There’s no evidence that multivitamins do healthy adults much good, but the supplements don’t seem to do much harm either, a federal panel said Wednesday.
Concluding a three-day conference convened by the National Institutes of Health, the panel called for further studies of multivitamins. Half of adults in the U.S. take multivitamins, helping to push annual sales of nutritional supplements to $23 billion.
Dr. J. Michael McGinnis of the National Institute of Medicine, the chairman of the panel, said the studies of multivitamins reviewed by the group were “especially thin” and most of the clinical trials were too short to determine the long-term effects of taking the supplements.
Consequently, he said, the panel had no opinion on whether healthy adults should take multivitamins. “The data is insufficient to make a recommendation for the general population,” McGinnis said after the meeting in Bethesda, Md.
Still, the panel found that some individual vitamins or minerals appeared to show specific benefits.
One well-designed trial suggested that antioxidants and zinc might slow the progression of age-related macular degeneration, the leading cause of blindness in the elderly, McGinnis said. Calcium and vitamin D supplements seem to have an effect on fracture risk and bone density in post-menopausal women, he added.
The panel endorsed consumption of folic acid by women of childbearing age to prevent congenital deformities of the nervous system, such as spina bifida.
Experts took a position against one supplement, beta carotene, a form of vitamin A. They said there was no reason for the general population to take beta carotene because studies consistently showed the vitamin failed to prevent chronic illnesses, such as cancer or heart disease.
The panel did not look at vitamin use by children or adults with poor diets or specific nutritional needs.
Most of the people who took multivitamins were in good health, the panel found, raising the possibility that some people might consume excessive amounts of certain nutrients.
Panel member Patsy Brannon of Cornell University said 1% to 11% of supplement users may exceed the maximum levels for some vitamins and minerals by adding pills to the nutrients in their diets. One study found that some people consumed too much niacin, which can damage the liver, she said.
Still, Brannon said, there was no reason for people to stop taking multivitamins.
“If you choose to take a supplement, the simplest advice I can give is to take one that provides 100% of the daily values,” she said, adding that such supplements would not put people with good diets in danger of exceeding maximum nutrient levels.
Andrew Shao of the Council for Responsible Nutrition, a trade group that represents supplement manufacturers, said he was disappointed that the panel dismissed the multivitamin studies it reviewed as weak and poorly conducted.
Shao said the industry welcomed further research, but added that supplement makers could not afford to conduct the long-term controlled studies that the panel sought because they “cost hundreds of millions of dollars.”