Omega-3 supplements may not help prevent heart attacks in patients who have survived a heart attack, a new study found.

In a study called ALPHA-OMEGA, Netherland researchers had 4,837 men and women who were being treated for heart disease consume 20 grams of Omega-3 enriched margarine spread on three to four slices of bread daily for three years. The participants, aged 60 to 80, were divided into four groups and given margarine supplemented with omega-3, margarine enriched with alpha-linolenic acid (ALA), margarine fortified with all three fatty acids, or a placebo.

No difference was shown in the chance of experiencing another cardiac event between the heart attack survivors who took higher intake of omega-3s and those who did get added omega-3s, according to the study published online by the New England Journal of Medicine.

Omega-3 fatty acid-enriched margarines "had no effect on the rate of major cardiovascular events," said researcher Daan Kromhout, PhD, MPH, of Wageningen University in the Netherlands.

Kromhout says that one possible explanation for the findings is that "the patients in this trial were very well treated," with about 85% of the volunteers taking statins to lower their cholesterol and many receiving clinical care and other medications to control their blood pressure. Since the patients were already at relatively low risk for death or another heart attack, the benefits of omega-3 fats may not have been significant and difficult to prove.

Omega-3, found in fatty fish such as salmon, herring and tuna, can lower triglyceride levels, reduce the risk of abnormal heartbeats, and slow the growth of atherosclerotic plaques. Many foods are fortified with the beneficial fat including margarine, peanut butter and cheese.

The current recommendations by the American Heart Association advice most adults to consume two meals of fatty fish each week, an average of 400 mg to 500 mg of omega-3s in the diet per day. For people with heart disease, the recommendation is to double that amount.

Diabetes and those who are at increased risk of heart disease but are not receiving proper treatment may experience significant benefit from the added fats, said Kromhout. Diabetic patients in the study who ate margarine with omega-3 fats had about 50 percent fewer heart deaths and abnormal heart rhythms.

Heart experts say the best way to get omega-3s is from dietary sources. Studies have yet to prove that supplements, in the form of fish-oil capsules, can definitely lower the risk of heart disease.