Panel Finds Conflicting Data on Multivitamin Benefit
Thursday, May 18, 2006
A federal panel concluded yesterday that there is not enough evidence to recommend for or against use of multivitamins and minerals -- the popular dietary supplements taken by more than half of American adults in the hope of preventing heart disease, cancer and other chronic illnesses.
Americans spend an estimated $23 billion annually on various multivitamins and multi-mineral supplements, the 13-member panel found. One of the latest federally funded national surveys showed that 52 percent of adults reported taking multivitamins. Slightly more than a third of those surveyed said that they take these products regularly.
Several studies suggest that consumers believe that taking a multivitamin promotes health and can prevent some common diseases, but the evidence for both is "quite thin," said the panel's chairman, J. Michael McGinnis, senior scholar at the National Academy of Sciences' Institute of Medicine.
Some of the evidence had conflicting results. For example, studies found a clear protective benefit against lung cancer for those who eat a diet rich in fruit and vegetables. But when Scandinavian scientists gave study volunteers beta carotene, commonly found in orange-colored fruit and vegetables, the risk of lung cancer in smokers increased.
Other research suggests that male smokers may have a reduced risk of prostate cancer if they take Vitamin E. "But nonsmokers may not," Meir Stampfer, chairman of epidemiology at the Harvard School of Public Health, told the panel.
The bottom line for multivitamins, McGinnis said, "is that we don't know for sure that they're benefiting from them. In fact, we're concerned that some people may be getting too much of certain nutrients."
The panel found only three situations in which vitamins or other supplements appear to offer a clear protective edge:
· Prevention of birth defects of the brain and spine by giving women of child-bearing age folic acid, one of the B vitamins -- what one panel member called a "home run." Since 1998, food has been fortified with folic acid. Women who plan to become pregnant are urged to boost folic acid intake to help prevent spina bifida and other neural tube defects.
· Reduction of macular degeneration, one of the leading causes of age-related blindness. A 2001 federally funded study by the National Eye Institute concluded that diet supplementation with vitamins C and E, beta carotene and the minerals zinc and copper reduced the risk of vision loss in people with early signs of macular degeneration. No effect on cataracts was reported.
· Lowering the risk of bone fractures in post-menopausal women through calcium and Vitamin D supplements.
But the panel also found that multivitamins "are virtually unregulated" by the federal government. It advised Congress to expand the Food and Drug Administration's authority and resources to require manufacturers to disclose adverse events, ensure quality production and facilitate consumer reporting of adverse events.
The dietary supplement industry criticized the panel for not considering less scientifically rigorous studies that point to multiple benefits from multivitamin and mineral use.
"They have done exactly what they set out to do, which is a review based solely on randomized controlled trial data, which results in a misleading picture," said Annette Dickinson, past president of the Council for Responsible Nutrition, an industry trade association.
"There's huge evidence that these products are safe," Dickinson said.