The vitamin industry has long touted antioxidants as a way to improve health by filling in gaps in diet, but a new review of studies found no evidence that the nutrition supplements extend life. Worse, the review authors said that some antioxidants could increase risk for death.
The reviewers want more regulation of the nutraceuticals industry, but an antioxidant researcher with the U.S. Department of Agriculture said that call for stricter monitoring overreaches the conclusions of the review.
The meta-analysis of 67 randomized studies found that supplemental antioxidants do not reduce mortality and that some -- including vitamin A, beta-carotene and vitamin E -- could increase mortality. The review combined evidence from more than 200,000 people.
"The harmful effects of antioxidant supplements are not confined to vitamin A," said review co-author Christian Gluud, M.D. "Our analyses also demonstrate rather convincingly that beta-carotene and vitamin E lead to increased mortality compared to placebo."
The review appears in a recent issue of The Cochrane Library, a publication of The Cochrane Collaboration, an international organization that evaluates medical research. Systematic reviews draw evidence-based conclusions about medical practice after considering both the content and quality of existing medical trials on a topic.
Most people do eat not enough fruits and vegetables to ensure an adequate intake of vital nutrients. However, it is unclear if supplementation can provide benefits akin to a healthy diet and if some antioxidants are, in fact, harmful. Antioxidants are nutrients such as vitamin E, vitamin C, or beta carotene that have been marketed as a way to counter the damaging effects of oxygen in the tissues.
The review included studies of healthy adults and adults diagnosed with specific, stable medical conditions. The authors excluded studies with children or pregnant women, or studies that evaluated supplements as treatment for acute diseases, such as malignant cancer. It also excluded studies that used supplements for replacement of nutrient deficits.
The review authors recommend greater regulation of antioxidant supplements and make a "plea for urgent political action," said Gluud, 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 in Denmark.
"We should request that the regulatory authorities dare to regulate the industry without being financially dependent on the very same industry," Gluud said.
However, nutrition science expert Jeffrey Blumberg, Ph.D., said the reviewers go too far in their recommendations for more stringent regulation of antioxidant supplements.
"I could find nowhere in this report any review of regulatory practices and effectiveness or the evaluation of public health policies, procedures or perspectives," Blumberg said.
Blumberg is director of the Antioxidants Research Laboratory at the USDA Human Nutrition Research Center on Aging and a professor with the Friedman School of Nutrition Science and Policy at Tufts University. He was not involved in the review.
A supplement-industry trade group questions both the review conclusions and the study selection process for the analysis.
"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," said Andrew Shao, Ph.D., vice president of scientific and regulatory affairs for the Council for Responsible Nutrition, a supplement industry trade association in Washington, D.C.
Shao maintained that antioxidant supplements are safe additions to a healthy diet.
The review only includes studies in which someone died.
Gluud defended his methodology, saying it is important to include only large, randomized controlled trials to assess mortality. Most of the trials that showed no deaths were not "proper preventative trials," he said.
Blumberg raised concerns about the use of "all-cause mortality" as a yardstick for antioxidants' influence on health and life. "All-cause mortality" includes deaths resulting from everything from cancer to a train wreck.
Blumberg said: "There is no basis in biology to presume that one or more of these nutrients can kill through any and all possible mechanisms of action."
Reference: Bjelakovic G, et al. Antioxidant supplements for prevention of mortality in healthy participants and patients with various diseases (Review). Cochrane Database of Systematic Reviews 2008, Issue 2.
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