Previous research has found that eating oily fish such as tuna and salmon can reduce the risk of sudden cardiac death caused by a particular type of irregular heartbeat. This study suggests fish-oil supplements, rather than dietary fish oil, could be a therapy without side effects for heart patients.

The finding is from an analysis of data from the GISSI-Prevenzione trial. That study found that 1 gram daily of n-3 polyunsaturated fatty acids (PUFA) – found in fish oil and known also as omega-3 fatty acids – significantly reduced the risk of death overall and sudden death in people who had heart attacks.

The benefits were not due to changes in cholesterol levels or by reducing potentially fatal blood clotting.

The new analysis reveals that the lower mortality rate for the n-3 PUFA patients, compared with patients who got a placebo, resulted largely from a 42 percent reduction in sudden cardiac deaths at three months follow-up.

“That was a surprise,” says lead author Roberto Marchioli, M.D., head of the laboratory of clinical epidemiology of cardiovascular disease at Consorzio Mario Negri Sud, a research institute in Santa Maria Imbaro, Italy. “The risk of death, and sudden death, is higher in the first months after a heart attack. It is exactly in this period that the effect on sudden death was noted.”

The analysis also shows that the lifesaving benefit of n-3 PUFA is likely due to reducing episodes of potentially fatal irregular heartbeats, called arrhythmias. About 250,000 people in the United States die each year from coronary heart disease without reaching the hospital alive. Most of these deaths are probably due to sudden death caused by an arrhythmia.

“This study is important because there is no really effective therapy for arrhythmias,” says Alexander Leaf, M.D., professor of clinical medicine at Harvard Medical School in Boston, who wrote an accompanying editorial about the new findings.

The Italian researchers note that study participants ate a Mediterranean-style diet – high in fruits, vegetables, olive oil and fish. Yet, despite the same healthy diet, those who received the n-3 PUFA supplements had fewer sudden deaths than those who did not. N-3 PUFA are essential fatty acids – the body needs them to function properly but does not make them. Humans must obtain them through food, which in the case of n-3 PUFA means eating fish, such as salmon, tuna or mackerel.

In the GISSI-Prevenzione study, researchers enrolled 11,323 patients throughout Italy who had suffered recent heart attacks and randomized them into four groups.

In addition to standard medical treatment and lifestyle counseling for their condition, 2,835 participants received 1 gram of n-3 PUFA daily (equal to one fatty fish meal); 2,830 took 300 milligrams of vitamin E daily; another 2,830 took both; and 2,828 took a placebo.

In the new analysis, Marchioli and his colleagues found that at three months, patients treated with n-3 PUFA had significantly lower mortality than those not taking the supplements (1.1 percent vs. 1.6 percent). By the end of the trial at 42 months follow-up, mortality was 8.4 percent for those on n-3 PUFA and 9.8 percent for those not taking it.

The reduction of sudden cardiac death risk from n-3 PUFA treatment was nearly significant at 3 months (0.5 percent vs. 0.7 percent for those not on the supplement). By the study’s end at 42 months, the risk of sudden death was 2.0 percent for people taking n-3 PUFA, vs. 2.7 percent for those who did not.

“The mortality benefit was mainly due to a reduction in sudden death,” Marchioli says.

How n-3 PUFA protects the heart is unknown. However, Leaf and his colleagues have shown that the fatty acids play an important role in regulating the electrical activity of heart muscle cells. “They stabilize these cells so they are very resistant to arrhythmias,” he says.

Leaf also notes that these findings support a theory that an imbalance of n-3 PUFA and fatty acids called n-6 PUFA promote arrhythmias. He suggests that adding n-3 PUFA to an already healthy diet, while reducing n-6 PUFA (which are abundant in plant seed cooking oils – i.e. corn, safflower, sunflower seed oils), improved the ratios of the two types of fatty acids, therefore, decreasing the risk of sudden death.

Marchioli emphasizes that the study findings need to be confirmed.

The American Heart Association does not recommend fish oil supplements (capsules) and will not recommend then until there is compelling evidence that they benefit overall cardiovascular health.

Instead, the association recommends consuming two servings of fish twice a week. Fish are a good source of protein without the high saturated fat found in fatty meat products.

Co-authors are Federica Barzi, M.S.; Elena Bomba, M.D.; Carmine Chieffo, M.D.; Domenico Di Gregorio, M.D.; Rocco Di Mascio, M.D.; Maria Grazia Franzosi, M.D.; Enrico Geraci, M.D.; Giacomo Levantesi, M.D.; Aldo Pietro Maggioni, M.D.; Loredana Mantini, M.D.; Rosa Maria Marfisi, M.S.; G. Mastrogiuseppe, M.D.; Nicola Mininni, M.D.; Gian Luigi Nicolosi, M.D.; Massimo Santini, M.D.; Carlo Schweiger, M.D.; Luigi Tavazzi, M.D.; Gianni Tognoni, M.D.; Corrado Tucci, M.D.; and Franco Valagussa, M.D.

Note: If no author is given, the source is cited instead.

• Cholesterol
• Heart Disease
• Dietary Supplements and Minerals

• Fisheries
• Fish
• Invasive Species

• Oily fish
• Coronary heart disease
• Ischaemic heart disease
• Saturated fat
• Unsaturated fat
• Cardiac arrest