Micronutrients

Overview

Micronutrients are those nutrients we require in relatively small quantities. They are vitamins and minerals, and our good health requires them in milligram and microgram amounts. Recall that fats, carbohydrates and proteins are macronutrients, meaning that we require them in relatively large quantities. We consume the macronutrients in gram amounts. For example, we might have 200 grams of carbohydrate, 100 grams of protein and 50 grams of fat, yet only 18 mg of iron and 400 micrograms of folate.

Vitamins are carbon-containing molecules and are classified as either water-soluble or fat-soluble. They can be changed and inactivated by heat, oxygen, light and chemical processes. The amount of vitamins in a food depends on the growing conditions, processing, storage and cooking methods. Minerals do not contain carbon, and are not destroyed by heat or light. Unlike other nutrients, minerals are in their simplest chemical form. Minerals are elements. Whether found in bone, seashells, cast iron pots or the soil, they are they same as the minerals in our food and our bodies. The mineral content of plant foods varies with the soil content and the maturation of the plant.

On This Page:

  1. Water-Soluble Vitamins
  2. Fat-Soluble Vitamins
  3. Major Minerals
  4. Trace Minerals

Water-Soluble Vitamins

Assortment of vitamin and supplement pills of varying size and colorIf you look to vitamins for a jolt of energy, you are looking in the wrong place – even if a supplement bottle says, “promotes energy,” or makes some other similar vague statement. Vitamins are not energy boosters. Many B vitamins do, however, participate in energy-yielding chemical reactions in the body. This is confusing because calorie is another word for energy. It’s clearer to say that B vitamins help the body get calories from food. While you’re unlikely to get more pep by taking vitamins, eating vitamin-rich foods will certainly help you maintain health.

  1. Vitamin B1 - Thiamin
    • Functions: Assists in carbohydrate and amino acid metabolism
    • Recommended Intakes of Thiamin: Your thiamin needs are proportional to your energy or calorie needs. The more calories you consume, the greater your need for this vitamin. The beauty is that the more calories you consume, the more thiamin you automatically consume anyway. The RDA for adult women and men is 1.1 and 1.2 mg, respectively.
    • Sources of Thiamin: Though thiamin is found in most food groups, Americans get most of their thiamin from fortified breakfast cereals and enriched grains such as rice and pasta. Pork, beans and peas are additional sources.
    • When You Get Too Much or Too Little Thiamin: There are no known toxicity symptoms of thiamin. Thiamin deficiency is not common in the U.S., however alcoholics and those who eat a junk food-heavy diet are at risk. A diet of highly processed, but unenriched foods provides ample calories with little thiamin. Additionally, alcohol contributes calories without providing good nutrition, and it interferes with thiamin absorption. Thiamin deficiency disease is called beriberi and is characterized by weight loss, confusion, irritability, nerve damage and muscle wasting. Beriberi became understood in the nineteenth century when refining grains became popular. Populations whose major source of energy was white or polished rice became inflicted with a fatal nerve disease thought to be an infection, but it was really a lack of this B vitamin.
  2. Vitamin B2 - Riboflavin
    • Functions: Assists in carbohydrate and fat metabolism
    • Recommended Intakes of Riboflavin: The RDA for riboflavin also reflects energy needs with higher riboflavin intakes recommended for those whose calorie needs are higher. The RDA for adult women and men is 1.1 and 1.3 mg, respectively.
    • A few crimini mushrooms, one of them sliced in halfSources of Riboflavin: Diary products, fortified cereals and enriched grains are major contributors of dietary riboflavin. Mushrooms and organ meats such as liver are additional sources.
    • When You Get Too Much or Too Little Riboflavin: The body readily excretes excess riboflavin, so there are no apparent toxicity symptoms. Like thiamin deficiency, riboflavin deficiency is uncommon, but alcoholism increases an individual’s risk. The symptoms include swollen mouth and throat, dermatitis and anemia.
  3. Niacin - Nicotinamide, Nicotinic Acid
    • Functions:
      • Assists in carbohydrate and fat metabolism
      • Helps with cell differentiation
      • Participates in DNA replication and repair
    • Recommended Intakes of Niacin: The RDA for adult women and men is 14 and 16 mg, respectively.
    • Sources of Niacin: Meat, poultry, fish, fortified breakfast cereals and enriched grains are good sources of niacin.
    • When You Get Too Much or Too Little Niacin: Large doses of nicotinic acid - one form of niacin – lower LDL (bad) cholesterol and raise HDL (good) cholesterol. Doctors may prescribe it for cholesterol management, but patients frequently reject it for its common side effect. Flushing or itching, heat and tingling on the face and upper body make this a difficult treatment for many to stick with.  Because of this and the potential for liver damage, the Tolerable Upper Intake Level (UL) for niacin for adults is 35 mg/day. Severe niacin deficiency leads to pellagra characterized by the 4 Ds: dermatitis, dementia, diarrhea and eventually death. Niacin deficiency is rare in the U.S. today, but was once common in the southern states where residents subsisted on corn. Without proper treatment, corn binds niacin making it unavailable to the body. Niacin deficiency became less common after World War II when food manufacturers began enriching grains with niacin and other nutrients and because the postwar affluence allowed people to purchase niacin-rich meat, poultry and fish.
  4. Vitamin B6 – Pyridoxine, Pyridoxal, Pyridoxamine
    • Functions:
      • Assists in protein and carbohydrate metabolism
      • Supports blood cell synthesis and neurotransmitter synthesis
    • Recommended Intakes of B6: Since B6 is important in protein metabolism, individuals with very high protein diets require increased B6. The RDA for men and women is 1.3 mg until age 51 when it increases to 1.7 mg per day for men and 1.5 mg per day for women. 
    • A bowl of chickpeasSources of B6: Fortified breakfast cereals are especially good sources of vitamin B6. Other sources include bananas, chickpeas, white potatoes, sunflower seeds, beef and poultry.
    • When You Get Too Much or Too Little B6: Many people falsely believe that water-soluble vitamins have only minor toxicity symptoms. Large doses of vitamin B6 cause nerve damage that may be irreversible. The UL for vitamin B6 is 100 mg/day. Alcoholism increases the risk of vitamin B6 deficiency just as it does for many other B vitamins. Otherwise deficiencies are rare. Symptoms include anemia, dermatitis, depression, confusion and convulsions.
  5. Vitamin B12 - Cobalamin
    • Functions:
      • Participates in the metabolism of folate
      • Helps protect the myelin sheath, the coating that surrounds and protects nerve fibers

