The Truth About Vitamin D: Why You Need Vitamin D

WebMD feature series on vitamin D

From the WebMD Archives

Why do I need vitamin D?

Your body must have vitamin D to absorb calcium and promote bone growth. Too little vitamin D results in soft bones in children (rickets) and fragile, misshapen bones in adults (osteomalacia). You also need vitamin D for other important body functions.

Vitamin D deficiency has now been linked to breast cancer, colon cancer, prostate cancer, heart disease, depression, weight gain, and other maladies. These studies show that people with higher levels of vitamin D have a lower risk of disease, although they do not definitively prove that lack of vitamin D causes disease -- or that vitamin D supplements would lower risk.

The Vitamin D Council -- a scientist-led group promoting vitamin D deficiency awareness -- suggests vitamin D treatment might be found helpful in treating or preventing autism, autoimmune disease, cancer, chronic pain, depression, diabetes, heart disease, high bloodpressure, flu, neuromuscular diseases, and osteoporosis. However, there have been no definitive clinical trials.

That's why the Institute of Medicine expert committee's November 2010 review found no conclusive evidence that vitamin D, by itself, offers wide-ranging health benefits.

"Despite the many claims of benefit surrounding vitamin D in particular, the evidence did not support a basis for a causal relationship between vitamin D and many of the numerous health outcomes purported to be affected by vitamin D intake," the IOM committee concluded.

The only proven benefit of vitamin D is its role in helping calcium build strong bones. But that's far from the whole story. Vitamin D helps regulate the immune system and the neuromuscular system. Vitamin D also plays major roles in the life cycle of human cells.

Vitamin D is so important that your body makes it by itself -- but only after skin exposure to sufficient sunlight. This is a problem for people in northern climates. In the U.S., only people who live south of a line drawn from Los Angeles to Columbia, S.C., get enough sunlight for vitamin D production throughout the year.

Dark skin absorbs less sunlight, so people with dark skin do not get as much vitamin D from sun exposure as do light-skinned people. This is a particular problem for African-Americans in the northern U.S.

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WebMD Feature Reviewed by Laura J. Martin, MD on November 30, 2010

Sources

SOURCES:

Ross, A.C. Institute of Medicine, "Dietary Reference Intakes for Calcium and Vitamin D," Nov. 30, 2010

Cannell, J.J. and Hollis, B.W. Alternative Medicine Review, March 2008; vol 13: pp 6-20.

Holick, M.F. Journal of Clinical Endocrinology and Metabolism, March 2008; vol 93: pp 677-681.

Autier, P. and Gandini, S. Archives of Internal Medicine, Sept. 10, 2007; vol 167: pp 1730-1737.

Holick, M.F. and Chen, T.C. American Journal of Clinical Nutrition, 2008; vol 87: pp 1080S-1086S.

Bordelon, P. American Family Physician, Oct. 15, 2009; vol 80: pp 841-846.

Rovner, A.J. and O'Brien, K.O. Archives of Pediatric and Adolescent Medicine, June 2008; vol 162: pp 513-519.

Pepper, K.J. Endocrinology Practice, 2009; vol 15: pp 95-103.

WebMD Health News: " Vitamin D Deficiency Worsens Breast Cancer?"

WebMD Feature: " Are You Getting Enough Vitamin D?"

WebMD Health News: " Vitamin D Deficiency May Hurt Heart."

WebMD Health News: " Calcium/Vitamin D Slows Weight Gain."

WebMD Health News: " Vitamin D Fights Colon Cancer."

WebMD Health News: " Vitamin D Compounds May Fight Prostate Cancer."

National Institutes of Health Office of Dietary Supplements, Dietary Supplement Fact Sheet: Vitamin D, updated Nov. 13, 2009.

The Vitamin D Council web site.

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