The Truth About Vitamin D
Get answers to commonly asked questions about vitamin D.
Mikio A. Nihira, MD
The hottest topic in medicine isn't the newest drug or the latest surgical device. It's vitamin D.
What brought the simmering debate to a boil was a 2007 study showing that people taking normal vitamin D supplements were 7% less likely to die than those who didn't take the daily supplements.
A year later, a major study found that when women with low vitamin D levels get breast cancer, they have a much higher chance of dying from their cancer than women with normal vitamin D levels.
That was surprising news. But just as surprising are assertions that many men, women, and children have insufficient blood levels of this important vitamin.
How many? Data suggest many of us don't get the vitamin D we need. For example, one study of childbearing women in the Northern U.S. found insufficient vitamin D levels in 54% of black women and in 42% of white women.
These findings led the American Academy of Pediatrics to double the recommended amount of vitamin D a child should take -- and have led many doctors to advise their adult patients to increase their vitamin D intake.
Not so fast, says an expert panel convened by the prestigious Institute of Medicine. In its long-awaited November 2010 report, the IOM committee expressed dismay at the idea that many people are vitamin D deficient.
"Of great concern recently have been reports of widespread vitamin D deficiency in the North American population," the committee wrote. "The concern is not well founded. In fact, 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."
The IOM committee put its emphasis on what science has proved, not on what studies may suggest. Using this conservative approach, the committee found no proof that vitamin D has health effects beyond building strong bones.
"While the current interest in vitamin D as a nutrient with broad and expanded benefits is understandable, it is not supported by the available evidence," the IOM committee concluded.
Next: Why do I need vitamin D?
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