    • Recommended Intakes of B12: The RDA is 2.4 micrograms for both men and women.
    • Sources of B12: There are no sources of B12 in foods of vegetable origin, so strict vegans will need a supplement. Fish, beef, poultry and dairy contain naturally occurring vitamin B12. Vegans can obtain B12 from fortified breakfast cereals and fortified soy products as well as supplements.
    • When You Get Too Much or Too Little B12: There are no known toxicity effects of vitamin B12. A healthy individual who switches from an omnivorous diet to a vegan diet will not become vitamin B12 deficient right away because we can store enough B12 in the liver to last two years. Older people are at risk for vitamin B12 deficiency because many have a stomach condition that decreases the absorption of this vitamin. Too little vitamin B12 causes a type of anemia called megaloblastic anemia. The red blood cells grow very large and have a short life span. Because of vitamin B12’s role in protecting the myelin sheath, a deficiency also causes neurological symptoms including tingling, numbness, cognitive changes, disorientation and dementia. These neurological defects may or may not be reversible. Pernicious anemia is the form of B12 deficiency resulting from an autoimmune disease that damages the stomach and inhibits vitamin B12 absorption. Pernicious anemia is treated with vitamin B12 injections.
  6. Folate – Folic Acid (synthetic form)
    • Functions:
      • Assists in DNA synthesis and cell division
      • Participates in amino acid metabolism
      • Required for the maturation of cells including red blood cells

    • Recommended Intakes of Folate: The RDA for men and women is 400 micrograms. The RDA during pregnancy increases to 600 micrograms.
    • One glass of orange juiceSources of Folate: Fortified breakfast cereals and enriched grains are important sources of folic acid. Other reliable sources of folate include legumes, green leafy vegetables, orange juice, wheat germ and liver.
    • When You Get Too Much or Too Little Folate: Excess folic acid may mask a deficiency of vitamin B12 by reversing or preventing anemia. Unfortunately, the neurological effects of a lack of vitamin B12 still continue without early obvious signs. The UL for adults is 1,000 micrograms from folic acid supplements and fortified foods. Because folate is required for cell division, too little folate causes megaloblastic anemia just as a lack of vitamin B12 does. Inadequate folate stores and intakes are linked to increased risks of birth defects such as spina bifida and anencephaly (neural tube defect in which all or part of the brain is missing). Low folate intake is also linked to increased risks of heart disease and cancer.
  7. Vitamin C – Ascorbic Acid
    • Functions:
      • Enhances iron absorption
      • Helps with collagen synthesis
      • Acts as an antioxidant
      • Regenerates vitamin E
      • Plays a role in immune function
      • Assists in the synthesis of neurotransmitters, DNA and hormones

