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Vitamin D


[Vitamin D: What is it? | What are the sources of Vitamin D?]
[Recommended Dietary Allowance]
[When can vitamin D deficiency occur?]
[Who may need extra vitamin D to prevent a deficiency]
[Vitamin D issues and controversies | Too much vitamin D]
[Selected food sources for Vitamin D | References]

Vitamin D: What is it?
The major biologic function of vitamin D is to maintain normal blood levels of calcium and phosphorus4. Vitamin D aids in the absorption of calcium, helping to form and maintain strong bones. It promotes bone mineralization in concert with a number of other vitamins, minerals, and hormones. Without vitamin D, bones can become thin, brittle, soft, or misshapen. Vitamin D prevents rickets in children and osteomalacia in adults, which are skeletal diseases that result in defects that weaken bones5,6.

Vitamin D, calciferol, is a fat-soluble vitamin. It is found in food, but also can be made in your body after exposure to ultraviolet rays from the sun1,2. Vitamin D exists in several forms, each with a different activity. Some forms of vitamin D are relatively inactive in the body, and have limited ability to function as a vitamin. The liver and kidney help convert vitamin D to its active hormone form3.

What are the sources of vitamin D?

[Food sources | Exposure to sunlight]

Food Sources
Fortified foods are the major dietary sources of vitamin D4. Prior to the fortification of milk products in the 1930s, rickets (a bone disease seen in children) was a major public health problem in the United States. Milk in the United States is fortified with 10 micrograms (400 IU) of vitamin D per quart, and rickets is now uncommon in the US7.

One cup of vitamin D fortified milk supplies about one-fourth of the estimated daily need for vitamin D for adults. Although milk is fortified with vitamin D, dairy products made from milk such as cheese, yogurt, and ice cream are generally not fortified with vitamin D. Only a few foods naturally contain significant amounts of vitamin D, including fatty fish and fish oils4. The table of selected food sources of vitamin D suggests dietary sources of vitamin D.

Exposure to sunlight
Exposure to sunlight is an important source of vitamin D. Ultraviolet (UV) rays from sunlight trigger vitamin D synthesis in the skin7,8. Season, latitude, time of day, cloud cover, smog, and suncreens affect UV ray exposure8. For example, in Boston the average amount of sunlight is insufficient to produce significant vitamin D synthesis in the skin from November through February. Sunscreens with a sun protection factor of 8 or greater will block UV rays that produce vitamin D, but it is still important to routinely use sunscreen whenever sun exposure is longer than 10 to 15 minutes. It is especially important for individuals with limited sun exposure to include good sources of vitamin D in their diet.

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What is the Recommended Dietary Allowance for vitamin D for adults?
The Recommended Dietary Allowance (RDA) for Vitamin D is the average daily dietary intake level that is sufficient to meet the nutrient requirements of nearly all (97-98%) healthy individuals in each life-stage and gender group4. There is insufficient evidence to establish a RDA for vitamin D. Instead, an Adequate Intake (AI), a level of intake sufficient to maintain healthy blood levels of an active form of vitamin D, has been established. The 1998 AIs4 for vitamin D for adults, in micrograms (mcg) and International Units (IUs) are:

Life-Stage

 Men

 Women

Ages 19-50

5 mcg* or 200 IU

5 mcg* or 200 IU

Ages 51-69

10 mcg* or 400 IU

10 mcg* or 400 IU

Ages 70+ 15mcg* or 600 IU 15 mcg* or 600 IU
*1 mcg vitamin D + 40 International Units (UI)

Estimates of vitamin D intake in the United States are not available because dietary surveys do not assess vitamin D intake. Dietary intake of vitamin D is largely determined by the intake of fortified food4.

When can vitamin D deficiency occur?
A deficiency of vitamin D can occur when dietary intake of vitamin D is inadequate, when there is limited exposure to sunlight, when the kidney cannot convert vitamin D to its active form, or when someone cannot adequately absorb vitamin D from the gastrointestinal tract7.

