Just "D" Facts about Vitamin D

Benefits of Moderate UV Sunshine Exposure

It may be vitamin D’s day in the sun

Posted by D3forU on July 16, 2010

It may have untapped potential in fighting or preventing disease. But are we getting enough of it in our systems?

Two advocacy groups have sprung up in the United States to promote the substance. Food industry executives are exploring ways to fortify more products. And PubMed, an international database of medical literature, shows that 2,274 studies referencing the vitamin have been published — just this year.

“Vitamin D is one hot topic,” says Connie Weaver, a professor of foods and nutrition at Purdue University in Indiana.

More recent research shows that receptors for it are found in almost every organ and tissue system in the body, suggesting that deficiencies may affect many types of cell functions.

When exposed to sunlight, the skin makes the vitamin, but not everyone spends the five minutes a day or so outside that is necessary for synthesis — and many more people today wear sunscreen to prevent skin cancer.

“A large portion of people fall into the at-risk category, and they would benefit from being brought out of that category,” Fleet says. “The question is: Is the current requirement enough to keep most people out of the at-risk category?”

A study of 13,000 Americans, published in March in the Archives of Internal Medicine, found that 50% to 75% have suboptimal levels by current standards. A level of 20 nanograms per milliliter of 25-hydroxyvitamin D — the form most commonly measured in blood — has traditionally been considered sufficient.

Most people 50 and older aren’t meeting the current recommendations, Weaver says.

“The largest source is sunshine, but not everyone can depend on that,” Weaver says. “The elderly, dark-skinned people, higher-latitude dwellers all have trouble getting enough from sun.” In darker-skinned people, melatonin in the skin blocks absorption of the ultraviolet rays needed to make the vitamin; older people don’t appear to synthesize it from the sun as well as younger people.

Some scientists argue that levels of 40 to 60 ng/mL would be far better for disease prevention. That would require daily intake much higher than the current 200 to 600 IU.

The July issue of the Annals of Epidemiology(09)X0007-4, devoted to vitamin D research, links the vitamin to lower risks of cancers of the breast, colon, ovaries and prostate. Animal and lab studies also demonstrate its importance in many of the cellular mechanisms that control cancer, such as cell growth, cell death, inflammation and DNA repair.

Five studies on colorectal cancer and breast cancer, taken together, showed that people with levels higher than 34 to 52 ng/mL had a 50% reduced cancer risk, says Cindy D. Davis, a researcher at the National Cancer Institute’s Nutritional Science Research Group.

Such studies are not proof that the vitamin influences disease development, points out Dr. Karen E. Hansen, an assistant professor at the University of Wisconsin who studies bone health. “People with higher vitamin D may just be healthier for other reasons,” she says.

But evidence linking higher blood levels to diabetes and cardiovascular disease is also mounting. A study in December in the Journal of the American College of Cardiology found that deficiency may increase the risk of cardiovascular disease. Other studies have tied lower levels to an increased risk of hypertension, diabetes, stroke and congestive heart failure.

Even for bone health, some studies suggest that about 700 to 800 IU a day are needed to prevent fractures in people over 50, Hansen says. She recommends 800 IU a day, with calcium, to her patients.

Already, however, the American Society of Clinical Oncology has recommended a higher intake for breast cancer patients who are deficient.

In October, the American Academy of Pediatrics said children should get 400 IU a day, double the current recommendation.

In November, 18 University of California researchers issued a statement saying 2,000 IU is appropriate for most people.

“I think some of the more vocal advocates are pushing the medical community to move forward” before adequate research is completed, Fleet says.

Dozens of more scientifically rigorous studies are in progress that could help resolve the questions about how much people should consume.

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