Refining the prescription for fish oil

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Refining the prescription for fish oil

Fish oil may not help those with implanted defibrillators.

Omega-3 fatty acids are a big reason why fish is extolled as a heart-healthy food. Yet research showing that fish oil doesn't seem to help people with an implantable cardioverter/defibrillator (ICD) suggests that the benefits of omega-3s might not extend to everyone.

Our bodies can't make omega-3 fats. Oily fish such as salmon, sardines, herring, and mackerel are good sources of two omega-3s, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). A third, alpha-linolenic acid (ALA), comes from plants, especially flaxseed, walnuts, soybeans, and canola oil. Only 10% to 15% of ALA is converted to the more powerful omega-3s; the rest is burned for energy.

A high intake of omega-3 fatty acids from fish or fish oil reduces the odds of dying from cardiovascular disease. One way omega-3 fats may do this is by keeping the heart from lapsing into potentially deadly rhythms such as ventricular tachycardia and ventricular fibrillation.

If fish oil does, indeed, prevent abnormal heart rhythms, could it act as a safer alternative to drugs used for that very purpose?

Studies muddy the water

Researchers set out to test this question in people with known rhythm problems — those who had an ICD because they had experienced ventricular tachycardia or ventricular fibrillation. The results haven't been as clear as expected, and they've created some confusion about fish oil.

The latest trial, the Study on Omega-3 Fatty Acids and Ventricular Arrhythmia, included 546 men and women with ICDs. Half took 2 grams of fish oil a day, and half took a placebo. After two years, the number of ICD-generated shocks and pacing therapies to stop arrhythmias and the number of deaths were very similar in both groups, with a small but not statistically significant edge for fish oil. The results were published in the June 14, 2006, Journal of the American Medical Association.

An earlier Harvard-led trial similarly found a possible, though not definitive, reduction in potentially deadly arrhythmias and deaths among 200 people with ICDs who took fish oil compared with an equal number who took a placebo. But another American trial of 200 people with ICDs showed an opposite trend, with more of those in the fish oil group getting shocks for an arrhythmia.

Balancing act

These studies don't mean that omega-3 fatty acids and fish oil are a bust for everyone. But they do suggest that omega-3s don't affect all arrhythmias the same way. Fish oil may work better against arrhythmias caused by heart attacks or poor blood flow to the heart than those caused by electrical or genetic malfunctions, says Dr. Christine M. Albert, who directs the Center for Arrhythmia Prevention at Harvard-affiliated Brigham and Women's Hospital.

Several large trials under way in 2006 aim to determine if fish oil helps or harms people with defibrillators and to define who would most benefit from taking it. In the meantime, the American Heart Association's advice on fish and fish oil (see "Fish or fish oil?") is a good guide.

Last updated:	September 05, 2008