May 1, 2008 — A report published in the Cochrane Database of Systematic Reviews (April 16, 2008), concludes that antioxidant supplements have little effect on mortality.
Researchers looked at 67 randomized trials with 232,550 participants. The aim of the research was to assess the effect of antioxidants on mortality in primary or secondary prevention, randomized trials.
The scientists searched The Cochrane Library (Issue 3, 2005), MEDLINE (1966 to October 2005), EMBASE (1985 to October 2005), and the Science Citation Index Expanded (1945 to October 2005).
They included all primary and secondary prevention randomized clinical trials on antioxidant supplements (beta-carotene, vitamin A, vitamin C, vitamin E, and selenium) versus placebo or no intervention. Included participants were either healthy (primary prevention trials) or had any disease (secondary prevention trials).
Researchers concluded that the antioxidant supplements had no significant effect on mortality in a random-effects meta-analysis, but significantly increased mortality in a fixed-effect model.
In the trials with a low-risk of bias, the antioxidant supplements significantly increased mortality. When the different antioxidants were assessed separately, analyses including trials with a low risk of bias and excluding selenium trials found significantly increased mortality by vitamin A, beta-carotene, and vitamin E, but no significant detrimental effect of vitamin C. Low-bias risk trials on selenium found no significant effect on mortality.
They said the current evidence does not support the use of antioxidant supplements in the general population or in patients with certain diseases. The combined evidence suggests that additional research on antioxidant supplements is needed.
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. Further research and systematic reviews on these types of interventions are therefore warranted.
Source: G Bjelakovic, D Nikolova, LL Gluud, RG Simonetti, C Gluud, “Antioxidant supplements for prevention of mortality in healthy participants and patients with various disease ,” Cochrane Database of Systematic Reviews (April 16, 2008).