A 40-month study of more than 4,800 heart patients showed taking low doses of omega-3 fatty acids in margarine did not significantly reduce rates of serious heart attacks and other cardiovascular events.
The finding raised questions about the benefits of omega-3, which has been shown in previous studies to make for healthier hearts.
The margarines used in the study were developed for the researchers by food and consumer goods giant Unilever.
Doctors, however, are unlikely to rush to change clinical practice. Many already prescribe omega-3 fish oil capsules to reduce triglycerides, a type of blood fat linked to clogged arteries.
To investigate, researchers randomly assigned use of one of four margarines on bread instead of their regular spread - one containing no extra omega-3 fatty acids; one with 400 milligrams a day of extra eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA); one with 2 grams of alpha-linolenic acid (ALA); and one with a combination of EPA-DHA and ALA.
All the men and women in the study were between 60 and 80 years old and had suffered a heart attack roughly four years previously.
While no overwhelming protective effect was seen for the omega-3 enriched margarines, there was a reduction in repeat heart attacks and other cardiovascular events in women who took ALA margarine, although this was not statistically significant. Diabetes patients also showed a possible benefit.
Researchers note that the results indicate that more investigation is required into the efficacy of omega-3 enriched margarines.
The results of the study, which was supported by the Netherlands Heart Foundation, the National Institutes of Health, and Unilever, were also published in the New England Journal of Medicine.
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