After a recent review of 67 randomized studies, researchers concluded that supplemental antioxidants do not reduce mortality and that some could, in fact, increase mortality. As a result, the researchers called for more stringent regulation of antioxidant supplements.
The review, “Antioxidant supplements for prevention of mortality in healthy participants and patients with various diseases,” appears in The Cochrane Library, a publication of The Cochrane Collaboration, an international organization that evaluates medical research. The objective of the study was to assess the effect of antioxidant supplements on mortality in primary or secondary prevention randomized clinical trials.
The meta-analysis included a total of 232,550 participants randomized to antioxidant supplements (beta-carotene, vitamin A, vitamin C, vitamin E and selenium) vs. placebo or no intervention. Twenty-one trials included 164,439 healthy participants; 46 trials included 68,111 participants with various diseases (including gastrointestinal, cardiovascular, neurological, ocular, dermatological, rheumatoid, renal, endocrinological or unspecified diseases).
A total of 17,880 of 136,023 participants (13.1%) randomized to antioxidant supplements, and 10,136 of 96,527 participants (10.5%) randomized to placebo or no intervention died. In the analyses of the trials with low risk of bias, beta-carotene, vitamin A and vitamin E significantly increased mortality. There were no significant differences between the effects of antioxidant supplements in healthy participants (primary prevention trials) or participants with various diseases (secondary prevention trials). Randomized trials with adequate bias control found no significant effect of vitamin C. In some of the analyses, selenium appeared to reduce mortality.
The review did not assess antioxidant supplements for treatment of specific diseases (tertiary prevention); antioxidant supplements for patients with demonstrated specific needs of antioxidants; or the effects of antioxidants contained in fruits or vegetables.
The review authors recommend greater regulation of antioxidant supplements and make a “plea for urgent political action,” said Dr. Christian Gluud, review co-author and director of medical science, associate professor and department head of the Copenhagen Trial Unit at the Centre for Clinical Intervention Research and Copenhagen University Hospital, Denmark. “We should request that the regulatory authorities dare to regulate the industry without being financially dependent on the very same industry.”
Jeffrey Blumberg, Ph.D., director of the Antioxidants Research Laboratory, USDA Human Nutrition Research Center on Aging, and a professor with the Friedman School of Nutrition Science and Policy, Tufts University, Medford, MA, questions the report’s conclusions: “I could find nowhere in this report any review of regulatory practices and effectiveness or the evaluation of public health policies, procedures or perspectives.”
Andrew Shao, Ph.D., vice president of scientific and regulatory affairs for the Council for Responsible Nutrition, Washington, D.C., a supplement industry trade association, also raised doubts about the review and its conclusions. “Four hundred five studies which showed no deaths were excluded from the meta-analysis, which if included, clearly would have altered the outcome of the meta-analysis,” he said.
