Q. Should I take fish oil capsules daily to prevent heart disease?

A. Eating fish or taking fish oil capsules (which contain the omega-3 fatty acids EPA and DHA) is claimed to reduce heart disease. The high omega-3 fatty acid content of oily fish in the diet of Eskimos and other fish eaters supposedly leads to their lower heart disease risk. However, it may be that something else in their heredity, lifestyle or diet is responsible.

In 2003, Dr. Michael Burr and others from England published a randomized study (the most accurate kind of study) in the European Journal of Clinical Nutrition of 3,114 men with angina, or chest pain due to blockage of their heart vessels. After several years, those who took fish oil capsules had 45 percent more deaths from heart disease than those who did not.

And in a meta-analysis updated this year, the highly regarded Cochrane Collaboration did the largest, most comprehensive review yet on this issue. They found 48 randomized studies involving 36,913 people. Some got extra omega-3 fatty acids in the form of oily fish (like mackerel, salmon, trout, tuna, etc.), fish oil capsules, or plant oils like flax seed oil, and the rest did not. They found that oily fish, fish oil capsules or plant oils, either alone or in combination, did not reduce heart disease, cancers or deaths. This held true for both healthy people and those at high risk for heart disease.

Some have suggested that fish oils reduce dangerous heart palpitations, so-called ventricular tachycardia and fibrillation. Well, in the June 15, 2005 issue of the Journal of the American Medical Association, those who had defibrillators implanted in their heart to prevent such dangerous rhythms actually had a worsening of such rhythms after starting fish oils.

And though fish oils reduce fats called triglycerides, they also worsen LDL (bad cholesterol). Finally, toxins like PCBs, dioxins and mercury may be present in oily fish or fish oils, and are higher in farmed versus wild salmon. Because of toxic effects on the growing brain, children and women of child-bearing age should avoid fish with high mercury levels like shark, swordfish, kajiki (Pacific blue marlin), tuna, ono and opah. Canned white albacore tuna has 3 times more mercury than canned light tuna. Regarding fish oil capsules: Consumer Reports tested 16 brands and did not detect mercury, dioxins or PCBs, though I'd still be careful. But fish is nutritious, and if you still want omega-3-rich fish low in mercury, eat fish like salmon, trout or bass. But I no longer recommend fish oil capsules to my patients.

Dr. Landis Lum is a family-practice physician for Kaiser Permanente and an associate clinical professor at the University of Hawai'i's John A. Burns School of Medicine.

Send your questions to Prescriptions, Island Life, The Advertiser, P.O. Box 3110, Honolulu, HI 96802; fax 535-8170; or write islandlife@honoluluadvertiser.com. This column is not intended to provide medical advice.