MICRONUTRIENTS FOR OLDER ADULTS
Victoria J. Drake, Ph.D.
Nutritional needs change throughout the various stages of life. While overall caloric needs tend to decrease with age, the requirements for individual micronutrients (vitamins and nutritionally-essential minerals) do not decrease. In fact, the needs for some micronutrients, such as calcium and vitamin D, actually increase with age: adults older than 50 years require higher intakes of these two micronutrients. Older adults may also need more dietary antioxidants, such as vitamins C and E, as well as certain B vitamins, including vitamin B6, folate, and vitamin B12. Micronutrient deficiencies are quite common in the U.S. and other countries, and older adults are especially vulnerable. Since physical activity levels generally decline with increasing age, older adults have lower energy requirements than younger adults. Therefore, it is particularly important for older adults to choose nutrient-rich foods and take a daily multivitamin-mineral supplement. Adequate intake of micronutrients not only ensures that current metabolic needs are met but also may reduce one's risk for chronic diseases, including heart disease, cancer, and osteoporosis, that are more common in older adults.
Micronutrient deficiencies in older adults are most likely caused by a combination of factors, including poor dietary intake and physiological changes that accompany aging. The more common micronutrient deficiencies in older adults are grouped into functional groups; their importance in the body is discussed below.
Compared to younger adults, adults older than 50 years require higher amounts of two micronutrients important in bone metabolism, calcium and vitamin D. Intestinal absorption of calcium declines with age, as does the capacity to endogenously synthesize vitamin D in the skin. Intestinal absorption of the mineral magnesium may also slightly decline with age, and the recommended intake is higher in adults older than 30 years. All three micronutrients are essential for bone health.
Calcium is the most common mineral in the human body, with about 99% of total body calcium residing in bones and teeth; the remaining 1% is found in blood and soft tissues. It is extremely important that people meet dietary intake recommendations for calcium. Otherwise, the body will demineralize bone in order to maintain blood levels of calcium within a narrow range, which is essential for normal physiological function. Bone demineralization can lead to bone fragility, osteoporosis, and bone fracture. To minimize deleterious effects to bone, older men and postmenopausal women should consume a total (diet plus supplements) of 1,200 mg/day of calcium. Total intake of calcium should not exceed 2,500 mg daily.
Adequate vitamin D nutriture is required for optimal calcium absorption, normal bone growth, and maintenance of bone density. Vitamin D also has important roles in maintaining muscle strength. Thus, inadequate vitamin D status results in loss of bone integrity and muscle weakness; both can potentially increase the likelihood of falls and bone fractures in older adults. Clinical trials examining the risk of osteoporotic fracture in older adults have generally found that vitamin D supplementation can slow losses in bone density and decrease the incidence of bone fracture. Some studies suggest that the supplemental threshold for any benefit on bone integrity is 700 IU (17.5 mcg) daily.
Because vitamin D is found in few foods, sun exposure is the main source for vitamin D. However, older adults have a reduced capacity to synthesize vitamin D in skin upon exposure to ultraviolet-B radiation. Older adults also have impaired conversion of vitamin D to its active form in the kidneys. Thus, supplemental vitamin D is especially important for older adults. Emerging evidence suggests that a daily supplemental intake of 2,000 IU of vitamin D may help protect older adults from breast, ovarian, and colon cancers.
The majority of U.S. adults, regardless of age, do not meet the recommended dietary allowance (RDA) for magnesium. Elderly adults are especially at risk for magnesium deficiency due to relatively low dietary intakes, reduced intestinal absorption, and increased urinary losses of the mineral. Magnesium deficiency can lead to a number of health problems because the mineral plays several diverse roles in the body. Magnesium is a cofactor for more than 300 metabolic reactions, including those required for energy production, nucleic acid (DNA and RNA) synthesis, and protein synthesis. Moreover, magnesium is necessary for normal muscle and nerve function, as well as bone health. In fact, about 60% of all magnesium in the body is located in the skeleton, where it plays a structural role. Magnesium deficiency can impair calcium and vitamin D metabolism, leading to bone loss. Some studies have found that inadequate dietary intake of magnesium and/or low serum levels of magnesium are associated with reductions in bone mineral density. It is not yet known whether magnesium supplementation could prevent loss of bone integrity. Few multivitamin-mineral supplements contain more than 100 mg of magnesium because the resulting pill would be too bulky. Because older adults are more likely to have impaired kidney function, they should avoid taking more than 350 mg/day of supplemental magnesium without medical consultation. Eating magnesium-rich foods is safe because, in contrast to supplemental magnesium salts, adverse effects have not been identified from magnesium occurring naturally in food.
Together, adequate nutritional status of calcium, vitamin D, and magnesium is necessary for maintenance of bone health and prevention of bone-related diseases in older adults.
Vitamins C and E have several functions in the body and have major roles as antioxidants.
Vitamin C is the most effective water-soluble antioxidant in human plasma. An antioxidant is a substance that prevents or reduces damage caused by free radicals that are generated during normal cellular metabolism and upon exposure to environmental toxins, such as cigarette smoke. Vitamin C and other antioxidants protect various molecules in the body, including proteins, lipids, and nucleic acids (DNA and RNA), from oxidative damage by free radicals. While it is not yet known whether older adults have higher vitamin C requirements, some older populations reportedly have daily intake levels lower than the current recommended dietary allowance (75 mg/day for women and 90 mg/day for men). The RDA, set by the Food and Nutrition Board of the Institute of Medicine, is based on prevention of a deficiency and not on the prevention of chronic diseases or the promotion of optimum health. Studies conducted at the National Institutes of Health indicate that plasma and circulating cells in healthy, young subjects attain maximal concentrations of vitamin C at a dose of about 400 mg/daya dose much higher than the current RDA. 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. 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, or cataract.
