitamin D, consistent with the recommendations of the Endocrine Society (39). Given the average vitamin D content of the diets of children, supplementation may be necessary to meet these recommendations. The American Academy of Pediatrics currently suggests that all children receive 400 IU of supplemental vitamin D daily (26) — an amount that is typically found in multivitamin supplements.

The tolerable upper intake level (UL) — the highest level of daily intake of a specific nutrient likely to pose no risk of adverse health effects in almost all individuals — for children ages 4 to 8 years is 3,000 IU/day (75 μg/day) of vitamin D; the UL for boys and girls ages 9 to 13 years is 4,000 IU (100 μg/day).

Vitamin E

The RDA for vitamin E in children, expressed as an amount of the α-tocopherol form of the vitamin, was based on extrapolations from intake recommendations for adults, accounting for differences in lean body mass and increased needs of growth during childhood. The RDA is 7 mg/day (10.5 IU/day) for children ages 4 to 8 years and 11 mg/day (16.5 IU/day) for boys and girls ages 9 to 13 years (40). A US national survey, NHANES 1999-2000, found that children ages 4 to 8 years had an average intake of 5.2 mg/day of α-tocopherol; this survey found that average α-tocopherol intakes for boys and girls ages 9 to 13 years were 6.0 mg/day and 5.3 mg/day, respectively (41). These intakes are below the current RDA. Surveys in The Republic of Korea and Germany have also reported low intakes of vitamin E in children (42, 43). However, true vitamin E deficiency is rare and has been observed only in cases of severe malnutrition, genetic defects affecting the α-tocopherol protein, and fat malabsorption syndromes; see the article on Vitamin E.

Minerals

Calcium

About 99% of calcium in the body is found in bones and teeth (44). Adequate intake of calcium throughout childhood and adolescence is important for proper mineralization of growing bones, attainment of peak bone mass, and reduction of risk for osteoporosis in adulthood (38). Thus, dietary intake recommendations for calcium in children are established based on the calcium intake needed to support bone accretion and overall calcium retention (i.e., the dietary intake needed to achieve positive calcium balance) (38). The RDA is 1,000 mg/day for children ages 4 to 8 years and 1,300 mg/day for boys and girls ages 9 to 13 years. Calcium intake recommendations are higher in children ages 9 to 13 to account for increased needs of the mineral during puberty (38).

Many American children have dietary calcium intakes below current recommendations, with girls having lower intakes than boys. A recent study reported daily calcium intake in children using data from NHANES 2003-2006, a US national survey (37). An estimated 17% of boys and 33% of girls between the ages of 4 and 8 have total calcium intakes (dietary plus supplemental intakes) of 800 mg/day or less. For children in this age group, average intake from supplements in those who took supplemental calcium (29% of boys; 26% of girls) was 99 mg/day and 87 mg/day for boys and girls, respectively. In children 9 to 13 years old, only 23% of boys and 15% of girls met the RDA for calcium, even though 20% of boys and 24% of girls took supplemental calcium (average supplemental calcium intake of 104 mg/day for boys and 80 mg/day for girls) (37). Dairy products, which provide about 72% of the calcium in the American diet (44), represent rich and absorbable sources of calcium. Milk contains 300 mg of calcium per cup; therefore, children ages 4 to 8 and children ages 9 to 13 could meet the RDA for calcium by drinking 3.3 or 4.3 cups of milk daily, respectively. Certain vegetables and grains also provide calcium, but their bioavailability is lower compared with dairy. For more information on dietary sources of calcium and calcium bioavailability, see the article on Calcium. If children do not meet the RDA through diet alone, LPI recommends supplemental calcium. Children’s multivitamin/mineral supplements generally provide no more than 150 mg of calcium.

The Nutrition Facts label of packaged foods lists calcium content in one serving as a percent of the Daily Value (DV), with the DV being 1,000 mg. Since the RDA for children ages 4 to 8 is 1,000 mg/day, the listed amount of calcium on the food label directly provides a percentage of the RDA. However, because the RDA for children ages 9 to 13 years is higher, the percentage of the DV listed would be an overestimation of the percentage of the RDA.

Fluoride

The mineral fluoride is important for the prevention of dental caries (tooth decay). Specific cariogenic (cavity-causing) bacteria found in dental plaque are capable of metabolizing certain carbohydrates (sugars) and converting them to organic acids that can dissolve tooth enamel. If unchecked, the bacteria may penetrate deeper layers of the tooth and progress into the soft pulp tissue at the center. Untreated caries can lead to severe pain, local infection, tooth loss or extraction, nutritional problems, and serious systemic infections in susceptible individuals (45). Increased fluoride exposure, most commonly through water fluoridation, has been found to decrease dental caries (46). Fluoride consumed in water appears to have a systemic effect in children before teeth erupt, as well as a topical (surface) effect in children and adults after teeth have erupted. The FNB set an adequate intake (AI) recommendation based on estimated intakes (0.5 mg/kg of body weight) that have been shown to reduce the occurrence of dental caries most effectively without causing the unwanted side effect of tooth enamel mottling, a white speckling or mottling of the permanent teeth known as dental fluorosis (47). The AI of fluoride for children ages 4 to 8 years is 1 mg/day, and the AI for boys and girls ages 9 to 13 years is 2 mg/day. For information about sources of fluoride, see the article on Fluoride.

Additionally, fluoridated toothpastes are very effective in preventing dental caries but add considerably to fluoride intake of children, especially young children who are more likely to swallow toothpaste. Researchers estimate that children under 6 years of age ingest an average of 0.3 mg of fluoride from toothpaste with each brushing, and swallowing fluoride-containing toothpaste is a major source of excess fluoride intake in this age group. Children who ingest more than two or three times the recommended fluoride intake are at increased risk of dental fluorosis. To prevent dental fluorosis while providing optimum protection from tooth decay, it is recommended that parents supervise children under 6 years of age while brushing with fluoridated toothpaste. In addition to discouraging the swallowing of toothpaste, children should be encouraged to use no more than a pea-size application of toothpaste and to rinse their mouths with water after brushing (47, 48). Fluoride supplements, available only by prescription, are intended for children living in areas with low water fluoride concentrations for the purpose of bringing their intake to approximately 1 mg/day (47). For more information about dental fluorosis, see the article on Fluoride.

Iodine

Iodine is required for the synthesis of the thyroid hormones, triiodothyronine (T₃) and thyroxine (T₄). To meet the body's demand for thyroid hormones, the thyroid gland traps iodine from the blood and incorporates it into thyroid hormones that are stored and released into the circulation when needed. In target tissues, such as the liver and the brain, T₃, the physiologically active thyroid hormone, can bind to thyroid receptors in the nuclei of cells and regulate gene expression. In target tissues, T₄, the most abundant circulating thyroid hormone, can be converted to T₃ by selenium-containing enzymes known as deiodinases. In this manner, thyroid hormones regulate a number of physiologic processes, including growth, development, metabolism, and reproductive function (49, 50).

Iodine deficiency is now accepted as the most common cause of preventable brain damage in the world. The spectrum of iodine deficiency disorders (IDD) includes mental retardation, hypothyroidism, goiter, and varying degrees of other growth and developmental abnormalities (49, 51). Iodine deficiency is associated with goiter; the incidence of goiter is higher in girls than boys. Children in iodine-deficient areas show poorer school performance, lower IQs, and a higher incidence of learning disabilities than matched groups from iodine-sufficient areas. A meta-analysis of 18 studies concluded that iodine deficiency alone lowered mean IQ scores in children by 13.5 points (52, 53).

Global estimates indicate that 31.5% of children between the ages of 6 and 12 years (266 million total children) has insufficient iodine intake (54). Major international efforts have produced dramatic improvements in the correction of iodine deficiency in the 1990s, mainly through the use of iodized salt in iodine-deficient countries (55). Today, 70% of households in the world use iodized salt (57), but iodine deficiency in children is still a major public health concern worldwide (57-59). For more information on the international effort to eradicate iodine deficiency, visit the websites of the Iodine Global Network or the World Health Organization.

The RDA of iodine for children aged 4 to 8 years is 90 μg/day, and the RDA for boys and girls aged 9 to 13 years is 120 μg/day. The intake recommendation for children in this younger age group was based on results of a balance study in eight-year-old children who did not have goiters (60). Results of a balance study in children ages 9 to 13 years indicated that a minimum of 55 μg/day of iodine is needed (60), but the RDA for this older age group was set by extrapolating from the adult recommendation based on metabolic body weight (55). The amount of iodine in iodized salt and the contribution of iodized salt to total iodine intake vary by nation. In the US, iodized salt contains an average of 45 mg of iodine per kilogram and 20% of the salt consumed by Americans is iodized. Salt used in processed foods and the fast food industry is generally not iodized (61). However, the US is currently considered to be iodine-sufficient (62). Seafood is rich in iodine because marine animals can concentrate the iodine from seawater, and certain types of seaweed (e.g., wakame) are also very rich in iodine (see Table 3 in the article on Iodine). Dairy products are also relatively good sources of iodine. However, iodine content of plant foods depends on the iodine content of the soil (63).

Iron

Iron is an essential component of hundreds of proteins and enzymes involved in various aspects of metabolism, including oxygen transport and storage, electron transport and energy metabolism, antioxidant and beneficial pro-oxidant functions, oxygen sensing, and DNA synthesis (9, 64-68); see the article on Iron). Iron is stored in the body as ferritin, and serum level of ferritin is a good clinical indicator of iron status in children (69). Iron deficiency, which is the most common nutritional deficiency in the world, is a major public health problem, especially in developing nations, but it is also prevalent in industrialized nations. Severe iron deficiency leads to iron-deficiency anemia, which affects more than 30% of the global population (2 billion people) (70). Iron-deficiency anemia results when there is inadequate iron to support normal red blood cell formation. The anemia of iron deficiency is characterized as microcytic and hypochromic, meaning red blood cells are measurably smaller than normal and their hemoglobin content is decreased. At this most severe stage of iron deficiency, symptoms may be a result of inadequate oxygen delivery due to anemia and/or sub-optimal function of iron-dependent enzymes. Low red cell count, low hematocrit, and low hemoglobin concentrations are all used in the clinical diagnosis of iron-deficiency anemia (71). 

Most observational studies have found relationships between iron-deficiency anemia in children and poor cognitive development, poor school achievement, and behavior problems. However, it is difficult to separate the effects of iron-deficiency anemia from other types of deprivation in such studies, and confounding factors may contribute to the association between iron deficiency and cognitive deficits (72). Yet, several possible mechanisms link iron-deficiency anemia to altered cognition. For example, any cognitive benefit associated with iron supplementation could be possibly due to changes in nerve myelination, which have been observed in iron-deficient animals (73). Iron has an important role in the development of the cells that produce myelin (74); as noted above, the myelin sheath is the insulating layer of tissue comprised of lipids and proteins that surrounds nerve fibers. This sheath acts as a conduit in an electrical system, allowing for rapid and efficient transmission of nerve impulses (19). Iron is also important for enzymes involved in the synthesis of certain neurotransmitters and for DNA synthesis (75).

Children between the ages of 4 and 13 years are at lower risk of iron deficiency compared to younger or older children because infants, toddlers, and adolescents generally have higher growth rates (9). The RDA of iron for children ages 4 to 8 years is 10 mg/day, and the RDA for boys and girls ages 9 to 13 years is 8 mg/day. Girls in this latter age group who start to menstruate need an additional 2.5 mg/day of iron. These intake recommendations were based on a factorial modeling approach that accounts for the amount of iron needed to replace basal losses (losses in urine, feces, and sweat) and the iron requirements associated with growth (increases in hemoglobin, the oxygen-carrying pigment in red blood cells mass; increases in iron content of tissues; and for the younger age group, increases in iron storage). The intake recommendations also account for average bioavailability (the fraction of iron retained and used by the body) of dietary iron in these age groups (76).

The amount of bioavailable iron in food (or supplements) is influenced by the iron nutritional status of the individual and also by the form of iron (heme or nonheme). Individuals who are anemic or iron deficient absorb a larger percentage of the iron they consume (especially nonheme iron) than individuals who are not anemic and have sufficient iron stores (77, 78). In addition, heme iron, found in meat, poultry, and fish, is more readily absorbed and its absorption is less affected by other dietary factors than nonheme iron — the form found in plants, dairy products, fortified foods, and supplements. Although heme iron generally accounts for only 10-15% of the iron found in the diet, it may provide up to one third of total absorbed dietary iron (67, 77). The absorption of nonheme iron is strongly influenced by enhancers and inhibitors present in the same meal (77, 78). For instance, vitamin C strongly enhances the absorption of nonheme iron by reducing dietary ferric iron (Fe³⁺) to ferrous iron (Fe²⁺) and forming an absorbable, iron-ascorbic acid complex. Organic acids, such as citric, malic, tartaric, and lactic acids, also enhance nonheme iron absorption. Further, consumption of meat, poultry, and fish enhance nonheme iron absorption, but the mechanism for this increase in absorption is not clear (76, 77). Inhibitors of nonheme iron absorption include phytic acid, which is present in legumes, grains, and rice. In fact, small amounts of phytic acid (5 to 10 mg) can reduce nonheme iron absorption by 50%. The absorption of iron from legumes, such as soybeans, black beans, lentils, mung beans, and split peas, has been shown to be as low as 2% <a href=">(64, 76). Additionally, polyphenols found in some fruit, vegetables, coffee, tea, wines, and spices can markedly inhibit the absorption of nonheme iron, but this effect is reduced by the presence of vitamin C (64, 76). Soy protein, such as that found in tofu, has an inhibitory effect on iron absorption that is independent of its phytic acid content (76).

Magnesium

The mineral magnesium is involved in more than 300 essential metabolic reactions that are generally involved in energy production and the synthesis of nucleic acids (DNA and RNA), proteins, carbohydrates, and lipids (79). Magnesium also plays structural roles in bone, cell membranes, and chromosomes and is also required for various cellular processes, including ion transport across cell membranes, cell signaling, and cell migration (80).

The RDA of magnesium for children ages 4 to 8 years, which is 130 mg/day, was derived by extrapolating data from magnesium balance studies in older children (79). The RDA for boys and girls ages 9 to 13 years is 240 mg/day. This recommendation was based on data from magnesium balance studies in children of this age (81, 82). Good dietary sources of magnesium include nuts and green leafy vegetables because magnesium is part of chlorophyll — the green pigment in plants. Meats and milk have an intermediate magnesium content, with milk providing 24-39 mg per cup (79, 83). Refined foods generally have the lowest magnesium content. Analysis of data from the NHANES study found that US children ages 2 to 12 years who consumed three or more daily servings of whole grains had significantly increased magnesium intakes (84).

Sodium

The 2010 Dietary Guidelines for Americans recommend that children should limit their sodium intake to 1,500 mg/day to lower blood pressure and thus reduce their risk of cardiovascular and kidney diseases in adulthood (85). In 2004, the FNB set the AI for children by extrapolating from the adult AI using relative energy intakes. The AI for children 4 to 8 years is 1,000 mg/day, which translates to 2.5 grams of salt per day, and the AI for boys and girls 9 to 13 years is 1,200 mg/day, which translates to 3 grams of salt per day (86).