    • Special interest in vitamin C in the treatment or prevention of the common cold: A review of the research does not suggest that vitamin C supplements prevent colds in the general public. However, among those subjected to extreme cold or engaging in extreme physical activity, vitamin C doses ranging between 250 mg/day to 1000 mg/day reduced the incidence of colds by 50%. Taken before the onset of a cold, supplemental vitamin C appears to slightly reduce the length of the cold.
    • Recommended Intakes of Vitamin C: The RDA for men and women is 90 and 75 milligrams respectively. Smokers should add and additional 35 milligrams per day.
    • A kiwi cut in halfSources of Vitamin C: Vitamin C is present in fruits and vegetables. Rich sources include bell peppers, citrus fruits, strawberries, pineapple, kiwifruit, potatoes, tomatoes, broccoli and leafy greens.
    • When You Get Too Much or Too Little Vitamin C: The UL is 2,000 mg. Excess vitamin C may cause nosebleeds, nausea and gastrointestinal distress including cramps and diarrhea. In individuals with kidney disease, too much vitamin C may lead to kidney stones. Some research suggests that large doses of vitamin C may increase oxidation within the body, the opposite effect of its antioxidant role. Vitamin C deficiency is called scurvy and is characterized by bleeding in the gums, small hemorrhages on the arms and legs, bone pain, fractures and depression.

Fat-Soluble Vitamins

Fat-soluble vitamins accumulate in the liver and fat tissues. These reserves may be released when dietary intakes are low. There is research, however, suggesting that blood levels of vitamin D may be low even in the presence of significant storage in the fat.

Because they can be stored so readily, the fat-soluble vitamins may be toxic in large doses.

