Omega-3 Fish Oil: Separating Fact From Fiction

JoAnn E. Manson, MD, DrPH


April 20, 2012

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Hello, this is Dr. JoAnn Manson, Professor of Medicine at Brigham and Women's Hospital and Harvard Medical School. I would like to talk with you today about the marine omega-3 fatty acids (fish oil) and prevention of cardiovascular disease, separating fact from fiction.

Another dietary supplement is in the news recently, and it seems to be another flip-flop message where conventional wisdom is being overturned by randomized clinical trials. The study was published in the Archives of Internal Medicine [1]recently, a meta-analysis of 14 randomized trials conducted by the Korean Meta-analysis Study Group, reaching the conclusion that omega-3 supplements do not prevent cardiovascular disease.

Several points should be kept in mind. First, all of these randomized trials were secondary prevention trials. These were high-risk participants. Also, many of these trials were short-term, with an average duration of only 2 years. Some of the trials were as short as 1 year. A wide range of doses was tested -- as little as 400 mg in some trials -- with an average dose of 1.7 g daily. [Editor's note: Dr. Manson made these observations in a commentary on the study, also published in Archives of Internal Medicine.[2]]

But most important, because all of these trials were secondary-prevention high-risk studies, many of the participants were taking other medications, such as statins, aspirin, angiotensin-converting enzyme (ACE) inhibitors, beta-blockers, and medications that may have interfered with the ability to detect a moderate benefit from omega-3s. This is why it is particularly important that randomized trials of omega-3s be done in primary-prevention trials, with average-risk populations. Such trials have not yet been published. Our research group is conducting a primary-prevention trial (the vitamin D and omega-3 trial) in a usual-risk population.

While waiting for the results from these additional primary-prevention trials, what can clinicians do? It is still important to recommend regular consumption of fish for our patients. The American Heart Association recommends at least 2 servings per week of fish, and it is best to recommend the dark, fatty fish that are high in EPA/DHA such as salmon, mackerel, tuna, herring, and sardines. A diet that is high in fish has been linked to a reduced risk for cardiovascular disease in many observational studies.

Furthermore, the fish would replace less healthful sources of protein, such as red meat or processed meats high in saturated fats. For patients who don't eat fish (eg, vegetarians and vegans), it would be worthwhile to recommend increased intake of alpha-linolenic acid (ALA) or plant-derived sources of omega-3, such as flaxseed, canola, and soybean oil.

Overall we should still be recommending a diet that is high in fish. The omega-3s still have a role in the treatment of high triglyceride levels, including the prescription omega-3s. This specific issue was not addressed by these trials. At the present time, there isn't conclusive evidence that recommending fish oil supplements will prevent cardiovascular events. Stay tuned for additional research.

Thank you very much for your attention. This is JoAnn Manson.


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