Summary

Our bony skeleton provides support, protection, and mobility for the body and constitutes a major storage site for calcium and phosphorus. Bone health is intrinsically linked to calcium (and phosphorus) metabolism. Calcium concentrations in the blood must be maintained within a very narrow concentration range to preserve normal physiological functions (e.g., muscle contraction, nerve impulse conduction, constriction and relaxation of blood vessels). Because these functions are essential, the body will use calcium stored in bone to maintain normal blood calcium concentrations when calcium intake is inadequate. However, this is done at the expense of our skeleton.

It is well established that malnutrition diminishes the ability of bone to grow, respond to mechanical forces, and act as a homeostatic buffer to regulate calcium concentration in body fluids. Therefore, to fulfill its functions, our skeleton relies on adequate supply of nutrients, in particular large amounts of calcium and phosphorus that must come from the diet. At a minimum, getting the recommended dietary allowances (RDA) for calcium and vitamin D is necessary to maximize bone development in children and young adults and limit bone loss later in life; whether intakes above the RDA for these micronutrients might reduce the risk of fracture in older adults is debated. There is little evidence to suggest that supplementation of other micronutrients with essential roles in bone health (fluoride; magnesium; and vitamins A, B, C, and K) at levels above current recommendations may be of further benefit. Striving to reduce phosphorus and sodium intakes while increasing intakes of potassium is likely to indirectly benefit bone health through improving overall health. Finally, physical activity is highly beneficial to bone health during development and throughout life.

Overview of Bone Biology

Bone functions

The skeleton serves two major functions at the same time:

  • A structural function – Strong bones support and protect our body and allow us to move about on dry land.
  • A reservoir function – Bones contain large amounts of calcium and phosphorus and thus provide a reserve supply for these minerals.

To fulfill its functions, bone tissue is constantly remodeled.

Bone modeling and remodeling

The skeleton is an active tissue. Two bone-making processes are involved in the development, growth, and shaping of bones, as well as the continuous renewal of bone tissue throughout life:

  • During childhood and adolescence, new bone tissue is formed at particular sites but broken down at other sites, allowing bones to grow in size and shape. The process is called bone modeling.
  • During adulthood, bone remodeling involves the removal and replacement of bone at the same sites in order to:
    • replace old bone that can become brittle
    • repair small cracks or deformation
    • release calcium and phosphorus into the circulation when need arises (i.e., dietary inadequacy, pregnancy, lactation)

The two main types of cells responsible for bone (re)modeling are osteoblasts and osteoclasts.

Bone composition

Bone tissue is a composite material:

  • ~35% of organic protein matrix, largely made up of a single protein: type I collagen.
  • ~65% of inorganic mineral, primarily calcium and phosphorus that form insoluble crystals of hydroxyapatite.

The bone matrix is made of triple helices of collagen arranged into fibrils and assembled into large fibers. This constitutes the interior scaffolding of bone onto which bone mineral is deposited.

Determinants of adult bone health

Bone mass and architecture are determined by our genes but also significantly influenced by external factors:

  • Mechanical forces – linked to physical activity – applied onto the skeleton throughout life are essential to shape and maintain normal bone mass
  • Essential nutrients (particularly calcium and phosphorus) supplied by the diet are needed to build and maintain bone tissue

Exercise and diet can significantly affect the ability to achieve one's genetically determined peak bone mass. High peak bone mass reduces the risk of osteoporosis and fracture later in life.

Bones weaken when:

  • They are not subjected to adequate amounts of mechanical loading and weight bearing.
  • They need to supply calcium and phosphorus because dietary intakes are persistently inadequate (see Highlight).
  • The rate of bone degradation starts to exceed the rate of bone formation in our thirties, leading to an inevitable loss of bone mass with age.
HIGHLIGHT: CALCIUM-REGULATING HORMONES AND BONE HEALTH
Blood calcium is tightly controlled by hormones, including the parathyroid hormone (PTH) and vitamin D, which influence bone health. Calcium concentrations in the blood must be maintained within a very narrow concentration range to preserve normal physiological functions (e.g., muscle contraction, nerve impulse conduction, constriction and relaxation of blood vessels). Because these functions are essential, the body will use calcium stored in bone to maintain normal blood calcium concentrations when calcium intake is inadequate. Indeed, in response to blood calcium lowering and when calcium from food is limited, PTH and vitamin D can prompt bone degradation, which releases calcium (and phosphorus) into the circulation, thereby threatening bone integrity. It is thus critical to obtain enough calcium from food to limit bone loss in response to fluctuating blood calcium concentrations.

Bone Conditions

Rickets and osteomalacia

Vitamin D deficiency, which impairs the intestinal absorption of calcium and phosphorus, can result in the formation of poorly mineralized bone.

  • In children, rickets is characterized by bone weakness, fractures, bowing of long bones, and overgrowth of cartilage at bone ends.
  • In adults, failure to mineralize the collagen matrix leads to the softening of bones – a condition called osteomalacia – with risk of deformities and fractures.

Osteoporosis

  • This is a condition of increased bone fragility and risk of fracture due to loss of bone mass. Clinically, osteoporosis is defined as a bone mineral density (BMD) that is greater than 2.5 standard deviations below the mean BMD of a young adult.
  • The main therapeutic strategy involves blocking bone degradation.