Zinc

The mineral zinc is essential for growth and development, immune function, neurological function, and reproduction. Zinc plays a number of catalytic, structural, and regulatory roles in cellular metabolism (see the article on Zinc). Zinc deficiency is a major public health concern and has been estimated to affect more than 2 billion people in less developed nations (87). Children are at increased risk for zinc deficiency, which can lead to delayed physical growth, impaired immunity, and possibly to delayed mental development. Mild forms of this mineral deficiency, which are common in both developing and developed nations, appear to have negative effects on growth and development (23, 88). However, the lack of a sensitive indicator of mild zinc deficiency hinders the scientific study of its health implications.

Mild zinc deficiency contributes to impaired physical growth in children (88, 89). Significant delays in linear growth and weight gain, known as growth retardation or failure to thrive, are common features of mild zinc deficiency in children. In the 1970s and 1980s, several randomized, placebo-controlled studies of zinc supplementation in young children with significant growth delays were conducted in Denver, Colorado. Modest zinc supplementation (5.7 mg/day) resulted in increased growth rates compared to placebo (89). More recently, a number of larger studies in developing countries observed similar results with modest zinc supplementation. A meta-analysis of growth data from zinc intervention trials recently confirmed the widespread occurrence of growth-limiting zinc deficiency in young children, especially in developing countries (90). Although the exact mechanism for the growth-limiting effects of zinc deficiency are not known, recent research indicates that zinc availability affects cell-signaling systems that coordinate the response to the growth-regulating hormone, insulin-like growth factor-1 (IGF-1) (91, 92).

Adequate zinc intake in children is essential in maintaining the integrity of the immune system (23, 93), and zinc deficiency is associated with increased susceptibility to a variety of infectious agents (94). The adverse effects of zinc deficiency on immune system function are likely to increase the susceptibility of children to infectious diarrhea, and persistent diarrhea contributes to zinc deficiency and malnutrition. It has been estimated that diarrheal diseases result in the deaths of about 3 million children each year (95). Zinc supplementation in combination with oral rehydration therapy has been shown to significantly reduce the duration and severity of acute and persistent childhood diarrhea and to increase survival in a number of randomized controlled trials (96, 97). Recently, a meta-analysis of randomized controlled trials concluded that zinc supplementation reduces the frequency, severity, and duration of diarrheal episodes in children under five years of age (98). The World Health Organization and the United Nations Children's Fund currently recommend zinc supplementation as part of the treatment for diarrheal diseases in young children (99). Zinc supplementation may also reduce the incidence of lower respiratory infections, such as pneumonia. A pooled analysis of a number of studies in developing countries demonstrated a substantial reduction in the prevalence of pneumonia in children supplemented with zinc (100). A recent meta-analysis found that zinc supplementation reduced the incidence but not duration of pneumonia or respiratory tract illnesses in children under five years of age (98). Due to conflicting reports (101-104), it is not yet clear whether zinc supplementation has utility in treating childhood malaria.

Because a sensitive indicator of zinc nutritional status is not readily available, the RDA for zinc was based on a number of different indicators of zinc nutritional status and represents the daily intake likely to prevent deficiency in nearly all individuals in a specific age and gender group. The RDA for children ages 4 to 8 years is 5 mg/day, and the RDA for boys and girls ages 9 to 13 years is 8 mg/day (105). Shellfish, beef, and other red meats are rich sources of zinc. Nuts and legumes are relatively good plant sources of zinc. Zinc bioavailability (the fraction of zinc retained and used by the body) is relatively high in meat, eggs, and seafood because of the relative absence of compounds that inhibit zinc absorption and the presence of certain amino acids (cysteine and methionine) that enhance zinc absorption. The zinc in whole-grain products and plant proteins is less bioavailable due to their relatively high content of phytic acid, a compound that inhibits zinc absorption (106). The enzymatic action of yeast reduces the level of phytic acid in foods. Therefore, leavened whole-grain breads have more bioavailable zinc than unleavened whole-grain breads (105).

Other Nutrients

Choline

Choline can be synthesized by the body in small amounts, but dietary intake is needed to maintain health (107). Choline and its metabolites have a number of essential biological functions. Choline is used in the synthesis of specific phospholipids (i.e., phosphatidylcholine and sphingomyelin) that are structural components of cell membranes and also precursors for certain cell-signaling molecules. Choline is needed for myelination of nerves and is a precursor for acetylcholine, a neurotransmitter involved in muscle action, memory, and other functions (108-110). For more information about the role of choline in the body, see the article on Choline.

Due to the lack of data in children, intake recommendations for choline in children were extrapolated from adult recommendations using metabolic body weight, accounting for growth. The AI for children aged 4 to 8 years is 250 mg/day, and the AI for boys and girls aged 9 to 13 years is 375 mg/day (108). A number of foods contain choline, but eggs, meats, and milk are the primary sources in the American diet (111).

Essential fatty acids

α-Linolenic acid (ALA), an omega-3 fatty acid, and linoleic acid (LA), an omega-6 fatty acid, are considered essential fatty acids because they cannot be synthesized by humans. The long-chain omega-6 fatty acid, arachidonic acid (AA), can be synthesized from LA, and two long-chain omega-3 fatty acids, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), can be synthesized from ALA (112). These polyunsaturated fatty acids have a number of biological activities that are generally important for the structure and function of cell membranes, vision, eicosanoid synthesis, regulation of gene expression, and nervous system function (see the article on Essential Fatty Acids).

Dietary intake recommendations for ALA and LA in children were based on median intakes of American children, a population where omega-3 and omega-6 fatty acid deficiencies are not observed. The AI of ALA for children ages 4 to 8 years is 0.9 g/day, while the AI of ALA for children ages 9 to 13 years is 1.2 and 1.0 g/day for boys and girls, respectively. The long-chain omega-3 fatty acids, EPA and DHA, can contribute to these intake recommendations. Flaxseeds, walnuts, and their oils are among the richest dietary sources of ALA, but canola oil is also an excellent source of ALA. Oily fish, such as salmon, tuna, trout, and sardines, are the major dietary source of EPA and DHA (113). The AI of LA for children ages 4 to 8 years is 10 g/day, while the AI of LA for boys and girls ages 9 to 13 years is 12 and 10 g/day, respectively. Sources of LA include vegetable oils, such as soybean, safflower, and corn oil, nuts, seeds, and some vegetables (see the article on Essential Fatty Acids).

Safety

The FNB sets a tolerable upper intake level (UL) for most micronutrients. The UL is the highest level of daily nutrient intake likely to pose no risk of adverse health effects in almost all individuals of a specified age group. This level applies to total daily intake from food, water, and supplements. Due to the potential for adverse effects, it is recommended that individuals not exceed the UL. Thus, individuals should use the UL as a guide to limit daily micronutrient intake, not as a recommended level of intake (114). Table 3 lists the UL for children ages 4 to 8 years, and Table 4 lists the UL for children ages 9 to 13 years.

Note that many children’s multivitamin/mineral supplements on the market contain more than the RDA for several micronutrients when taken at the suggested dosage by age. Some even contain micronutrients (e.g., vitamin A, folic acid, copper, and zinc) at levels equivalent to the UL; this concern is for children younger than 9 years old. The Food and Nutrition Board of the Institute of Medicine recommends that daily nutrient intake from food and supplements not exceed the UL for each micronutrient. There is no evidence that consumption of micronutrients at or above the UL results in any health benefits in children, and the UL should not be exceeded except under medical supervision. Children often consume vitamin and mineral-fortified foods like cereal, and their total intake of certain micronutrients like vitamin A, folic acid, copper, and zinc from fortified foods, other dietary intake, and from supplements should be determined to ensure that the UL is not exceeded. It is also important to note that the daily values (DVs) listed on supplement labels in the US do not reflect the current intake recommendations (RDA or AI). Another caution is that many children’s supplements look like candy but should never be labeled as such and, because of safety concerns, should be kept out of reach of children.

Conclusion

A healthy diet in children is important to provide nutrients that support optimum physical growth and cognitive development and to also establish healthy eating behaviors that lower risk of chronic diseases in adulthood. Although it is generally advised that micronutrients should be obtained from food, many children do not reach daily intake recommendations for select micronutrients, including vitamins A, C, D, and E, and some minerals, such as calcium and magnesium (37, 115).

Therefore, the Linus Pauling Institute recommends that children ages 4 to 13 years take a daily multivitamin/mineral supplement with 100% of the daily value (DV) for most vitamins and essential minerals, keeping the following suggestions in mind:

• Since the DV for vitamin A for those ages 4 and older (5,000 IU) is considerably higher than the current RDA for children ages 4 to 8 years (1,333 IU/day) and 9 to 13 years (2,000 IU/day), LPI recommends looking for a children’s multivitamin/mineral supplement containing no more than 2,500 IU (750 μg) of vitamin A, of which at least 50% comes from β-carotene.
• In general, multivitamin/mineral supplements contain only a small percentage of the RDA for calcium and magnesium; therefore, intake of calcium and magnesium from dietary sources, such as low-fat milk, is important. If the RDAs for these minerals (1,000 and 1,300 mg/day for calcium and 130 and 240 mg/day for magnesium for children 4 to 8 years and 9 to 13 years, respectively) are not met through diet plus the multivitamin/mineral supplement, LPI recommends an additional, combined calcium-magnesium supplement for children.
• Because there are limited dietary sources of vitamin D and many children use sunscreens, which block skin synthesis of vitamin D, LPI recommends that all children ages 4 to 13 years should have a daily intake of 600 to 1,000 IU (15 to 25 μg) of vitamin D, consistent with the recommendations of the Endocrine Society (39). Given the average vitamin D content in the diets of children, supplementation may be necessary to meet this recommendation.

Authors and Reviewers

Written in August 2011 by:
Victoria J. Drake, Ph.D.
Linus Pauling Institute
Oregon State University

Reviewed in August 2011 by:
Dennis M. Bier, M.D.
Professor of Pediatrics, Baylor College of Medicine
Director, Children’s Nutrition Research Center
Houston, Texas

This article was underwritten, in part, by a grant from Bayer Consumer Care AG, Basel, Switzerland.

DRIs for sodium and potassium updated 4/12/19  Copyright 2011-2024  Linus Pauling Institute

References

Micronutrient Requirements of Adolescents Ages 14 to 18 Years

Introduction

Adolescence — the transitional stage of development between childhood and adulthood — is associated with marked physical growth, reproductive maturation, and cognitive transformations. Physical changes begin in early adolescence during puberty, when sexual maturity is reached and reproduction is possible (1). Girls generally begin their adolescent growth spurt at an earlier age (9 years of age) than boys (11 years of age); the pubertal growth spurt lasts between two to four years, with the average rate of linear growth being 5-6 cm/year (2-2.4 in/year). Boys experience greater gains in height compared to girls because of a higher rate of growth and a longer growth spurt (2). Gains in linear growth are accompanied by increases in body weight and changes in body composition. Weight gain in girls typically happens six months following the greatest gains in linear growth, whereas weight gain in boys is usually coincident with increases in height. Throughout adolescence, boys gain more lean (fat-free) mass than girls, and girls experience greater increases in adiposity, which is required for normal menstruation (3). Moreover, approximately half of adult bone mass is obtained during adolescence (4), with boys experiencing greater gains in bone size and bone mass compared to girls (5).

In addition to physical growth, reproductive maturation occurs during adolescence. Maturation of the reproductive organs and development of secondary sexual characteristics, including facial hair in males and breast development in females, take place during puberty. Girls also experience menarche — the first occurrence of menstruation — during this developmental stage, typically following the peak period of gains in height and weight (6). Adolescence is further characterized by cognitive, emotional, and psychosocial development (2).

Good nutrition is needed to support the growth and developmental changes of adolescence. Undernutrition, in general, has been shown to delay the adolescent growth spurt (7). Overnutrition, a form of malnutrition where macronutrients (carbohydrates, fats, proteins) are supplied in excess of the body’s needs, can lead to obesity and is a concern in industrialized nations. In the developed world, adolescents are increasingly consuming energy-rich, nutrient poor diets comprised of fast food, processed foods, and sugar-sweetened beverages (8-10). Studies have also shown that many adolescents do not come close to meeting intake recommendations for nutrient-rich foods, such as fruit, vegetables, and milk (11, 12). Together, these dietary behaviors place adolescents at increased risk for micronutrient deficiencies. This article discusses micronutrient requirements of adolescents aged 14 to 18 years, an age range that is used by the Food and Nutrition Board (FNB) of the US Institute of Medicine to establish dietary reference intakes. Due to limited data, many of the micronutrient intake recommendations for adolescents are extrapolated from recommendations for adults using a formula that accounts for metabolic body weight and growth (13), not unique physiological changes during adolescence. Metabolic body weight is determined by calculating the 0.75 power of body mass (body mass^0.75) (14). To account for growth, the equation used to derive a Recommended Dietary Allowance (RDA) or Adequate Intake (AI) involves an age group-specific growth factor (13). The FNB set different micronutrient intake recommendations for children 9 to 13 years, an age range that encompasses puberty and early stages of adolescence (15); discussion of the micronutrient requirements of younger children is included in a separate article (see Micronutrient Needs of Children Ages 9 to 13 Years).

Micronutrient Needs of Adolescents Aged 14 to 18 Years

For each micronutrient, the FNB sets an RDA or AI for adolescents aged 14 to 18 years. These recommendations are gender specific to account for the unique nutritional needs of males and females as they undergo the physiological changes of adolescence. Table 1 lists the RDA for each micronutrient by gender. The RDA should be used in the planning of diets for individuals. A more detailed discussion of the requirements of certain micronutrients for adolescents can be found below.

Vitamins

Vitamin A

Vitamin A is a fat-soluble vitamin that is essential for growth and development, normal vision, the expression of selected genes, immunity, and reproduction (16). Vitamin A deficiency in children and adolescents is a major public health problem worldwide, especially in less developed countries (17, 18). Even marginal or subclinical deficiencies in vitamin A may have adverse effects on bone growth and sexual maturation of adolescents (19). Because of its role in immunity, inadequate intake of this vitamin also increases risk for infectious diseases (20).

Studies in industrialized countries have reported inadequate intakes of vitamin A among adolescents (21-23). Serum retinol binding protein (RBP) concentrations have been shown to increase throughout the stages of puberty, indicating that vitamin A is needed for adolescent development (24). However, few vitamin A supplementation studies have been done in adolescents; most supplementation studies have included younger children who are more susceptible to vitamin A deficiency.

The RDA for vitamin A is based on the amount needed to ensure adequate stores (four months) of vitamin A in the body to support normal reproductive function, immune function, vitamin A-dependent gene expression, and vision (16). Vitamin A intake recommendations for adolescents were derived by extrapolating the recommendation for adults using metabolic body weight, accounting for growth. The RDA for adolescent boys aged 14 to 18 years is 900 μg per day of Retinol Activity Equivalents (RAE), which is 3,000 international units (IU); the RDA for adolescent girls aged 14 to 18 years is 700 μg of RAE, which is equivalent to 2,333 IU. For information on vitamin A content in foods, see the article on Vitamin A.

