Vitamin D: The research vs. the hype

Claims about vitamin D are everywhere: on the Internet, on medical TV talk shows and, it seems, in the news nearly every week with the release of one study after another.

Vitamin D is an essential nutrient the skin produces when hit by sunlight. The amount produced varies, depending on skin pigmentation, age and where you live, among other factors. Foods such as milk, yogurt, cereal and orange juice, when fortified, also contain vitamin D.

The sunshine vitamin, as it's been called, is getting lots of exposure and has been linked to lowering the risk of breast cancer, depression and multiple sclerosis, among other illnesses. A few weeks ago, a report stated that pregnant women who are vitamin D deficient put their children at risk for language problems. Last week, another study linked vitamin D levels to workplace productivity.

SALES GROWING

All this attention has boosted U.S. sales of vitamin D nearly 30 percent in 2010 to almost $550 million, according to the Nutrition Business Journal. But the growth and hype have fueled a debate within the medical community over the benefits of vitamin D, as well as how much a person needs.

"There are no clinical trials that show vitamin D is a benefit for these conditions," said Christopher Gallagher, professor of medicine at Creighton University in Omaha and board member of the Institute of Medicine, which reviewed vitamin D intake last year. "The only data we have at this time is that vitamin D has an effect on bone health."

Proponents of higher vitamin D levels point to promising research and say the federal guidelines for daily vitamin D requirements are too low. They say the deficiency is costing Americans money and, sometimes, their health. "This deficiency has been linked to a lot of serious health problems," said Dr. John Cannell, a retired physician living in San Luis Obispo, Calif., who sells a line of the vitamin.

For years, Cannell gave his patients the same advice that doctors have been giving for decades: Stay out of the sun. "We should have added, 'But don't forget to get your vitamin D,' " he said.

Challenging the claims

In 2010, in response to the debate about vitamin D, the Institute of Medicine, the health arm of the National Academy of Sciences, updated the official federal recommendations for vitamin D intake for the first time since 1997. A 14-member committee concluded that most Americans up to age 70 need no more than 600 international units of vitamin D per day. Older people may need as much as 800 units. The report challenged claims that Americans are vitamin D deficient. Many doctors can easily test vitamin D levels during routine blood work.

"The majority of Americans and Canadians are getting enough vitamin D and calcium, the committee determined from reviewing national surveys of blood levels," read the report.

Those on both sides of the vitamin D debate said they are waiting for the results of the most comprehensive study on the issue: Brigham and Women's Hospital and Harvard Medical School in Boston are conducting the VITAL study. In the project, 20,000 men and women across the United States are taking daily dietary supplements of vitamin D3 (2000 IU) or omega-3 fatty acids to see if they reduce the risk of developing cancer, heart disease and strokes. Results are expected to take several years.

For now, Gallagher of the Institute of Medicine advises caution.

"There are some people who act as if vitamin D is the cure for everything," he said. "Remember, the same was said about vitamin A and vitamin E" -- nutrients ultimately found to be potentially harmful in high doses. "This thinking can be dangerous," he said.