Fish oil, rich in omega-3 fatty acids (primarily EPA and DHA), has been extensively studied for its effects on cardiovascular health. The scientific rationale for its use stems from early epidemiological studies observing low rates of cardiovascular disease (CVD) in populations with high fish consumption, such as the Greenland Inuit. Subsequent randomized controlled trials and meta-analyses have shown that fish oil supplementation can lower triglyceride levels, reduce blood pressure modestly, and exert anti-inflammatory and antithrombotic effects, all of which are beneficial for cardiovascular health.

However, while early studies suggested a significant reduction in major cardiovascular events and mortality, more recent large-scale trials (such as ASCEND, VITAL, and STRENGTH) have produced mixed results. Some benefits have been observed, particularly for reductions in triglycerides and, in some populations, non-fatal cardiac events. The most robust effect is on lowering triglyceride levels, a known risk factor for CVD. The prescription-grade omega-3 product icosapent ethyl (VASCEPA) has shown reductions in cardiovascular events in high-risk patients, as demonstrated in the REDUCE-IT trial. Nonetheless, evidence for routine use of fish oil supplements in the general population for primary or secondary prevention of CVD is less clear.

Overall, fish oil is widely recommended for triglyceride lowering, and there is moderate evidence supporting its role in specific cardiovascular contexts. The strength of evidence for broad cardiovascular event reduction is moderate (rated 3/5) due to variability in trial results and population differences.