Vitamin B₆

Vitamin B₆ is required for heme synthesis and in the synthesis and metabolism of amino acids — the building blocks of proteins. Thus, the vitamin has obvious relevance to adolescent growth and health. Dietary intake recommendations of vitamin B₆ for adolescents were established by extrapolating data from adults, using metabolic body weight and accounting for growth. The RDA for boys aged 14 to 18 years is 1.3 mg/day, and the RDA for girls aged 14 to 18 years is 1.2 mg/day (25). Only a few studies have evaluated vitamin B₆ status specifically in adolescents. In an analysis of American adolescent girls (aged 12-16 years), mean dietary intake of vitamin B₆ was 1.2 mg/day; however, one-third of the girls not taking vitamin B₆-containing supplements had either marginal or deficient vitamin B₆ status (26). The same investigators found more than 40% vitamin B₆ inadequacy when a group of 112 adolescent girls (12- and 14-year-old) were followed for two years (27). Results of more recent studies have suggested that most American and European adolescents are meeting current intake recommendations for vitamin B₆ (28, 29), although a study in Canada found that more than half of adolescent males aged 14 to 18 years did not meet the Estimated Average Requirement (EAR) of 1.1 mg/day for vitamin B₆ (22). For information on dietary sources of the vitamin, see the article on Vitamin B₆.

Folate

The B vitamin, folate, is required as a coenzyme to mediate the transfer of one-carbon units. Folate coenzymes act as acceptors and donors of one-carbon units in a variety of reactions critical to the endogenous synthesis and metabolism of nucleic acids (DNA and RNA) and amino acids (30, 31). Thus, folate has obvious importance in growth and development. Moreover, higher intakes of folate in adolescents have been linked to better academic achievement (32). Like other B vitamins, adolescent intake recommendations for folate were extrapolated from adult recommendations, using metabolic body weight and accounting for growth. The RDA for adolescents aged 14 to 18 years is 400 μg/day of dietary folate equivalents (33).

When considering naturally occurring folate in foods, results of a national survey indicate that almost 80% of individuals aged 2-18 years in the US have intakes below the EAR, which is 330 μg/day of dietary folate equivalents for adolescents aged 14-18 years. However, when accounting for intake from fortified foods, less than 5% of individuals in that age group have intakes below the EAR (34). The US Food and Drug Administration implemented legislation in 1998 requiring the fortification of all enriched grain products with folic acid (35). Globally, more than 50 countries have mandatory programs of wheat-flour fortification with folic acid, but flour fortification is not common in Europe (36). Dietary folate inadequacy is common among adolescents in European nations, especially girls (29).

Vitamin B₁₂

Vitamin B₁₂ is needed for two types of reactions in the human body. One is transmethylation (methyl transfer between two molecules) that leads to the synthesis of the amino acid methionine from homocysteine. Methionine, in turn, is required for the synthesis of S-adenosylmethionine, a methyl group donor used in many biological methylation reactions, such as the methylation of sites within DNA and RNA (37). The second sort of reaction is isomerization (rearrangement of a molecule). Vitamin B₁₂ acts as a coenzyme for methylmalonyl-CoA mutase to convert methylmalonyl-CoA to succinyl-CoA, an important step for the metabolism of proteins and lipids. Both transmethylation and isomerization reactions are essential for the metabolism of components of the myelin sheath of nerve cells and for the metabolism of neurotransmitters. Accordingly, vitamin B₁₂ deficiency damages the myelin sheath covering cranial, spinal, and peripheral nerves, resulting in neurological damage (38, 39). The myelin sheath is the insulating layer of tissue made up of lipids and proteins that surrounds nerve fibers. This sheath acts as a conduit in an electrical system, allowing rapid and efficient transmission of nerve impulses (40). In some cases, neurologic symptoms caused by vitamin B₁₂ deficiency can be reversed by vitamin treatment (38), but reversibility seems to be dependent upon the duration of the associated neurologic complications (41).

Although myelination primarily occurs during fetal development and early infancy, it continues through childhood, adolescence, and stages of early adulthood (42, 43). Because of the role of vitamin B₁₂ in myelination and other metabolic processes, it is important for adolescents to meet dietary intake recommendations. The RDA of vitamin B₁₂ for adolescent boys and girls aged 14 to 18 years is 2.4 μg/day (41), extrapolated from the recommendation for adults.

Vitamin B₁₂ is naturally present only in animal products, such as meat, poultry, fish (including shellfish), and to a lesser extent in milk, but it is not generally present in plant products or yeast (44). Vitamin B₁₂ deficiency has been reported in adolescents on very restricted or strict vegetarian diets (45, 46). Because vitamin B₁₂ is stored in the liver, it may take three to six years for clinical symptoms to manifest (45). Thus, adolescents who have vegan diets need adequate intake from fortified foods or supplemental vitamin B₁₂.

Vitamin C

Vitamin C has a number of important roles during growth and development, including being required for the synthesis of collagen, carnitine, and neurotransmitters (47). Vitamin C is also a highly effective antioxidant and is important for immunity (see the article on Immunity). Further, vitamin C strongly enhances the absorption of nonheme iron by reducing dietary ferric iron (Fe³⁺) to ferrous iron (Fe²⁺). Specifically, iron absorption is two- to three-fold higher with co-ingestion of 25 to 75 mg of vitamin C (48). This has special relevance to adolescent health, considering the fact that iron deficiency is prevalent among adolescents, especially girls (see the section on Iron). The RDA for adolescents aged 14 to 18 years, which was extrapolated from recommendations for adults based on relative body weight, is 75 mg/day and 65 mg/day of vitamin C for boys and girls, respectively (49).

Data on vitamin C intake among adolescents are limited, but a recent US national survey, the 2003-2004 National Health and Nutrition Examination Survey (NHANES), found that serum vitamin C concentrations of adolescents (aged 12-19 years) were lower in adolescents compared to younger children (6-11 years), and adolescent girls had higher levels than adolescent boys (50). In this analysis, 2.7% of adolescent boys and 3.9% of adolescent girls had overt vitamin C deficiency that could result in clinical symptoms of scurvy. A cross-sectional analysis of European adolescents (aged 12.5-17.5 years) also noted higher vitamin C status among adolescent girls compared to boys, and compared to the US survey, the prevalence of overt vitamin C deficiency was lower in European adolescents (51). For information on food sources, see the article on Vitamin C.

Vitamin D

Vitamin D is a fat-soluble vitamin that is essential for maintaining normal calcium metabolism and is therefore necessary for bone health. Severe vitamin D deficiency in infants and children results in the failure of bone to mineralize, leading to a condition known as rickets, but cases of rickets have also been reported during stages of puberty and adolescence (52-53). Rapidly growing bones are most severely affected by rickets. The growth plates of bones continue to enlarge, but in the absence of adequate mineralization, weight-bearing limbs (arms and legs) become bowed. Inadequate vitamin D during puberty and adolescence might prevent the attainment of peak bone mass and final height (54-56) and could possibly increase the risk of osteoporosis or other diseases in adulthood, but more studies on these associations are needed.

In 2010, the Food and Nutrition Board (FNB) of the Institute of Medicine set an RDA based on the amount of vitamin D needed for bone health and assuming minimal sun exposure; the RDA is 600 IU/day (15 μg/day) for adolescents aged 14 to 18 years. In the US, milk is voluntarily fortified with 400 IU (10 μg) of vitamin D per quart (946 mL); thus, adolescents would need to consume about 6 cups of milk daily to meet the RDA. Although fish is the best source of vitamin D in the diet, fortified foods and beverages are likely the major dietary source of vitamin D for US adolescents. In Canada, fortification of milk and margarine is mandatory, with milk containing 35-45 IU per 100 mL (331-426 IU per quart) and margarine containing 530 IU per 100 grams (57), but vitamin D fortification of foods is less common in European nations (58). In addition to diet, vitamin D can be endogenously synthesized in the skin upon exposure to ultraviolet-B radiation from sunlight; however, sunscreens effectively block skin synthesis of vitamin D and vitamin D synthesis is diminished in northern latitudes during winter (see the article on Vitamin D).

Analysis of data from NHANES 2005-2006 found that average total vitamin D intakes (from diet and supplements combined) in US adolescents (aged 14 to 18 years) were 6.9 μg/day (276 IU/day) for boys and 5.0 μg/day (200 IU/day) for girls — well below the current RDA. This analysis also found that 16% of adolescent boys and 27% of adolescent girls took vitamin D-containing supplements (59). Because sun exposure can substantially affect body vitamin D levels, measuring 25-hydroxyvitamin D — the major circulating form of vitamin D — is a more useful indicator of vitamin D status. However, studies assessing vitamin D status in adolescents have used various cutoffs to define vitamin D deficiency and insufficiency and there is no consensus of what level constitutes adequacy.

It is assumed that a dietary intake of 600 IU (15 μg)/day results in a serum 25-hydroxyvitamin D level of 20 ng/mL (50 nmol/L), which the FNB considers as the cut-off point for vitamin D adequacy (60). However, many researchers believe that higher levels may benefit health. NHANES found that more than 25% of US adolescents (12-19 years) had serum 25-hydroxyvitamin D concentrations lower than 20 ng/mL (50 nmol/L) and about 75% of adolescents had levels lower than 32 ng/mL (80 nmol/L) (61). Some studies have found a higher prevalence of vitamin D deficiency among European adolescents (19, 62). Ethnic and seasonal differences have also been reported, with higher levels in whites compared to blacks (61, 63) and in summertime compared to wintertime (62, 64, 65). Moreover, several studies have reported low vitamin D status among adolescents living in sunny climates (63, 66-68).

Oral vitamin D supplementation has been shown to improve vitamin D status among adolescents (69, 70), and one double-blind, placebo-controlled trial found that improvements in vitamin D status were accompanied by some musculoskeletal benefits in adolescent girls (70). Although more supplementation studies are needed, ensuring vitamin D adequacy throughout childhood and adolescence seems prudent. The Linus Pauling Institute recommends that adolescents aged 14 to 18 years should have a daily intake of 600 to 1,000 IU (15 to 25 μg) of vitamin D, consistent with the recommendations of the Endocrine Society (71). According to the Endocrine Society, at least 600 IU/day may be required to maximize bone health, and 1,000 IU/day may be needed to increase serum levels above 30 ng/mL (75 nmol/L) (71). Given the average vitamin D content of the diets of adolescents, supplementation may be necessary to meet this recommendation. The American Academy of Pediatrics currently suggests that all adolescents who do not get 400 IU/day of vitamin D through dietary sources should take 400 IU of supplemental vitamin D daily (72) — an amount that is typically found in multivitamin supplements.

Vitamin E

The RDA of vitamin E for adolescents, expressed as an amount of the α-tocopherol form of the vitamin, was based on extrapolations from intake recommendations for adults, accounting for differences in lean body mass and increased needs of growth during adolescence. The RDA is 15 mg/day (22.5 IU/day) for boys and girls ages 14 to 18 years (73). A US national survey, NHANES 1999-2000, found that adolescent boys and girls aged 14 to 18 years had average intakes of 7.5 mg/day and 5.7 mg/day of α-tocopherol, respectively. Moreover, 92% of adolescent boys and more than 99% of adolescent girls of this age group had daily intakes below the EAR of 12 mg/day (74). Vitamin E intake has been reported to be similarly low in adolescents in Spain (21), Switzerland (23), Brazil (75), France (76), and Germany (77). However, true vitamin E deficiency is rare and has been observed only in cases of severe malnutrition, genetic defects affecting the α-tocopherol protein, and fat malabsorption syndromes; see the article on Vitamin E.

Minerals

Calcium

About 99% of calcium in the body is found in bones and teeth (78). Adequate intake of calcium throughout childhood and adolescence is important for proper mineralization of growing bones, attainment of peak bone mass, and reduction of risk of bone fracture and osteoporosis in adulthood. Dietary intake recommendations for calcium in adolescents were established using a factorial method that summed average calcium accretion and calcium losses to urine, feces, and sweat and also adjusted for calcium absorption (60). Specifically, data used by the FNB to determine calcium accretion came from a recent longitudinal study in 642 Caucasian adolescents aged 14 to 18 years (79). The authors of this study estimated that the daily calcium requirement is higher in boys than girls; however, the FNB concluded that the differences were relatively small and it would be more practical to establish a single recommendation for all adolescents. Thus, the RDA was set at 1,300 mg/day; this level of calcium intake is expected to cover the needs of 97.5% of adolescents.

Many US adolescents have dietary calcium intakes below the RDA, with girls having lower intakes than boys. A recent analysis of data from NHANES 2003-2006, a US national survey, found that 42% of adolescent boys and only 10% of adolescent girls (14-18 years) had dietary calcium intakes above 1,300 mg/day. When accounting for use of calcium-containing supplements (19% and 24% of boys and girls, respectively; average supplemental intake of 142 and 182 mg/day of calcium in boys and girls, respectively), 42% of adolescent boys and only 13% of adolescent girls had total daily intakes above the current RDA (59). A recent publication that reviewed average calcium intake among adolescents in 23 nations found that boys generally have intakes of ~100-200 mg/day higher than girls and that many adolescents do not meet intake recommendations (80).

Dairy products, which provide about 72% of the calcium in the American diet (78), represent rich and absorbable sources of calcium. Milk contains 300 mg of calcium per cup; therefore, adolescents could meet the RDA for calcium by drinking 4.3 cups of low-fat milk daily. However, NHANES data show that US adolescents (12-19 years) on average consume only about 1 cup of milk daily (81). Lactose intolerance may prevent some adolescents from consuming milk, and consumption of soft drinks and other sweetened beverages might displace milk consumption in adolescents (82).

Certain vegetables and grains also provide calcium, but their bioavailability is lower compared with dairy. For more information on dietary sources of calcium and calcium bioavailability, see the article on Calcium. The Nutrition Facts label of packaged foods lists calcium content in one serving as a percent of the Daily Value (DV), with the DV being 1,000 mg. Since the RDA for adolescents is 1,300 mg/day, the percentage of the DV listed on the food label would be an overestimation of the percentage of the RDA. If adolescents do not meet the RDA through diet alone, LPI recommends supplemental calcium. Multivitamin/mineral supplements generally provide no more than 200 mg of calcium.

Iron

Iron is an essential component of hundreds of proteins and enzymes involved in various aspects of metabolism, including oxygen transport and storage, electron transport and energy metabolism, antioxidant and beneficial pro-oxidant functions, oxygen sensing, and DNA synthesis (44, 83-85); see the article on Iron. Iron deficiency, which is the most common nutritional deficiency in the world, is a major public health problem, especially in developing nations, but it is also prevalent in industrialized nations, notably in women of childbearing age. Severe iron deficiency leads to iron-deficiency anemia; anemia affects more than 30% of the global population (2 billion people) (81). Adolescents have increased requirements for iron due to rapid growth. In particular, adolescent girls are at a heightened risk of iron deficiency due to inadequate intake of dietary iron, especially heme iron; increased demands of growth; and iron loss that occurs with menstruation. Following puberty, adolescent girls have lower iron stores compared to adolescent boys (87).

