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.
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. Two weeks ago, a report stated that pregnant women who are vitamin D deficient put their children at risk for language problems. This week, another study linked vitamin D levels to workplace productivity.
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 time, 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.
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.
Though he has retired from practicing medicine, Cannell works full time promoting vitamin D as the executive director of the Vitamin D Council, a nonprofit he founded in 2003. "We have a deficiency epidemic," he said.
Last year, 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. The elderly may need as much as 800 units. The report challenged claims that Americans are vitamin D deficient.
"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 November 2010 report.
Some maintain the recommended levels are too low.
"They still don't have it right," said Cannell, who takes 5,000 international units daily. He said it would be difficult to have too much vitamin D. "Worrying about vitamin D toxicity is like worrying about drowning in a desert when you're dying of thirst."
Why all the fuss about vitamin D?
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 also contain vitamin D.
Nowadays, people go outdoors less and cover up with sunscreen more and may not be getting as much vitamin D as they need, said Ishwarlal Jialal, professor of pathology and laboratory medicine at the UC Davis Health System.
That may be what has happened in the Sacramento area.
Last year, UC Davis researchers found a surprising result in the first study to examine vitamin-D status in patients with metabolic syndrome living in Northern California, said Jialal. Metabolic syndrome is a name for risk factors, such as extra weight around the waist, which could lead to coronary disease, stroke or diabetes.
Researchers were surprised to learn that Sacramento-area residents had lower vitamin D levels on average than Southern California residents. Jialal said the study did not specifically link vitamin D deficiency and metabolic syndrome but that the results were noteworthy.
"Thirty percent of patients with metabolic syndrome have vitamin-D deficiency, and even many subjects in the control group had inadequate levels," said Jialal.
"Considering our climate and healthy lifestyles here, these findings were unexpected," he said. "We have an illusion that people in California go out and get sunshine, but that's not that case here."
Some contend that increasing vitamin D levels can be the answer to increasing worker productivity.
"We found a strong relationship between low vitamin D (levels) and working effectively," said Jeff Erydske of the Penny George Institute for Health and Healing in Minneapolis. He said low levels of vitamin D have been attributed to migraines, diabetes and other maladies.
Erydske said inexpensive vitamin D pills can play a role in reducing "presenteeism," where employees show up for work but don't get much done. Some studies say the problem costs U.S. employers more than $150 billion a year, according to the institute. Its study will be released in the March issue of the Journal of Occupational and Environmental Medicine.
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 U.S. 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. Recruitment was completed last year, and 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 harmful to some people.
"This thinking can be dangerous," he said. "You have to do the trials."