Epidemiologic data suggest that omega-3 fatty acids derived from fish oil reduce cardiovascular disease. The clinical benefit of dietary fish oil supplementation in preventing cardiovascular events in both high and low risk patients is unclear.

To assess whether dietary supplements of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) decrease cardiovascular events across a spectrum of patients.

MEDLINE, Embase, the Cochrane Database of Systematic Reviews, and citation review of relevant primary and review articles.

Prospective, randomized, placebo-controlled clinical trials that evaluated clinical cardiovascular end points (cardiovascular death, sudden death, and nonfatal cardiovascular events) and all-cause mortality in patients randomized to EPA/DHA or placebo. We only included studies that used dietary supplements of EPA/DHA which were administered for at least 1 year.

Data were abstracted on study design, study size, type and dose of omega-3 supplement, cardiovascular events, all-cause mortality, and duration of follow-up. Studies were grouped according to the risk of cardiovascular events (high risk and moderate risk). Meta-analytic techniques were used to analyze the data.

We identified 11 studies that included a total of 39 044 patients. The studies included patients after recent myocardial infarction, those with an implanted cardioverter defibrillator, and patients with heart failure, peripheral vascular disease, and hypercholesterolemia. The average dose of EPA/DHA was 1.8 +/- 1.2 g/day and the mean duration of follow-up was 2.2 +/- 1.2 years. Dietary supplementation with omega-3 fatty acids significantly reduced the risk of cardiovascular deaths (odds ratio [OR]: 0.87, 95% confidence interval [CI]: 0.79-0.95, p = 0.002), sudden cardiac death (OR: 0.87, 95% CI: 0.76-0.99, p = 0.04), all-cause mortality (OR: 0.92, 95% CI: 0.85-0.99, p = 0.02), and nonfatal cardiovascular events (OR: 0.92, 95% CI: 0.85-0.99, p = 0.02). The mortality benefit was largely due to the studies which enrolled high risk patients, while the reduction in nonfatal cardiovascular events was noted in the moderate risk patients (secondary prevention only). Meta-regression failed to demonstrate a relationship between the daily dose of omega-3 fatty acid and clinical outcome.

Dietary supplementation with omega-3 fatty acids should be considered in the secondary prevention of cardiovascular events.