In addition to the negative effects of iron deficiency on physical growth, iron deficiency during adolescence may impair immunity (see the article on Nutrition and Immunity) as well as cognition. Iron is needed for proper development of oligodendrocytes (the brain cells that produce myelin) (88), and the mineral is also a required cofactor for several enzymes that synthesize neurotransmitters (89). Iron deficiency — even levels not associated with anemia — during important stages of brain development, such as adolescence, may have detrimental consequences. A double-blind, placebo-controlled trial in 73 adolescent girls (aged 13-18 years) with non-anemic iron deficiency found that high-dose iron supplementation (260 mg/day of elemental iron) for eight weeks resulted in greater improvement in verbal learning but not in other cognitive domains (90). Another study reported that one-month iron supplementation beyond that included in a prenatal vitamin improved some measures of attention and short-term memory in young pregnant women (aged 14-24 years) without severe iron deficiency (91). Clinical trials of iron supplementation to date have been mostly done in other age groups; large, well-designed trials in adolescents are needed to determine the effects of iron supplementation on cognition.

Dietary intake recommendations for adolescents were based on a factorial modeling approach that accounts for the amount of iron needed to replace basal losses (losses in urine, feces, and sweat), iron requirements associated with growth (increases in hemoglobin and iron content of tissues), and iron losses associated with menstruation in girls. The intake recommendations also account for average bioavailability (the fraction of iron retained and used by the body) of dietary iron for this age group (92). The RDA of iron is 11 mg/day for adolescent boys and 15 mg/day for adolescent girls. A US national survey, NHANES 2001-2002, found that average dietary intake of iron was 19.1 mg/day in adolescent boys and 13.3 mg/day in adolescent girls; however, 16% of adolescent girls had intakes below the EAR of 7.9 mg/day. Because several different criteria have been used to identify iron deficiency, it is difficult to report the prevalence of iron deficiency among adolescents.

The amount of bioavailable iron in food (or supplements) is influenced by the iron nutritional status of the individual and also by the form of iron (heme or nonheme). Individuals who are anemic or iron deficient absorb a larger percentage of the iron they consume (especially nonheme iron) than individuals who are not anemic and have sufficient iron stores (94, 95). Heme iron, found in meat, poultry, and fish, is more readily absorbed, and its absorption is less affected by other dietary factors than nonheme iron — the form found in plants, dairy products, fortified foods, and supplements. Although heme iron generally accounts for only 10-15% of the iron found in the diet, it may provide up to one third of total absorbed dietary iron (83, 95). The absorption of nonheme iron is strongly influenced by enhancers and inhibitors present in the same meal. For instance, vitamin C strongly enhances the absorption of nonheme iron by reducing dietary ferric iron (Fe3+) to ferrous iron (Fe2+) and forming an absorbable, iron-ascorbic acid complex. Organic acids, such as citric, malic, tartaric, and lactic acids, also enhance nonheme iron absorption. Further, consumption of meat, poultry, and fish enhance nonheme iron absorption, but the mechanism for this increase in absorption is not clear (92, 94). Inhibitors of nonheme iron absorption include phytic acid, which is present in legumes, grains, and rice. Polyphenols found in some fruit, vegetables, coffee, tea, wines, and spices can also markedly inhibit the absorption of nonheme iron, but this effect is reduced by the presence of vitamin C (92, 96). Soy protein, such as that found in tofu, has an inhibitory effect on iron absorption that is independent of its phytic acid content (92).

Magnesium

The mineral magnesium is involved in more than 300 essential metabolic reactions that are generally involved in energy production and the synthesis of nucleic acids (DNA and RNA), proteins, carbohydrates, and lipids (97). Magnesium also plays structural roles in bone, cell membranes, and chromosomes and is also required for various cellular processes, including ion transport across cell membranes, cell signaling, and cell migration (98).

The RDA of magnesium for those aged 14 to 18 years, 410 mg/day for boys and 360 mg/day for girls, was derived from results of balance studies in adolescents. Good dietary sources of magnesium include nuts, and green leafy vegetables because magnesium is part of chlorophyll — the green pigment in plants. Meats and milk have an intermediate magnesium content, with milk providing 24-39 mg per cup (97). Refined foods generally have the lowest magnesium content. Although data are limited, some studies have found that a large percentage of adolescents have magnesium intakes below recommended levels (100-102). Data on magnesium intake among adolescents are lacking. In an analysis of NHANES data, US adolescents who consumed milk (plain or flavored) had higher daily magnesium intakes than adolescents who did not drink milk (103). However, NHANES data show that US adolescents (12-19 years) on average only consume about 1 cup of milk daily (81). Low-fat milk, nuts, whole grains, and green leafy vegetables are important sources of magnesium for adolescents. If adolescents do not meet the RDA through dietary sources, LPI recommends a combined magnesium-calcium supplement.

Potassium

Potassium is required for maintenance of cellular membrane potential and thus for nerve impulse transmission, muscle contraction, and heart function. In general, adolescents have low intakes of fruit, vegetables, and dairy products (104-106) — foods that are rich in potassium. Low intakes of potassium, coupled with high intakes of sodium (see section on Sodium), have been linked to elevations in blood pressure and a heightened risk of hypertension and stroke later in life (see the article on Potassium). In a study that followed 2,368 adolescent girls for nine years, lower intakes of potassium were associated with a higher incidence of hypertension (107). Fruit, vegetables, low-fat milk, and nuts are all good sources of potassium, and increasing intake of these foods during adolescence should help regulate blood pressure and may decrease risk of chronic disease during adulthood.

Sodium

In 2019, the FNB set the AI for adolescents by extrapolating from the adult AI using relative energy intakes; however, since energy intakes of adolescents are similar to that of adults, the recommendations are identical: 1,500 mg/day of sodium (108). The 2010 Dietary Guidelines for Americans recommend limiting sodium intake to 1,500 mg/day to lower blood pressure and thus reduce risk of cardiovascular disease and kidney diseases in adulthood. However, daily sodium intake in US adolescents (aged 12-19 years) is 3,000 mg in girls and 4,000 mg/day in boys (109). Low-sodium interventions in adolescents have shown some improvement in blood pressure, but compliance to such a diet is problematic (110, 111).

Zinc

The mineral zinc is essential for growth and development, immune function, neurological function, and reproduction. Zinc plays a number of catalytic, structural, and regulatory roles in cellular metabolism (see the article on Zinc). Zinc deficiency, which is estimated to affect more than 2 billion people in less developed nations (112), can retard normal growth, impair cognitive development, and delay sexual maturation (113, 114). Adolescents are at increased risk of zinc deficiency due to the demands of growth (115). Mild zinc deficiency, which is common in both the developing and developed world, may also have negative effects on growth and development (47, 116); however, the lack of a sensitive indicator of mild zinc deficiency hinders the scientific study of its health implications.

Because a sensitive indicator of zinc nutritional status is not readily available, the RDA for zinc was based on a number of different indicators of zinc nutritional status and represents the daily intake likely to prevent deficiency in nearly all individuals in a specific age and gender group. The RDA for adolescent boys and girls, aged 14 to 18 years, is 11 mg/day and 9 mg/day, respectively (113). A US national survey, NHANES 2001-2002, found that average dietary intake of zinc was 15.1 mg/day in adolescent boys and 9.5 mg/day in adolescent girls; only 4% of adolescent boys had intakes less than the EAR (8.5 mg/day), but 26% of adolescent girls had intakes less than the EAR (7.3 mg/day).

Shellfish, beef, and other red meats are rich sources of zinc; nuts and legumes are relatively good plant sources of zinc. Zinc bioavailability (the fraction of zinc retained and used by the body) is relatively high in meat, eggs, and seafood because of the relative absence of compounds that inhibit zinc absorption and the presence of certain amino acids (cysteine and methionine) that enhance zinc absorption. However, the zinc in whole-grain products and plant proteins is less bioavailable due to their relatively high content of phytic acid, a compound that inhibits zinc absorption (117). The enzymatic action of yeast reduces the level of phytic acid in foods. Therefore, leavened whole-grain breads have more bioavailable zinc than unleavened whole-grain breads (113).

Adolescent Pregnancy

Pregnancy during adolescence — a time when the girl is still growing herself — has been associated with increased risk of miscarriage, prematurity, low birth weight infants (<2,500 grams), and increased maternal and neonatal mortality (2, 118-119). Pregnant adolescents are also at a heightened risk for pregnancy-related complications, including pregnancy-induced hypertension and anemia (119). Because they are growing themselves, it is extremely important for pregnant adolescents to meet dietary intake recommendations. Recommendations for some key micronutrients needed for adolescent growth, including calcium, magnesium, phosphorus, and zinc, are higher than those for older pregnant women; see the discussion of Micronutrient Requirements During Pregnancy in a separate article. Pregnant adolescents are at increased risk for select micronutrient inadequacies, especially iron, zinc, calcium, magnesium, folate, vitamin B₆, vitamin D, and vitamin E (2, 120-121). Adequate nutrition is important not only for a healthy pregnancy outcome but also for the overall and skeletal health of the adolescent. A recent cross-sectional study of 719 postmenopausal women associated their pregnancy during adolescence with lower bone mineral density at several sites and a two-fold higher risk of osteoporosis compared to women without a history of adolescent pregnancy (122). However, it is not known whether adequate calcium intake during adolescent pregnancy might prevent age-related declines in bone mineral density or osteoporosis.

Safety

The FNB establishes a tolerable upper intake level (UL) for most micronutrients. The UL is the highest level of daily nutrient intake likely to pose no risk of adverse health effects in almost all individuals of a specified age group. This level applies to total daily intake from food, water, and supplements. Due to the potential for adverse effects, it is recommended that individuals not exceed the UL. Thus, individuals should use the UL as a guide to limit daily micronutrient intake, not as a recommended level of intake (123). There is no evidence that consumption of micronutrients at or above the UL results in any health benefits for adolescents, and the UL should not be exceeded except under medical supervision. Table 2 lists the UL for adolescents.

Conclusion

A healthy diet throughout puberty and adolescence is important to provide nutrients that support optimal physical growth and cognitive development. Although it is generally advised that micronutrients should be obtained from food, many adolescents do not reach daily intake recommendations for select micronutrients from diet alone. Therefore, the Linus Pauling Institute recommends that adolescents aged 14 to 18 years take a daily multivitamin/mineral supplement with 100% of the daily value (DV) for most vitamins and essential minerals, keeping the following suggestions in mind:

• Since the DV for vitamin A for those ages 4 and older (5,000 IU) is considerably higher than the current RDA for adolescents aged 14 to 18 years (3,000 IU/day for boys and 2,333 IU/day for girls), LPI recommends looking for a multivitamin/mineral supplement that provides no more than 2,500 IU (750 μg) of preformed vitamin A (usually labeled as vitamin A acetate or vitamin A palmitate) and no more than 2,500 IU of additional vitamin A as β-carotene.
• In general, multivitamin/mineral supplements contain only a small percentage of the RDA for calcium and magnesium; therefore, intake of calcium and magnesium from dietary sources, such as low-fat milk, is important. If the RDAs for these minerals (1,300 mg/day for calcium; 410 and 360 mg/day for magnesium for adolescent boys and girls, respectively) are not met through diet plus the multivitamin/mineral supplement, LPI recommends an additional, combined calcium-magnesium supplement for adolescents.
• Because there are limited dietary sources of vitamin D and many adolescents use sunscreens, which block skin synthesis of vitamin D, LPI recommends that all adolescents aged 14 to 18 years should have a daily intake of 600 to 1,000 IU (15 to 25 μg) of vitamin D, consistent with the recommendations of the Endocrine Society (71). Given the average vitamin D content in the diets of adolescents, supplementation may be necessary to meet this recommendation.

Authors and Reviewers

Written in July 2012 by:
Victoria J. Drake, Ph.D.
Linus Pauling Institute
Oregon State University

Reviewed in July 2012 by:
Pamela S. Hinton, Ph.D.
Associate Professor
Department of Nutrition and Exercise Physiology
University of Missouri
Columbia, Missouri

This article was underwritten, in part, by a grant from Bayer Consumer Care AG, Basel, Switzerland.

DRIs for sodium and potassium updated 4/12/19  Copyright 2012-2024  Linus Pauling Institute

References

Micronutrient Needs During Pregnancy and Lactation

Introduction

Nutrient needs during the life stages of pregnancy and lactation are increased relative to women who are not pregnant or lactating. Mathematical models predict that energy requirements increase by an estimated 300 kcal/day during the second and third trimesters of pregnancy and by 500 kcal/day during lactation (1). In practice, most women will require only approximately 200 additional kcal/day due to reduced levels of physical activity during pregnancy and to increased lipolysis of fat stores during breast-feeding [personal communication with Dr. Berthold Koletzko]. Relative to the increased energy requirement, the requirements for many micronutrients (vitamins and nutritionally essential minerals) are even higher during pregnancy and lactation; this article discusses micronutrient needs during these life stages.

Micronutrient Requirements During Pregnancy

Pregnancy is associated with increased nutritional needs due to physiologic changes of the woman and the metabolic demands of the embryo/fetus. Proper maternal nutrition during pregnancy is thus imperative for the health of both the woman and the offspring. Maternal malnutrition during pregnancy has been associated with adverse outcomes, including increased risk of maternal and infant mortality, as well as low-birth-weight newborns (<2,500 grams) — a measure that accounts for preterm birth and intrauterine growth restriction of the fetus (2, 3). Select nutrient deficiencies have also been linked to congenital anomalies and birth defects. In addition, gestational undernutrition has been implicated in increasing the offspring’s susceptibility to chronic disease (i.e., type 2 diabetes, hypertension, coronary heart disease, and stroke) in adulthood, a phenomenon sometimes called Barker’s hypothesis, the thrifty phenotype hypothesis, or the fetal origin of adult disease hypothesis (4, 5). Maternal undernutrition often refers to malnutrition caused by insufficient caloric (energy) intake from macronutrients (carbohydrates, proteins, and lipids) during pregnancy, but micronutrient deficiencies are also a form of undernutrition. Multiple micronutrient deficiencies commonly co-exist in pregnant women (6).

Daily requirements for many micronutrients during pregnancy are higher to meet the physiologic changes and increased nutritional needs of pregnancy. Good nutritional status prior to conception is also important for a healthy pregnancy. For instance, folic acid supplementation during the periconceptional period (about one month before conception until the end of the first trimester) dramatically reduces the incidence of devastating birth defects called neural tube defects (see Folate below). Thus, folic acid supplementation (at least 400 μg/day) is recommended for all women capable of becoming pregnant (7-9). A well-balanced diet throughout pregnancy is necessary to supply the developing embryo/fetus with micronutrients. In addition to folic acid supplementation, iron supplementation is generally needed to meet the increased demands for this mineral during pregnancy (see the section on Iron below).

The Food and Nutrition Board (FNB) of the Institute of Medicine establishes life-stage specific dietary reference intakes (DRIs) for each micronutrient; these reference values should be used to plan and assess dietary intakes in healthy people (10, 11). The DRIs include the estimated average requirement (EAR), the recommended dietary allowance (RDA), the adequate intake (AI), and the tolerable upper intake level (UL). The RDA, which is the average daily dietary intake level of a nutrient sufficient to meet the requirements of almost all (97.5%) healthy individuals in a specific life stage and gender group, should be used in the planning of diets for individuals (12). The FNB establishes an AI when an RDA cannot be determined. The below recommendations are specific to the life stages of pregnancy and lactation. For most micronutrients, the RDA or AI for pregnant women is increased compared to nonpregnant women of the same age (Table 1). The discussion below largely focuses on these recommendations for select micronutrients during pregnancy but also notes major concerns for micronutrient toxicity or teratogenicity. The UL is the highest level of daily intake that is likely to pose no risk of adverse health effects in almost all individuals of a specified life stage. For the UL for each micronutrient during pregnancy, see Table 2.

