Goran Bjelakovic, M.D., of the Center for Clinical Intervention Research, Copenhagen University Hospital, Denmark, and colleagues conducted an analysis of previous studies to examine the effects of antioxidant supplements – beta carotene, vitamins A, E, C and selenium – on all-cause death of adults included in primary and secondary prevention trials. Using electronic databases and bibliographies, the researchers identified and included 68 randomised trials with 232,606 participants in the review and meta-analysis. The authors also classified the trials according to the risk of bias based on the quality of the methods used in the study, and stratified trials as low-bias risk (high quality) or high-bias risk (low quality).
In an analysis that pooled all low-bias risk and high bias risk trials, there was no significant association between antioxidant use and mortality. Among low-bias trials, use of beta carotene, vitamin A, and vitamin E was associated with seven percent, 16 percent and four percent, respectively, increased risk of mortality, whereas there was no increased mortality risk associated with vitamin C or selenium use.
"Our systematic review contains a number of findings. Beta carotene, vitamin A, and vitamin E given singly or combined with other antioxidant supplements significantly increase mortality. There is no evidence that vitamin C may increase longevity," the authors write. "Our findings contradict the findings of observational studies, claiming that antioxidants improve health".
The scientists tried to find explanations: “By eliminating free radicals from our organism, we interfere with some essential defensive mechanisms. Antioxidant supplements are synthetic and not subjected to the same rigorous toxicity studies as other pharmaceutical agents.” A better understanding of mechanisms and actions are needed, the researchers state.
MEDICA.de; Source: American Medical Association