Does fish oil help with heart disease? What the research does and doesn't show

The evidence doesn't support fish oil as risk-free for heart rhythm. Across large cardiovascular trials totaling more than 81,000 people, omega-3 supplementation was associated with a higher rate of atrial fibrillation, and the risk rose with dose — highest in trials testing more than 1 gram a day, present but smaller in trials testing 1 gram a day or less.

What the evidence doesn't support

It doesn't support the idea that fish oil is neutral for heart rhythm at every dose — the largest analysis of cardiovascular outcome trials found a dose-dependent increase in atrial fibrillation risk. It doesn't support omega-3 as a treatment for existing heart disease, and it doesn't support prescription-strength findings from 1-to-4-gram trials as evidence for what a standard over-the-counter softgel, at a few hundred milligrams a day, would do to cardiovascular risk or heart rhythm.

What the trials found

A 2021 systematic review and meta-analysis in Circulation pooled 7 large randomized cardiovascular outcome trials testing marine omega-3 supplementation, covering 81,210 people with a median follow-up of 4.9 years. Omega-3 supplementation was associated with an increased risk of atrial fibrillation overall (hazard ratio 1.25). When trials were split by dose, the increased risk was smaller in trials testing 1 gram a day or less (hazard ratio 1.12) and larger in trials testing more than 1 gram a day (hazard ratio 1.49). A meta-regression across the pooled trials found the atrial fibrillation risk rose by about 11% for every additional gram of omega-3 dosed per day.

One of the trials inside that pooled analysis was REDUCE-IT, which tested 4 grams a day of a purified prescription EPA drug in 8,179 statin-treated people with established cardiovascular disease, or diabetes plus other risk factors. Over roughly five years, the treatment group had fewer cardiovascular events overall (17.2% versus 22.0% on placebo) but more hospitalizations specifically for atrial fibrillation or flutter (3.1% versus 2.1%). A separate, larger pooling of 86 trials and 162,796 people — the Cochrane review of omega-3 and cardiovascular outcomes — found little or no overall effect on all-cause mortality, cardiovascular events, stroke, or arrhythmia across the full dose range studied (0.5 grams a day to more than 5 grams a day), which sits in some tension with the dose-specific atrial fibrillation finding above: a small risk was detectable when trials were grouped and analyzed by dose, but disappeared when averaged across the full range in a different analysis.

Questions people ask

Can fish oil cause heart palpitations or atrial fibrillation?

Trials pooling more than 81,000 people found a higher rate of atrial fibrillation with omega-3 supplementation, and the risk was dose-dependent — higher in trials testing more than 1 gram a day. Palpitations that feel new, frequent or severe are worth reporting to a doctor regardless of what supplements you take.

Does fish oil cause afib at typical over-the-counter doses?

The trials that found this risk tested doses at or above 1 gram a day, several times a standard softgel serving. No trial has isolated the atrial fibrillation risk at the lower doses found in most over-the-counter fish oil, so that specific question hasn't been directly tested.

Is fish oil good for heart disease?

The research is mixed and dose-dependent, not a simple yes. A purified, high-dose prescription EPA drug reduced cardiovascular events in one large trial of people already diagnosed with cardiovascular disease, while the largest pooled review of 86 trials found little or no overall effect at any dose, and atrial fibrillation risk rose with dose across the pooled cardiovascular trials.

When to talk to a doctor

An irregular heartbeat, new palpitations, or an existing diagnosis of heart disease or atrial fibrillation calls for a doctor's evaluation, not a supplement decision made alone. Fish oil is not a treatment for heart disease or arrhythmia, and nothing in the evidence above supports using it in place of prescribed cardiac care. If you take a blood thinner or heart medication, or are pregnant or nursing, talk to a doctor before adding any supplement.

Related reading: fish oil and blood pressure: what the research does and doesn't show, fish oil and cholesterol: what the research does and doesn't show, fish oil benefits: what the research does and doesn't show, and fish oil side effects.