Vitamins

Biotin

Biotin is needed as a cofactor for carboxylase enzymes and for the attachment of biotin to molecules, such as proteins, in a process known as "biotinylation" (13). Rapidly dividing cells of the developing fetus require the vitamin for synthesis of essential carboxylase enzymes and for histone biotinylation. Although maternal biotin deficiency in certain strains of mice causes malformations in the offspring, namely cleft palate and limb shortening (14, 15), a link between biotin deficiency and birth defects in humans has not been observed.

Experimentally induced, marginal biotin deficiency results in the increased urinary excretion of 3-hydroxyisovaleric acid (3-HIA) and decreased urinary excretion of biotin and the biotin catabolites, bisnorbiotin (BNB) and biotin disulfoxide (BSO) (16, 17). Abnormally elevated urinary excretion of 3-HIA and abnormally decreased urinary excretion of biotin are the most extensively validated biomarkers of low biotin status (18).

Two observational studies have reported that there is an increased urinary excretion of 3-HIA during pregnancy, though other indices of biotin status were not consistently altered (19, 20). Similarly, a 2014 feeding study in which all subjects consumed a mixed diet with a known amount of biotin (average daily intake, 57 μg biotin/day), urinary 3-HIA excretion was higher in pregnant compared to nonpregnant women, while urinary biotin and BNB excretion did not differ between the groups (21). Supplementation with biotin (300 μg/day for 14 days) reduced urinary 3-HIA and increased urinary biotin excretion in pregnant women with elevated 3-HIA; however, this intervention did the same for nonpregnant controls considered to have normal biotin status (22).

Elevated urinary excretion of 3-HIA during pregnancy could be due to several possibilities. Some suggest that it reflects marginal biotin deficiency and the need for more biotin during pregnancy (23, 24). Alternatively, increased 3-HIA in isolation could reflect altered leucine metabolism or renal handling of organic acids during pregnancy (18).

At this time, the AI for biotin (30 μg/day) is the same for pregnant and nonpregnant women. Biotin is widespread in food, though its concentration varies substantially (see the article on Biotin). Based on dietary intake data from the National Health and Nutrition Examination Survey (NHANES) II (18, 25) and the above-mentioned feeding study (21), a typical mixed diet provides approximately 40 to 60 μg of biotin/day.

Folate

The terms folate and folic acid are often used interchangeably, but folic acid is the synthetic form of the vitamin that is only found in fortified food and supplements. Folic acid is more bioavailable than folate from food (see the article on Folate); folic acid is converted to biologically active forms of folate in the body. Folate is needed for amino acid and nucleic acid (DNA and RNA) metabolism. Adequate folate status is critical to embryonic and fetal growth — developmental stages characterized by accelerated cell division. In particular, folate is needed for closure of the neural tube early in pregnancy, and periconceptional supplementation with folic acid has been shown to dramatically reduce the incidence of neural tube defects (NTDs) (reviewed in 26 and 27). NTDs are devastating congenital malformations that can occur as either anencephaly or spina bifida. Because these birth defects occur between 21 to 27 days after conception (28), often before many women recognize their pregnancy, it is recommended in the US that all women capable of becoming pregnant take supplemental folic acid (7).

A recent systematic review of five trials, including 7,391 women, found that periconceptional folic acid supplementation, alone or with other micronutrients, was associated with a 69% lower risk of NTDs (risk ratio (RR), 0.31; 95% confidence interval (CI), 0.17 to 0.58) (29). The RDA for pregnant women is 600 μg/day of dietary folate equivalents (DFE), which is equivalent to 300 μg/day of synthetic folic acid on an empty stomach or 353 μg/day of synthetic folic acid with a meal (see the article on Folate). The US Preventive Services Task Force recommends a daily supplement of 400-800 μg of folic acid, in addition to consuming food folate from a varied diet, for all women planning or capable of pregnancy (9). Supplemental folic acid use at the higher end of this suggested range has been recommended by some (27, 30), and 800 μg/day from supplements plus dietary intake is safe for women of childbearing age.

Multivitamin/mineral supplements marketed in the US commonly contain 400 μg of folic acid, and many prenatal supplements marketed in the US contain 800 μg of folic acid. Folic acid may also be present in the food supply: several countries have programs of mandatory folic acid fortification to help reduce the incidence of NTDs; for example, the US FDA implemented legislation in 1998 requiring the fortification of all enriched grain products with folic acid at a level of 140 μg folic acid/100 g of product (31). Mandatory fortification in the US has resulted in a 28 percent reduction (an estimated 1,326 births/year) in the prevalence of NTDs (32).

Doses greater than 1 mg/day of folic acid are used pharmacologically to treat hyperhomocysteinemia and to prevent reoccurrence of NTDs (33). Women who have had a previous NTD-affected pregnancy may be advised to consume up to 4 to 5 mg/day (4,000 to 5,000 μg/day) of folic acid if they are planning a pregnancy, but this level of supplementation should be prescribed by their medical provider (see the CDC recommendations and the World Health Organization [WHO] guidelines).

A new form of folate, 5-methyltetrahydrofolate (5-MTHF), has been proposed as an alternative to folic acid. 5-MTHF is less likely to mask a severe vitamin B₁₂ deficiency, exhibits lower interaction potential with antimalarial drugs, and may be preferable for women with an MTHFR polymorphism (26, 34). While the effect of 5-MTHF supplementation on NTDs has not yet been evaluated, it is at least as effective as folic acid at raising red blood cell folate status and reducing homocysteine concentrations in nonpregnant healthy young women (35-38) and lactating women (39).

Inadequate folate status may also be linked to other birth defects, such as cleft lip, cleft palate, and limb malformations, but there are insufficient data to evaluate the effect of folic acid supplementation on these outcomes (26). However, results of some case-control studies (40-44) and controlled trials (45, 46) have suggested that periconceptional supplementation with a multivitamin containing folic acid may protect against congenital cardiovascular malformations, especially conotruncal (outflow tract) and ventricular septal defects. A 2006 systematic review and meta-analysis concluded that such supplementation was associated with a 22% lower risk of cardiovascular defects in case-control studies and a 39% lower risk in cohort studies and randomized controlled trials (47).

Impaired folate status during pregnancy may also be associated with other adverse pregnancy outcomes. Elevated blood homocysteine concentrations, considered an indicator of functional folate deficiency, have been associated with increased risk of preeclampsia, premature delivery, low placental weight, low birth weight, very low birth weight (<1,500 grams), small for gestational age, neural tube defects (NTDs), and stillbirth (48-50). Thus, it is reasonable to maintain folic acid supplementation throughout pregnancy, even after closure of the neural tube, in order to decrease the risk of other potential problems during pregnancy.

Riboflavin

Riboflavin is a component of flavocoenzymes involved in energy metabolism, as well as antioxidant functions. The Food and Nutrition Board of the Institute of Medicine recommends that all pregnant women consume 1.4 mg of riboflavin daily. Riboflavin deficiency has been implicated in preeclampsia — a pregnancy-associated complication characterized by elevated blood pressure, protein in the urine, and edema (significant swelling). Preeclampsia is estimated to affect 2%-8% of all pregnancies (51), and about 5% of women with preeclampsia progress to eclampsia, a significant cause of maternal death (52). Eclampsia is characterized by seizures, in addition to high blood pressure and increased risk of hemorrhage (severe bleeding) (52). Although the specific causes of preeclampsia are not known, decreased intracellular concentrations of flavocoenzymes could cause mitochondrial dysfunction, increase oxidative stress, and interfere with nitric oxide release and thus blood vessel dilation. All of these changes have been associated with preeclampsia, but there have been few studies on the association of riboflavin nutritional status and the condition. A study in 154 pregnant women at high risk for preeclampsia found that those who were riboflavin deficient were 4.7 times more likely to develop preeclampsia than those who had adequate riboflavin nutritional status (53). However, a small randomized, double-blind, placebo-controlled trial in 450 pregnant women at high risk for preeclampsia found that supplementation with 15 mg of riboflavin daily did not prevent the condition (54).

Vitamin A

Adequate maternal status of vitamin A is critical for a healthy pregnancy. Forms of the vitamin, known as retinoids, are involved in the regulation of gene expression, cellular proliferation and differentiation, growth and development, vision, and immunity (see the article on Vitamin A). The retinoids, retinol and retinoic acid, are essential for embryonic and fetal development (55); for example, retinoic acid functions in forming the heart, eyes, ears, and limbs (56). Animal studies demonstrate that severe vitamin A deficiency or excess during critical periods of development results in a spectrum of malformations, especially affecting craniofacial structures, limbs, and visceral organs (57).

Forms of vitamin A are also necessary for maternal health. Vitamin A deficiency during pregnancy has been linked to impaired immunity, increased susceptibility to infection, increased risk of maternal morbidity and mortality (58-61), and night blindness (62). Vitamin A deficiency may exacerbate iron-deficiency anemia (see section on Iron below); co-supplementation with vitamin A and iron seems to ameliorate anemia more effectively than either micronutrient supplement alone (63). Vitamin A deficiency is a major public health problem in developing nations, where availability of foods containing preformed vitamin A (retinol) and provitamin A carotenoids is limited (for information on food sources of vitamin A, see the article on Vitamin A). The RDA during pregnancy is 750 to 770 μg/day (2,500 to 2,567 IU/day) of preformed vitamin A (see Table 1 above).

Although normal embryonic and fetal development require sufficient maternal vitamin A intake, consumption of excess preformed vitamin A during pregnancy causes birth defects. An increased risk of vitamin A-associated birth defects has not been observed at supplemental doses below 3,000 μg (10,000 IU)/day of preformed vitamin (64). However, because a number of foods in the US are fortified with preformed vitamin A, the Linus Pauling Institute recommends that pregnant women avoid multivitamin or prenatal supplements that contain more than 750 μg (2,500 IU) of preformed vitamin A. Vitamin A from β-carotene is not known to increase the risk of birth defects (58), although the safety of high-dose β-carotene supplements in pregnancy has not been well studied. Moreover, pharmacological use of retinoids by pregnant women causes serious birth defects; thus, tretinate, isotretinoin (Accutane), and other retinoids should not be used during pregnancy or if there is a possibility of becoming pregnant (65). Use of tretinoin (Retin-A), a topically applied retinoid, exhibits very low systemic absorption, but is not recommended during pregnancy due to possible risks (66). It is important to note that retinoids tend to be very long acting; birth defects have been reported to occur months after discontinuing retinoid therapy (57). Retinoids are used therapeutically to treat retinitis pigmentosa, acute promyelocytic leukemia, various skin diseases, and other conditions.

Vitamin B₆

Vitamin B₆ has diverse roles in the body, including nervous system function, red blood cell formation and function, steroid hormone function, nucleic acid synthesis, and niacin formation. Pyridoxal, pyridoxine, and pyridoxamine are three forms of the vitamin. The RDA for vitamin B₆ during pregnancy is 1.9 mg/day. Vitamin B₆ has been used since the 1940s to treat nausea during pregnancy. The results of two double-blind, placebo-controlled trials that used 25 mg of pyridoxine every eight hours for three days (67) or 10 mg of pyridoxine every eight hours for five days (68) suggest that vitamin B₆ may be beneficial in alleviating morning sickness. Each study found a slight but significant reduction in nausea or vomiting in pregnant women. A third randomized trial compared high-dose (10 mg/day) and low-dose (1.28 mg/day) vitamin B₆ in 60 pregnant women experiencing nausea and/or vomiting prior to the twelfth week of gestation (69). After two weeks, nausea and vomiting scores decreased to an equal extent in both supplementation groups. A 2014 pooled analysis indicates that supplemental vitamin B₆ alone may be effective in alleviating nausea, but not vomiting, during pregnancy (70). Vitamin B₆ at the above-mentioned dosages is considered safe during pregnancy, and the vitamin has been used in pregnant women without any evidence of fetal harm (68, 71).

Vitamin B₆ was included in the medication Bendectin (a delayed-release formulation of 10 mg doxylamine succinate [an antihistamine] and 10 mg pyridoxine hydrochloride [vitamin B₆]), which was prescribed for the treatment of morning sickness and later withdrawn from the market in 1983 due to unproven concerns that it increased the risk of birth defects (72). Since that time, several investigations have shown the combination of doxylamine/pyridoxine to be both effective and safe, and in 2013, the US Food and Drug Administration approved this same formulation for the treatment of nausea and vomiting in pregnancy (reviewed in 73 and 74). The American and Canadian Colleges of Obstetrics and Gynecology and the Association of Professors of Gynecology and Obstetrics recommend the combination of doxylamine/pyridoxine as first-line therapy for nausea and vomiting during pregnancy (reviewed in 75).

The tolerable upper intake level (UL) for vitamin B₆ during pregnancy is 80 to 100 mg/day; see Table 2.

Vitamin B₁₂

In humans, vitamin B₁₂ is needed as a cofactor for two enzymes. One converts homocysteine to the amino acid, methionine. Methionine is required for the synthesis of S-adenosylmethionine, a methyl group donor used in many biological methylation reactions (76). DNA methylation that occurs during embryonic and fetal development modulates gene expression, cell differentiation, and the formation of organs (77). Thus, adequate vitamin B₁₂ status during pregnancy is critical.

Inadequate dietary intake of vitamin B₁₂ causes elevated homocysteine concentrations, which have been associated with adverse pregnancy outcomes, including preeclampsia, premature delivery, low placental weight, low birth weight, very low birth weight (<1,500 grams), small for gestational age, neural tube defects (NTDs), and stillbirth (48-50). Moreover, low serum concentrations of vitamin B₁₂ during pregnancy have been linked to an increased risk for NTDs (78), and there is concern that folic acid supplementation during pregnancy may mask the clinical diagnosis of vitamin B₁₂ deficiency. For these reasons, adequate vitamin B₁₂ intake during pregnancy (RDA=2.6 μg/day) is important.

To ensure a daily intake of 6 to 30 μg of vitamin B₁₂ in a form that is easily absorbed, the Linus Pauling Institute recommends that women who are planning a pregnancy take a daily multivitamin supplement or eat a breakfast cereal fortified with vitamin B₁₂ (for more information, see the article on Vitamin B₁₂).

