It was a rough week for fish oil supplements. An article in the New York Times reported on research indicating that fish oil supplements do not reduce the risk of heart attack or stroke in people with a history of heart disease, or in people with risk factors for heart disease. Meanwhile, a new study came out speculating that fish oil may reduce the effectiveness of chemotherapy. Yet, as a whole, the body of research on fish oil is more complicated than either the New York Times article or the new study suggest, and includes some compelling evidence on the benefits of fish oil:

• A 2012 meta-analysis of 20 studies, published in JAMA, concluded that fish oil supplements reduced all-cause mortality by 4% and cardiac death by 9%, although the decreases were not statistically significant.
• However, a subpopulation of patients within the meta-analysis, consisting of over 11,000 people with a recent heart attack who were taking fish oil supplements, had a 20% lower risk of all-cause mortality and a 30% lower risk of cardiovascular death, compared to the placebo group.
• While the meta-analysis did not find statistically significant differences between the placebo and fish oil groups, it may have included flawed studies that skewed the results. For example, the meta-analysis included a very large study that enrolled over 18,000 men and women in Japan: this study did not find a strong effect for fish oil on heart health. Yet, because Japanese consumption of seafood is so high to begin with, it was unlikely that the addition of fish oil supplements would improve heart health considerably.
• Further, as the New York Times article points out, much of the recent research has involved high-risk populations. These populations may have had health that was declining too rapidly for fish oil to make a considerable difference, as opposed to generally healthy populations who may have seen a preventative effect from taking fish oil.
• For cardiovascular problems, such as high cholesterol, doctors often prescribe statin drugs. Yet statins, like fish oil, are anti-inflammatory. Therefore, taking statins and fish oil at the same time may leave little room for fish oil to have a noticeable anti-inflammatory effect.
• As for side-effects, the New York Times article reports anecdotal evidence that fish oil may increase bleeding when used with aspirin. However, there has been no research demonstrating a clinically significant increase in bleeding risk associated with the use of aspirin and fish oil in combination, as compared with aspirin alone.
• Finally, the new study on fish oil and chemotherapy only measured increases of certain types of fats in healthy volunteers taking fish oil. In some animal studies, those fats interfered with chemotherapy. Nevertheless, the new study did not directly investigate whether, fish oil actually reduced the effectiveness of chemotherapy in humans. While there may be a possibility that fish oil could interfere with certain chemotherapy drugs, more research is needed to support this conclusion. In addition, some studies have shown that fish oil may have some benefits for cancer patients, such as helping to slow weight loss.

The bottom line? Despite receiving some negative press, fish oil supplements may offer some important benefits, with only limited side-effects confirmed to date. In particular, the bulk of the evidence suggests that fish oil can improve heart health in people who are not regular fish eaters and who are not taking statin drugs. Studies have also shown that fish oil may help with a wide range of other health issues, including some dermatological, gastrointestinal, neurological, and psychiatric conditions. Of course, always consult a healthcare professional before taking a supplement.

Source: New York Times and JAMA Oncology