  1. Vitamin A – Retinol, Retinal, Retinoic Acid, Provitamin A - Carotenoids
    • Functions:
      • Required for night vision and color vision
      • Needed for cell differentiation
      • Supports immune function
      • Aids both male and female reproductive processes
      • Required for bone health
    • Additional Functions of Carotenoids: Research is mounting that carotenoids have health benefits. For example, lutein and zeaxanthin may protect the eye from cataracts and age-related macular degeneration. Lycopene, crytoxanthin, beta-carotene and alpha-carotene might be cancer-protective.
    • Recommended Intakes of Vitamin A: The RDA for males and females aged 14 years and older is 900 and 700 micrograms, respectively.
    • Egg yolk sitting in a half of an egg shellSources of Vitamin A: Sources for preformed vitamin A come from animal foods only. They include liver, egg yolks and whole milk. Carotenoids are precursors to vitamin A. Sources of these precursors, referred to as provitamin A, include broccoli, spinach, carrots, sweet potatoes, cantaloupe, peaches and other dark green and yellow/orange fruits and vegetables.
    • When You Get Too Much or Too Little Vitamin A: The UL for vitamin A is 3000 micrograms. Excess preformed vitamin A can cause birth defects including cleft palate and spontaneous abortions. Pregnant women should not take supplements or medications containing preformed vitamin A (retinol). Instead they should use pre-natal supplements that have beta-carotene as the vitamin A source. High doses of vitamin A are also linked to increased hip fractures in older women. Excess beta-carotene can cause carotenodermia, a harmless condition that turns the skin yellowish in color. Even though beta-carotene is an antioxidant, supplements may increase the risk of lung cancer among smokers. Too little vitamin A may cause night blindness and even permanent blindness, increased infections, impaired growth and reproductive function.
  2. Vitamin D – Cholecalciferol
    • Functions:
      • Regulated blood calcium levels
      • Supports bone health
    • Recommended Intakes of Vitamin D: The AI for males and females aged 1 to 70 is 600 IU (International Units). After age 70, the AI jumps to 800 IU.
    • Two salmon steaks with a lemon wedge garnishSources of Vitamin D: The best source of vitamin D is sunlight. Ultra violet light triggers the synthesis of vitamin D in your skin. With increased use of sunscreen and fewer work hours and leisure time outdoors, many people do not synthesize adequate vitamin D. There are few food sources of naturally occurring vitamin D. They include fatty fish such as salmon and tuna, egg yolks, beef liver and some mushrooms. Fortified milk, orange juice, breakfast cereals and other foods are additional sources.
    • When You Get Too Much or Too Little Vitamin D: The UL for adults and children aged 9 and older is 4,000 IU. Excess vitamin D can cause hypercalcemia, dangerously high levels of calcium in the blood. Hypercalcemia can cause bone loss and kidney stones. It may also affect the nervous system, heart, lungs, kidneys and blood vessels. Vitamin D deficiency results in weak bones. In children, this is called rickets and is characterized by bowlegs and other skeletal deficiencies. In adults, low vitamin D levels cause osteomalacia and osteoporosis, which lead to an increased risk of bone fractures. Researchers are studying vitamin D for it’s potential role in the prevention of certain cancers and autoimmune diseases such as multiple sclerosis and Crohn’s disease. It is possible that low vitamin D could increase the risk of developing one of these diseases.
  3. Vitamin E – Tocopherol
    • Functions. Protects cell membranes from oxidation
    • Recommended Intakes of Vitamin E: The RDA for men and women is 19 mg.
    • Sources of Vitamin E: Seeds, nuts, vegetable oils and fortified breakfast cereals are among the best sources of vitamin E.
    • When You Get Too Much or Too Little Vitamin E: Vitamin E is relatively nontoxic, but large doses from supplements may interfere with blood clotting. The UL is 1,000 mg of supplemental vitamin E, however, some studies have shown increased mortality with lower doses. Vitamin E deficiency is rare in healthy people. It manifests as hemolytic anemia, the early destruction of red blood cells because of the lack of vitamin E to protect them from oxidation.
  4. Vitamin K – Phylloquinone, Menaquinones
    • Functions:
      • Assists in blood clotting
      • Aids bone formation
    • Recommended Intakes of Vitamin K: The AI (Adequate Intake) for men is 120 micrograms and 90 micrograms for women.
    • Small pile of Brussels sproutsSources of Vitamin K: Animal foods contain little vitamin K. Good sources include Brussels sprouts, broccoli, spinach and other leafy green vegetables, black-eyed peas and soybeans. We get additional vitamin K from the normal bacteria thriving in our colons.
    • When You Get Too Much or Too Little Vitamin K: Both vitamin K toxicity and deficiency are rare. When present, a deficiency of vitamin K causes impaired blood clotting. Suboptimal intakes of vitamin K are linked to reduced bone density and increased risk of fractures.

Major Minerals

Major minerals are the ones that the body requires in amounts of at least 100 milligrams per day. They are sodium, potassium, chloride, phosphorus, calcium, magnesium and sulfur. The first four are included in the discussion of fluid and electrolytes.

  1. Calcium
    • Functions:
      • Major component of bones and teeth
      • Required for muscle contraction
      • Required for nerve transmission
      • Plays a role in cellular metabolism
      • Aids blood clotting
    • Recommended Intakes of Calcium: The AI for adults aged 19 to 50 is 1000 mg. Because calcium is so critical to preventing bone disease later in life, the AI is higher for adolescents and teens since they can still build bone mass. The AI for males and females aged nine to 18 is 1300 milligrams. For those aged 51 and older, the AI is 1200.
    • An opened can of sardinesSources of Calcium: Americans get about half of their calcium from dairy foods. Chinese cabbage, kale and turnip greens contain absorbable calcium. Spinach and some other vegetables contain calcium that is poorly absorbed. Sardines and other canned fish with bones are additional sources. Some foods such as orange juice and bread are fortified with calcium, and some tofu is processed with calcium making it another source of this mineral.
    • When You Get Too Much or Too Little Calcium: The UL for calcium is 2,500 milligrams. Excess calcium may cause mineral imbalances because it interferes with the absorption of iron, magnesium, zinc and others. Too little calcium causes osteoporosis. Some research connects low calcium intake to increased risks of high blood pressure, colon cancer and preeclampsia (high blood pressure and excess protein in the urine of a woman more than 20 weeks pregnant).
  2. Magnesium
    • Functions:
      • Assists enzymes in more than 300 chemical reactions in the body
      • Supports cellular activity
      • Participates in muscle contraction
      • Aids blood clotting
      • A component of bone

