For heart patients who have surgically implanted defibrillators to shock their weakened hearts back into rhythm, fish oil supplements are not a good idea and in fact appear to do more harm than good.
Researchers have found, in a study of 200 patients with the electrical devices, that when half took fish oil supplements and the other half olive oil, those who consumed fish oil had more episodes of the dangerous heart arrhythmia that often precedes heart attacks.
Previous studies had found that fish oil, whether absorbed from eating fish such as cod or in supplement form, reduced by about 25 percent the risk of fatal heart attacks in survivors of a previous attack.
Scientists now believe that the omega-3 polyunsaturated fatty acids contained in fish oil eases blood flow by reducing lipid levels in the blood.
The fish oil's ingredients may also induce changes in heart cell walls that smooths passage of electrical charges that trigger heartbeats.
Study author Merritt Raitt of the Portland, Oregon, Veterans Affairs Medical Center, says they went into the study with the strong belief that fish oil was going to prevent arrhythmia and lessen the shocks that are so uncomfortable, but records from the devices showed fish oil had the exact opposite effect.
Almost two-thirds of the patients who took fish oil and suffered from tachycardia, or rapid heartbeat, had episodes over a six-month period, twice the rate of those taking a placebo.
Forty-six percent of the patients who suffered from fibrillation, where the heart flutters, and who took fish oil had episodes compared to 36 percent of placebo-taking patients.
Raitt says it may be that fish oil in these patients is proarrhythmic and makes these abnormal rhythms occur when they would not otherwise.
He also says that proarrhythmia is a danger with all drugs that affect heart rhythm and is more common the sicker the heart is, and it may just be that fish oil is proarrhythmic in people who have defibrillators.
Roughly 150,000 Americans each year receive the increasingly popular defibrillators, and Raitt says most defibrillator patients also take some type of heart medication but there are few studies examining the combination.