Fish Oil and Prostate Cancer – A Whopper of a Tale

by | Jul 15, 2013 | Articles, Cancer, Conditions, Men's Health, Supplements

Headlines this week proclaim that taking fish oil supplements leads to an increased risk of prostate cancer.  “Very fishy”, I thought, since this contradicts volumes of published research that touts many health benefits of fish oil supplementation.  After a careful review of the study, I am left thinking, “please… really?”  This is a fish tale that would turn a minnow into Moby Dick.

The study titled “Serum Phospholipid Fatty Acids and Prostate Cancer Risk: Results From the SELECT Trial” was released in the July 10, 2013 issue of the Journal of the National Cancer Institute.  The authors, Kristal, Brasky, et al, found that a higher blood level of an omega-3 fatty acid, one found in fish oil, was associated with an increased risk of developing prostate cancer.

About Fatty Acids

First a necessary refresher on fatty acids…  There are two kinds of fatty acids the body can’t make, and thus it is essential they come dietary sources, which is why they are called “essential” fatty acids.  These two, the omega-3 and omega-6 fatty acids are both necessary for good health, but only when taken in balance with one another.

The omega-3 fatty acids, known as DHA and EPA, are found primarily in dark meat fish such as salmon or anchovies, or from precursors found in walnuts and flaxseed.  Fish oil is well established as having a strong anti-inflammatory effect and numerous studies confirm that higher omega-3 levels are associated with lower all cause mortality, lower deaths from sudden cardiac arrest and decreased markers of cellular aging.  Omega-3 fatty acids are precursors for important hormones, help control inflammation and immune function, and are normal components of healthy cell membranes.

Omega-6 fatty acids, on the other hand, particularly in excess, have been shown to promote inflammation, thicken blood and tighten blood vessels.  Linoleic acid (LA) is the main dietary source for omega-6 fatty acids and is found in seeds and nuts, and especially the vegetable oils made from them, such as soybean, palm and sunflower oils.  Poultry, grains, and some seeds and nuts are dietary sources of omega-6 fatty acids, but most of our dietary source in the American diet comes from snack foods, cookies, crackers, and sweets as well as many fast foods.  It is estimated that as much as 20% of daily calories in the American diet come from soybean oil alone.

Excess omega-6 fatty acids from the diet will convert to another inflammation causing fatty acid called Arachidonic Acid (AA), which further breaks down to the chemicals that actually cause the inflammation in the body, the prostaglandins, leukotrienes and thromboxanes.  Note that drugs such as Ibuprofen and Aspirin work to lower inflammation by blocking the various pathways that break down AA.  Excessive intake of the omega-6 fatty acids are linked to increased rates of inflammatory diseases such as arthritis, heart disease and cancer.

“Trans-fats” (TF) are abnormal fatty acids with unnatural bends in their molecular structure, thus the “trans” notation, and are found in artificial fats such as hydrogenated oils.  They also result from oils being heated to the point of bending and breaking their chemical chains.  TF are not naturally found in the body yet become embedded in cell walls and muck up cellular machinery throughout the body while causing inflammation.  TF are also common in processed and packaged foods.

The Devil is in the Details

Now back to the trial in question in which 2,227 men were selected after a 7-year period of time during which 834 men had developed prostate cancer and 1393 men had not.  Blood levels were obtained for omega-3 fatty acids including DHA and EPA, omega-6 fatty acids and TF.  All men in the study underwent prostate biopsies during or at the end of the study to prove the presence or absence of prostate cancer.

The results of the study were surprising in that the men with cancer had higher blood levels of omega-3 fatty acids, specifically DHA, while having lower levels of the inflammation causing TF and omega-6 fatty acids.  The men with the highest levels of omega-3 fatty acids were between 43% and 71% more likely to have prostate cancer depending upon the severity.  EPA levels did not correlate with cancer risk.

While this was technically a good study, there are numerous problems with reaching any sort of bold conclusion about whether or not fish oil supplementation causes prostate cancer.

First, the study results are an “association” which never proves causation.  The varying levels of fatty acids could be the result of cancer rather than the cause, or the different cancer rates could be due to common unmeasured toxins or heavy metals found in fish from contaminated water.

Second, the levels of fatty acids in general were much lower than those from other studies in which fish oil was actually given to patients, and supplementing fish oil was not even part of the SELECT study.  There is no indication that study participants took fish oil capsules or ate any certain amount of fish.

Third, there are plenty of studies in which subjects did supplement with fish oil and had either had no increased risk of prostate cancer or an actual decreased risk of prostate cancer (Terry, 2001; Leitzman, 2004; Mina, 2008; Szymanski, 2010).  Even the same authors just a few years ago reached the same conclusion showing “no correlation between fish oil consumption and the risk of prostate cancer” (Brasky, 2011).

The Whopper

“We’ve shown once again that use of nutritional supplements may be harmful,” said Dr. Alan Kristal, the paper’s senior author.  Wow… really?

This study, and the seriously flawed SELECT study from whence the data came, did not include any sort of documentation about fish oil supplementation and was not set up to even investigate this association.  The results are indeed interesting and merit further research to help sort out the relationship between fatty acids and cancer risk, however, to conclude from this study that fish oil supplementation causes prostate cancer, now that is a whopper.


Scott Rollins, MD, is Board Certified with the American Board of Family Practice and the American Board of Anti-Aging and Regenerative Medicine.  He specializes in bioidentical hormone replacement for men and women, thyroid and adrenal disorders, fibromyalgia and other complex medical conditions.  He is founder and medical director of the Integrative Medicine Center of Western Colorado ( and Bellezza Laser Aesthetics (   Call (970) 245-6911 for an appointment or more information.

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