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May 17, 2006 -- Tens of millions of Americans are taking daily multivitamins with almost no information about their safety or effectiveness, a federal panel of experts concluded Wednesday.
More than half of U.S. adults regularly take multivitamins and other supplements, a market that garners about $23 billion for industry, according to a National Institutes of Health committee. But the vast majority of the time, they're doing so with no known benefits, it concluded.
"The science base is especially thin with respect to the health impact of multivitamins," said J. Michael McGinnis, MD, a senior scholar at the National Academies of Science who chaired the NIH panel issuing the report.
Shortage of Data
The committee was called to review studies on the health effects of multivitamins sold across the nation in grocery stores, pharmacies, and health food stores. But experts said that too few studies exist to say with any certainty whether the products are useful.
"Overall we find that the available data are insufficient to make a firm recommendation for or against their use," McGinnis said. The studies that exist are not in-depth enough to draw meaningful conclusions, he added.
In theory, multivitamins can help replenish nutrient levels for Americans, who are notoriously bad at maintaining proper nutritionnutrition.
But researchers say little is known about whether vitamins serve that purpose in most people. Some studies suggest that more health-conscious people are the ones who take vitamins in the first place, meaning the products may be missing those they could help the most.
Vitamin Endorsements
The report did recognize a handful of individual vitamins with enough data behind them to conclude they're helpful.
Panelists endorsed antioxidants and zinc for preventing the eye disease macular degenerationmacular degeneration. They also noted that folic acid supplementation in pregnant women has helped drastically lower the incidence of birth defects.
The combination of calcium and vitamin D supplementation has also been shown to lower fracture risk by helping to boost bone densitybone density in postmenopausal women, the report states.
But experts also worried that not enough attention is being paid to potential risks of multivitamins. Some nutrients, like vitamin C, are easily excreted in urine and are relatively harmless.
But others, including vitamin E, zinc, selenium, and iron can be toxic at high levels. High levels of vitamin D can cause dangerous elevation of calcium in the blood. One expert referenced a study, which showed that up to 11% of vitamin users exceed safe levels of niacin intake, putting them at potential risk for liver problems.
Call for Regulation
Federal law requires drug manufacturers to report any adverse effects caused by their products to the FDA. But no similar requirement exists for vitamin and supplement makers.
Wednesday's report called on Congress to enact a law that would compel supplement companies to report side effects so the FDA can track them.
Panelist William Vaughn told reporters that three other scientific reviews, including one conducted by the Institute of Medicine, had recommended the extra FDA authority. "We hope this fourth one will push it over the top," said Vaughn, a senior policy analyst with Consumers Union.
Dan Fabricant, PhD, an official with the National Nutritional Foods Association, a supplement industry group, said additional safety regulations were unnecessary. He said more than 100 million adults use multivitamins with no discernable danger.
"If there was any type of health risk, even with higher doses, we would have seen it by now," Fabricant, the group's vice president for scientific affairs, tells WebMD.
SOURCES: National Institutes of Health State-of-the-Science Conference on Multivitamin/Mineral Supplements and Chronic Disease Prevention Consensus Statement, May 17, 2006. J. Michael McGinnis, MD, senior scholar, National Academies of Science, chair, NIH panel. William Vaughn, senior policy analyst, Consumers Union, member NIH Panel. Daniel Fabricant, PhD, vice president for scientific affairs, National Nutritional Foods Association.