Do omega-3 fatty acids help against heart rhythm disorders?

High doses of omega-3 increase the risk of atrial fibrillation. Several large randomised trials have shown this, both for pure EPA and for a combination of EPA and DHA. The effect is small but measurable, and appears to be dose-dependent. Why this is the case is not yet known.

On the question of whether omega-3 protects against dangerous ventricular arrhythmias or sudden cardiac death, the picture is mixed. Two early trials found a reduction in sudden cardiac death, but later randomised studies could not replicate this. In people with angina pectoris (chest pain caused by oxygen deprivation), some reviews even identified an increased risk. In patients who already carry an implantable defibrillator, the results are outright contradictory. A broadly proven anti-arrhythmic effect does not exist.

There is one exception that turns out somewhat more positively: in two large Italian trials (in patients after a heart attack and in people with heart failure), a specifically registered omega-3 medicine based on ethyl esters (1 gram per day) reduced the number of deaths due to arrhythmias. The authors emphasise that ordinary fish oil from a shop is not an equivalent alternative to this specific medicine.

Omega-3 does lower resting heart rate and improves heart rate variability, presumably through a direct effect on the heart's natural pacemaker. Whether this also makes a clinically meaningful difference is unclear. In randomised research, no benefit has been found for the prevention of atrial fibrillation after cardiac surgery or for recurrent atrial fibrillation. After decades of research, a generally protective effect on heart rhythm disorders remains unproven.