by Dr. Bill Rawls
Last Updated 10/31/16
Does fish oil really cause cancer? Over the past few weeks, the news media has been saturated with reports that omega-3 fatty acids increase the risk of prostate cancer. This is very contrary to current information suggesting that consumption of omega-3 fatty acids (from dietary sources and supplements) decreases risk of cardiovascular disease, cancer and virtually all chronic diseases.
As often happens, any clinical study that is contrary to the norm generates a flurry of sensational articles in the news media; this typically results in very broad (and sometimes inappropriate) scientific conclusions derived from a limited amount of information. As a longtime practicing physician with expertise in natural medicine, I know that while science can be very valuable, it comes with its own set of limitations.
The study cited, “Plasma Phospholipid Fatty Acids and Prostate Cancer Risk,” was published in the Journal of the National Cancer Institute in July of 2013 (Theodore M. Brask, PhD., et. al.). In the study, 834 patients with prostate cancer were compared with 1,393 male controls without prostate cancer. A single blood sample of fatty acids was taken from each cancer patient and compared with that of a random control. The result? Patients with high and low grade prostate cancer were found to have slightly (but significantly) increased blood levels of omega-3 fatty acids from marine sources (EPA, DHA) when compared to controls. This finding did not, however, define cause. The author’s conclusion that consumption of omega-3 fatty acids increases risk of prostate cancer is purely speculative.
So, before you throw out your fish oil supplements and remove salmon from your diet, consider a few important facts. First, the only information provided about the participants were height and weight, Prostate Specific Antigen levels (screening test for prostate cancer), incidence of diabetes, and family health history. There is no mention of whether patients were taking fish oil supplements or how often they were eating fish; in fact, there is no dietary history mentioned at all. For those of us who consider diet to be a critical variable in defining cancer risk, this seems to be a significant oversight on the part of those conducting the study. Considering most of the study participants lived in the United States, we can assume they were following a high-fat, high-carb processed foods diet–a fact that could dramatically skew the results.
Additionally, this study stands in stark contrast to studies of people groups who eat lots of oily fish. There are three populations to take note of; the Japanese, Okinawans and Inuit people consume the highest concentrations of oily fish in the world and also boast very low rates of cardiovascular disease, breast cancer and prostate cancer. The elderly Okinawan population is a particularly well studied group. Okinawan elders consume large amounts of vegetables and beans (including high concentrations of fermented soy), oily fish rich in omega-3 fatty acids several times per week, minimal meat and dairy, and virtually no processed food. They have the lowest incidence of prostate cancer in the world; their rate is 80% lower than the average rate of prostate cancer in North America! (The Okinawan Program, Willcox, Willcox and Suzuki, 2001)
For me, this omega-3 and prostate cancer study raises more questions than it provides answers. There are hundreds and possibly thousands of studies linking omega-3 fatty acid consumption (both dietary and supplements) with reduction of cardiovascular risk and overall chronic disease risk. One contrary study may not be enough to change recommendations, though all information is important and we should continue to study this topic. I do feel very strongly, however, that if you are going to eat oily fish or take fish oil supplements, you should accompany it with a healthful diet and active lifestyle!
Note: Even the best of clinical studies are limited because all variables can never be completely controlled, and the conclusions found in any study are very dependent on the questions asked. Conclusions should be based on all information available and not on one single clinical study.