The classic vitamin D deficiency diseases are rickets and osteomalacia. In children, vitamin D deficiency causes rickets, which results in skeletal deformities. In adults, vitamin D deficiency can lead to osteomalacia, which results in muscular weakness in addition to weak bones5,6,7.

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Who may need extra vitamin D to prevent a deficiency?
Older Americans (greater than age 50) are thought to have a higher risk of developing vitamin D deficiency9. The ability of skin to convert vitamin D to its active form decreases as we age4, 10-12. The kidneys, which help convert vitamin D to its active form, sometimes do not work as well when people age. Therefore, some older Americans may need vitamin D from a supplement.

It is important for individuals with limited sun exposure to include good sources of vitamin D in their diets8, 13-15. Homebound individuals, people living in northern latitudes such as in New England and Alaska, women who cover their body for religious reasons, and individuals working in occupations that prevent exposure to sunlight are at risk of a vitamin D deficiency. If these individuals are unable to meet their daily dietary need for vitamin D, they may need a supplement of vitamin D.

Individuals who have reduced ability to absorb dietary fat (fat malabsorption) may need extra vitamin D because it is a fat soluble vitamin. Some causes of fat malabsorption are pancreatic enzyme deficiency, Crohn's disease, cystic fibrosis, sprue, liver disease, surgical removal of part or all of the stomach, and small bowel disease6. Symptoms of fat malabsorption include diarrhea and greasy stools16.

Vitamin D supplements are often recommended for exclusively breast-fed infants because human milk may not contain adequate vitamin D17-20. The Institute of Medicine states that "With habitual small doses of sunshine breast- or formula-fed infants do not require supplemental vitamin D." Mothers of infants who are exclusively breastfed and have a limited sun exposure should consult with a pediatrician on this issue. Since infant formulas are routinely fortified with vitamin D, formula fed infants usually have adequate dietary intake of vitamin D.

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What are some current issues and controversies about vitamin D?
[Osteoporosis | Cancer | Steroids | Alzheimer's disease]

Vitamin D and osteoporosis
It is estimated that over 25 million adults in the United States have, or are at risk of developing osteoporosis21. Osteoporosis is a disease characterized by fragile bones. It results in increased risk of bone fractures. Having normal storage levels of vitamin D in your body helps keep your bones strong and may help prevent osteoporosis in elderly, non-ambulatory individuals, in post-menopausal women, and in individuals on chronic steroid therapy.

Researchers know that normal bone is constantly being remodeled (broken down and rebuilt). During menopause, the balance between these two systems is upset, resulting in more bone being broken down (resorbed) than rebuilt. Estrogen replacement, which limits symptoms of menopause, can help slow down the development of osteoporosis by stimulating the activity of cells that rebuild bone.

Vitamin D deficiency, which occurs more often in post-menopausal women and older Americans4,9,10-12, has been associated with greater incidence of hip fractures22. A greater vitamin D intake from diet and supplements has been associated with less bone loss in older women23. Since bone loss increases the risk of fractures, vitamin D supplementation may help prevent fractures resulting from osteoporosis.

In a group of women with osteoporosis hospitalized for hip fractures, 50 percent were found to have signs of vitamin D deficiency. Treatment of vitamin D deficiency22 can result in decreased incidence of hip fractures, and daily supplementation with 20 mcg (800 IU) of vitamin D may reduce the risk of osteoporotic fractures in elderly populations with low blood levels of vitamin D24. Your physician will discuss your need for vitamin D supplementation as part of an overall plan to prevent and/or treat osteoporosis when indicated.

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Vitamin D and cancer
Laboratory, animal, and epidemiologic evidence suggest that vitamin D may be protective against some cancers. Some dietary surveys have associated increased intake of dairy foods with decreased incidence of colon cancer25-27. Another dietary survey associated a higher calcium and vitamin D intake with a lower incidence of colon cancer28. Well-designed clinical trials need to be conducted to determine whether vitamin D deficiency increases cancer risk, or if an increased intake of vitamin D is protective against some cancers. Until such trials are conducted, it is premature to advise anyone to take vitamin D supplements to prevent cancer.

