News

Fish-oil supplements aren't the miracle medicine they've been made out to be, according to an article published in today's Canadian Medical Association Journal.

In fact, researchers say, there's no evidence that everyone with heart problems should be taking fish oil. Some studies have shown benefits of fish oil for heart patients, while in other studies the supplements made no difference or did more harm than good.

Lead author David Jenkins says his suspicions were aroused by the near-universal acclaim for fish oil and the omega-3 fatty acids it contains.

"There are always downsides," said Dr. Jenkins, a professor of medicine and nutritional science at the University of Toronto who runs the Clinical Nutrition and Risk Factor Modification Centre at St. Michael's Hospital. "When we actually looked at the data, we saw there was a great diversity of results."

The Heart and Stroke Foundation of Canada suggests people should eat fish, especially fatty fish, at least twice a week. Omega-3 fats in oily fish make the blood less likely to form clots, lower blood fat levels and protect against irregular heartbeats that cause sudden death from cardiac arrest. About 2 per cent of the population at low risk of coronary heart disease takes fish-oil supplements. But fish oil can also have harmful effects, such as an increased risk of bleeding, especially at high doses.

Dr. Jenkins and his co-authors analyzed large studies that looked at heart patients and fish-oil supplements. (They didn't consider fish oil's effect on joint pain, Alzheimer's disease, depression or any of the many other conditions for which it is sometimes recommended.)

The research so far doesn't support the enthusiasm for fish oil, Dr. Jenkins said. In three major studies he and his co-authors analyzed, one found benefits to fish oil, another found that taking fish oil actually left heart patients in worse shape, and the third found that the supplements had no effect.

Fish-oil supplements seem to give the most benefit to patients who are already taking anti-heart-attack drugs such as beta blockers, Dr. Jenkins said. There is no evidence, he said, that fish oil alone helps people as a preventive measure.

"We don't have a study that tells us it reduces mortality," Dr. Jenkins said. Given the lack of clear evidence on fish oil, he said, "We need to be much more cautious in making blanket statements."

Dr. Jenkins said the medical community should study fish oil more carefully, with large trials to determine exactly what effect the supplements have on heart patients. But already food manufacturers are trying to capitalize on fish oil's good reputation by adding omega-3 fatty acids to eggs, bread and other food.

"Do I think the time has come for putting fish oil into everything? Absolutely not," Dr. Jenkins said.