Fracture

  • The risk of osteoporotic fracture is influenced by bone mass, bone quality (microarchitecture, geometry), and propensity to fall (balance, mobility, muscular strength).
  • An online tool, FRAX, has been designed to calculate your 10-year probability of fracture, using your BMD measurement and taking additional risk factors into account.
DEFINITIONS
Osteoblasts - cells involved in making bone
Osteoclasts - cells involved in breaking down bone
Bone mineral density (BMD) - a measure of the amount of mineral (calcium and phosphorus) that deposited onto bone matrix made of proteins in a specific area or volume of bone; a proxy measure of bone mass
Hydroxyapatite crystals - calcium phosphate salts forming crystals ((Ca)10(PO4)6(OH)2) that constitutes the main mineral in teeth and bones
Peak bone mass - refers to the maximum amount of bone reached by an individual, usually during young adulthood; it also captures maximum bone strength
Physical activity - any movement produced by muscle contraction and resulting in energy expenditure above the resting level
RDA - recommended dietary allowance. It is the nutrient intake value that is estimated to meet the requirement of nearly all healthy people of a particular gender and age group in a population. It is a target value for an individual.

For references and more information, read the report of the Surgeon General on Bone Health and Osteoporosis (2004).

 

Nutrition Research

DEFINITIONS
Test tube (in vitro) experiment - a research experiment performed in a test tube, culture dish, or other artificial environment outside of a living organism; in vitro is a Latin phrase meaning in glass
Animal experiment - a research experiment performed in a laboratory animal; many different animal species are studied in the laboratory, including terrestrial (land), aquatic (water), and microscopic animals
Observational study - a human research study in which no experimental intervention or treatment is applied, and participants are simply observed over time
Randomized controlled trial - a human research study in which participants are randomly assigned to receive an active treatment or an inert (control) treatment. This type of study tests the efficacy of an active treatment on a specific outcome compared to a control.
Placebo - a substance without therapeutic effect

 

Protein-energy Malnutrition (PEM)

What it is

General

  • PEM is most common in developing nations, the elderly, hospitalized individuals, and those with chronic diseases that interfere with nutrient absorption and utilization.
  • Clinical PEM conditions usually observed in developing countries include:
    • marasmus characterized by wasting of tissues, particularly muscles and subcutaneous fat, due to severe restrictions in all sources of energy intake (including dietary protein)
    • kwashiorkor characterized by edema due to severe restrictions in dietary protein
    • marasmic kwashiorkor have clinical features of both marasmus and kwashiorkor
  • In Western countries, marasmus-type PEM is usually observed in elderly people in the community or in long-term care, whereas low-albumin PEM is found in hospitalized patients.
  • PEM is usually accompanied by deficiencies in essential micronutrients required for bone health.

Bone-specific

  • Without protein and calories, all of the body's essential functions suffer, although bone health is not immediately affected. Yet, the effects of PEM on bone are obvious in two situations:
    • during bone growth in children and adolescents, when PEM causes growth retardation, delays maturation, and may lead to stunting
    • in older adults, PEM may compromise many aspects of health leading to falls and fracture. Protein supplementation after bone fracture limits bone loss and reduces serious complications, including death.
What we know
  • Higher protein intakes are associated with greater bone mass density and lower risk of fracture.
  • Adequate protein intakes are needed to maintain muscle mass and limit falls and fractures in older adults.
  • Higher protein intakes are likely to be protective unless calcium intakes are inadequate, in which case higher protein intakes may be harmful.
DEFINITIONS
Albumin - a major blood protein. It contributes to regulate blood volume (through "colloid osmotic pressure") and transports various molecules (fatty acids, metals, ions, hormones, etc.) in the circulation
Low-albumin protein-energy malnutrition (PEM) - laboratory diagnosis of marginal PEM usually includes measures of serum albumin. However, albumin is not a specific indicator of PEM as its concentration in blood is altered in many conditions other than PEM
Protein-energy malnutrition (PEM) - PEM severity ranges from mild deficiencies in macronutrients to the severe forms of marasmus and kwashiorkor
Stunting - defined as height-for-age <2 standard deviations (SD) below the WHO Child Growth Standards median. Stunting of stature due to malnutrition is linked to stunting of mental development.

For references and more information, see the section on Protein-energy malnutrition (PEM) in the in-depth article on Immunity.

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Essential Polyunsaturated Fatty Acids (PUFAs)

What they are

General

  • Essential PUFAs cannot be synthesized by the body and they must come from the diet.
  • They are structural components of every cell in the body and are converted to compounds that influence inflammation and immunity.
  • There are two classes of essential PUFAS: omega-3 and omega-6.

Bone-specific

  • Evidence from animal studies suggest that PUFAs can promote the development of stronger bones through increasing (i) calcium absorption, (ii) mineral deposition onto bone, and (iii) differentiation and activity of osteoblasts.
What we know
    Evidence from only a few heterogeneous, randomized controlled studies is too limited to conclude whether higher intakes of PUFAs might benefit bone health.
DEFINITIONS
Osteoblasts - cells involved in making bone
Differentiation - the process by which a cell acquires biochemical and functional features in order to assume a specific function

 

There are two essential fatty acids: linoleic acid (an omega-6 polyunsaturated fatty acid) and alpha-linolenic acid (an omega-3 polyunsaturated fatty acid). These fatty acids are considered essential nutrients because they cannot be made in the body and must be consumed in the diet. Vegetable oils, especially safflower oil, sunflower oil, and corn oil, are a good source of linoleic acid.Flax and chia sees, walnuts, canola oil, and soybean oil are good sources of alpha-linoleic acid. Inside body tissues, the essential fatty acids are converted to long-chain fatty acids. Due to low efficiency of conversion, it is recommended to obtain eicosapentaenoic acid (EPA) and docosapentaenoic acid (DHA) from additional sources. Oily fish, fish oil supplements, krill oil supplements, and algae oil supplements are good sources of EPA and DHA.