Vitamin D and steroids
Corticosteroid medications are often prescribed to reduce inflammation from a variety of medical problems. These medicines may be essential for a person's medical treatment, but they have potential side effects, including decreased calcium absorption29,30. There is some evidence that steroids may also impair vitamin D metabolism, further contributing to the loss of bone and development of osteoporosis associated with steroid medications30. For these reasons, individuals on chronic steroid therapy should consult with their physician or registered dietitian about the need to increase vitamin D intake through diet and/or dietary supplements.

Vitamin D and Alzheimer's Disease
Adults with Alzheimer's disease have increased risk of hip fractures31. This may be because many Alzheimer's patients are homebound, and frequently sunlight deprived. Alzheimer's disease is more prevalent in older populations, so the fact that the ability of skin to convert vitamin D to its active form decreases as we age also may contribute to increased risk of hip fractures in this group4,10-12. One study of women with Alzheimer's disease found that decreased bone mineral density was associated with a low intake of vitamin D and inadequate sunlight exposure32. Physicians evaluate the need for vitamin D supplementation as part of an overall treatment plan for adults with Alzheimer's disease.

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What is the health risk of too much vitamin D?
There is a high health risk associated with consuming too much vitamin D33. Vitamin D toxicity can cause nausea, vomiting, poor appetite, constipation, weakness, and weight loss34. It can also raise blood levels of calcium, causing mental status changes such as confusion. High blood levels of calcium also can cause heart rhythm abnormalities. Calcinosis, the deposition of calcium and phosphate in soft tissues like the kidney can be caused by vitamin D toxicity4.

Consuming too much vitamin D through diet alone is not likely unless you routinely consume large amounts of cod liver oil. It is much more likely to occur from high intakes of vitamin D in supplements. The Food and Nutrition Board of the Institute of Medicine considers an intake of 25 mcg (1,000 IU) for infants up to 12 months of age and 50 mcg (2,000 IU) for children, adults, pregnant, and lactating women to be the tolerable upper intake level (UL). A daily intake above the UL increases the risk of adverse health effects and is not advised.

Selected Food Sources of vitamin D4, 36, 37
As the 2000 Dietary Guidelines for Americans state, "Different foods contain different nutrients. No single food can supply all the nutrients in the amounts you need"35. The following table suggests dietary sources of vitamin D. As the table indicates, fortified foods are a major source of vitamin D. Breakfast cereals, pastries, breads, crackers, cereal grain bars and other foods may be fortified with 10% to 15% of the DV for vitamin D. It is important to read the nutrition facts panel of the food label to determine whether a food provides vitamin D.

If you want more information about building a healthful diet, refer to the Food Guide Pyramid.

Table of Selected Food Sources
of Vitamin D

Food

International Units

%DV*

Cod liver oil, 1 Tbs.

1,360 IU

340

Salmon, cooked, 3 1/2 oz.

360 IU

90

Mackerel, cooked, 3 1/2 oz.

345 IU

90

Sardines, canned in oil, drained, 3 1/2 oz.

270 IU

70

Eel, cooked, 3 1/2 oz.

200 IU

50

Milk, nonfat, reduced fat, and whole, vitamin D fortified, 1 c.

98 IU

25

Margarine, fortified, 1 Tbs.

60 IU

15

Cereal grain bars, fortified w/ 10% of the DV, 1 each

50 IU

10

Pudding, 1/2 c. prepared from mix and made with vitamin D fortified milk

50 IU

10

Dry cereal, vitamin D fortified w/ 10%* of DV, 3/4 c.
*Other cereals may be fortified w/ more or less vitamin D

40-50 IU

10

Liver, beef, cooked, 3 1/2 oz.

30 IU

8

Egg, 1 whole
(vitamin D is present in the yolk)

25 IU

6

* DV = Daily Value. DVs are reference numbers based on the Recommended Dietary Allowance (RDA). They were developed to help consumers determine if a food contains a lot or a little of a specific nutrient. The DV for vitamin E is 30 International Units (or 20 mg). The percent DV (%DV) listed on the nutrition facts panel of food labels tells adults what percentage of the DV is provided by one serving. Percent DVs are based on a 2,000-calorie diet. Your Daily Values may be higher or lower depending on your calorie needs. Foods that provide lower percentages of the DV will contribute to a healthful diet.

