The British study made a bit of a splash in the press when it was published in March, 2006, as did another negative one appearing in the June 14, 2006, issue of the Journal of the American Medical Association. That study found that fish oil supplements, the most common supplement source of omega-3 fatty acids, didn't prevent abnormal heart rhythms in patients who had implanted defibrillators, devices that shock the heart into beating regularly when normal rhythm goes dangerously awry.
Both of these studies are interesting but really don't tell us much about what happens to healthy people who take fish oil preventively. It is no big surprise that fish oil might not overcome serious, established problems in patients with heart disease, as was the case in the JAMA study. The British study was a meta-analysis of several other studies of the effect of fish oil on heart disease, cancer, and stroke. The finding was that it didn't help, but here, too, the message is not as alarming as it sounds when trumpeted on the 11 o'clock news. Researchers commenting on it found fault with the way the study was designed. You have to put the recent findings in perspective and hold them up against broad evidence accumulated over many years showing that fish oils offer significant protection against heart disease, cancer and stroke.
I haven't seen any study findings impressive enough to warrant a change in my view of fish oil. I still take two grams a day, and I recommend fish oil (or another source of supplemental omega-3 fatty acids) for everyone. It seems to protect against heart disease by "thinning" the blood and reducing inflammation, which is the root cause of coronary artery disease. There is also good evidence that fish oil reduces the risk of cancer and enhances mood. It can relieve depression and other mental disorders, and has even been shown to reduce the rate of violence in prisons.
Try not to react to the headlines and sound bites that now seem to accompany every new medical study on subjects that resonate with the public. Truly valuable therapies and treatments tend to prove themselves out over time, so at least wait until all opinions are in before forming a judgment.
Andrew Weil, M.D.