Science News - July 16,, 2011

not, suggesting that a population getting more vitamin D would be healthier overall. A recent Nebraska study links increased vitamin D intake to less cancer risk, for example, while Japanese scientists find that the vitamin helps fight influenza. Other recent work has connected higher levels of vitamin D with lower risks of hypertension, Parkinson’s disease and heart disease.

With these studies in hand, the Endocrine Society put out its own recommendations in the July Journal of Clinical Endocrinology & Metabolism. The society, the world’s oldest and largest group devoted to hormone research, called for vitamin D intake levels two to three times higher than the IOM’s recommendations.

More randomized trials are needed to settle the question, says Patsy Brannon, a molecular nutritionist at Cornell University and a member of the IOM panel. Until then, she says, it would be difficult to justify raising the levels further. It might even be imprudent because soaring levels could be toxic, she says.

That’s almost too much for nutritional biochemist Bruce Hollis to bear. A longtime vitamin D researcher at the Medical University of South Carolina in Charleston, Hollis recently oversaw a randomized controlled trial showing that low blood levels of vitamin D in pregnant women may lead to more preterm births. He has called for much higher doses. “These new IOM levels won’t accomplish anything,” Hollis says. “It’s just insane.”

Cancer connection

Endocrinologist Robert Heaney of Creighton University in Omaha, Neb., has spent a good part of his career compiling evidence that vitamin D has value in bone health and beyond, particularly in the fight against cancer. In a recent study, his team randomly assigned 1,180 healthy postmenopausal women to receive calcium, a placebo or 1,100 IU of vitamin D plus calcium daily.

Over four years, the trial data showed that those on the placebo had higher cancer rates than the other groups, but the findings revealed little difference

between those getting calcium alone or calcium with vitamin D. Since cancer starts microscopically and can grow undetected for months or years, the researchers also ran an analysis that skipped the first year — an effort to discount preexisting cancers. During the last three years of the study, 6. 8 percent of the placebo group and 3. 6 percent of those getting only calcium developed cancer, compared with 2.0 percent of those getting vitamin D plus calcium, Heaney’s team reported in 2007 in the American Journal of Clinical Nutrition.

The Nebraska study is one of many looking for a possible link between elevated cancer risk and low vitamin D in the blood. Researchers have found a similar association between vitamin D and colon cancer and the formation of precancerous growths in the colon called polyps. And Michael Holick, a biochemist and endocrinologist at Boston University, can reel off studies demonstrating less prostate and ovarian cancer in populations with high sun exposure (meaning higher vitamin D levels).

Holick, who chaired the commit-
tee that put out the Endocrine Society
guidelines, acknowledges a risk of skin
cancer from sun exposure in his 2010
book The Vitamin D Solution. But he and
others have estimated, based on rates
of cancer in the northern and south-
ern United States, that lives saved from
greater sun exposure would far exceed
those lost to skin cancer.

Tenacious D

Using an entirely different bag of tricks, vitamin D can stifle infections, a capability that was presaged nearly a century ago when doctors successfully treated

Degrees of D people’s vitamin D blood levels differ because of various factors, including skin color and sun exposure. Though scientists disagree on the level needed for good health, most peg the value between 20 and 40 nanograms per milliliter. Data below come from specific populations.