Clinical Question: Does supplementation with omega-3 fatty acids decrease mortality, cardiovascular disease, or cancer in adults?

Setting: Various (meta-analysis)

Study Design: Systematic review

Synopsis: In this update of a previous Cochrane review, authors identified 48 randomized controlled trials and 41 cohort studies evaluating the effect of fish oil supplementation on overall mortality, cardio-vascular disease, and cancer in adults. The authors identified these studies through the usual Cochrane methodology and analyzed the results from randomized trials separately from cohort data. The studies included patients with or without preexisting coronary heart disease. As a result, the authors combined primary and secondary prevention research.

Omega-3 fatty acids were given as supplements or a recommendation was made to eat more oily fish. In randomized trials enrolling more than 30,000 patients, omega-3 supplementation did not significantly reduce mortality (relative risk [RR] = 0.87; 95% confidence interval [CI], 0.73 to 1.03) or the likelihood of a cardiovascular event (RR = 1.09; CI, 0.87 to 1.37). Long-chain omega-3 fatty acids did not produce results different from short-chain fats. Cancer was neither increased nor decreased in clinical trials or cohort studies. The lack of benefit demonstrated in this study conflicts with the results of an earlier meta-analysis of the effect in patients with coronary heart disease (Bucher HC, et al. N-3 polyunsaturated fatty acids in coronary heart disease: a meta-analysis of randomized controlled trials. Am J Med 2002;112:298–304). However, this is the second study published after the meta-analysis that did not find a benefit overall.

Bottom Line: Overall, omega-3 fatty acid supplementation does not decrease mortality or cardiovascular disease compared with placebo. This study combined primary and secondary prevention; that is, it included persons with or without coronary heart disease. (Level of Evidence: 1a)