Vitamin C is able to regenerate another dietary antioxidant, vitamin E, from its oxidized form. Vitamin E actually refers to a family of eight fat-soluble antioxidants, but alpha-tocopherol is the only form that is actively maintained in the body. Alpha-tocopherol functions as an antioxidant in lipid compartments of the body, quenching the propagation of lipid peroxidation in cellular membranes. In addition, alphatocopherol prevents the oxidation of fats in low-density lipoprotein (LDL). LDL transports cholesterol from the liver to the peripheral tissues. Because oxidized LDL has been implicated in the development of atherosclerosis, several studies have examined whether vitamin E is protective against cardiovascular diseases. Moreover, since the brain is particularly vulnerable to oxidative stress, vitamin E may also help prevent neurodegenerative diseases. It has been estimated that more than 90% of Americans do not meet the dietary recommendations for vitamin E15 mg (22.5 IU) daily for all adults. A daily supplement of 200 IU of natural source d-alpha-tocopherol (RRR-alpha-tocopherol), taken with a fat-containing meal, may help protect adults from chronic diseases.
Compared to younger adults, older adults may have increased requirements for some of the B vitamins that are involved in energy production and other metabolic reactions.
Vitamin B6 has several different functions in the body, participating as a cofactor for more than 100 enzymes. This vitamin is important in neurotransmitter synthesis, red blood cell formation and function, niacin formation from the amino acid tryptophan, steroid hormone function, and nucleic acid synthesis. Vitamin B6 intake recommendations for adults older than 50 years are higher than those for younger adults, perhaps because the vitamin's metabolism is altered with aging. Mechanistic studies are needed to determine exactly why older adults require higher intakes. Despite higher recommendations for older adults, several surveys have found that over half of individuals over age 60 consume less than the current RDA (1.7 mg/day for men and 1.5 mg/day for women). Thus, it would be prudent for older adults to take a daily multivitamin supplement, which generally provides at least 2 mg of vitamin B6.
Folate and folic acid are two terms often used interchangeably; the former refers to folates found naturally in foods, while the latter refers to the more bioavailable, synthetic form that is used in vitamin supplements and fortified foods. Dietary intake recommendations for folate are not higher in older adults compared to younger people. However, there is some concern that intake recommendations are not being met in some older adults, especially the elderly, presumably due to low intake of fruits and vegetables. Even marginal deficiencies can elevate blood homocysteine levels, possibly increasing risk for cardiovascular diseases, as well as Alzheimer's disease and other types of dementia.
Along with folate, adequate intake of vitamin B12 is necessary to avoid increased blood levels of homocysteine. In humans, vitamin B12 is only required for two biochemical reactions: to make the amino acid methionine from homocysteine (folate is also needed) and to make a compound that is involved in the production of energy and in the synthesis of hemoglobin, the oxygen-carrying pigment in red blood cells.
The prevalence of vitamin B12 inadequacy increases with age, making older adults more susceptible to deficiency. If the deficiency is not corrected, anemia as well as neurological and gastrointestinal symptoms can result. Deficiency symptoms may take years to manifest because the vitamin can be stored in the body. Older adults are more vulnerable to vitamin B12 deficiency because they are more likely to be affected by atrophic gastritis, a chronic inflammation of the lining of the stomach, which ultimately results in stomach atrophy and decreased stomach acid production. Reductions in stomach acid impair the release of vitamin B12 from proteins in food. Thus, food-bound vitamin B12 malabsorption results in individuals with atrophic gastritis. It has been estimated that 10-30% of older adults are affected by this condition. Therefore, some nutritionists recommend that adults older than 50 years take 100 to 400 mcg of supplemental vitamin B12 daily. Absorption of the synthetic, crystalline form of vitamin B12 found in dietary supplements and fortified foods is not impaired by atrophic gastritis.
Daily intake requirements for the select micronutrients mentioned above are listed in the table above. For each micronutrient, the Food and Nutrition Board of the Institute of Medicine establishes a recommended dietary allowance (RDA) or adequate intake (AI) level. The Linus Pauling Institute generally supports the recommendations of the IOM, but any discrepancies in dietary recommendations are listed in the rightmost column of the table. These and other micronutrients can be obtained by eating nutrient-dense, healthful foods. A daily multivitamin-mineral supplement is important for added insurance that micronutrient requirements are met. In general, men and postmenopausal women should not take a multivitamin-mineral containing iron, and older adults should not take iron supplements unless they have been diagnosed with iron deficiency. Additionally, vitamin A toxicity may occur at lower doses in older adults than in younger adults. The Linus Pauling Institute recommends taking a multivitamin supplement that provides no more than 2,500 IU of vitamin A or a supplement that provides 5,000 IU of vitamin A of which at least 50% comes from beta-carotene. High-potency vitamin A supplements should not be used without medical supervision due to the risk of toxicity. More information on micronutrients for older adults can be found in the LPI Micronutrient Information Center.
Last updated January 2009