alexa Antioxidant supplements for preventing gastrointestinal cancers.
Pharmaceutical Sciences

Pharmaceutical Sciences

Pharmaceutica Analytica Acta

Author(s): Bjelakovic G, Nikolova D, Simonetti RG, Gluud C

Abstract Share this page

Abstract BACKGROUND: Oxidative stress may cause gastrointestinal cancers. The evidence on whether antioxidant supplements are effective in preventing gastrointestinal cancers is contradictory. OBJECTIVES: To assess the beneficial and harmful effects of antioxidant supplements in preventing gastrointestinal cancers. SEARCH STRATEGY: We identified trials through the trials registers of the four Cochrane Review Groups on gastrointestinal diseases, The Cochrane Central Register of Controlled Trials in The Cochrane Library (Issue 2, 2007), MEDLINE, EMBASE, LILACS, SCI-EXPANDED, and The Chinese Biomedical Database from inception to October 2007. We scanned reference lists and contacted pharmaceutical companies. SELECTION CRITERIA: Randomised trials comparing antioxidant supplements to placebo/no intervention examining occurrence of gastrointestinal cancers. DATA COLLECTION AND ANALYSIS: Two authors (GB and DN) independently selected trials for inclusion and extracted data. Outcome measures were gastrointestinal cancers, overall mortality, and adverse effects. Outcomes were reported as relative risks (RR) with 95\% confidence interval (CI) based on random-effects and fixed-effect model meta-analysis. Meta-regression assessed the effect of covariates across the trials. MAIN RESULTS: We identified 20 randomised trials (211,818 participants), assessing beta-carotene (12 trials), vitamin A (4 trials), vitamin C (8 trials), vitamin E (10 trials), and selenium (9 trials). Trials quality was generally high. Heterogeneity was low to moderate. Antioxidant supplements were without significant effects on gastrointestinal cancers (RR 0.94, 95\% CI 0.83 to 1.06). However, there was significant heterogeneity (I(2) = 54.0\%, P = 0.003). The heterogeneity may have been explained by bias risk (low-bias risk trials RR 1.04, 95\% CI 0.96 to 1.13 compared to high-bias risk trials RR 0.59, 95\% CI 0.43 to 0.80; test of interaction P < 0.0005), and type of antioxidant supplement (beta-carotene potentially increasing and selenium potentially decreasing cancer risk). The antioxidant supplements had no significant effects on mortality in a random-effects model meta-analysis (RR 1.02, 95\% CI 0.97 to 1.07, I(2) = 53.5\%), but significantly increased mortality in a fixed-effect model meta-analysis (RR 1.04, 95\% CI 1.02 to 1.07). Beta-carotene in combination with vitamin A (RR 1.16, 95\% CI 1.09 to 1.23) and vitamin E (RR 1.06, 95\% CI 1.02 to 1.11) significantly increased mortality. Increased yellowing of the skin and belching were non-serious adverse effects of beta-carotene. In five trials (four with high risk of bias), selenium seemed to show significant beneficial effect on gastrointestinal cancer occurrence (RR 0.59, 95\% CI 0.46 to 0.75, I(2) = 0\%). AUTHORS' CONCLUSIONS: We could not find convincing evidence that antioxidant supplements prevent gastrointestinal cancers. On the contrary, antioxidant supplements seem to increase overall mortality. The potential cancer preventive effect of selenium should be tested in adequately conducted randomised trials. This article was published in Cochrane Database Syst Rev and referenced in Pharmaceutica Analytica Acta

Relevant Expert PPTs

Relevant Speaker PPTs

Recommended Conferences

Peer Reviewed Journals
Make the best use of Scientific Research and information from our 700 + peer reviewed, Open Access Journals
International Conferences 2017-18
Meet Inspiring Speakers and Experts at our 3000+ Global Annual Meetings

Contact Us

© 2008-2017 OMICS International - Open Access Publisher. Best viewed in Mozilla Firefox | Google Chrome | Above IE 7.0 version