    • Recommended Intakes of Magnesium: The RDA for men and women aged 19 to 30 years is 400 and 310 milligrams per day, respectively. For older adults, the RDA bumps up to 420 milligrams and 320 milligrams for men and women, respectively.
    • Sources of Magnesium: Leafy greens, potatoes, whole grains, nuts, seeds and legumes are good sources of magnesium.
    • When You Get Too Much or Too Little Magnesium: The UL for magnesium is 350 milligrams from supplements or medicines because it may cause diarrhea. Severe toxicity may cause confusion, loss of kidney function, difficulty breathing and cardiac arrest. Individuals with kidney Doctor taking a patient's blood pressuredisease are at higher risk for magnesium toxicity. Overt symptoms of magnesium deficiency in healthy people are rare. However, a magnesium deficiency can occur in individuals with kidney disease, alcoholism or prolonged diarrhea. Early signs of poor magnesium status are loss of appetite and weakness. Later signs are muscle cramps, irritability, confusion and cardiac abnormalities. Many people consume suboptimal amounts of magnesium, and low magnesium stores may be related to increased risk of cardiovascular disease, high blood pressure, type 2 diabetes and immune dysfunction.
  3. Sulfur
    • Functions:
      • Helps maintain acid-base balance
      • Assists in some of the liver’s drug-detoxifying pathways
      • A component of some vitamins and amino acids
    • Recommended Intakes of Sulfur: There is no Dietary Reference Intake (DRI) for sulfur
    • Sources of Sulfur: Since sulfur is a component of amino acids, protein-rich foods are good sources of sulfur.
    • When You Get Too Much or Too Little Sulfur: There are no known deficiency or toxicity symptoms.

Trace Minerals

The minerals that the body requires in amounts less than 100 milligrams per day are referred to as trace minerals. They are chromium, copper, fluoride, iodine, iron, manganese, molybdenum, selenium and zinc. Because iron metabolism is the most complicated of the nine, it will be discussed in greater detail.

  1. Iron
    • Functions:
      • Carries oxygen throughout the body
      • Assists in energy metabolism and other enzyme-mediated chemical reactions
      • Supports immune function
      • Involved in the production of neurotransmitters, chemicals that carry messages between nerve cells
      • Participates in the development of the brain and nervous system
    • Recommended Intakes of Iron: The RDA for men and postmenopausal women is 8 mg. Because of their monthly blood losses, the RDA for premenopausal women jumps to 18 mg. The RDA during pregnancy jumps even more to 27 milligrams to provide adequate iron stores for the infant. If the mother’s iron status is poor, the baby will not have enough stored iron to last the first six months of life.
    • Chicken livers on a cutting boardSources of Iron: Iron has two types: heme and non-heme. Heme iron is only present in animal flesh. Beef, liver, clams and oysters are excellent sources of iron. Additional sources are poultry, fish and pork. Non-heme iron can be found naturally in tofu, legumes, spinach, raisins, and other plant foods. It is the form of iron used in fortified and enriched foods such as breakfast cereals, bread and pasta. As an excess of iron is highly toxic, the human body tightly regulates the amount of iron it absorbs. Depending on the body’s need for iron, we absorb approximately 15 to 35% of the heme iron we ingest, but significantly less of the non-heme iron. Eating meats including fish and poultry and vitamin C-rich foods enhances the absorption of non-heme iron. Thus, you will absorb more iron from legumes, for example, if when you eat them, you also eat fresh tomatoes or an orange.
    • When You Get Too Much or Too Little Iron: The UL for males and females aged 14 and above is 45 mg. It is 40 mg for younger individuals. Side effects of too much iron are gastrointestinal and include nausea, vomiting, diarrhea and constipation. Accidental overdose of multivitamin/mineral supplements or other iron-containing products is the leading cause of poisoning deaths among young children in the U.S. Immediate emergency medical care is critical because death can occur quickly. In addition to gastrointestinal symptoms, the child may experience rapid heartbeat, dizziness and confusion.

