Background: It is a given that fish oil is good for you, right? It is replete with omega-3 fatty acids, which are marketed to improve health in a number of areas. But now we have a surprising study showing that men with the highest levels of these substances (the type found in fish but not vegetable sources) appearing to increase the risk of prostate cancer. In fact, men with the very highest levels had a 1.7x increase in the risk of high-grade prostate cancer, the most aggressive form of the disease.
The authors had previously found that men who had the highest levels of one omega-3 fatty avid called DHA (docosahexaenoic acid) had double the risk of high-grade prostate cancer. Other studies found similarly.
The details: To try to confirm their earlier findings, the team examined data from a different prostate cancer trial called SELECT, or Selenium and Vitamin E Cancer Prevention Trial. That study showed more cases of prostate cancer among men who took vitamin E alone for about 5 years, when compared to placebo (non-active pill). The effect was even stronger when they looked at omega-3 fatty acids (the kind in fish (not vegetable) oils. In the current study, thise with the highest blood levels had a 1.7x increase risk in high-grade, aggressive prostate cancer (and an overall increase of 1.44x for prostate cancer overall).
My take: Fish oil supplements in very high doses may be dangerous, at least with respect to prostate cancer incidence. This study suggests that the use of this nutritional supplement may actually be harmful. What the study does not do is address the effects of fish oil among those who already have prostate cancer. In fact, some studies (not definitive in my view) hint that fish oil may be beneficial among men who already have the disease. Still, this study reminds us that we have to be judicious with supplements, and to follow the evidence.
The study also does not tell us whether we should eat fish only in moderation. The heavy metal mercury (which can be found in fatty fish) does not appear to be associated with prostate cancer. On the other hand, the difference between the group with the highest levels of omega-3s in their blood and those with e lowest translates to about what I would get eating a nice Pacific salmon twice a week. And fatty acids found in vegetable oils, flaxseeds, and other vegetable sources (including alpha-linoleic acid, or ALA) does not affect prostate cancer risk. Finally, recent studies have also shown that taking extra omega-3 has little effect on heart disease.
The small print: The material presented herein is informational only, and is not designed to provide specific guidance for an individual. Please check with a valued health care provider with any questions or concerns. As for me, I am a Harvard- , Yale- and UPenn-educated radiation oncologist, and I practice in the Seattle, WA (USA) area. I feel genuinely privileged to be able to share with you. If you enjoyed today’s offering, please consider clicking the follow button at the bottom of this page.
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