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References

1. DeLuca HF and Zierold C. Mechanisms and functions of vitamin D. Nutr Rev 1998;56:S4-10.

2. Reichel H, Koeffler H, Norman AW. The role of vitamin D endocrine system in health and disease. N Engl J Med 1989;320:980-991.

3. van den Berg H. Bioavailability of vitamin D. Eur J Clin Nutr 1997;51 Suppl 1:S76-9.

4. Institute of Medicine, Food and Nutrition Board. Dietary Reference Intakes: Calcium, Phosphorus, Magnesium, Vitamin D and Fluoride. National Academy Press, Washington, DC, 1999.

5. Goldring SR, Krane S, Avioli LV. Disorders of calcification: Osteomalacia and rickets. In: LJ D, ed. Endocrinology. 3rd ed. Philadelphia: WB Saunders, 1995:1204-1227.

6. Favus MJ and Christakos S. Primer on the Metabolic Bone Diseases and Disorders of Mineral Metabolism. 3rd ed. Philadelphia, PA: Lippincott-Raven, 1996.

7. Holick MF. Vitamin D. In: Shils M, Olson J, Shike M, Ross AC, ed. Modern Nutrition in Health and Disease, 9th ed. Baltimore: Williams and Wilkins, 1999.

8. Holick MF. McCollum Award Lecture, 1994: Vitamin D: New horizons for the 21st century. Am J Clin Nutr 1994;60:619-630.

9. Chapuy MC Arlot ME, Duboeuf F, Brun J, Crouzet B, Arnaud S, Delmas PD, Meunier PJ. Vitamin D3 and calcium to prevent hip fractures in elderly women. N Engl J Med 1992;327:1637-42.

10. MacLaughlin J and Holick MF. Aging decreases the capacity of human skin to produce vitamin D3. J Clin Invest 1985;76:1536-1538.

11. Holick MF, Matsuoka LY, Wortsman J. Age, vitamin D, and solar ultraviolet. Lancet 1989;2:1104-1105.

12. Need AG, MorrisHA, Horowitz M, Nordin C. Effects of skin thickness, age, body fat, and sunlight on serum 25-hydroxyvitamin D. Am J Clin Nutr 1993;58:882-885.

13. Holick MF. Vitamin D. In: Shils M OJ, Shike M, ed. Modern Nutrition in Health and Disease. 8th ed. Philadelphia, PA: Lea & Febiger, 1994:308-325.

14. Webb AR, Kline L, Holick MF. Influence of season and latitude on the cutaneous synthesis of vitamin D3: Exposure to winter sunlight in Boston and Edmonton will not promote vitamin D3 synthesis in human skin. J Clin Endocrinol Metab 1988;67:373-378.

15. Webb AR, Pilbeam C, Hanafin N, Holick MF. An evaluation of the relative contributions of exposure to sunlight and of diet to the circulating concentrations of 25-hydroxyvitamin D in an elderly nursing home population in Boston. Am J Clin Nutr 1990;51:1075-1081.

16. Lo CW, Paris PW, Clemens TL, Nolan J, Holick MF. Vitamin D absorption in healthy subjects and in patients with intestinal malabsorption syndromes. Am J Clin Nutr 1985;42:644-649.

17. Daaboul J, Sanderson S, Kristensen K, Kitson H. Vitamin D deficiency in pregnant and breast-feeding women and their infants. J Perinatol 1997;17:10-4.

18. Emmett PM, Rogers IS. Properties of human milk and their relationship with maternal nutrition. Early Hum Dev 1997;49 Suppl:S7-28.

19. Duplechin RY, Nadkarni M, Schwartz RP. Hypocalcemic tetany in a toddler with undiagnosed rickets. Ann Emerg Med 1999;34:399-402.

