Eleven RCTs (39,044 participants) were included. Study size ranged from 59 to 18,645. Three studies contributed approximately 94% of the participants. All 11 studies reported random allocation. Nine studies (9,065 participants) were double blinded with allocation concealment; the two largest studies (29,979 participants) were not.
Dietary supplement of EPA/DHA reduced the risk of cardiovascular death (OR 0.87, 95% CI 0.79 to 0.95; 11 trials), sudden cardiac death (OR 0.87, 95% CI 0.76 to 0.99; six trials), all-cause mortality (OR 0.92, 95% CI 0.85 to 0.99; 11 trials) and non-fatal cardiovascular events (OR 0.92 95% CI 0.85 to 0.99; nine trials). All except one study in the sudden cardiac death analysis were in high-risk people. For other mortality outcomes, subgroup analyses showed that benefits were only evident in the high-risk groups. For non-fatal cardiovascular events, benefit was evident only in the moderate-risk group. There was no evidence of statistical heterogeneity for any analysis.
Meta-regression showed that there was no association between dose and treatment effect.