Higher omega-3 intake has little or no effect on mortality or cardiovascular events, review finds

Moderate- to high-quality evidence suggested little or no effect of increasing fish-based omega-3 fatty acids, while low- to moderate-quality evidence suggested that increasing plant-based omega-3s slightly reduces risk of cardiovascular events, risk of coronary heart disease mortality, and risk of arrhythmia.

Increasing intake of fish-based omega-3 fatty acids probably has little or no effect on the risk of all-cause mortality or cardiovascular events, but plant-based omega-3s may provide some benefit, a recent Cochrane review concluded.

Researchers reviewed 79 randomized controlled trials (25 at low summary risk of bias) that included a total of 112,059 participants with varying risks for cardiovascular disease living mainly in high-income countries. The duration of the trials ranged from 12 to 72 months. Most trials compared supplementation and/or advice to increase intake of long-chain omega-3 polyunsaturated fatty acids from oily fish or alpha-linolenic acid (ALA) from plants versus usual or lower intake.

Results were published online on July 18 by the Cochrane Library.

Moderate- to high-quality evidence suggested little or no effect of increasing long-chain omega-3 polyunsaturated fatty acids on the outcomes studied: all-cause mortality (relative risk [RR], 0.98; 95% CI, 0.90 to 1.03), cardiovascular mortality (RR, 0.95; 95% CI, 0.87 to 1.03), cardiovascular events (RR, 0.99; 95% CI, 0.94 to 1.04), coronary heart disease mortality (RR, 0.93, 95% CI, 0.79 to 1.09), stroke (RR, 1.06; 95% CI, 0.96 to 1.16), or arrhythmia (RR, 0.97; 95% CI, 0.90 to 1.05). Although increased intake appeared to reduce coronary heart disease events (RR, 0.93; 95% CI, 0.88 to 0.97), this finding was not maintained in sensitivity analyses.

Increasing ALA intake also made little or no difference in all-cause mortality (RR, 1.01; 95% CI, 0.84 to 1.20), cardiovascular mortality (RR, 0.96; 95% CI, 0.74 to 1.25), and coronary heart disease events (RR, 1.00; 95% CI, 0.80 to 1.22). Low- to moderate-quality evidence did, however, suggest that increasing ALA reduces risk of cardiovascular events from 4.8% to 4.7% (RR, 0.95; 95% CI, 0.83 to 1.07), risk of coronary heart disease mortality from 1.1% to 1.0% (RR, 0.95; 95% CI, 0.72 to 1.26), and risk of arrhythmia from 3.3% to 2.6% (RR, 0.79; 95% CI, 0.57 to 1.10). The authors estimated a number needed to treat of 1,000 to prevent a cardiovascular event or death from coronary heart disease and a number needed to treat of 143 to prevent one case of arrhythmia. Any effects on stroke were unclear.

The authors noted limitations of the analysis, such as the inability to assess potential severe harms (e.g., bleeding, pulmonary embolism, deep venous thrombosis) of increased omega-3 intake due to insufficient data. They also noted variability in how the studies collected cardiovascular outcomes.

“In light of the evidence in this review it would be appropriate to review official recommendations supporting supplemental [long-chain omega-3] fatty acid intake,” they wrote. “ALA is an essential fatty acid, an important part of a mixed diet, and increasing intakes may be very slightly beneficial for prevention or treatment of cardiovascular disease.”