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Calcium

What it does

General

  • Calcium plays an essential role in cell-signaling pathways and is therefore fundamental to virtually all physiological functions.

Bone-specific

  • Calcium is a major structural component of bones and teeth.
  • When dietary calcium intakes are low, the body uses calcium from bones to maintain total calcium in blood within a narrow range (8.9-10.1 milligrams/deciliter [mg/dL]), thereby preserving normal physiological functions.
What we know
  • Chronically low calcium intakes in growing individuals may prevent the attainment of optimal peak bone mass.
  • Once peak bone mass is reached, low calcium intakes may contribute to accelerate bone loss and increase the risk of osteoporosis and fracture.
  • The benefit of supplemental calcium (and vitamin D) on fracture risk might be restricted to institutionalized elderly people.
  • Whether calcium intakes beyond the RDA can reduce fracture risk in community-dwelling older adults is debated.
    • The US National Osteoporosis Foundation supports the use of supplemental calcium (1,000-1,200 mg/day) and vitamin D (800-1,000 international units [IU]/day) as a public health intervention to reduce the burden of fractures in all middle-aged adults. Similar recommendations have been made by the American Geriatrics Society.
    • In contrast, the US Preventive Services Task Force advised against daily calcium and vitamin D supplementation for the primary prevention of fracture in older adults.
DEFINITIONS
Cell-signaling pathway - a cascade of events triggers by a signal outside a cell and resulting in a functional change inside the cell. Cell-signaling pathways play important roles in regulating numerous cellular functions in response to changes in a cell's environment. Also refers to as cell transduction pathways or signaling cascades
Peak bone mass - for an individual, it refers to the maximum amount of bone acquired by the time a stable skeletal state has been attained and depends on both genetic and environmental (lifestyle) factors
Primary prevention - it refers to a range of activities undertaken to prevent or reduce the risk of an injury or disease before it occurs

For references and more information:

Calcium Flashcard. Main Functions: 1) structural component of bones and teeth, 2) regulates nerve transmission and muscle contraction, 3) helps maintain a healthy blood pressure, and 4) helps maintain acid-base balance in the blood. Good Sources: dairy (yogurt, milk, cheese), plain yogurt, 8 ounces or 1 cup = 415 mg; sardines (canned) 1 can or 3.75 ounces = 351 mg; green leafy vegetables (kale, bok choy), collard greens (cooked), one-half cup = 300 mg; mg= milligrams. Daily Recommendation: 1,000 mg for men 19-70 years, 1,200 mg for men 71+ years; 1,000 mg for women 19-50 years, 1,200 mg for women 51+ years. Special Notes: 1) Many Americans do not consume enough calcium. Just 3 servings of dairy per day would meet the recommendation. For those who don't consume dairy, calcium-fortified juices, cereals, and milk alternatives are a good substitute. 2) To maximize absorption from supplements, take no more than 500 mg at a time.

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Fluoride

What it does

General

  • Fluoride is the ionic form of the naturally occurring fluorine element.
  • Fluoride-containing dental products and adequate intakes of fluoride reduce the occurrence of caries throughout life by promoting tooth mineralization.

Bone-specific

  • Fluoride increases the structural stability of bones through interacting with calcium phosphate salts.
What we know
  • The level of exposure achieved through community water fluoridation (<3.4 mg/day) is unlikely to be helpful in the prevention of osteoporosis and fracture.
  • Trials found that supplementation with daily doses ≤20 mg of fluoride reduced the risk of fracture.
    • The FDA does not currently approve the use of fluoride supplementation in the prevention and treatment of osteoporosis.
DEFINITIONS
Caries - cavities or holes in the outer layer of a tooth – the enamel and dentin
Community water fluoridation - refers to the controlled addition of fluoride to water as a public health measure to decrease the incidence of dental caries
FDA - US Food and Drug Administration
Ionic form - an ion. Here, fluoride is a negatively charged ion (=anion) resulting from the fluoride atom having gained one electron (a negatively charged subatomic particle)
Tooth mineralization - the process by which calcium and phosphorus are deposited into dentin and enamel

For references and more information, see the section on Fluoride in the in-depth article on Bone Health.

Fluoride Flashcard. Main Functions: (1) Structural component of bones and teeth, and (2) Prevents cavidties by (a) promoting tooth mineralizations and (b) inhibiting the activity of acid-producing bacteria that cause tooth decay. Good Sources: water (fluoridated water, 1 cup or 8 ounces = 0.2-0.3 milligrams) and tea (black tea, 1 cup or 8 ounces = 0.2-0.5 mg). Daily Recommendation: 4 mg for men and 3 mg for women. Special Notes: (1) Dental products are also a source of fluoride and (2) Claims that fluoride increases the risk of several chronic diseases are not supported by extensive scientific research.

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Magnesium

What it does

General

  • Magnesium is a cofactor for enzymes that catalyzes hundreds of essential reactions in the metabolism of carbohydrates, fats, and proteins.
  • Magnesium is required for the synthesis of ATP, which is involved in virtually all cellular processes.
  • Magnesium binds to negatively charged molecules and has a structural role in chromosomes and cell membranes.