Vitamin C and Vitamin E

Because oxidative stress has been implicated in the pathogenesis of preeclampsia (79), nutritional status of the two antioxidant vitamins, vitamin C and vitamin E, may be important in preventing the condition. These vitamins have other biological functions; for more information, see the separate articles on Vitamin C and Vitamin E. Several trials have investigated whether supplementation with vitamins C and E improves pregnancy-associated hypertension or preeclampsia, but evidence supporting such an effect is largely lacking. An early placebo-controlled trial found that supplementation with 1,000 mg/day of vitamin C and 400 mg of vitamin E (RRR-α-tocopherol) was associated with a 61% reduction in the incidence of preeclampsia in women at increased risk for the condition (80). However, more recent randomized controlled trials have not found supplementation at these dosages to be effective in preventing preeclampsia in high- or low-risk women (81-84). Nevertheless, adequate intake of antioxidant vitamins is important throughout pregnancy. According to data from the US National Health and Nutrition Examination Survey (NHANES), 42%-46% and 85%-94% of US adults do not meet the estimated average requirement (EAR) for vitamin C and vitamin E, respectively (85). The Linus Pauling Institute’s recommends that adults, including pregnant women, reach daily intakes of at least 400 mg of vitamin C and 15 mg (22.5 IU) of vitamin E.

Vitamin D

In 2010, the FNB of the Institute of Medicine set the RDA for vitamin D at 15 μg (600 IU)/day for all pregnant women (86). The FNB based this recommendation on a limited number of studies using bone health as the only indicator, assuming minimal sun exposure. Vitamin D, however, has a number of other roles in disease prevention and health (see the article on Vitamin D), and several vitamin D researchers believe that vitamin D requirements for adults, including pregnant women, are higher than the current RDA (87-91). Moreover, a number of studies indicate that vitamin D deficiency and insufficiency are quite common among pregnant women (92-101).

Low vitamin D status in pregnancy has been associated with an increased risk of adverse outcomes for both the mother and the infant. For pregnant women, vitamin D deficiency (serum 25-hydroxyvitamin D less than 50 nmol/L [20 ng/mL]) has been associated with an increased risk of preeclampsia and gestational diabetes (102, 103). For infants, low maternal vitamin D status has been associated with an increased risk of preterm birth (birth before 37 weeks of gestation) and low birth weight (a newborn weighing less than 2,500 grams) (104-106). A pooled analysis of 15 randomized controlled trials concluded that vitamin D supplementation raises serum 25-hydroxyvitamin D during pregnancy and may reduce the risk of preeclampsia, low birth weight, and preterm birth; notably, combined supplementation of vitamin D and calcium may increase the risk of preterm birth (107).

Vitamin D is found in very few foods, and prenatal supplements often contain only 10 μg (400 IU) of vitamin D. Sunlight exposure is the main source of the vitamin: vitamin D₃ (cholecalciferol) is synthesized in skin cells following exposure to ultraviolet-B radiation. However, the contribution of sun exposure to vitamin D status depends on many factors, including latitude, skin color, amount of skin exposed, duration of exposure, and the use of sunscreens, which effectively block skin production of vitamin D. Thus, vitamin D supplementation throughout pregnancy is likely needed to achieve body concentrations thought to benefit fetal and maternal health. The Linus Pauling Institute recommends that generally healthy adults, including pregnant women, take 2,000 IU (50 μg) of supplemental vitamin D daily. Because sun exposure, diet, skin color, and obesity have variable, substantial impact on body vitamin D concentrations, measuring serum concentrations of 25-hydroxyvitamin D — the clinical indicator of vitamin D status — is important. The Linus Pauling Institute recommends aiming for a serum 25-hydroxyvitamin D level of at least 75 nmol/L (30 ng/mL).

Vitamin K

The adequate intake (AI) for vitamin K (90 μg/day for women aged 19-50 years and 75 μg/day for those aged 14-18 years) is not increased during pregnancy, and a tolerable upper intake level (UL) has not been set for vitamin K. However, if taken during pregnancy, a number of drugs, including warfarin, rifampin, isoniazid, and anticonvulsants, may increase the risk of neonatal vitamin K deficiency and hemorrhagic disease of the newborn (108).

Placental transfer of vitamin K is low, thus all infants are born with low concentrations of vitamin K. A small proportion of newborns (0.25 to 1.1%) does not have enough vitamin K to make their blood clot and may develop vitamin K deficiency bleeding (VKDB) (109). There are three categories of VKDB depending on the age of onset: early (0-24 hours), classic (one to seven days), and late (two to 12 weeks) (110-112). Early VKDB is seen mainly in infants of mothers taking drugs that inhibit vitamin K, as listed above. Classic VKDB is more common and presents as bruising, gastrointestinal blood loss, or bleeding from the umbilicus, skin, or site of circumcision. Late VKDB is particularly concerning as it can lead to life-threatening intracranial bleeding. Randomized controlled trials have demonstrated that prophylactic intramuscular (IM) vitamin K injection of the newborn raises plasma vitamin K concentration, reduces PIVKA II (a marker of vitamin K deficiency), improves prothrombin time, and decreases the risk of classic VKDB compared to placebo (reviewed in 111). Administration of multiple oral doses of vitamin K can reduce PIVKA II concentrations and raise plasma vitamin K concentration but is associated with an increased incidence of late VKDB (109, 111, 113). The American Academy of Pediatrics and several international professional organizations recommend that all babies receive 0.5 to 1.0 mg intramuscular vitamin K₁ injection shortly after birth to prevent VKDB (109, 110, 114). 

Minerals

Calcium

Although 200 to 250 mg/day of calcium is transferred to the fetus, primarily in the last trimester, dietary intake requirements of calcium are not increased due to maternal physiological adaptations. In particular, the efficiency of intestinal calcium absorption doubles during pregnancy, and the mineral can also be transiently mobilized from maternal stores (i.e., the skeleton) to support fetal needs for calcium. Permanent demineralization of bone during pregnancy has not been observed (86, 115). Moreover, there is no evidence from randomized controlled trials that calcium supplementation during pregnancy confers any benefit to maternal or fetal bone health (116, 117). The RDA is 1,300 mg/day for women aged 14-18 years and 1,000 mg/day for women aged 19-50 years.   

Calcium intake during pregnancy, however, may influence the risk for pregnancy-induced hypertension (PIH). PIH, which occurs in 10% of pregnancies and is a major health risk for pregnant women and the fetus, is a term that includes gestational hypertension, preeclampsia, and eclampsia. Gestational hypertension is defined as an abnormally high blood pressure that usually develops after the 20^th week of pregnancy. In addition to gestational hypertension, preeclampsia includes the development of edema (severe swelling) and proteinuria (protein in the urine). Preeclampsia may progress to eclampsia in which life-threatening convulsions and coma may occur (118). Risk factors for PIH include first pregnancies, multiple gestations (e.g., twins or triplets), chronic high blood pressure, diabetes, and some autoimmune diseases. Although the cause of PIH is not entirely understood, calcium metabolism appears to play a role. Low calcium intake during pregnancy may: (1) stimulate parathyroid hormone release, thereby increasing intracellular calcium and vascular smooth muscle contractility; and/or (2) stimulate renin release, leading to vasoconstriction and retention of sodium and fluid (119). Data from observational studies suggest an inverse relationship between dietary calcium intake and the incidence of PIH (120). Additionally, a recent systematic review of randomized, placebo-controlled trials (RCTs) reported that calcium supplementation during pregnancy (≥1,000 mg/day) was associated with a 35% lower risk of high blood pressure and a 55% lower risk of preeclampsia; the risk reduction for preeclampsia was even stronger for women considered to be at high risk for the condition (78% lower risk compared to placebo) and women with low dietary intake of calcium (64% lower risk compared to placebo) (121). This analysis also found that calcium supplementation lowered the risk of preterm birth by 24%, but no significant effect of calcium supplementation was found regarding the risk of stillbirth, admission to neonatal intensive care unit, or neonatal mortality before hospital discharge. Of four RCTs that monitored maternal death or serious morbidity, one RCT (122) reported a 20% reduced risk for the "severe maternal morbidity and mortality index" (a summary indicator defined as the presence of at least one of the following outcomes: maternal admission to intensive care or any special care unit, eclampsia, severe preeclampsia, placental abruption, HELLP syndrome [hemolysis, elevated liver enzymes, and low platelet count], renal failure, or death) with calcium supplementation; no events occurred in the other three RCTs (121).

Chromium

Chromium is known to enhance the action of insulin; therefore, several studies have investigated the utility of chromium supplementation for the control of blood glucose concentrations in type 2 diabetes (see the article on Chromium). However, its use in gestational diabetes — a condition that affects 4.6%-9.2% of all pregnancies in the US (123) — has not been well studied. Gestational diabetes is a glucose intolerance that usually appears in the second or third trimester of pregnancy; blood glucose concentrations must be tightly controlled to prevent adverse effects on the developing fetus and other pregnancy complications. After delivery, glucose tolerance generally reverts to normal, but women are at a heightened risk of developing type 2 diabetes (124). In fact, a recent systematic review and meta-analysis found that the risk of developing type 2 diabetes in women diagnosed with gestational diabetes is more than 7-fold higher than women not diagnosed with gestational diabetes (125). Gestational diabetes is also considered a risk factor for cardiovascular disease (124). Two observational studies found that serum concentrations of chromium in pregnant women were not associated with glucose intolerance or gestational diabetes (126, 127), although serum chromium concentrations may not necessarily reflect tissue chromium concentrations. An eight-week placebo-controlled trial in 24 women with gestational diabetes found that supplementation in the form of chromium picolinate (4 μg/day of chromium per kilogram of body weight) was associated with lower fasting blood glucose and insulin concentrations (128). However, it is important to note that insulin therapy was still required to normalize the severely elevated blood glucose concentrations. Thus, more research, especially from randomized controlled trials, is needed to determine whether chromium supplementation has any utility in the treatment of gestational diabetes. 

Iodine

Iodine requirements are increased by more than 45% during pregnancy: the RDA for pregnant women is 220 μg/day compared to 150 μg/day for women who are not pregnant. Adequate intake of this mineral is needed for maternal thyroid hormone production, and thyroid hormone is needed for myelination of the central nervous system and is thus essential for normal fetal brain development (129). If iodine deficiency leads to inadequate production of thyroid hormone during pregnancy, irreversible brain damage in the fetus may occur (130). Severe maternal iodine deficiency has also been associated with increased incidence of miscarriage, stillbirth, and birth defects (131).

One of the most devastating effects of severe maternal iodine deficiency is congenital hypothyroidism (132). A severe form of congenital hypothyroidism may lead to a condition that is sometimes referred to as cretinism and result in irreversible mental retardation. Cretinism occurs in two forms, neurologic and myxedematous, although there is considerable overlap between them. The neurologic form is characterized by mental and physical retardation and deafness; it results from maternal iodine deficiency that affects the fetus before its own thyroid is functional. The myxedematous or hypothyroid form is characterized by short stature and mental retardation (133). Severe maternal iodine deficiency has also been linked to neurocognitive deficits in the offspring (134). In severely iodine-deficient pregnant women, iodine supplementation effectively reduces rates of cretinism, and improves offspring cognitive function and survival (reviewed in 135). The timing of iodine supplementation appears to be important: supplementation should be initiated prior to conception and early in pregnancy (before the 10^th week of gestation) in order to see beneficial effects on offspring neurocognitive outcomes (135).

Even mild forms of maternal iodine deficiency may have adverse effects on cognitive development in the offspring (136), though this outcome is less well studied. Randomized controlled trials conducted in moderately iodine deficient pregnant women demonstrate that iodine supplementation increases thyroid gland volume but has no effect on thyroid hormone concentrations compared to placebo (reviewed in 130 and 135). The extent to which supplementation in moderately iodine deficient pregnant women affects neurocognitive outcomes in their offspring is currently under investigation (137).

Iodine deficiency is now accepted as the most common cause of preventable brain damage in the world (131). Thus, adequate intake of the mineral throughout pregnancy is critical. A daily supplement providing 150 μg of iodine, as recommended by the American Thyroid Association (138), will help to ensure that US pregnant women consume sufficient iodine. However, it is important to note that several prenatal supplements and some multivitamin/mineral supplements on the market in the US do not contain iodine (139), presumably because manufacturers assume that women receive sufficient iodine through iodized salt and other food sources. For more information on iodine and iodine deficiency disorders, see the article on Iodine.

Iron

Iron requirements are significantly increased during pregnancy: the RDA is 27 mg/day for pregnant women of all ages compared to 15 to 18 mg/day for nonpregnant women. Many women have dietary iron intakes below current recommendations. National surveys in the US indicate that the average dietary iron intake is about 12 mg/day in nonpregnant women and 15 mg/day in pregnant women (140). Iron is needed for a number of biological functions (see the article on Iron), but during pregnancy, the mineral is generally needed to support growth and development of the fetus and placenta and to meet the increased demand for red blood cells to transport oxygen. Intestinal absorption of dietary iron increases during the second and third trimesters to accommodate for expansion of red cell mass (140). Maternal blood volume expands by almost 50% during pregnancy, which results in a hemodilution of red blood cells (141).

Despite maternal physiologic changes that enhance iron absorption, many women develop iron-deficiency or iron-deficiency anemia during pregnancy. The World Health Organization estimates that the worldwide prevalence of anemia among pregnant women is 42%; the prevalence of anemia is much higher in less developed nations compared with industrialized nations, with almost 90% of these anemic women living in Africa or Asia (142). In pregnant women in the US, the prevalence of iron deficiency is 18%, and the prevalence of iron-deficiency anemia is 5% (143). Anemias can be caused by deficiencies in other micronutrients, such as folate or vitamin B₁₂, but iron deficiency is the primary cause of anemia during pregnancy (1). Severe iron-deficiency anemia has been associated with an increased risk of maternal death (142) and with an increased risk of low birth weight infants (<2,500 grams), premature delivery, and perinatal mortality (144).

Two 2015 systematic reviews evaluated the effect of routine iron supplementation compared to placebo or no treatment on maternal and birth outcomes (145, 146). Both reviews found that routine supplementation with iron improved maternal iron status and decreased the risk of iron deficiency and iron-deficiency anemia at term. There is some indication that maternal iron supplementation could improve birth outcomes (namely preterm birth and low birth weight) in developing countries, but the evidence was deemed of low quality (146). Women taking higher doses of iron (≥60 mg/day) tended to have abnormally high hemoglobin values at term and were more likely to report side effects (146); side effects of high-dose iron supplements include nausea, constipation, vomiting, and diarrhea.

Iron status of the woman at the time of conception is important for a healthy pregnancy, to avoid postpartum anemia, and to provide the breast-feeding infant with sufficient iron stores until six months of age, when complementary feeding is recommended. Because of the increased demands for the mineral during the second and third trimesters of pregnancy, iron supplementation (30 mg/day) is usually recommended beginning at 12 weeks’ gestation (147). Absorption of nonheme iron, which is the form of iron found in supplements, is affected by a number of enhancers (e.g., vitamin C) as well as inhibitors (e.g., polyphenols found in tea and coffee). In general, iron supplements are better absorbed on an empty stomach. High doses of iron supplements taken together with zinc supplements on an empty stomach can inhibit the absorption of zinc (140, 148); supplemental iron at 38 to 65 mg/day of elemental iron may decrease zinc absorption (149). For more information about dietary and supplemental sources of iron, as well as the side effects and safety of iron, see the article on Iron. 

Magnesium

The mineral magnesium plays a number of important roles in the structure and the function of the human body (see the article on Magnesium), and adequate intake of the mineral is needed for normal embryonic and fetal development. National dietary surveys indicate that magnesium insufficiency is relatively common in the US, with 56% of American adults not meeting the EAR — the nutrient intake value that is estimated to meet the requirement of half of the healthy individuals in a particular life stage and gender group (150). Good sources of magnesium include green leafy vegetables, whole grains, and nuts (see the article on Magnesium). Several multivitamin/mineral and prenatal supplements do not contain magnesium or contain no more than 100 mg of magnesium.

