Antioxidant supplements for prevention of mortality in healthy participants and patients with various diseases

Resumo

BACKGROUND: Our previous systematic review has demonstrated that antioxidant supplements may increase mortality. We have now updat-ed this review. OBJECTIVES: To assess the beneficial and harmful effects of antioxidant supplements for prevention of mortality in adults. METHODS: Search methods: We searched The Cochrane Library, Medline, Embase, Lilacs, the Science Citation Index Expanded, and Conference Proceed-ings Citation Index-Science to February 2011. We scanned bibliogra-phies of relevant publications and asked pharmaceutical companies for additional trials. Selection criteria: We 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. Data collection and analysis: Three authors extracted data. Random-effects and fixed-effect model meta-analyses were conducted. Risk of bias was considered in order to minimize the risk of systematic errors. Trial sequential analyses were conducted to minimize the risk of ran-dom errors. Random effects model meta-regression analyses were per-formed to assess sources of intertrial heterogeneity. MAIN RESULTS: Seventy-eight randomized trials with 296,707 partici-pants were included. Fifty-six trials including 244,056 participants had low risk of bias. Twenty-six trials included 215,900 healthy participants. Fifty-two trials included 80,807 participants with various diseases in a stable phase. The mean age was 63 years (range 18 to 103 years). The mean proportion of women was 46%. Of the 78 trials, 46 used the par-allel-group design, 30 the factorial design, and 2 the cross-over design. All antioxidants were administered orally, either alone or in combina-tion with vitamins, minerals, or other interventions. The duration of sup-plementation varied from 28 days to 12 years (mean duration 3 years; median duration 2 years). Overall, the antioxidant supplements had no significant effect on mortality in a random-effects model meta-analysis (21,484 dead/183,749 (11.7%) versus 11,479 dead/112,958 (10.2%); 78 trials, relative risk (RR) 1.02, 95% confidence interval (CI) 0.98 to 1.05) but significantly increased mortality in a fixed-effect model (RR 1.03, 95% CI 1.01 to 1.05). Heterogeneity was low with an I2- of 12%. In meta-regres-sion analysis, the risk of bias and type of antioxidant supplement were the only significant predictors of intertribal heterogeneity. Meta-regres-sion analysis did not find a significant difference in the estimated inter-vention effect in the primary prevention and the secondary preventiontrials. In the 56 trials with a low risk of bias, the antioxidant supplements significantly increased mortality (18,833 dead/146,320 (12.9%) versus 10,320 dead/97,736 (10.6%); RR 1.04, 95% CI 1.01 to 1.07). This effect was confirmed by trial sequential analysis. Excluding factorial trials with potential confounding showed that 38 trials with low risk of bias dem-onstrated a significant increase in mortality (2822 dead/26,903 (10.5%) versus 2473 dead/26,052 (9.5%); RR 1.10, 95% CI 1.05 to 1.15). In trials with low risk of bias, beta-carotene (13,202 dead/96,003 (13.8%) versus 8556 dead/ 77,003 (11.1%); 26 trials, RR 1.05, 95% CI 1.01 to 1.09) and vitamin E (11,689 dead/97,523 (12.0%) versus 7561 dead/73,721 (10.3%); 46 trials, RR 1.03, 95% CI 1.00 to 1.05) significantly increased mortality, whereas vitamin A (3444 dead/24,596 (14.0%) versus 2249 dead/16,548 (13.6%); 12 trials, RR 1.07, 95% CI 0.97 to 1.18), vitamin C (3637 dead/36,659 (9.9%) versus 2717 dead/ 29,283 (9.3%); 29 trials, RR 1.02, 95% CI 0.98 to 1.07), and selenium (2670 dead/39,779 (6.7%) versus 1468 dead/22,961 (6.4%); 17 trials, RR 0.97, 95% CI 0.91 to 1.03) did not significantly affect mortality. In univariate meta-regression analysis, the dose of vitamin A was significantly associated with increased mortality (RR 1.0006, 95% CI 1.0002 to 1.001, P = 0.002). AUTHORS’ CONCLUSIONS: We found no evidence to support antioxi-dant supplements for primary or secondary prevention. Beta-carotene and vitamin E seem to increase mortality, and so may higher doses of vi-tamin A. Antioxidant supplements need to be considered as medicinal products and should undergo sufficient evaluation before marketing.