Fish oil not as beneficial for the heart as thought: Study

By Dr. Ananya Mandal, MDApr 10 2012

There are millions who take fish oil supplements, hoping to keep their hearts healthy. A new study shows that the benefits may be questionable and especially questioned whether they can replace a healthy, balanced diet.

Fish oil, a combination of omega-3 fatty acids that has attracted much research on its effects on heart health. So far, the evidence has been inconclusive -- some studies have found fish oil has been major in preventing heart attacks, strokes and sudden cardiac death, while others have found fish oil has no benefits at all.

For this new study researchers from South Korea analyzed 14 clinical trials involving more than 20,000 patients with cardiovascular disease who had taken fish oil supplements for at least one year and found the supplements did not reduce their risk of having another heart attack, stroke, congestive heart failure or any other cardiovascular catastrophe. The study was published today in the Archives of Internal Medicine.

“There is no evidence that omega-3 supplementation is effective for secondary prevention of cardiovascular disease,” says Seung-Kwon Myung, M.D., a professor of family medicine at Seoul National University, in South Korea, and a co-author of the review.

The new review, known as a meta-analysis, is the first of its kind since 2009. 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.

“The fish oil story is still fishy,” said Dr. Robert Eckel, a professor at the University of Colorado School of Medicine and past president of the American Heart Association. According to the Nutrition Business Journal, over-the-counter fish oil supplements gathered in $739 million in 2009 alone, according to a report in Forbes magazine. Foods fortified with extra omega-3s, such as margarine and peanut butter, roped in nearly $4 billion for manufacturers in 2010, according to Packaged Facts. GlaxoSmithKline makes prescription fish oil, Lovaza, intended to treat people with high blood fats, called triglycerides. The prescription form delivers omega-3s at high does – about 1,000 mg. Over-the-counter fish oil supplements typically contain as little as 300 mg of two omega-3 fatty acids, EPA and DHA. “The question is, what do these relatively small doses of omega 3 fatty acids do? As this study shows they do nothing,” Eckel said.

Eckel added that there is no evidence showing that fish oil is harmful. But others say the possible heart benefits of fish oil should not be so quickly dismissed. In a commentary published with the study, Drs. Frank Hu, a professor of nutrition and epidemiology at the Harvard School of Public Health, and Jo Ann Manson, chief of preventive medicine at Brigham and Women's Hospital in Boston, said the authors excluded two large studies investigating omega-3 fatty acids that found beneficial effects of fish oil supplements.

Those studies would have swayed the analysis to show a protective effect of fish oil against cardiovascular disease, they wrote, and “the data should not simply be ignored in evaluating overall evidence.” Hu and Manson also suggest that fish oil may seem to have less benefit for patients because of the widespread use of cardiovascular medications, such as statins, beta-blockers and ACE inhibitors. In some of the studies showing that fish oil had few benefits for heart health, as many of 94 percent of the study participants were taking statins.

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.

“It is currently more difficult to show additional benefit when patients are treated aggressively with everything else,” said Dr. Chip Lavie, medical director of cardiac rehabilitation and prevention at the John Ochsner Heart and Vascular Institute in New Orleans. Lavie also noted that many of the trials evaluated in the analysis gave such small doses of fish oil to patients that it's not hard to understand why they got few benefits from the supplement. “The very best studies in my opinion still show some benefits,” he said.

The American Heart Association currently recommends that people get their dose of omega-3 fatty acids from eating two servings of fatty fish, such as salmon, mackeral, tuna, sardines, per week. For the fish-averse, a slightly different kind of omega-3 fatty acid can be found in flaxseed, walnuts soybeans and canola oils. Until the benefits of fish oil supplements can be confirmed or ruled out, heart patients and others trying to maintain a healthy heart should get their omega-3s directly from fatty fish such as salmon and tuna, Myung says. He recommends “at least two servings of fish per week” - but not supplements - to his own patients. “Supplements will never be a replacement for a healthy dietary pattern,” Manson said adding, “I think the evidence is strong enough to recommend at least two servings per week of fish, preferably the darker, fatty fish that are high in omega-3 fatty acids.”