Preeclampsia-eclampsia is a disease that is unique to pregnancy and may occur anytime after 20 weeks’ gestation. Preeclampsia is defined as the presence of elevated blood pressure and protein in the urine; severe swelling (edema) may also be present. Eclampsia occurs with the addition of seizures to these symptoms. Approximately 5%-8% of women with preeclampsia go on to develop eclampsia in developing countries, which is a significant cause of maternal death (84).

A 2014 pooled analysis of randomized controlled trials concluded that oral magnesium supplementation during pregnancy has no significant effect on perinatal mortality, small-for-gestational age, or the risk of preeclampsia (151). Intravenous administration of high-dose magnesium sulfate has been the treatment of choice for preventing eclamptic seizures that may occur in association with preeclampsia-eclampsia in late pregnancy or during labor (152-154). Magnesium is believed to relieve cerebral blood vessel spasm and promote peripheral vasodilation, thereby increasing blood flow to the brain (155-157).

Zinc

The RDA for zinc is increased during pregnancy (from 8 mg/day-9 mg/day to 11 mg/day-12 mg/day), and pregnant women, especially teenagers, are at increased risk of zinc deficiency. It has been estimated that 82% of pregnant women in the world may have inadequate intake of dietary zinc (158), leading to poor nutritional status of the mineral. Poor nutritional status of zinc during pregnancy has been associated with a number of adverse outcomes, including low birth weight (<2,500 grams), premature delivery, labor and delivery complications, and congenital anomalies (159). However, the results of maternal zinc supplementation trials in the US and developing countries have been mixed (160). A 2014 systematic review of 16 randomized controlled trials found that zinc supplementation during pregnancy was associated with a 14% reduction in premature deliveries; the lower incidence of preterm births was observed mainly in low-income women (161). This analysis, however, did not find zinc supplementation to benefit other indicators of maternal or infant health.

It is important to note that supplemental levels of iron (38 to 65 mg/day of elemental iron), but not dietary levels of iron, may decrease zinc absorption (149). Because iron supplementation is often recommended during pregnancy (see Iron above), pregnant women who take more than 60 mg/day of elemental iron may want to take a prenatal or multivitamin-mineral supplement that also includes zinc (162).

Other Nutrients

Choline

Choline can be synthesized by the body in small amounts, but dietary intake is needed to maintain health (163). Choline is essential for embryonic and fetal brain development, liver function, and placental function (164). The choline metabolite betaine is a source of methyl (CH₃) groups required for methylation reactions; DNA methylation that occurs during embryonic and fetal development modulates gene expression, cell differentiation, and the formation of organs (77). A mother delivers large amounts of choline to the fetus across the placenta and to the infant via breast milk, placing an increased demand on maternal stores of choline during pregnancy and lactation (164). The induction of de novo choline synthesis by the high levels of estrogen during pregnancy helps to meet this increased demand (165). Additionally, pregnant women are encouraged to consume choline-rich foods, such as eggs, meat, and seafood (for dietary sources, see the article on Choline). The adequate intake (AI) for pregnant women is 450 mg/day of choline, slightly higher than the 425 mg/day recommended for nonpregnant women (166).

Case-control studies have reported mixed results regarding the relationship between dietary choline intake or blood choline concentration and the risk of neural tube defects (NTDs). One case-control study reported a lower risk of having an NTD-affected pregnancy in those with the highest intake of betaine and choline combined (167), while two other studies found no association between maternal choline intake and NTD risk (168, 169). Similarly, one case-control study found low serum choline concentration was associated with a higher risk of NTDs (170), while another study found no such association (171). Additionally, it is not known if supplementation with choline or betaine, like supplementation with folic acid (see Folate above), will lower the incidence of NTDs. More research is needed to determine whether choline is involved in the etiology of NTDs.

Maternal intake of choline during pregnancy could possibly affect cognitive abilities of the offspring. Choline supplementation in pregnant rats, as well as rat pups during the first month of life, leads to improved performance in spatial memory tests months after choline supplementation has been discontinued (172). A review by McCann et al. discusses the experimental evidence from rodent studies regarding the availability of choline during prenatal development and cognitive function in the offspring (173). It is not clear whether findings in rodent studies are applicable to humans. One randomized controlled trial demonstrated that choline supplementation (750 mg/day of choline in the form of phosphatidylcholine administered from week 18 of gestation through 90 days postpartum) in pregnant women consuming a moderate-choline diet (approximately 360 mg/day) was safe but did not enhance infant cognitive function at 10 or 12 months of age (174).

Finally, choline is important for homocysteine metabolism during pregnancy. Methyl groups derived from choline may be used to convert homocysteine to methionine. Elevated blood homocysteine concentrations have been associated with increased risk of preeclampsia, premature delivery, low placental weight, low birth weight (<2,500 grams), very low birth weight (<1,500 grams), small for gestational age, NTDs, and stillbirth (48-50).

Essential fatty acids

Although not micronutrients, certain fatty acids are required in the maternal diet during pregnancy and lactation; the US Institute of Medicine’s adequate intake (AI) recommendations for omega-3 and omega-6 fatty acids during pregnancy and lactation are listed in the separate article on Essential Fatty Acids. For more information on the importance of omega-3 fatty acids during these life stages, see two sections in the separate article on essential fatty acids: Visual and neurological development and Pregnancy and lactation. Information about environmental contaminants in fish and supplements is included in the sections, Contaminants in fish and Contaminants in supplements. 

Safety in Pregnancy

Maternal Micronutrient Requirements During Lactation

Breast-feeding confers health benefits to the child, as well as the mother (175). Breast milk is the ideal source of nutrition for the infant and also contains a number of bioactive compounds important in immunity, such as antibodies, cytokines, antimicrobial agents, and oligosaccharides (176). The American Academy of Pediatrics recommends exclusive breast-feeding for the first six months of infancy, followed by continued breast-feeding as complementary foods are introduced, with continuation of breast-feeding until 12 months postpartum or longer as mutually desired by the mother and child (177). The World Health Organization recommends exclusive breast-feeding for the first six months of life and continued breast-feeding, with complementary feeding, up to two years or more postpartum (178). There are, however, a few exceptions when breast-feeding is contraindicated, including those listed on the CDC website.

Lactation is extremely energy expensive (exceeding pre-pregnancy demands by approximately 500 kcal/day), and macronutrient requirements for breast-feeding women are even higher than during pregnancy (175). Likewise, the intake recommendations (RDA or AI) for most micronutrients, which are based on amounts secreted in breast milk, are higher for lactating women compared to pregnant women (see Table 3). One notable exception is the RDA for iron, which is significantly lower during lactation (9 to 10 mg/day) compared to pregnancy (27 mg/day) (140). Breast milk is considered to be low in iron; however, the iron content of breast milk is not influenced by changes in maternal iron status, such as through maternal supplementation (59). The RDA for folate is also lower during lactation compared with pregnancy. Dietary intake recommendations for calcium remain unchanged for lactating women compared to recommendations for nonlactating women, and calcium content in breast milk does not reflect maternal intake of the mineral. Adequate calcium is maintained in breast milk because of maternal physiological changes that involve transient bone resorption; increased maternal intake of calcium through diet and supplementation does not prevent maternal bone demineralization, and studies have shown that maternal bone mineral content is restored upon weaning (179).

In general, the amounts of water-soluble vitamins (B vitamins and vitamin C) in breast milk reflect maternal intake from diet and/or supplements. Thus, meeting daily intake recommendations for these micronutrients is important for the health of the child. Maternal vitamin deficiencies can negatively affect infant growth and development; for instance, vitamin B₁₂ deficiency during infancy can impair brain development and cause neurological problems (180). Vitamin B₁₂ deficiency has been documented in nursing infants of mothers who have untreated pernicious anemia and also in women who are strict vegetarians (vegans) (181). Vitamin B₁₂ is found only in foods of animal origin and fortified foods, and lactating women who follow vegetarian diets should take supplemental vitamin B₁₂. Vitamin B₁₂ deficiency that results from pernicious anemia can easily be corrected with high-dose daily supplementation or with monthly intramuscular injections of the vitamin (see the article on Vitamin B₁₂). However, there has been relatively little research on the effect of oral vitamin B₁₂ supplementation in lactating women, and it has been suggested that supplementation during lactation may be too late to restore adequate milk concentrations and infant status (182). Supplementation during pregnancy may more effectively improve infant vitamin B₁₂ status. For instance, oral daily vitamin B₁₂ supplementation (50 μg/day) administered from <14 weeks gestation through 6 weeks postpartum significantly increased maternal plasma and breast milk concentrations of vitamin B₁₂ and improved infant vitamin B₁₂ status (183). The concentrations of other water-soluble vitamins in breast milk, including thiamin, riboflavin, and vitamin B₆, are also strongly dependent on maternal intake of these vitamins (59, 182). Likewise, vitamin C concentration in human milk varies with the vitamin C status of the mother. Vitamin C supplementation can moderately increase concentrations of the vitamin in breast milk, especially in lactating women with poor vitamin C status (184), and maternal intakes of 100 mg/day maximize the amount of vitamin C in breast milk (185).

Compared to water-soluble vitamins, the concentrations of fat-soluble vitamins (vitamins A, D, E, and K) in breast milk are less correlated with maternal dietary intake. The RDA for vitamin A during lactation is 1,200 to 1,300 μg/day (4,000 to 4,333 IU/day). At such levels of maternal intake, breast milk is a good source of vitamin A and provides the infant with a sufficient amount of the vitamin (186). In contrast, breast milk is considered to be low in vitamins D and K. Vitamin D concentrations in human milk are dependent on maternal vitamin D status, which is determined by the woman’s sun exposure and dietary and supplemental intake. Vitamin D concentrations are low in breast milk, presumably because many women have insufficient vitamin D status. Vitamin D supplementation during lactation has been shown to improve vitamin D status in the woman and the infant (187). The RDA for lactating women is 600 IU/day of vitamin D, but intake at this level in the absence of sun exposure likely results in insufficient amounts for the infant. To prevent vitamin D deficiency and rickets in infants, the American Academy of Pediatrics recommends that all breast-fed and partially breast-fed infants be given a vitamin D supplement of 400 IU/day (177). Liquid vitamin D supplements are commercially available for infant supplementation. The Linus Pauling Institute recommends that all adults take 2,000 IU/day of supplemental vitamin D and aim for a serum 25-hydroxyvitamin D level of at least 75 nmol/L (30 ng/mL). Human milk is also relatively low in vitamin K. Thus, exclusively breast-fed newborns are at increased risk for vitamin K deficiency. In general, newborns have low vitamin K status for the following reasons: (1) vitamin K is not easily transported across the placental barrier; (2) the newborn's intestines are not yet colonized with bacteria that synthesize vitamin K; and (3) the vitamin K cycle may not be fully functional in newborns, especially premature infants (188). Vitamin K deficiency in newborns may result in a bleeding disorder called vitamin K deficiency bleeding (VKDB). Because VKDB is life-threatening and easily prevented, the American Academy of Pediatrics and a number of similar international organizations recommend that an injection of phylloquinone (vitamin K₁) be administered to all newborns shortly after birth (110, 114, 177). Additionally, the vitamin E content in breast milk varies with maternal diet and vitamin E supplement use (184, 186). The RDA for vitamin E during lactation is 19 mg/day (28.5 IU/day) of α-tocopherol. National surveys indicate that more than 90% of US adults have daily vitamin E intakes below 12 mg (18 IU) (85). 

Maternal dietary intake recommendations for the 14 essential minerals during lactation are shown in Table 3. The content of minerals in breast milk does not correlate well with maternal intake or status, except for iodine and selenium (1, 176). Iodine requirements are increased during lactation: breast-feeding women require 290 μg/day of iodine compared to 220 μg/day for pregnant women and 150 μg/day for nonpregnant, nonlactating women (129). Iodine-deficient women who are breast-feeding may not be able to provide sufficient iodine to their infants who are particularly vulnerable to the effects of iodine deficiency (see the article on Iodine). A daily supplement providing 150 μg of iodine, as recommended by the American Thyroid Association (138), will help to ensure that US breast-feeding women consume sufficient iodine during these critical periods. Additionally, the RDA for selenium is slightly higher for lactating women (from 60 to 70 μg/day), and selenium content in breast milk reflects maternal intake (189).

Safety in Lactation

The tolerable upper intake level (UL) for each micronutrient is shown in the Table 4. The UL, established by the Food and Nutrition Board of the Institute of Medicine, is the highest level of daily intake that is likely to pose no risk of adverse health effects in almost all individuals.

Authors and Reviewers

Originally written in July 2011 by:
Victoria J. Drake, Ph.D.
Linus Pauling Institute
Oregon State University

Updated in March 2016 by:
Giana Angelo, Ph.D.
Linus Pauling Institute
Oregon State University

Reviewed in August 2016 by:
Berthold V. Koletzko, M.D., Ph.D.
Professor for Paediatrics, Ludwig-Maximilians-University of Munich
Dr. von Hauner Children’s Hospital, Univ. of Munich Medical Center,
Campus Innenstadt
Munich, Germany

The 2016 update of this article was underwritten, in part, by a grant from Bayer Consumer Care AG, Basel, Switzerland.

DRIs for potassium and sodium updated 4/12/19  Copyright 2011-2024  Linus Pauling Institute

References

Micronutrients for Older Adults

Introduction

Listed below are vitamin and mineral dietary intake recommendations for individuals over the age of 50 years. For each micronutrient, the Food and Nutrition Board of the Institute of Medicine establishes a recommended dietary allowance (RDA) or adequate intake (AI). Generally, the Linus Pauling Institute supports the recommendations of the Food and Nutrition Board, but any discrepancies in dietary recommendations are listed in the rightmost column of the table. Additionally, more information on the Linus Pauling Institute recommendation for a specific micronutrient can be found by clicking on the name of the micronutrient of interest.

Linus Pauling Institute Recommendations

Vitamins

Biotin

Presently, there is no indication that older adults have an increased requirement for biotin. If dietary biotin intake is not sufficient, a daily multivitamin/mineral supplement will generally provide an intake of at least 30 μg/day of biotin.

Folate

The Linus Pauling Institute recommends that adults take a 400 μg supplement of folic acid daily, in addition to folate and folic acid consumed in the diet. A daily multivitamin/mineral supplement, containing 100% of the Daily Value (DV) for folic acid provides 400 μg of folic acid. Even with a larger than average intake of folic acid from fortified food, it is unlikely that an individual's daily folic acid intake would regularly exceed the tolerable upper intake level (UL) of 1,000 μg/day established by the Food and Nutrition Board. The recommendation for 400 μg/day of supplemental folic acid as part of a daily multivitamin/mineral supplement, in addition to a folate-rich diet, is especially important for older adults because blood homocysteine levels tend to increase with age.

