Some Seek Guidelines to Reflect Vitamin D's Benefits
Friday, July 4, 2008
A flurry of recent research indicating that Vitamin D may have a dizzying array of health benefits has reignited an intense debate over whether federal guidelines for the "sunshine vitamin" are outdated, leaving millions unnecessarily vulnerable to cancer, heart disease, diabetes and other ailments.
The studies have produced evidence that low levels of Vitamin D make men more likely to have heart attacks, breast and colon cancer victims less likely to survive, kidney disease victims more likely to die, and children more likely to develop diabetes. Two other studies suggested that higher Vitamin D levels reduce the risk of dying prematurely from any cause.
In response to these and earlier findings, several medical societies are considering new recommendations for a minimum daily Vitamin D intake, the American Medical Association recently called for the government to update its guidelines, and federal officials are planning to launch that effort.
But many leading experts caution that it remains premature for people to start taking large doses of Vitamin D. While the new research is provocative, experts argue that the benefits remain far from proven. Vitamin D can be toxic at high doses, and some studies suggest it could increase the risk for some health problems, experts say. No one knows what consequences might emerge from exposing millions of people to megadoses of the vitamin for long periods.
"The data are intriguing and serve as, no pun intended, food for further fruitful research," said Mary Frances Picciano, at the Office of Dietary Supplements of the National Institutes of Health. "But beyond that, the data are just not solid enough to make any new recommendations. We have to be cautious."
The current clash is the latest in a long, often unusually bitter debate. Some skeptics question whether funding by the tanning, milk and vitamin industries is biasing some advocates. Frustrated proponents accuse skeptics of clinging to outdated medical dogma.
"It feels kind of ridiculous working in this field sometimes," said Reinhold Vieth, a professor of nutritional sciences and pathobiology at the University of Toronto. "Every week, I get interviewed about the next important publication about Vitamin D. But this field remains mired in the muck."
Vieth is one of a small but vocal cadre of researchers pushing doctors and patients to stop waiting for new official guidelines. Physicians should routinely test their patients for Vitamin D deficiencies, and more people -- especially African Americans -- should take supplements and increase their exposure to the sun, they say.
"The bottom line is we now recognize that Vitamin D is important for health for both children and adults and may help prevent many serious chronic diseases," said Michael F. Holick, a professor of medicine, physiology and biophysics at Boston University.
Scientists have long known that Vitamin D is a vital nutrient the skin produces when hit by ultraviolet light from sunlight and other sources. The amount of Vitamin D produced varies, depending on where the person lives, skin pigment, age and other factors. African Americans and other dark-skinned people, and anyone living in northern latitudes, make far less than other groups.
With people spending more time indoors surfing the Web, watching television, working at desk jobs, and covering up and using sunblock when they do venture outdoors, the amount of Vitamin D that people create in their bodies has been falling. Milk and a few other foods are fortified with Vitamin D, and it occurs naturally in others, such as fatty fish, but most people get very little through their diets.
"Humans evolved in equatorial Africa wearing no clothes," said Robert P. Heaney, a leading Vitamin D researcher at Creighton University in Omaha. "Now we get much less direct sunlight, and so we don't make nearly as much Vitamin D."
A number of studies have found that deficiencies may be common, with perhaps half of adults and children having what some consider inadequate levels. Federal guidelines call for people to get 200 to 600 international units a day, depending on age and other factors. But those recommendations were last updated in 1997 and were aimed primarily at preventing bone diseases, such as rickets in children and osteoporosis in the elderly.
Since then, studies have indicated that Vitamin D offers a plethora of health benefits, possibly protecting against heart disease, many forms of cancer, immune system disorders such as multiple sclerosis and rheumatoid arthritis, infectious diseases such as tuberculosis and the flu, and perhaps mental illnesses including schizophrenia and depression.
"Vitamin D has a global effect on many systems," said Bruce Hollis, a professor of pediatrics, biochemistry and molecular biology at the Medical University of South Carolina.
The Canadian Cancer Society upped its recommendation to 1,000 units a day last year. Hollis and others believe Americans should routinely consume at least 2,000 international units a day.
"The first thing we'd see is a reduction by 80 percent in the incidence of Type 1 diabetes," said Cedric Garland, a professor of family and preventive medicine at the University of California at San Diego. "The next thing we'd see is a reduction by about 75 percent of all invasive cancers combined, as well as similar reductions in colon cancer and breast cancer, and probably about a 25 percent reduction in ovarian cancer."
Holick urges people to take 1,000 international units a day along with a multivitamin with 400 international units, as well as exposing their arms and legs to the sun for about 15 minutes several times a week.
But others have reservations. Dermatologists worry that encouraging people to get unprotected sun exposure or use tanning salons may increase the rate of skin cancer.
"We're in the middle of a skin cancer epidemic," said C. William Hanke, president of the American Academy of Dermatology. "Tanning is risky and dangerous behavior. Ultraviolet light is classified as a carcinogen. We need to protect our skin."
Studies of other nutrients, such as Vitamin E, beta carotene and folate, have previously produced similarly promising findings only to turn out to be ineffective or even possibly dangerous, others say.
"We've gotten very excited in the past," said Alice Lichtenstein, a professor of nutrition at Tufts University who is a spokeswoman for the American Heart Association.
"It seems like an easy answer: We don't have to worry about losing weight or exercising. While I know the literature on Vitamin D is exploding, I think we have to be cautious until we've done the proper studies," Lichtenstein said.
Other skeptics go further, saying the Vitamin D already added to foods may be fueling increases in chronic diseases, such as diabetes and obesity.
"We call it a vitamin, but it's really a steroid," said Trevor G. Marshall, a molecular biologist at Murdoch University in Australia. "It's not something we should be playing with."
While still cautious, another skeptic, Leonard Lichtenfeld, deputy chief medical officer at the American Cancer Society, acknowledges that the evidence for Vitamin D is getting harder to ignore.
"I had a fair degree of skepticism. But now, while not a full-blown proponent, I believe it's definitely an area that needs more attention," Lichtenfeld said.
The National Academies' Institute of Medicine is negotiating with NIH and the Agriculture Department to make Vitamin D the first nutrient to be reassessed under a new system of evaluating nutritional requirements.
"Within the last four or five months, it's become a much more intensive dialogue," said Christine Taylor of the institute's Food and Nutrition Board. She cautioned, however, that the review, which could begin as early as the fall and take more than year, might leave the current recommendation unchanged.
"Some would argue there are significant new data about Vitamin D," Taylor said. "That doesn't mean that would change the requirement. But it implies a timely review is in order."