USA TODAY - JULY 15, 2008
By Mary Brophy Marcus, USA TODAY

Testing for vitamin D levels, once uncommon, has skyrocketed as medical studies raise awareness about vitamin D deficiencies, according to three of the USA's largest medical diagnostic labs. Physicians agree that they're increasingly using the blood test to find out whether their patients are low on the vital vitamin. Richard Reitz, a medical director with Quest Diagnostics of Madison, N.J., says tests ordered for vitamin D grew by about 80% from May 2007 to May 2008. Burlington, N.C.-based Lab Corp. of America witnessed a 90% leap in D test requests from 2007 to 2008, says Eric Lindblom, the company's senior vice president of investor and media relations. Neither company would release the actual numbers for competitive reasons. The Mayo Clinic in Rochester, Minn., another of the country's largest diagnostic labs, processed 424,582 tests in 2007, up 74% from 2006. Ravinder Singh, co-director for the endocrine lab at Mayo, expects that the clinic will tally more than 500,000 tests by the end of 2008.

DEFICIENCY: Lack of vitamin D rampant in teens, infants
ADULTS: Many unaware they're low on 'sunshine vitamin'

The jump in vitamin D testing comes after a slew of emerging research — much of which has been published in the past few years — linking vitamin D deficiency with some infectious diseases, cancers, cardiovascular disease and autoimmune disorders, says Patsy Brannon, professor of nutritional sciences at Cornell University. Other research indicates that many Americans are deficient in vitamin D, and that is also fueling the testing trend, says Catherine Gordon, director of the bone health program at Children's Hospital Boston. Though specialists who treat bone-related conditions and the elderly regularly run D tests, now even primary-care physicians and pediatricians are ordering the blood analysis. "Even a year ago, vitamin D testing wasn't really being talked about among physicians in a major way. But now I am testing 100% more than I did in the past," says Janet Pregler, director of the Iris Cantor-UCLA Women's Health Center and a professor of medicine at UCLA. 

A normal vitamin D test result is 30 ng/mL (nanograms/milliliter) or above. If a reading dips below that, a patient is considered insufficient; under 20 ng/mL, and he or she is tagged deficient. Supplements and D-rich foods, such as fortified milk, may be recommended for patients with low D levels, Gordon says. The UV rays in sunshine also activate one form of vitamin D in the body, but increased sun exposure can lead to skin cancer. Boston Medical School's Michael Holick, a professor of medicine, physiology and biophysics, says everyone should be taking 1,000 IUs (international units) of vitamin D a day, even though the Institute of Medicine recommends only 200 IUs a day for children and 400 IUs daily for adults. But UCLA's Pregler says the million-dollar question remains: "Will supplementing D-deficient patients prevent disease?" 

See the original article as well as a chart that shows what food have vitamin D in its natural form