Niacin

Dietary surveys indicate that 15% to 25% of older adults do not consume enough niacin in their diets to meet the RDA (16 mg NE/day for men and 14 mg NE/day for women), and that dietary intake of niacin decreases between the ages of 60 and 90 years. Thus, it is advisable for older adults to supplement their dietary intake with a multivitamin/mineral supplement, which will generally provide at least 20 mg of niacin daily.

Pantothenic acid

Presently, there is little evidence that older adults differ in their intake or requirement for pantothenic acid. Most multivitamin/mineral supplements provide at least 5 mg/day of pantothenic acid. The Linus Pauling Institute supports the recommendation by the Food and Nutrition Board of 5 mg/day of pantothenic acid for older adults. A varied diet should provide enough pantothenic acid for most people. Following the Linus Pauling Institute recommendation to take a daily multivitamin/mineral supplement, containing 100% of the Daily Value (DV), will ensure an intake of at least 5 mg/day of pantothenic acid.

Riboflavin

Some experts in nutrition and aging feel that the RDA of riboflavin (1.3 mg/day for men and 1.1 mg/day for women) leaves little margin for error in people over 50 years of age (1, 2). A study of independently living people between 65 and 90 years of age found that almost 25% consumed less than the recommended riboflavin intake, and 10% had biochemical evidence of deficiency (3). Epidemiological studies of cataract prevalence indicate that riboflavin intakes of 1.6 to 2.2 mg/day may reduce the risk of developing age-related cataracts. Additionally, older people suffering from acute ischemic stroke were found to be deficient for riboflavin (4), and riboflavin deficiency has been linked to a higher risk of fracture in postmenopausal women with the MTHFR 677T variant (5). Individuals whose diets may not supply adequate riboflavin, especially those over 50 years of age, should consider taking a multivitamin/mineral supplement, which generally provides at least 1.7 mg/day of riboflavin.

Thiamin

Presently, there is no evidence that the requirement for thiamin is increased in older adults, but some studies have found inadequate dietary intake and thiamin insufficiency to be more common in elderly populations (2). Thus, it would be prudent for older adults to take a multivitamin/mineral supplement, which will generally provide at least 1.5 mg of thiamin/day.

Vitamin A

Presently, there is little evidence that the requirement for vitamin A in older adults differs from that of younger adults. Additionally, vitamin A toxicity may occur at lower doses in older adults than in younger adults. Further, data from observational studies suggested an inverse association between intakes of preformed vitamin A in excess of 1,500 μg RAE (5,000 IU)/day and risk of hip fracture in older people (see the Safety section in the article on Vitamin A). Yet, following the Linus Pauling Institute’s recommendation to take a multivitamin/mineral supplement daily could supply as much as 5,000 IU/day of retinol, the amount that has been associated with adverse effects on bone health in older adults. For this reason, we recommend taking a multivitamin/mineral supplement that provides no more than 2,500 IU (750 μg) of preformed vitamin A (usually labeled vitamin A acetate or vitamin A palmitate) and no more than 2,500 IU of additional vitamin A as β-carotene. As for all age groups, high potency vitamin A supplements should not be used without medical supervision due to the risk of toxicity.

Vitamin B₆

Early metabolic studies have indicated that the requirement for vitamin B₆ in older adults is approximately 2 mg daily (6). Yet, the analysis of the US population survey (NHANES) 2003-2004 showed that adequate vitamin B₆ status and low homocysteine levels were associated with total vitamin B₆ intakes equal to and above 3 mg/day in people aged 65 years and older (7). The Linus Pauling Institute recommends that older adults take a multivitamin/mineral supplement, which provides at least 2.0 mg of vitamin B₆ daily.

Vitamin B₁₂

Because vitamin B₁₂ malabsorption and vitamin B₁₂ deficiency are more common in older adults, the Linus Pauling Institute recommends that adults older than 50 years take 100 to 400 μg/day of supplemental vitamin B₁₂.

Vitamin C

Although it is not yet known with certainty whether older adults have higher requirements for vitamin C, some older populations have been found to have vitamin C intakes considerably below the RDA of 75 and 90 mg/day for women and men, respectively. A vitamin C intake of at least 400 mg daily may be particularly important for older adults who are at higher risk for age-related chronic diseases. In addition, a meta-analysis of 36 publications examining the relationship between vitamin C intake and plasma concentrations of vitamin C concluded that older adults (aged 60-96 years) have considerably lower plasma levels of vitamin C following a certain intake of vitamin C compared with younger individuals (aged 15-65 years) (8), suggesting that older adults have higher vitamin C requirements. Pharmacokinetic studies in older adults have not yet been conducted, but evidence suggests that the efficiency of one of the molecular mechanisms for the cellular uptake of vitamin C declines with age (9). Because maximizing blood levels of vitamin C may be important in protection against oxidative damage to cells and biological molecules, a vitamin C intake of at least 400 mg daily is particularly important for older adults who are at higher risk for chronic diseases caused, in part, by oxidative damage, such as heart disease, stroke, certain cancers, and cataract.

Vitamin D

The Linus Pauling Institute recommends that generally healthy adults take 2,000 IU (50 μg) of supplemental vitamin D daily. Most multivitamins contain 400 IU of vitamin D, and single ingredient vitamin D supplements are available for additional supplementation. Sun exposure, diet, skin color, and obesity have variable, substantial impact on body vitamin D levels. To adjust for individual differences and ensure adequate body vitamin D status, the Linus Pauling Institute recommends aiming for a serum 25-hydroxyvitamin D level of at least 80 nmol/L (32 ng/mL). Numerous observational studies have found that serum 25-hydroxyvitamin D levels of 80 nmol/L (32 ng/mL) and above are associated with reduced risk of bone fractures, several cancers, multiple sclerosis, and type 1 (insulin-dependent) diabetes. Daily supplementation with 2,000 IU (50 μg) of vitamin D is especially important for older adults because aging is associated with a reduced capacity to synthesize vitamin D in the skin upon sun exposure.

Vitamin E

The RDA for adults of all ages is 15 mg (22.5 IU) per day of α-tocopherol. Notably, more than 90% of individuals aged two years and older in the US do not meet the daily requirement for vitamin E from food sources alone. Major sources of vitamin E in the American diet are vegetable oils, nuts, whole grains, and green leafy vegetables. LPI recommends that healthy older adults take a daily multivitamin/mineral supplement, which usually contains 30 IU of synthetic vitamin E, or 90% of the RDA.

Vitamin K

Older adults are at increased risk of osteoporosis and hip fracture. Because adequate intake of vitamin K is essential in maintaining bone health, the Linus Pauling Institute recommends that adults take a multivitamin/mineral supplement and consume at least one cup of dark green leafy vegetables daily. Although the AI for vitamin K was recently increased, it is not clear if it will be enough to optimize the γ-carboxylation of vitamin K-dependent proteins in bone (see the section on Osteoporosis in the article on vitamin K). Multivitamins generally contain 10 to 25 μg of vitamin K, whereas vitamin K or "bone" supplements may contain 100 to 120 μg of vitamin K. To consume the amount of vitamin K associated with a decreased risk of hip fracture in the Framingham Heart Study (about 250 μg/day) (10), an individual would need to eat a little more than ½ cup of chopped broccoli or a large salad of mixed greens every day. In addition to taking a multivitamin/mineral supplement and eating at least one cup of dark green leafy vegetables daily, replacing dietary saturated fat (e.g., butter and cheese) with monounsaturated fat (e.g., olive and canola oils) will increase dietary vitamin K intake and may also decrease the risk of cardiovascular disease.

Minerals

Calcium

To minimize bone loss, older men (>70 years) and postmenopausal women should consume a total (diet plus supplements) of 1,200 mg/day of calcium. Men aged 51-70 years should consume 1,000 mg of calcium per day. No multivitamin/mineral supplement contains the RDA for calcium (1,000-1,200 mg/day) because the resulting pill would be too large to swallow. If your total daily calcium intake doesn't add up to 1,000 mg, LPI recommends taking an extra calcium supplement with a meal.

Chromium

Although the requirement for chromium is not known to be higher for older adults, one study found that chromium concentrations in hair, sweat, and urine decreased with age (11). Following the Linus Pauling Institute recommendation to take a multivitamin/mineral supplement containing 100% of the daily values (DV) of most nutrients should provide sufficient chromium for most older adults.

Because impaired glucose tolerance and type 2 diabetes are associated with potentially serious health problems, individuals considering high-dose chromium supplementation to treat either condition should do so in collaboration with a qualified health care provider.

Copper

Aging has not been associated with significant changes in the requirement for copper (12); thus, the Linus Pauling Institute recommendation for copper intake in older adults is the same as younger adults. The RDA for copper (900 μg/day for all adults) is sufficient to prevent deficiency, but the lack of clear indicators of copper nutritional status in humans makes it difficult to determine the level of copper intake most likely to promote optimum health or prevent chronic disease. A varied diet should provide enough copper for most people. For those who are concerned that their diet may not provide adequate copper, a multivitamin/mineral supplement will generally provide at least the RDA for copper.

Fluoride

The safety and public health benefits of optimally fluoridated water for prevention of tooth decay in people of all ages have been well established. The Linus Pauling Institute supports the recommendations of the American Dental Association and the Centers for Disease Control and Prevention, which include optimally fluoridated water and the use of fluoride toothpaste, fluoride mouth rinse, fluoride varnish, and when necessary, fluoride supplementation. Due to the risk of fluorosis, any fluoride supplementation should be prescribed and closely monitored by a dentist or physician. 

Iodine

The RDA for iodine (150 μg/day for men and women) is sufficient to ensure normal thyroid function. There is presently no evidence that iodine intakes higher than the RDA are beneficial. Most people in the US consume more than sufficient iodine in their diets, making supplementation unnecessary.

Iron

A study in an elderly population found that high iron stores were much more common than iron deficiency (13). Thus, older adults should not generally take nutritional supplements containing iron unless they have been diagnosed with iron deficiency. Moreover, it is extremely important to determine the underlying cause of the iron deficiency, rather than simply treating it with iron supplements.

Magnesium

Older adults are less likely than younger adults to consume enough magnesium to meet their needs and should therefore take care to eat magnesium-rich food in addition to taking a multivitamin/mineral supplement daily. However, no multivitamin/mineral supplement contains 100% of the DV for magnesium. If you don’t eat plenty of green leafy vegetables, whole grains, and nuts, you likely are not getting enough magnesium from your diet. Older adults are more likely to have impaired kidney function than younger individuals, they should avoid taking more than 350 mg/day of supplemental magnesium without medical consultation (see the section on Safety in the article on magnesium).

Manganese

The requirement for manganese is not known to be higher for older adults compared to younger adults. However, liver disease is more common in older adults and may increase the risk of manganese toxicity by decreasing the elimination of manganese from the body (see the section on Toxicity in the article on manganese). Manganese supplementation beyond 100% of the Daily Value (DV=2 mg/day) is not recommended.

Molybdenum

Because aging has not been associated with significant changes in the requirement for molybdenum (14), the Linus Pauling Institute recommendation for older adults is the same as that for younger adults. Specifically, the RDA for molybdenum, 45 μg/day for adults of all ages, is sufficient to prevent deficiency. Although the intake of molybdenum most likely to promote optimum health is not known, there is presently no evidence that intakes higher than the RDA are beneficial. Most people in the US consume more than sufficient molybdenum in their diets, making supplementation unnecessary. Following the Linus Pauling Institute's general recommendation to take a multivitamin/mineral supplement that contains 100% of the daily values (DV) for most nutrients is likely to provide 75 μg/day of molybdenum because the DV for molybdenum has not been revised to reflect the most recent RDA. Although the amount of molybdenum presently found in most multivitamin/mineral supplements is higher than the RDA, it is well below the tolerable upper intake level (UL) of 2,000 μg/day and should be safe for older adults.

Phosphorus

At present, there is no evidence that phosphorus requirements of older adults differ from that of younger adults, and a varied diet should easily provide the RDA (700 mg/day) of phosphorus for those over 50 years of age.

Potassium

A diet rich in fruit and vegetables that supplies 2.6-3.7 g/day of potassium is appropriate for healthy older adults because such diets are associated with decreased risk of stroke, hypertension, osteoporosis, and kidney stones. This recommendation does not apply to individuals who have been advised to limit potassium consumption by a health care professional (see the section on Safety in the article on potassium).

Selenium

Aging has not been associated with significant changes in the requirement for selenium. The Linus Pauling Institute supports the recommendation of the Food and Nutrition Board, which is 55 μg/day of selenium for adults of all ages. Although the amount of selenium in multivitamin/mineral supplements varies considerably, multivitamin/mineral supplements rarely provide more than the Daily Value (DV) of 70 μg. The average American diet is estimated to provide about 100 μg/day of selenium (15, 16). Thus, eating a varied diet and taking a daily multivitamin/mineral supplement should provide sufficient selenium for most adults in the US.

Sodium

There is consistent evidence that diets relatively low in salt (5.8 grams/day or less) and high in potassium are associated with decreased risk of high blood pressure and hypertension, as well as the associated risks of cardiovascular and kidney diseases. Diets low in sodium and rich in potassium are likely to be of particular benefit for older individuals, who are at increased risk of high blood pressure. Moreover, the Dietary Approaches to Stop Hypertension (DASH) trial demonstrated that a diet emphasizing fruit, vegetables, whole grains, nuts, and low-fat dairy products substantially lowered blood pressure, an effect that was enhanced by reducing salt intake to 5.8 grams/day or less. For more information on the DASH diet, see the article on Sodium. The Linus Pauling Institute recommends a diet that is rich in fruit and vegetables (at least 5 servings/day) and limits processed foods that are high in salt. Sensitivity to the blood pressure-raising effects of salt increases with age; therefore, consuming diets that are low in salt and high in potassium may especially benefit older adults.

Diets rich in potassium (≥2.6 g/day of potassium) and low in salt (5.8 grams/day or less) are likely to be of particular benefit for older adults, who are at increased risk of high blood pressure along with its associated risks of cardiovascular and kidney diseases. Since sensitivity to the blood pressure-raising effects of salt increases with age, consuming diets that are low in salt and high in potassium may especially benefit older adults.

Zinc

Although the requirement for zinc is not known to be higher for older adults, their average zinc intake tends to be considerably less than the RDA. A reduced capacity to absorb zinc, increased likelihood of disease states that alter zinc utilization, and increased use of drugs that increase zinc excretion may contribute to an increased risk of mild zinc deficiency in older adults. Because the consequences of mild zinc deficiency, such as impaired immune system function, are particularly relevant to the health of older adults, they should pay particular attention to maintaining adequate zinc intake.

Other nutrients

Choline

Little is known regarding the amount of dietary choline most likely to promote optimum health or prevent chronic disease in older adults. At present, there is no evidence to support a different intake of choline from that of younger adults (550 mg/day for men and 425 mg/day for women).

Essential fatty acids

α-Linolenic acid (ALA), an omega-3 fatty acid, and linoleic acid (LA), an omega-6 fatty acid, are considered essential fatty acids because they cannot be synthesized by humans. In 2002, the Food and Nutrition Board of the US Institute of Medicine established adequate intake (AI) levels for omega-6 and omega-3 fatty acids. Essential fatty acid recommendations for adults over the age of 50 are listed in Table 2. For more information on ALA and LA, see the article on Essential Fatty Acids.