Statement on Recent Report of Link Between Fish Oil and Prostate Cancer

Science Editor Richard A. Passwater, Ph.D.

 

A recent on-line journal article that incorrectly associates Fish Oil intake with increased prostate risk received widespread, non-peer-reviewed media coverage that could result in harming the health of millions of persons who may discontinue their omega-3 supplementation. (Brasky, T. M., Darke, A. K., Song, X., et a., Plasma Phospholipid Fatty Acids and Prostate Cancer Risk in the SELECT Trial. JNCI J Natl Cancer Inst (2013)  doi: 10.1093/jnci/djt174; First published online: July 10, 2013) The best that can be said of this article is that it is another example of “junk science.”

I question how this article was considered worthy of publication by the journal. As a result, I have conferred with my co-author and fish oil pioneer, Dr. Jørn Dyerberg and leading omega-3 researcher, Dr. Bill Harris. (The Missing Wellness Factors—EPA and DHA. Basic Health Publications, Inc. 20122) We see several issues in the article that raise questions to the authors’ results and their interpretation, but it any event this article must be taken into the context of the existing body of science that either shows no such effect or a protective effect of fish oil against prostate cancer.

The authors fail to deal in details with the results from the literature. Interestingly, this same team reported in 2010 that the use of fish oil supplements was not associated with any increased risk for prostate cancer. A 2010 meta-analysis of fish consumption and prostate cancer reported a reduction in late stage or fatal cancer among cohort studies, but no overall relationship between prostate cancer and fish intake. In 2001, a study found higher fish intake was associated with lower risk for prostate cancer incidence and death. In 2004, EPA and DHA intakes were found to reduce the risk of total and advanced prostate cancer in a cohort of 47,866 US men aged 40-75 years with no cancer history and followed for 14 y. In contrast to increased dietary intakes of ALA that may that increase the risk of advanced prostate cancer. The same group studying the same cohort had in 2003 found that each additional daily intake of 0.5 g of marine fatty acid from food was associated with a 24% decreased risk of metastatic cancer. Higher intakes of canned, preserved fish have been reported to be associated with reduced risk for prostate cancer. It has been reported that a higher omega-3 fatty acid intake predicted better survival for men who already had prostate cancer. Increased fish intake was associated with a 63% reduction in risk for aggressive prostate cancer in a case-control study. 

So there is actually considerable evidence favoring an increase in fish intake for prostate cancer risk reduction! I will discuss these findings and others in upcoming interviews with Dr. Jørn Dyerberg and Bill Harris.

Another issue not dealt with in the paper is comparing prostate cancer rates in countries with high and low fish intake and consequently high and low intake of marine omega-3 fatty acids, e.g. Japan versus the US. If the findings were true, then prostate cancer would be rampant in any country with high seafood consumption (Japan, Greenland etc.) and conversely, low level consumption should be protective. Clearly this is not the case. The Japanese typically eat about 8 times more omega-3 fatty acids than Americans do and their blood omega-3 fatty acid levels are twice as high, their prostate cancer risk would be much higher if the papers risk calculations were true, but the opposite is obviously the case.

In a paper entitled “Inuit are protected against prostate cancer,“ researchers concluded from autopsy findings in Greenland Inuits that “Our results suggest that in situ carcinoma is rare among Inuit and that their traditional diet, which is rich in omega-3 polyunsaturated fatty acids and selenium, may be an important protective factor.”

 As to the new report itself, we found it disconcerting that the reported EPA+DHA level in the plasma phospholipids in the study was 3.62% in the no-cancer control group, 3.66% in the total cancer group, 3.67% in the low grade cancer group, and 3.74% in the high-grade cancer group. These differences between cases and controls are very small, being within the normal variation. The lowest quartile would correspond to an omega-3 Index of <3.2 % and the highest to an Index of >4.8 %. These values are obviously low. So to conclude that regular consumption of 2 oily fish meals a week or taking fish oil supplements, both of which would result in an Omega-3 Index above the observed range, would increase risk for prostate cancer is extrapolating beyond the data.

We also question why they did not control for the correct risk factors to correct for bias. And, we ask, why did the authors of the study not report how long cancer patients had the blood levels of EPA + DHA reported in the study. Did they start eating more fish or begin taking fish oil supplements after they learned they had cancer?

Drs. Dyerberg, Harris and I will discuss these concerns and others and try to bring perspective to the role of EPA and DHA in upcoming columns.