Bone-specific

  • About 60% of magnesium is found in bone, which constitutes a reserve supply to regulate magnesium homeostasis in the body.
What we know
  • Higher magnesium intakes in a representative sample of the US population have been linked to lower risk of poor vitamin D status.
  • Evidence from trials is too limited to suggest that magnesium supplementation could be effective in reducing osteoporosis and fracture risk.
DEFINITIONS
ATP - adenosine triphosphate; an important compound for the storage of energy in cells
Homeostasis - a state of balance
Metabolism - the sum of the biochemical reactions by which a substance is assimilated and incorporated in the body to yield energy for all vital processes that sustain life

For references and more information:

Magnesium Flashcard. Main Functions: 1) Structural component of bones and teeth, 2) Regulates nerve transmission and muscle contraction, and 3) Assists in hundreds of essential cellular reactions. Good Sources: Whole Grains (wheat, oats, barley), brown rice, cooked, 1 cup = 86 mg; Green Leafy Vegetables (Swiss chard, spinach), spinach (boiled), 1 cup = 157 mg; Nuts (hazelnuts, cashews), almonds, 1 ounce or 23 almonds = 77 mg. Daily Recommendation: 400 mg for men 19-30 years, 420 mg for men 31 years and older; 310 mg for women 19-30 years, 320 mg for women 31 years and older. Special Notes: 1) Most people consume too little magnesium. 2) The Tolerable Upper Intake Level (UL) for magnesium is 350 mg/day from supplements. The UL does not apply to naturally occurring magnesium from food.

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Phosphorus

What it does

General

  • Phosphorus is an essential structural component of cell membranes and nucleic acids and is involved in many biological processes, such as bone mineralization, energy production, cell-signaling pathways, and acid-base homeostasis.

Bone-specific

  • Phosphorus and calcium form insoluble hydroxyapatite crystals that give bones their rigidity.
What we know
  • Although it could lead to rickets and osteomalacia, phosphorus deficiency is uncommon in healthy people.
  • Consumption of phosphoric acid [H3PO4-]-containing soft drinks in place of milk and other calcium-rich food represents a serious risk to bone health:
    • Levels of phosphorus intake currently experienced in the US have not been associated with a higher risk of osteoporosis.
    • Low calcium intakes rather than high phosphorus intakes are thought to damage bone health.
HIGHLIGHT:
  • Current intakes of phosphorus in the US population are well above the EAR (580 mg/day) and RDA (700 mg/day), with daily estimates of 1,602 mg/day in men and 1,128 mg/day in women.
    • Segments of the population that consumed more processed foods (high in phosphorus additives) and carbonated beverages (high in phosphoric acid) have intakes close to the UL for phosphorus (4,000 IU/day).
  • High phosphorus intakes (>RDA), together with a poor balance of intakes of other nutrients (calcium in particular), may ultimately be harmful to kidney function, cardiovascular health, and bone health.
      In particular, the substitution of ultra-processed foods and soft drinks for unprocessed meals, milk, and other calcium-rich food is likely to damage bone health on the long run.
DEFINITIONS
Acid-base homeostasis - refers to the balance between the acids and bases (i.e., the pH) of the body's fluids
Cell-signaling pathway - a cascade of events triggers by a signal outside a cell and resulting in a functional change inside the cell. Cell-signaling pathways play important roles in regulating numerous cellular functions in response to changes in a cell's environment. Also refers to as cell-transduction pathways or signaling cascades
Hydroxyapatite crystals - calcium phosphate salts forming crystals ((Ca)10(PO4)6(OH)2) that constitutes the main mineral in teeth and bones
Mineralization - the process by which calcium and phosphorus are laid on the organic tooth and bone matrices
Nucleic acids - refers to DNA (deoxyribonucleic acid) and RNA (ribonucleic acid)
Osteomalacia - sometimes called "adult rickets"; it is characterized by a softening of the bones in adults caused by a lack of matrix mineralization
Rickets - a condition characterized by soft and deformed bones and due to an impaired incorporation of calcium and phosphorus in growing bones
EAR - estimated average requirement. It is the nutrient intake value that is estimated to meet the requirement of 50% of the healthy people of a particular gender and age group in a population. It is also the best estimate of an individual's requirement and thus may be used to assess the adequacy of an individual's usual intake of the nutrient
RDA - recommended dietary allowance. It is the nutrient intake value that is estimated to meet the requirement of nearly all healthy people of a particular gender and age group in a population. It is a target value for an individual
UL - tolerable upper intake level. Set by the Institute of Medicine, the UL of a specific nutrient is the highest level of daily intake likely to pose no risk of adverse effects in almost all individuals of a specified age

For references and more information:

Phosphorus Flashcard. Main Functions: (1) Structural component of bones and teeth, DNA and RNA, and cell membranes; (2) Assists in energy production and storage; and (3) Physiological buffer. Good Sources: dairy products (yogurt, plan, nonfat, 8 ounces, 306 milligrams [mg]); meat (beef, poultry, fish), cooked salmon, 3 ounces, 315 mg; egg, 1 large, 86 mg. Daily Recommendation, 700 mg for all adults. Special Notes: (1) Phosphorus deficiency is very uncommon and usually only observed in cases of near-total starvation or in rare, inherited kidney disorders. (2) High blood phosphorus concentration is linked to increased risks of cardiovascular disease and death. (3) The subsitution of phosphate-containing soft drinks and snack foods for milk and other calcium-rich food may compromise bone health.

