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"I was not surprised at these findings because I assumed that there was no benefit of omega-3 supplements," said lead researcher Dr. Seung-Kwon Myung, chief of the carcinogenesis branch of the National Cancer Center, Republic of Korea.
The study is published online April 9 in the Archives of Internal Medicine.
Many studies have demonstrated that eating fatty fish two or more times a week is linked with a lower risk of death from cardiovascular disease.
However, studies that looked at the potential cardiovascular benefits of fish oil supplements have produced mixed results.
Myung and his colleagues selected 14 studies that had been published in the medical literature. In all, the studies looked at more than 20,000 patients who had a history of cardiovascular disease.
The patients' average age was 63. Nearly 80 percent were men. The studies were published between 1995 and 2010. The daily dose of omega-3 fatty acid supplement ranged from about half a gram to nearly 5 grams a day.
The follow-up period ranged from one year to nearly five years.
Myung's team looked to see if the supplements made a difference in sudden cardiac death, heart attack, congestive heart failure, death from any cause, stroke or transient ischemic attacks (often called TIAs or mini-strokes).
The supplements did not reduce the risk of any of those problems.
The researchers did find a small reduction in cardiovascular death risk. However, that benefit disappeared when the researchers excluded a study they felt had major scientific problems.
Two large studies published in the past reported a positive effect of supplements on cardiovascular health, Myung said. "But those trials did not use placebos [for comparison]," Myung explained
Dr. Gordon Tomaselli, president of the American Heart Association, said he, too, is not surprised by the findings.
"The bottom line is for the secondary prevention of cardiovascular disease it looks like we can say having oily fish two or three times a week is good but replacing that fish with supplements doesn't replace the beneficial effects," said Tomaselli, director of cardiology at Johns Hopkins University School of Medicine in Baltimore.
The American Heart Association recommends that those without known heart disease eat a variety of fish, preferably oily fish, at least twice a week. It advises those with heart disease to eat about 1 gram of the omega-3 fatty acids EPA and DHA a day.
In an editorial accompanying the study, Drs. Frank Hu and JoAnn Manson, from the Harvard School of Public Health, pointed out that a diet high in fatty fish could help people replace less healthy sources of protein, such as red meat.
For those who don't like fish, they suggest eating plant-derived omega-3 fatty acids from flaxseed, walnut, soybean and canola oils.
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