Memo to adults with heart disease: If you're already eating a fair amount of fish and taking omega-3 fatty acid supplements, the extra boost may not be doing much to help your heart.
New research suggests that only patients with very low daily intake of certain omega-3 fatty acids, found in fish and some plants and nuts, are likely to reduce their risk of heart attacks or death if they take more supplements rich in these fatty acids.
The study supports research which has shown that, after a certain point, omega-3 supplements may not do much for the heart. It also comes as a new U.S. Government Accountability Office urged more authority for the Food and Drug Administration to inspect the quality and safety of supplements, whose manufacturers often make claims not supported by data.
"Based on data from this and previous studies also in other countries, we think that it is relevant to say that most cardiac patients who are well medically treated and eat at least a certain amount of fish per week, probably will not benefit from taking omega-3 supplements," Mari Manger, the study's lead author and a PhD candidate at University of Bergen in Norway, told Reuters Health by e-mail.
The study, published in the American Journal of Clinical Nutrition, followed more than 2,400 Norwegians, about 80 percent of them men, being treated for heart disease. All were on cholesterol-lowering drugs.
At the beginning of the study, all patients filled out a questionnaire about their eating habits, including the fish products and supplements such as cod liver oil that they had eaten over the past year. From this, the authors calculated how much of three different kinds of omega-3 fatty acids thought to be associated with heart health the subjects were getting in their diets and supplements.
The authors then tracked the patients for an average of almost 5 years for heart-related complications, including heart attacks and death. Except for patients who consumed the lowest levels of omega-3s, there was no relationship between how much a person consumed and whether they suffered a heart attack or other complication.
Only two percent of patients in the study consumed levels of two kinds of omega-3s below the recommended level.
Eating more fish and taking more supplements didn't prevent heart problems, although high levels of omega-3s didn't hurt the patients either.
These results may be atypical, said Dr. Alice Lichtenstein, a nutritional scientist at Tufts University, because the Norwegian diet differs from that of, say, Americans, who rarely consume fish oil. "This study doesn't refute current recommendations for individuals to consume more fish," Lichtenstein, who was not involved with the study, told Reuters Health.
"The current data indicates that there's probably a threshold" of benefits for omega-3s, "and that's why the recommendation (from the American Heart Association) is two fish meals a week."