Can Fish Oil Cause an Irregular Heartbeat?

Fish oil could worsen heart arrhythmias, in some cases.

Fish oil, which contains essential omega-3 fatty acids, has several potential heart benefits. Omega-3 fatty acids may help lower cholesterol levels and reduce the risk of ischemic stroke. But study results on the benefits of fish oil in treating or preventing heart arrhythmias -- irregular heartbeats that can lead to death -- have been mixed, with some studies showing a worsening of arrhythmias in people taking fish oil. Ask your doctor before taking fish oil if you have a history of heart disease.

How It Works

Heart arrhythmias occur when the electrical impulses in the heart do not fire in a coordinated fashion. Your heart responds to electrical impulses by contracting in a rhythmic fashion, with first the top two chambers -- the atria -- contracting and then the two lower chambers -- the ventricles -- pumping blood to the rest of the body. If the chambers don't contract at the right times, the heart may "quiver" rather than pump forcefully. Fish oil may prevent damage to the blood vessels of the heart by lowering high cholesterol levels and decreasing atherosclerosis, which can cause blockages in the blood vessels that lead to arrhythmias. Fish oil can also reduce inflammation and clot formation because of its blood thinning properties.


Studies Showing Negative Effects

A multi-center study conducted by researchers from the Portland VA Medical Center and reported in the June 2005 issue of "JAMA" examined the effects of fish oil vs. placebo on 200 patients with implantable cardioverters/defibrillators. Patients taking 1.8 mg of omega-3 fatty acids daily had a higher incidence of two arrhythmias, ventricular fibrillation, or VF, and ventricular tachycardia, or VT, than those taking placebo. At the end of 24 months, 65 percent of the group taking fish oil and 59 percent of the group taking placebo had experienced an episode of VF/VT.


Studies Showing Positive Effects

A Harvard Medical School study reported in the November 2005 issue of "Circulation," on the other hand, found a decrease in heart arrhythmias VF or VT in 402 patients with implantable cardioverters/defibrillators. Over an 11-month period, fish oil vs. placebo reduced the risk of arrhythmia by 38 percent, researchers reported.


Study results have not proven a definite benefit or definite harm from taking fish oil if you have a history of heart disease, including potentially fatal arrhythmias such as VF or VT. Talk with your doctor about the potential risks or benefits, especially if you already have an implantable cardioverter/debrillator due to previous arrhythmias.