Fish Oils and Prostate Cancer: Unraveling the Confusion

In early July of this year, the Journal of the National Cancer Institute published a study suggesting that omega-3 fatty acids increase the risk of aggressive prostate cancer by 70%.¹

This report quickly caused panic among millions of Americans who were convinced of the findings. The study also raised concern among hundreds of my own patients who regularly consume omega-3 fatty acids from fish oils in an attempt to reduce their risk of a various diseases, including cancer.

Furthermore, before any accredited authority figure had the opportunity to critically read and interpret the study, the media ran with it and published a number of unwarranted headlines, including:

“Fish oil may raise prostate cancer risk, study confirms”–NBC News

“Taking omega 3 supplements may increase the risk of prostate cancer”–Daily Mail

“Men might want to shun fish oils, study shows”–Seattle TimesDecoding the Study
The study revealed that the highest blood plasma levels of omega-3 fatty acids, particularly EPA, DHA, and DPA, were associated with the highest risk of advanced prostate cancer. The research also disclosed that higher levels of linoleic acid (or omega-6 fatty acids), which is typical in the American diet and potentially harmful, were associated with a lowered prostate cancer risk. The conclusion of the Brasky et al finding therefore suggests that the more fish or fish oil consumed, the greater the chance of developing prostate cancer, whereas more omega-6 consumption would reduce overall risk.

The data from this retrospective study were collected from the 2011 SELECT (Selenium and Vitamin E Cancer Prevention Trial), which was not designed to evaluate the effects of fish oils on prostate cancer. These researchers studied the plasma of the subjects after one blood draw from the initiation of the study, but plasma levels of EPA and DHA are poor biomarkers of long-term omega-3 intake. Red blood cell levels provide a much more accurate assessment of long-term fatty acid intake.

Another major flaw with this study is that there are other risk factors associated with prostate cancer that were not accounted for, including body mass index (BMI), lifestyle factors, and family history. Did the participants studied have high BMI? Did they have a disproportionate waist to hip ratio? Were they smokers? Did they have a strong family history of prostate cancer?

Even further, the researchers did not address whether the men who were studied obtained their omega-3 fatty acids from consuming fatty fish, taking supplements, or another source. In other words, there is no cause and effect in this study but merely a correlation. This would be like looking at whether most men with advanced prostate cancer drove black cars when going for their blood draw and analyzing whether fish oils cause prostate cancer or the fact that they drove black cars.

What Fish Oil/Prostate Cancer Studies Do Show
There are currently a number of well-designed studies showing the benefits of fish oils against prostate cancer:

• One study followed 6272 Swedish men over 30 years and assessed them based on their fish intake. Those who ate no fish had a 2- to 3-fold increase in the risk of developing prostate cancer compared with those who consumed large amounts of fish in their diet.²

• A prospective cohort study based on the Physician’s Health Study found that fish consumption (5 or more times per week) was not related to prostate cancer risk but was protective of prostate cancer–specific death.³

• Other studies have suggested a lowered prostate cancer risk associated with a higher intake of omega-3 fatty acids from fish in Swedish men and in Japanese and Brazilian men.

• One report from the Health Professionals Follow-up Study followed 47,882 men over 12 years and identified 2483 cases of prostate cancer within the study group. Of these, 617 were advanced and 278 were metastatic. Eating fish more than 3 times per week reduced the risk of prostate cancer but had an even greater impact on the risk of metastatic prostate cancer. For each additional 500 mg of marine fat consumed, the risk of metastatic disease decreased by 24%!⁴

• In a meta-analysis, Szymanski and his research team found a significant (63%) reduction in prostate cancer–specific mortality in those who consumed fish but found no link between eating high amounts of fish and the risk of developing prostate cancer.⁵Conclusions
When it comes to subjects as critical as these, it is absolutely vital to acknowledge trusted sources and avoid being misguided by faulty research and sensationalized headlines. Researchers should continue to study the role of omega-3 fatty acids in relation to prostate health. It is counterproductive, however, when reporters make assertions like those we have seen in the press lately, given that their results are in stark contrast to those of previous prospective studies.

The one positive outcome of these reports is that it will likely stimulate more research into the role of omega-3 fatty acids in relation to prostate health. On the converse side, the inaccurate and negative reports may lead to many men abandoning the use of fish oil supplements.

However, a great deal of clinical data prove the benefits of men consuming 1000 mg of EPA+DHA daily for general health. Those suffering from 1 of the more than 60 health conditions shown to be benefited by fish oil supplementation should increase their dosage to 3000 mg of EPA+DHA daily.

Lastly, a poor diet-even with the consumption of fish or fish oils-is still a poor diet and will likely not be protective. We know that a whole foods–based diet, rich in fresh, nutrient-dense fruits and vegetables, healthy fats, and lean protein, does make a positive difference in health outcomes.

References
1. Brasky TM, Darke AK, Song X, et al. Plasma phospholipid fatty acids and prostate cancer risk in the SELECT Trial. J National Cancer Inst Online. July 10, 2013. doi:10.1093/jnci/djt174.
2. Terry P, Lichtenstein P, Feychting M, et al. Fatty fish consumption and risk of prostate cancer. Lancet. 2001;357:1764-1766.
3. Chavarro JE, Stampfer MJ, Hall MN, et al. A 22-y prospective study of fish intake in relation to prostate cancer incidence and mortality. Am J Clin Nutr. 2008;88:1297-1303.
4. Augustsson K, Michaud DS, Rimm EB, et al. A prospective study of intake of fish and marine fatty acids and prostate cancer. Cancer Epidemiol Biomarkers Prev. 2003;12:64-67.
5. Szymanski KM, Wheeler DC, Mucci LA. Fish consumption and prostate cancer risk: a review and meta-analysis. Am J Clin Nutr. 2010;92:1223-1233.