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Potassium

What it does

General

  • Potassium is an essential mineral that helps maintain fluid and electrolyte balance, influences blood pressure, and is required for proper nerve conduction and muscle contraction.

Bone-specific

  • Potassium salts may prevent calcium release from bone and urinary calcium excretion that are caused by the consumption of excessively acidic diets.
What we know
  • Two 2-year randomized controlled trials found either no effect or an increase in bone mineral density in healthy older people supplemented with potassium.
  • Adopting a diet that increases potassium intake and reduces sodium intake (i.e., high in fruit, vegetables, and dairy, and low in meat) might help support bone health.
DEFINITIONS
Bone mineral density (BMD) - a measure of the amount of mineral (calcium and phosphorus) that deposited onto bone matrix made of proteins in a specific area or volume of bone; a proxy measure of bone mass
Electrolytes - minerals that dissociate into ions in body fluids; e.g., sodium chloride (NaCl) dissociates into sodium (Na+) and chloride (Cl-) ions
Excessively acidic diets - refers to diets that are high in sources of acid (fish, meat, cheese) and low in sources of alkali (fruit and vegetables)
Randomized controlled trial - an intervention study in subjects randomly allocated to receive an active treatment or an inert (control) treatment. This type of study tests the efficacy of an active treatment on a specific outcome compared to a control

For references and more information, see the section on Potassium in the in-depth article on Bone Health.

Potassium Flashcard. Main Functions: (1) maintains fluid and electrolyte balance, (2) Required for proper nerve conduction and muscle contraction, and (3) Influences blood volumen and blood pressure. Good Sources: Fruit (prunes, banana, orange juice); prunes (dried plums), one-half cup, 637 mg; banana, 1 medium, 422 mg; Vegetables (potato, tomato, artichoke), potato with skin, 1 medium, 926 mg. Daily Recommendation. 4,700 mg for adults. Special Notes: (1) Potassium and sodium work together. A diet high in potassium and low in sodium helps maintain a lower blood pressure. (2) Fruit, vegetables, and legumes are naturally high in potassium and low in sodium. (3) Most people consume too little potassium. In addition to fruit and vegetables, nuts and beans also provide potassium.

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Sodium

What it does

General

  • Sodium and chloride are electrolytes working together to control fluid volume, blood pressure, acid-base homeostasis, and membrane potential, thereby supporting normal physiological functions.

Bone-specific

  • 40% of total body sodium is found in bone; while half of it is trapped into bone structure, the other half can be used to replace blood sodium lost in the urine and feces if need arises.
  • Sodium increases calcium excretion in the urine: the more sodium is consumed, the more sodium is excreted in the urine, and the more calcium is lost in the urine.
What we know
  • Excess sodium can be harmful to bone health in older women especially when they have suboptimal calcium intakes.
  • Striving to lower sodium intake while ensuring adequate calcium intake to the recommended levels is a good way of supporting bone health.
DEFINITIONS
Acid-base homeostasis - refers to the balance between the acids and bases (i.e., the pH) of body fluids
Electrolytes - minerals that dissociate into ions in body fluids; e.g., sodium chloride (NaCl) dissociates into sodium (Na+) and chloride (Cl-) ions
Homeostasis - a state of balance
Membrane potential - refers to the electrical potential difference across cell membranes. It is the difference in concentrations of sodium (Na+) and potassium (K+) ions across the membrane that create this electrochemical gradient that is actively maintained by ion pumps

For references and more information, see the section on Sodium in the in-depth article on Bone Health.

Sodium Flashcard. Main Functions: (1) Maintains fluid and electrolyte balance. (2) Required for proper nerve conduction and muscle contraction. (3) Influences blood volume and blood pressure. Good Sources: Most dietary sodium comes from processed and restaurant food. Processed Foods (canned foods, lunch meat, potato chips), chicken noodle soup, canned, 1 cup, 789 mg; ham, minced, 3 ounces, 1,059 mg. Table Salt (sodium chloride): table salt, 1 teaspoon, 2,325 mg. Daily Recommendation: 1,500 mg for adults 19-50 years, 1,300 mg for adults 51-70 years, and 1,200 mg for adults 71 years and older. Special Notes: Most people consume too much sodium! (1) Diets low in sodium and high in potassium reduce fluid retention and favorably affect blood pressure. (a) Consuming 1,200 mg of sodium per day or less is associated with significant blood pressure reduction. (b) Fruit, vegetables, and legumes are naturally low in sodium and high in potassium.

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Vitamin A

What it does

General

  • Vitamin A (retinol) is a fat-soluble vitamin involved in the growth and differentiation of virtually all cells in the body.
  • Vitamin A is essential for normal vision, reproduction, development, and immune function.

Bone-specific

  • Animal studies found that both vitamin A deficiency and excess could cause bone abnormalities.
  • Very high vitamin A doses have been linked to hypercalcemia and bone resorption in humans.
What we know
  • Higher risk of osteoporosis and fracture have been reported with habitual vitamin A intakes greater than the RDA.
  • Striving for the RDA for vitamin A is a safe goal for optimizing bone health.
HIGHLIGHT:
  • Vitamin A supplements should be reserved for undernourished populations and those with evidence of vitamin A deficiency.
DEFINITIONS
Bone resorption - the breaking down of bone by osteoclasts
Differentiation - the process by which a cell become specialized in a particular function
Hypercalcemia - Abnormally high amount of calcium in blood
RAE - Retinol activity equivalent; RAE is the international standard of measure for vitamin A as retinol
RDA - Recommended dietary allowance. Set by the Institute of Medicine, the RDA is the average daily dietary intake level of a nutrient sufficient to meet the requirements of nearly all healthy individuals in a specific life stage and gender group

