Fish Oil Increases Risk of Cardiac Arrhythmias in Some Patients

In a new JAMA report, investigators found that fish oil may increase the risk of cardiac arrhythmias in some patients. The two-year study at Oregon Health and Science University included 200 patients with ventricular tachycardia or ventricular fibrillation who were receiving implantable cardioverter defibrillators. Participants were randomly assigned to receive capsules containing fish oil (1.8 grams/day) or olive oil placebo.

Among those initially diagnosed with ventricular tachycardia, 61 percent experienced arrhythmias treated by implantable defibrillator within six months, compared with 37 percent receiving placebo. At 12 and 24 months, the figures were 66 percent and 79 percent, respectively, for the fish oil group, compared with 43 percent and 65 percent for the placebo group (P = 0.007). A similar trend was apparent when all participants were included, although the increased risk was significant only for those with ventricular tachycardia.

Previous studies have had mixed results. Some have suggested a benefit of fish oils for some patients; others have shown increased arrhythmia risk. The Oregon investigators recommend against the routine use of fish oils in patients with ventricular arrhythmias.