      Hemochromatosis is a genetic defect that causes excessive iron absorption. Over time, iron can accumulate in and cause damage to various parts of the body. The result could be diabetes, liver cancer, cirrhosis of the liver and joint problems.

      Iron deficiency is the most common nutrient deficiency throughout the world. In the U.S., individuals experiencing rapid growth or blood losses are at increased risk for deficiency. These include young children over 6 months of age, adolescents, menstruating women and pregnant women. Because they consume no heme iron, vegetarians are also at increased risk. Iron deficiency results in anemia with symptoms ranging from fatigue to rapid heart rate to decreased tolerance to cold to decreased athletic performance. Pica, the eating of clay, paper, ice and other non-food items, especially during pregnancy, may also be a symptom of iron deficiency.
  2. Stacked dark chocolate bars containing nutsChromium: Chromium enhances the effects of insulin, and may thus, play a role in the development of glucose intolerance and type 2 diabetes. Whole grains, brewer’s yeast, nuts and dark chocolate are sources of chromium. Clinical assessment of chromium status is difficult.  
  3. Copper: Copper assists with the transport of iron. Rich sources of copper include liver, shellfish, legumes, nuts and seeds. Deficiencies or excesses of copper are rare in healthy people.
  4. Fluoride: Fluoride helps prevent dental caries. Nearly 99% of the body’s fluoride resides in the bones and teeth. The main source of fluoride is municipal water supplies that add fluoride to the water. Excess fluoride discolors and damages teeth.
  5. Iodine: Iodine is a component of the thyroid hormones, which regulate metabolic rate and body temperature. Sources of iodine include saltwater fish, liver, legumes, potatoes, iodized salt and dairy products. Iodine deficiency inhibits the synthesis of thyroid hormones resulting in hypothyroidism and it’s typical problems including fatigue, weight gain and intolerance to cold. Inadequate iodine intake is fairly common in some parts of the word and may affect as much as 30% of the world’s population. In recent years, the use of iodized salt has decreased deficiency cases. Under different circumstances, excess iodine can cause either hyperthyroidism or hypothyroidism. Both too little and too much iodine can cause goiter, an enlargement of the thyroid gland.
  6. Manganese: Manganese is important in many enzyme-mediated chemical reactions including enzymes involved in the synthesis of cartilage in skin and bone. Tea and coffee are significant sources of manganese in the American diet. Additional sources are nuts, whole grains, legumes and some fruits and vegetables. Magnesium deficiency is rare. Toxicity is also uncommon and is most frequently the result of exposure to airborne manganese dust. The UL for manganese is 11 mg per day.
  7. Molybdenum: Molybdenum assists several enzymes including one required for the metabolism of sulfur-containing amino acids. Peas, legumes and some breakfast cereals supply molybdenum. Both molybdenum deficiency and toxicity are rare. High doses of molybdenum, however, inhibit copper absorption.
  8. Selenium: Selenium is required for immune function and for the synthesis of thyroid hormones. Additionally, this mineral assists enzymes in protecting cell membranes from damage. Depending upon the soil in which they are grown, Brazil nuts are one of the richest sources of selenium. Organ meats, seafood, other meats and whole grains are additional sources. Low selenium intake may decrease an individual’s ability to fight viral infections. Some research also links low intakes to some cancers. Toxicity causes brittle hair and nails and is most likely to occur with supplements.
  9. Zinc: Zinc is critical for normal growth and sexual maturation. It plays a role in the immune system and is important to the proper function of at least 70 enzymes including one that helps protect cells from damage. Oysters, beef and clams are rich sources of absorbable zinc. Whole grains also contain zinc, but it is less available for absorption. Zinc deficiency causes delayed growth and sexual development, decreased immune function, altered sense of taste, hair loss and gastrointestinal distress. Zinc deficiency is uncommon in healthy people in the U.S. It is more common among populations that consume cereals as their primary source of nutrition. Zinc toxicity is rare.

For your overall health, each nutrient is as important as the next. Whether they are macronutrients or micronutrients, vitamins, major minerals or trace minerals, they each have a unique role. A deficiency in any will impact your wellbeing. Eating a diet with both a variety of food groups and a variety within food groups is your best protection against nutrient imbalances.

Next Nutrition Guide:

Sources

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  3. Office of Dietary Supplements, National Institutes of Health:http://ods.od.nih.gov/factsheets/list-all/ Accessed March and April 2012.
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