Who Benefits From Omega-3/Fish Oil Supplements?

This is Dr JoAnn Manson, professor of medicine at Harvard Medical School and Brigham and Women’s Hospital. I’d like to talk with you about a recent report in the British Medical Journal on the regular use of omega-3 fish oil supplements and the course of cardiovascular disease (CVD).

This is an observational study from the large-scale UK Biobank. The authors divided the participants into those with and those without CVD. In participants without CVD at baseline, those using fish oil supplements regularly had an increased incidence of both atrial fibrillation (AF) and stroke, whereas those with prevalent CVD had a reduction in the progression to major adverse cardiovascular events, which offset any increase in the risk for AF.

Observational studies of omega-3 supplements have potential limitations and confounding, and correlation in these studies does not prove causation. What do the randomized clinical trials of omega-3 supplements show? At least seven randomized trials have looked at AF. A meta-analysis published in Circulation in 2021 showed a dose-response relationship. In trials testing > 1 g/d of marine omega-3 fatty acids, there was close to a 50% overall increase in risk for AF. In studies testing lower doses, there was a very modest 12% increase and a significant dose-response gradient.

For the relationship between omega-3 supplements and major cardiovascular events, at least 15 individual randomized trials have been conducted. There actually have been more meta-analyses of these randomized trials than individual trials. The meta-analyses tend to show a significant reduction of coronary events with omega-3 supplementation, but no reduction in stroke. This is true in both primary and secondary prevention trials.

The one exception to this finding is the REDUCE-IT trial testing high-dose eicosapentaenoic acid (EPA) (4 g/day of icosapent ethyl), and there was a 25%-30% reduction in both cardiovascular events and stroke. But there has been some criticism of the mineral oil placebo used in the REDUCE-IT trial that it may have had adverse effects on biomarkers and might have interfered with the absorption of statins in the placebo group. So, it will be important to have a replication trial of the high-dose EPA, findings in a trial using an inert placebo such as corn oil.

What should be done in the meantime? It’s important to think about prescription omega-3s vs over-the-counter fish oil. The US Food and Drug Administration (FDA) has approved prescription omega-3 medications for several indications, including severely elevated triglyceride levels (> 500 mg/dL). In the REDUCE-IT trial, those who had moderate elevations of triglycerides (≥ 150 mg/dL) or prevalent CVD or diabetes, plus two additional risk factors, were also considered to have indications based on the FDA labeling for icosapent ethyl.

What about patients who don’t meet these criteria for prescription omega-3s? In the VITAL trial (the large-scale primary prevention trial), there was a similar reduction in coronary events but no effect on stroke. Those who seemed to benefit the most in terms of at least 40% reduction in coronary events were participants who had low fish consumption at baseline, had two or more risk factors for cardiovascular disease, or were African American. 

Someone who rarely or never eats fish and has multiple risk factors for CVD, but doesn’t meet criteria for prescription omega-3 medication, may want to discuss with their clinician the use of over-the-counter fish oil supplements. But fish oil and other dietary supplements will never be a substitute for healthy diet and healthy lifestyle. There is a national recommendation for one to two servings of fish per week. For those planning to take fish oil, it’s important to use reputable sources of the supplement, and check the bottle for a quality control seal. It’s also really important to avoid megadoses of fish oil, because high doses have been linked to an increased risk for AF and bleeding.