For references and more information:

Vitamin A (retinol) Flashcard. Main Functions: 1) Essential for site, dim-light adaptation, and color vision; 2) Supports reproductive health for both men and women; 3) Required for proper immune function; 4) Influences cell growth and development. Good Sources: There are two forms of dietary vitamin A: preformed vitamin A from animal products and provitamin A carotenoids from fruit and vegetables. Preformed Vitamin A: cod liver oil, 1 teaspoon = 1,350 micrograms retinol activity equivalents (RAE), 1 large egg = 80 micrograms RAE. Provitamin A (yellow & orange fruit & vegetables), sweet potato (baked), 1 cup = 1,922 micrograms RAE. Daily Recommendation: 900 micrograms RAE for men and 700 micrograms RAE for women. Special Notes: 1) RAE = a unit of measure for the vitamin A content of food. It reflects the amount of active vitamin A provided by the different types of food sources. 2) It is possible to ingest too much vitamin A (retinol). The Tolerable Upper Intake Level (UL) is 3,000 micrograms RAE of retinol/day. 3) There is no UL for provitamin A carotenoids because the liver controls their conversion to retinol.

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B Vitamins

What they do

General

    • The B vitamins, folate, vitamin B12, and vitamin B6, work together to convert homocysteine to methionine, an amino acid used in countless essential cellular activities.
    • Folate is required for DNA synthesis and the formation of new cells. Folate therefore supports the growth and repair of all tissues in the body, including bone.
    • Vitamin B12 helps convert food to useable energy, helps make red blood cells, and is required for proper nerve function.
    • Vitamin B6 helps convert food into useable energy and assists in the formation of neurotransmitters, red blood cells, proteins, and DNA.

Bone-specific

  • Abnormally high homocysteine concentration in blood is associated with reduced bone mineral density and osteopenia.
What we know
  • Meeting recommended intake levels for B vitamins with food and/or supplements helps to lower homocysteine concentration in blood.
  • However, trials found no evidence of an effect of B-vitamin supplementation on fracture risk reduction.
DEFINITIONS
Bone mineral density (BMD) - a measure of the amount of mineral (calcium and phosphorus) that deposited onto bone matrix made of proteins in a specific area or volume of bone; a proxy measure of bone mass
Homocysteine - a non-protein amino acid that is an intermediate in the synthesis of the essential amino acid methionine
Neurotransmitters - chemicals that are released from nerve cells and result in the transmission of an impulse to other nerve, muscle, or gland cells
Osteopenia - a condition of low bone mass that precedes osteoporosis

For references and more information, see the section on B Vitamins in the in-depth article on Bone Health.

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Vitamin C

What it does

General

  • Vitamin C (ascorbic acid) is a water-soluble vitamin that neutralizes a variety of reactive oxygen species, recycles important cellular antioxidants, augment the functional activity of immune cells, and helps make several proteins and peptide hormones.

Bone-specific

  • Vitamin C is required during the synthesis of collagen, which constitutes 90% of the bone matrix upon which bone minerals are deposited.
  • Animal studies found that vitamin C deficiency could impair collagen synthesis and the adhesion of osteoblasts onto the bone matrix.
What we know
  • Vitamin C status has not been consistently associated with measures of bone health in observational studies.
  • Prevention of bone loss in women with osteopenia was more effective when vitamin C, vitamin B6, and proline were co-supplemented with calcium and vitamin D, according to the results of one small trial.
DEFINITIONS
Antioxidants - compounds that prevent or repair the damage caused by reactive oxygen species
Hormones - a chemical released by a gland or a tissue, which regulates the activity of specific cells or organs
Osteoblasts - cells involved in making bone
Osteopenia - a condition of low bone mass that precedes osteoporosis
Proline - an amino acid used in the synthesis of proteins
Reactive oxygen species - highly unstable oxygen containing compounds that react easily with nearby structures, potentially causing damage

For references and more information, see the section on Vitamin C in the in-depth article on Bone Health.

Vitamin C (ascorbic acid) Flashcard. Main Functions: 1) Antioxidant defense, 2) Enhances immune function, 3) Needed to make collagen, carnitine, and the neurotransmitters serotonin and norepinephrine. Good Sources: Fruit, 1 medium-sized kiwifruit = 90 mg; strawberries, 1 cup whole, 85 mg; Vegetables (broccoli, kale, tomatoes), sweet red pepper (one-half cup, chopped) = 95 mg. Daily Recommendation is 400 mg for all adults. Special Notes: 1) Heat destroys vitamin C. Try to eat fresh foods and cook by steaming, microwaving, or stir-frying. 2) Vitamin C in food is identical to vitamin C in supplements. 3) The Daily Recommendation listed is specific to the LPI based on extensive review of the scientific evidence. The Institute of Medicine's Recommended Dietary Allowance (RDA) is 90 mg/day for men and 75 mg/day for women.

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Vitamin D

What it does

General

  • Vitamin D is made in the skin upon sunlight (UV) exposure and is also obtained from a few foods or supplements.
  • Vitamin D is a fat-soluble vitamin that helps regulate calcium and phosphorus homeostasis, promotes bone health and immune function, and influences cell growth and development.

