Do omega-3s help against cardiac arrhythmias?

Fish oil supplements (EPA and DHA) have no demonstrable benefit against cardiac arrhythmias in general. A large Cochrane meta-analysis of 30 randomised studies involving nearly 78,000 participants found a risk ratio of virtually 1.0, meaning: no measurable difference compared with placebo. The same research also showed that fish oil has little or no effect on total mortality or the total number of cardiovascular events. These findings come from large, well-designed studies.

There is, however, a serious safety warning for people who use high-dose fish oil supplements: multiple large, well-designed randomised studies show that high doses of omega-3 supplements, both pure EPA (icosapent ethyl) and the EPA+DHA combination, significantly increase the risk of atrial fibrillation (the most common clinically relevant cardiac arrhythmia). This effect is dose-dependent: higher doses carry a greater risk. Earlier research had actually hoped to prevent atrial fibrillation with omega-3, but those earlier promising results have not been confirmed in later, better-designed studies. High-dose fish oil is therefore not a treatment for atrial fibrillation, and moreover increases the risk of it.

The plant-based omega-3 fatty acid ALA (alpha-linolenic acid, found in, for example, flaxseed) provides, based on two studies with nearly 5,000 participants, limited evidence of a slight reduction in the risk of cardiac arrhythmias (risk ratio 0.73). The absolute benefit is small: on average, one in 91 people would need to be treated with ALA to prevent one case. The evidence is of moderate quality and rests on only two studies, so this is not an established fact, but it is noteworthy that ALA presents a more favourable picture than EPA or DHA.

The picture for sudden cardiac death caused by arrhythmias is more complex. Two older randomised studies found a reduction in sudden cardiac death at moderate to high doses of omega-3, and animal experiments show a direct anti-arrhythmic effect. However, these findings have not been widely replicated in later studies, and it is unclear whether EPA, DHA, or the combination is responsible. There are also older epidemiological data (association studies, not controlled trials) suggesting a link between eating fish containing DHA and fewer cases of sudden cardiac death. This remains unproven causality. Fish oil supplements cannot be recommended on this point based on current evidence.

Omega-3 fatty acids are not listed as a proven effective approach in a systematic review of lifestyle interventions for atrial fibrillation. Effective strategies for atrial fibrillation according to that same review are: blood pressure control, weight loss, stopping alcohol consumption, and treatment of sleep apnoea. Anyone wishing to reduce their risk of atrial fibrillation is therefore better off taking action in those areas than relying on omega-3 supplements.