The Truth About Vitamin D: Vitamin D Tests

WebMD feature series on vitamin D.

From the WebMD Archives

Will a vitamin D test tell me if I need more vitamin D?

That depends on whom you ask. As part of your regular blood test, your doctor can order a test for 25-hydroxyvitamin D (25-OHD).

The problem is not with the test. The problem is how to interpret the results. An expert committee convened by the Institute of Medicine in November 2010 concluded that "the cut-point values used to define deficiency, or as some have suggested, 'insufficiency,' have not been established systematically using data from studies of good quality."

Even so, most experts agree that anyone with a 25-OHD level of less than 15 ng/mL or 37.5 nmol/L (depending on the units reported by a lab) needs more vitamin D. A 2002 study found that 42% of African-American women of childbearing age had vitamin D levels below 15 ng/mL.

The IOM committee says that people are at risk of vitamin D deficiency at 25-OHD levels below 30 nmol/L (12 ng/mL), and that some people -- but not everyone -- may be at risk of vitamin D deficiency at 25-OHD levels from 30 nmol/L up to 50 nmol/L (12-20 ng/mL).

The Vitamin D Council considers the ideal 25-OHD level to be between 40 ng/mL and 70 ng/mL. But the IOM says there is no evidence of increased benefit at levels above 30 ng/mL, and that "there may be reason for concern" at levels above 50 ng/mL.

"There is a critical public health and clinical practice need for consensus cut-points for serum 25-OHD," the IOM committee states.

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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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