Bone-specific

  • Vitamin D stimulates the release of calcium from bone by activating osteoclasts.
What we know
  • Severe vitamin D deficiency (serum 25-hydroxyvitamin D values ≤12 nanograms/milliliter [ng/mL]) causes rickets in children and osteomalacia in adults.
    • The American Academy of Pediatrics suggests that all infants, children, and adolescents receive 400 IU/day of supplemental vitamin D.
  • Compared to younger individuals, older people are at increased risks of poor vitamin D status (serum 25-hydroxyvitamin D values between 12-20 ng/mL) and skeletal disorders due to less sun exposure, a lower capacity for vitamin D synthesis, and reduced dairy intake.
    • Intervention studies found little-to-no effect of vitamin D supplementation alone on fracture risk.
    • The US Preventive Services Task Force supports vitamin D supplementation for fall prevention in older adults (≥65 years).
DEFINITIONS
Homeostasis - a state of balance
Osteoclasts - cells involved in breaking down bone
Osteomalacia - sometimes called "adult rickets"; it is characterized by a softening of the bones in adults following mineral loss
Rickets - a condition characterized by soft and deformed bones in children and due to an impaired incorporation of calcium and phosphorus in growing bones
Serum 25-hydroxyvitamin D - a reliable measure of vitamin D status
HIGHLIGHT: RISK FACTORS FOR VITAMIN D DEFICIENCY
Some of the factors influencing vitamin D production in the skin or vitamin D absorption include:
  • Environmental conditions, concealed clothes, and sun protection measures.
  • Genetic variations, skin color, aging, magnesium deficiency, obesity, and specific diseases (e.g., cystic fibrosis, liver disease, inflammatory bowel disease).
  • Partial/exclusive breastfeeding may place infants at risk of vitamin D deficiency if they do not receive vitamin D supplementation and have little exposure to the sun.
HIGHLIGHT: VITAMIN D IN FOOD
Few foods contain vitamin D:
  • Some fatty fish (mackerel, salmon, sardines), eggs from vitamin D-fed hens, and mushrooms grown under UV light.
  • Dairy products, cereal, bread, and fruit juices may be fortified with vitamin D.

For references and more information:

Vitamin D (calciferol) Flashcard. Main Functions: 1) Facilitates absorption of calcium and phosphorus, 2) Promotes bone health, 3) Required for proper immune function, and 4) Influences cell growth and development. Good Sources: Fatty Fish (salmon, mackerel, sardines), pink canned salmon, 3 ounces = 465 IU or 11.6 micrograms; Canned mackerel, 3 ounces = 211 IU for 5.3 micrograms; Fortified food, low-fat milk, vitamin D fortified, 8 ounces = 98 IU or 2.5 micrograms. Daily Recommendation: 600-1,000 IU (15-25 micrograms) for chldren and adolesents (4-18 years), because vitamin D is scarcely found in food, it may be necessary to take supplements. 2,000 IU or 50 micrograms for all adults, this amount applies to supplemental vitamin D, which is recommended in addition to vitamin D from a mixed diet. Special Notes: 1) The Daily Recommendation listed is specific to the LPI based on extensive review of the scientific evidence. The Institute of Medicine's Recommended Dietary Allowance (RDA) is 600 IU (15 micrograms)/day for males and females who are 4-70 years old, and 800 IU (20 micrograms)/day for all adults over 70. 2) Vitamin D is considered a "Nutrient of Public Health Concern" because underconsumption is linked to adverse health outcomes. 3) More than 90% of Americans do not meet the dietary requirement for vitamin D. 4) our bodies make vitamin D upon skin exposure to UVB radiation from the sun. Darker skin color, northern latitude, and older age impede the amount of vitamin D produced.

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Vitamin K

What it does

General

  • Naturally occurring vitamin K refers to various fat-soluble compounds, classified as either vitamin K1 (phylloquinone) or vitamin K2 (menaquinones).
  • Vitamin K augments the calcium-binding capacity of many proteins, some of which are needed for proper coagulation.

Bone-specific

  • Several vitamin K-dependent proteins, like osteocalcin, matrix Gla protein, or Gla-rich protein, are found in bone tissue where they are involved in bone formation and turnover.
  • Low vitamin K bioavailability may affect the activity of vitamin K-dependent proteins, thereby contributing to bone mineralization defects.
What we know
  • Observational evidence suggests that poor vitamin K status may be linked to higher risks of osteoarthritis and fracture.
  • There is little evidence supporting a benefit of vitamin K supplementation in the prevention of osteoporosis.
HIGHLIGHT:
  • Vitamin K deficiency is uncommon in healthy adults.
  • Taking vitamin K supplements can interfere with the blood-thinning (anticoagulant) effect of vitamin K antagonists (e.g., warfarin).
  • The National Osteoporosis Foundation advises against the use of vitamin K supplements in people at risk of blood clots and those taking blood-thinning medications.
DEFINITIONS
Bioavailability - here, it refers to the amount of vitamin K that is available for the body to use
Coagulation - blood clotting
Osteoarthritis - a degenerative joint condition that is characterized by the breakdown of joint cartilage

For references and more information, see the section on Vitamin K in the in-depth article on Bone Health.

Vitamin K Flashcard. Main Functions: 1) Assists in blood clotting, 2) promotes bone calcification, and 3) Prevents blood vessel calcification. Good Sources: There are two forms of naturally occurring vitmain K: vitmain K1 (phylloquinone) and vitmain K2 (menaquinones). Vitamin K1 sources include green leafy vegetables and plant oils, kale (raw, chopped), 1 cup=472 micrograms; canola oil, 1 tablespoon=10 micrograms; Vitamin K2 sources are fermented food and gut bacteria: there is no dietary requiremetn for vitamin K2 at this time.