20. Mughal MZ, Salama H, Greenaway T, Laing I, Mawer EB. Lesson of the week: Florid rickets associated with prolonged breast feeding without vitamin D supplementation. BMJ 1999;318:39-40.

21. LeBoff MS, Kohlmeier L, Hurwitz S, Franklin J, Wright J, Glowacki J. Occult vitamin D deficiency in postmenopausal US women with acute hip fracture. J Am Med Assoc 1999;251:1505-1511.

22. Reid IR. The roles of calcium and vitamin D in the prevention of osteoporosis. Endocrinol Metab Clin North Am 1998;27:389-98.

23. Dawson-Hughes B, Harris SS, Krall EA, Dallal GE, Falconer G, Green CL. Rates of bone loss in postmenopausal women randomly assigned to one of two dosages of vitamin D. Am J clin Nutr 1995;61:1140-45.

24. Reid IR. Therapy of osteoporosis: Calcium, vitamin D, and exercise. Am J Med Sci 1996;312:278-86.

25. Holt PR. Studies of calcium in food supplements in humans. Ann N Y Acad Sci 1999;889:128-37.

26. Langman M and Boyle P. Chemoprevention of colorectal cancer. Gut 1998;43:578-85.

27. Glinghammar B, Venturi M, Rowland IR, Rafter JJ. Shift from a dairy product-rich to a dairy product-free diet: Influence on cytotoxicity and genotoxicity of fecal water--potential risk factors for colon cancer. Am J Clin Nutr 1997;66:1277-82.

28. La Vecchia C, Braga C, Negri E, Franceschi S, Russo A, Conti E, Falcini F, Giacosa A, Montella M, Decarli A. Intake of selected micronutrients and risk of colorectal cancer. Int J Cancer 1997;73:525-30.

29. Buckley LM, Leib ES, Cartularo KS, Vacek PM, Cooper SM. Calcium and vitamin D3 supplementation prevents bone loss in the spine secondary to low-dose corticosteroids in patients with rheumatoid arthritis. A randomized, double-blind, placebo-controlled trial. Ann Intern Med 1996;125:961-8.

30. Lukert BP and Raisz LG. Gucocorticoid-induced osteoporosis: Pathogenesis and management. Annals of Internal Medicine 1990;112:352-364.

31. Buchner DM and Larson EB. Falls and fractures in patients with Alzheimer-type dementia. J Am Med Assoc 1987;20:1492-5.

32. Sato Y, Asoh T, Oizumi K. High prevalence of vitamin D deficiency and reduced bone mass in elderly women with Alzheimer's disease. Bone 1998;23:555-7.

33. Veith R. Vitamin D supplementation, 25-hydroxyvitamin D concentrations, and safety. J Am Clin Nutr 1999;69:842-56.

34. Chesney RW. Vitamin D: Can an upper limit be defined? J Nutr 1989;119 (12 Suppl):1825-8.

35. Dietary Guidelines Advisory Committee, Agricultural Research Service, United States Department of Agriculture (USDA). Report of the Dietary Guidelines Advisory Committee on the Dietary Guidelines for Americans, 2000. http://www.ars.usda.gov/dgac

36. J P. Bowes and Church's Food Values of Portions Commonly Used. 17th ed. Philadelphia: Lippincot-Raven, 1998.

37. Nutrition Coordinating Center. Nutrition Data System for Research (NDS-R). Vol 4.01/29 ed. Minnesota: University of Minnesota, 1990.

This fact sheet was developed by the Clinical Nutrition Service, Warren Grant Magnuson Clinical Center, National Institutes of Health (NIH), Bethesda, MD, in conjunction with the Office of Dietary Supplements (ODS) in the Office of the Director of NIH. The mission of ODS is to strengthen knowledge and understanding of dietary supplements by evaluating scientific information, stimulating and supporting research, disseminating research results, and educating the public to foster an enhanced quality of life and health for the U.S. population. The Clinical Nutrition Service and the ODS would like to thank the expert scientific reviewers for their role in ensuring the scientific accuracy of the information discussed in this fact sheet.

Updated 12/2000

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