Fourteen RCTs (20,485 patients, range 59 to 6,975) were included. The mean Jadad score was 4.4 out of 5 (13 out of 14 trials scored 4 or 5).
Omega-3 fatty acid supplementation did not reduce the risk of overall cardiovascular events (RR 0.99, 95% CI, 0.89 to 1.09, Ι²=27%; 14 RCTs), risk of all-cause mortality (13 RCTs), sudden cardiac death (five RCTs), myocardial infarction (11 RCTs), fatal myocardial infarction (five RCTs), nonfatal myocardial infarction (seven RCTs), angina and unstable angina (seven RCTs), congestive heart failure (six RCTs) and transient ischaemic attack and stroke (seven RCTs). There was a significant reduction in cardiovascular death (RR 0.91, 95% CI 0.84 to 0.99, Ι²=0%; 11 RCTs), which became non-significant when a study with a significant baseline imbalance (for history of angina) was removed.
No significant preventive effect was observed in any of the subgroup analyses.
There was no evidence of publication bias. There were no significant differences between groups in occurrence of gastrointestinal problems (eight RCTs) and gastrointestinal bleeding (one RCT) adverse events.