Does Fish Oil Cause Prostate Cancer?
As seen on all major media outlets this week, an article published in the July 2013 issue of the Journal of the National Cancer Institute suggests there is an association between elevated plasma omega-3 fatty acid levels and a heightened risk of prostate cancer.
These results are shocking and very against what we know as the benefits of omega-3 oils. Therefore study must be interpreted with a significant degree of caution for a variety of reasons:
- The data came from what is referred to as a retrospective, nested, case-control study. The data was extracted from another, much larger, previously conducted trial that was not originally intended to examine the relationship between omega-3 fatty acid levels and prostate cancer. In other words, the original study was not designed to determine any of the conclusions reached in the analysis contained in the article.
- The study’s results conflict with the results from other studies that do suggest that omega-3 fatty acids offer a protective benefit against prostate cancer; and these other studies were, in fact, designed to analyze that very outcome. See link: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3629172/
- Identifying one particular physiologic marker in a group of individuals with a given condition – in this case, an elevated omega-3 level in men with prostate cancer – does not prove causation, especially when that marker can be influenced by a variety of factors such as diet or behavior and is only measured at a single point in time.
- It is also hugely important to realize that the authors of this study did not assess any of the participants’ dietary intake of fatty fish or omega-3 nutritional supplements – the study’s conclusions are based wholly on the results of a single blood test of their omega 3 levels. Therefore we cannot conclude that it is supplements which are the cause.
- The omega-3 index, which measures both EPA and DHA within red blood cells, is a much more accurate indicator of long-term omega-3 intake and tissue status than is the plasma omega-3 level, which is subject to significant day-to-day variability.
- A number of confounding risk factors might have influenced the purported outcomes in the study, despite attempts by the investigators to account for them:
- 53 percent of the subjects with prostate cancer were smokers.
- 64 percent of the cancer subjects regularly consumed alcohol.
- 30 percent of the cancer subjects had at least one first-degree relative with prostate cancer.
- 80 percent of the cancer subjects were overweight or obese.
- Considering the extensive body of literature that supports the anti-inflammatory effects of omega-3 fatty acids, there is no credible biological mechanism, nor is one suggested in the article, that would explain why these essential fatty acids might increase tumorigenesis.
Summary: Given the inconsistent data attributable to omega-3 fatty acids and prostate cancer, and acknowledging the broad range of health benefits that are almost universally accorded to omega-3 fatty acid consumption, it would be premature to stop eating fish or to discontinue taking omega-3 nutritional supplements on the basis of this study.
Thanks to Dr. Robert Roundtree, MD for compiling these bullet points and sharing them so we can better educate our patients on the reporting of science in the media.
In Good Health,
Dr. Kim Bruno