July 18, 2013

Fish Oil & Prostate Cancer

Articles by Dr. Erdman are for informational purposes, and are not to be taken as specific medical advice.

On July 10th, the headline read, “Men Might Want to Shun Fish oils, Study Shows.” This new study from the Fred Hutchinson Cancer Research Center supposedly shows a link between increased EPA/DHA levels in the blood and prostate cancer risk. Given all the positive health effects linked to fish oil intake, this study definitely seems out of step with previously shown benefits.

As I have said before, always try to find out more about who did the study, how it was performed and if it has been repeated by others. I am no expert in these activities, but I have found a great article written by an expert, Dr. Michael Murray. He is a leading authority on natural medicine, and has written over 30 books on health and nutrition. Much of the following information is attributed to this article: “How a SELECTed Bad Study Became Big News,” written on July 12, 2013, and published online at GreenMedinfo.com.

Dr. Murray says the pedigree of this study is impressive. It was published in the Journal of the National Cancer Institute and was conducted by researchers at the Fred Hutchinson Cancer Center in Seattle, WA. Yet, the data used is from the much maligned Selenium and Vitamin # Cancer Prevention Trial, or SELECT. That is the problem.

The SELECT study was a large clinical study that attempted to determine whether vitamin E could prevent prostate cancer. This study was, again, out of step with other studies showing positive prostate cancer reduction with vitamin E, in that it showed a 17% increase in prostate cancer in men who took vitamin E. That is just not shown in any other study.

Dr. Anthony Victor D’Amico, MD, who has a doctorate from MIT, says this: “The study really cannot make the conclusion that it’s trying to, because these types of studies are not cause and effect; that is, if you take fish oil you’re going to get an aggressive or some kind of prostate cancer.”

A study such as this, where they review and measure only blood samples taken and analyzed without removing other known predicators of prostate cancer; and where they have no knowledge of whether or not these men ever took fish oil or ate fish, draws a weak correlation, at best.

Dr. Murray brings up multiple important considerations about this study. First, it is not consistent with other studies showing the positive benefits of fish oil. This study did not include information or documentation of fish or fish oil intake in the study group. This study was not initially set up to evaluate these factors, hence its relevance is not as significant as studies designed to specifically determine the impact of omega 3 fatty acids on prostate cancer risk.

Again in this study there is no evidence that anybody in this study took fish oil supplements or even ate fish. They only measured plasma levels EPA/DHA, not how they got there. In usual circumstances, plasma levels of EPA/DHA reflect very recent intake and are a poor marker of long term omega 3 intake. Maybe those who showed prostate cancer recently increased their intake of omega 3’s to help them recover from it.
Without a dietary history, a racial breakdown, and other known prostate cancer risk factors being accounted for, there is no way of knowing that these findings are more than mere association, not cause and effect, as these authors are trying to intimate.

So, what do we know about fish oil and prostate cancer from other studies actually done to measure this link? A meta-analysis of all previously conducted studies shows some better conclusions for fish oil and prostate cancer. A 30 year study of 6,272 Swedish men showed those who ate NO fish had a two to three fold increase risk of prostate cancer. Another study, of 22 years, found that fish consumption greater than five times per week reduced the risk of dying from prostate cancer by 36%. A 12 year Harvard study involving 47,882 men showed that for every 500mg of marine fat ingested per week, there was a decrease of risk of developing metastatic prostate by 24%. And finally, a study of 47,866 men with no history of cancer initially, aged 40-75, followed over 14 years, showed those with the highest intake of EPA/DHA, had a 26% reduced risk of prostate cancer.

Based on the facts presented, do not quit taking fish oil. All fish oil is not created equally. This is one supplement that you must ensure purity and quality, or it is actually bad for you to take. Make sure it is excellent quality; fresh, not rancid (80% on superstore shelves are!); and not contaminated with unwanted things like heavy metals and pesticides. Cheap fish oil is usually not good fish oil! 1,000mg daily, for men, is recommended, If you are trying to treat one of the 60 ailments fish oil has been proven to help, you should consume at least 3,000mg daily.