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Alcoholic Beverages

What they do

General

  • Alcoholic beverages contain ethanol and other ingredients with bioactive properties with potential health effects.
  • When consumed in moderation (1-2 drinks/day), alcohol consumption has been associated with beneficial effects on the cardiovascular system.
  • Even modest intakes of alcohol may increase the risk of cancer.

Bone-specific

  • Animal studies showed that chronic alcohol exposure limits bone development in growing animals, ultimately affecting bone mechanical properties.
What we know
  • Regular light alcohol intake (1 drink/day in women and 2 drinks/day in men) is associated with lower bone loss over time and a lower risk of hip fracture.
  • Regular moderate intake is associated with a lower risk of hip fracture in men but not in women.
  • Regular heavy intake (≥4 drinks/day) is associated with a higher risk of hip fracture.
HIGHLIGHT
  • 1 standard alcoholic drink contains 14 g of alcohol, which is equivalent to:
    • 12 fluid ounces (fl oz) of beer (~5% of alcohol)
    • 8.5 fl oz of malt liquor (~9% of alcohol)
    • 5 fl oz of wine (~12% of alcohol)
    • 1.5 fl oz of distilled spirit (liquors; ~40% of alcohol)
  • Alcohol is metabolized differently in women and men such that recommendations have a lower threshold for women.
  • No alcohol should be consumed by:
    • women intending to be pregnant, pregnant, or breast-feeding
    • people taking over-the-counter or prescribed medications/with certain medical conditions
    • people planning to drive or engage in activities requiring coordination and alertness
    • recovering alcoholics
    • anyone aged <21 years (according to US alcohol legislation)

For references and more information:

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Coffee

What it does

General

  • Coffee is a complex mixture of carbohydrates, lipids, amino acids, minerals, and other bioactive compounds like caffeine that can influence human health.
  • Coffee consumption has been associated with lower risk of death due to cardiovascular disease or any cause.

Bone-specific

  • Coffee can increase calcium excretion in the urine; however, this is unlikely to affect calcium homeostasis and bone health in subjects with adequate calcium intakes.
What we know
  • Evidence from observational studies found no increase in the risk of fracture with coffee consumption.
  • Limiting coffee consumption to ≤3 cups/day and ensuring adequate calcium and vitamin D intakes should prevent any potential adverse effects of coffee on calcium balance and bone health.
DEFINITION

Homeostasis - a state of balance

For references and more information, see the section on Lifestyle factors in the in-depth article on Bone Health.

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Physical Activity

What it does

General

  • Together with a healthy diet, physical activity is a major contributor to achieving and maintaining good health.

Bone-specific

  • Physical activity is highly beneficial across all stages of bone development.
  • Bone adjusts its strength relative to the degree of bone stress, and the intensity and novelty of the load are important for building bone mass.
What we know
  • Evidence-based recommendations to maintain bone health during adulthood include:
    • 30-60 min/day of moderate-to-high intensity physical activity as a mix of weight-bearing, endurance activities (activities that involve jumping, and resistance exercises that strengthen muscles)
  • Exercising regularly is associated with less age-related bone loss over time and a lower risk of fracture.
    • However, there is no evidence that even high-intensity exercises can limit the bone loss due to menopause.
  • Even frail elderly people should remain as physically active as possible to preserve bone health.
HIGHLIGHT
  • Any amount of physical activity is better than none and will bring some benefits to health.
  • Exercising may be detrimental to bone health if the body does not receive the nutrients it needs to remodel bone tissue in response to impact and tension forces generated by physical activity.
DEFINITIONS
High-intensity physical activity - e.g., jogging, singles tennis, swimming continuous laps, or bicycling uphill
Menopause - describes the period of a woman's life when menstruation ceases
Moderate-intensity physical activity - e.g., brisk walking, doubles tennis, dancing, swimming, bicycling on a level terrain
Resistance exercise - e.g., lifting weights
Weight-bearing, endurance activities - e.g., tennis, stair climbing, jogging

For references and more information:

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Smoking

What it does

General

  • Cigarette smoking is responsible for ~500,000 deaths/year in the US
  • Cigarette smoking is a risk factor for numerous conditions, including several types of cancer, cardiovascular disease, airway disease, bone disease, and also diabetes, erectile dysfunction, and Alzheimer's disease

Bone-specific

  • Cigarette smoking lowers bone mineral density in particular by increasing the level of free radicals that damage bone tissue and altering the production of estrogen and vitamin D involved in bone metabolism
What we know
  • Smoking is associated with a higher risk of fracture and with delayed recovery from fracture.
  • Smoking cessation reverses (at least partially) the increase in risk of fracture reported in smokers compared to non-smokers.
  • Quitting smoking improves overall health – including bone health – and lowers the risk of early death.
DEFINITIONS
Bone mineral density (BMD) - a measure of the amount of mineral (calcium and phosphorus) that deposited onto bone matrix made of proteins in a specific area or volume of bone; a proxy measure of bone mass
Free radicals - very reactive atoms or molecules (with at least one unpaired electron) that can damage cell membranes and large molecules (like DNA) by stealing their electrons
Risk factor - defines any factor that can increase the likelihood of developing an injury or disease

For references and more information, see the section on Lifestyle factors in the in-depth article on Bone Health.

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The writing of this content was supported by a grant from Pfizer Inc.