Fact or Fiction

The popular press has distributed several articles stating that Omega 3 fish oil consumption was related to an increase in the incidence of prostate cancer and that the prostate cancers were more aggressive. The two articles most frequently referenced are the May 9, 2013 issue of The New England Journal and the July 12, 2013 Journal of the National Cancer Institute. A critical review and analysis of these two articles follows.


This study enrolled 12,513 patients with 6,244 patients randomly assigned to n-3 fatty acids and 6,269 to placebo. The initial plan for endpoint of the study was the “rate of death, nonfatal heart attack and nonfatal stroke”. At one year the primary end point was revised to “time of death from cardiovascular causes or admission to the hospital for cardiovascular causes”.

At a follow up of 5 years the primary endpoint occurred in 1,478 patients of whom 733 (11.7%) had received n-3 fatty acids and 745 (11.9%) had received placebo (no statistical difference).

The conclusion was that “In a large general-practice cohort of patients with multiple cardiovascular risk factors, daily treatment with n-3 fatty acids did not reduce cardiovascular mortality and morbidity”

There were 490 cases of cancer (the type of cancer was not specified) among patients who received n-3 fatty acids (7.9% of patients) versus 453 cases of cancer in the placebo arm (7.2%). The difference was not statistically significant.


  • The placebo was olive oil. But olive oil may have a positive effect on mortality and morbidity (cardiovascular events).
  • The type of cancer was not specified and the difference in the two groups was not significant.


Without a true placebo the conclusions of the authors are questioned.

The incidence of increased cancer risk in this group has a value that is not statistically significant, regardless of the site of the primary cancer.

The use of olive oil in the placebo arm has the potential of favorably affecting the incidence of cardiovascular events. The benefits of the Mediterranean diet are well known. Thus, the claims from the popular press are significantly flawed.


Do not be concerned about this studies’ recommendation about the lack of efficacy of Omega 3 fish oil. The American Heart Association and American College of Cardiology recommendations about the benefits of Omega 3 fish oil are on record. Talk to your internist or cardiologist if you have any questions.

Do not be concerned about Omega 3 and cancer risk. This article has no valid data to support discontinuation of Omega 3 due to an alleged increased risk of cancer.




This study was part of the SELECT trial (Selenium & Vitamin E Cancer Prevention Trial). An observation that vitamin E and selenium may decrease the incidence of prostate cancer led to this trial. In this study 35,534 patients were enrolled and randomized to take vitamin E or selenium alone, a combination of vitamin E and selenium, or a placebo. The initial data from this trial reported in 2008 showed that Vitamin E and selenium taken alone or together did not prevent or decrease the risk of developing prostate cancer. The 2011 update showed that there was a 17% increase in prostate cancer in those patients taking Vitamin E compared to placebo. The study is closed but follow up continues.

After publication of initial and updated results, another study looked at this population with regard to the incidence of prostate cancer and omega 3. Their conclusion was that there was an increased incidence of prostate cancer in those patients who had the highest level of omega 3 in their blood samples.


First, this was a “post hoc” study which means that after the study to evaluate the effect of vitamin E on the incidence of prostate cancer was completed, the patient group was evaluated for another potential relationship or conclusion—the study was NOT designed to look at this post hoc potential effect. In this case the group was studied for a potential relationship between omega 3 levels (NOT OMEGA 3 INTAKE) and prostate cancer.

The study which evaluated omega 3 levels found that there was a significantly higher incidence of prostate cancer in the group of men with the highest levels of omega 3 in their blood samples. Note again that this second study looked at the original population which was not chosen or evaluated for dietary or supplement intake.


“This was a large, well designed study...However, it cannot show that fish oil supplements cause prostate cancer and it is possible that other factors affected men’s risk (although the researchers tried to take these into account)”.

- Quote from an article in the Journal of the American Medical Association

“The research did not look at the participants’ diets or whether they took omega 3 supplements. They based their conclusions on omega 3 blood levels”.

- Quote from an article in the Journal of the American Medical Association

“Don’t stop taking omega-3 fatty acid fish oils for fear of increasing the risk of prostate cancer. The JNCI article was flawed, and other research suggests that omega-3 fatty acid fish oils may actually play a protective role in prostate cancer prevention”.

- Quote from a Time Magazine synopsis quoting the Journal of the National Cancer Institute:


  • There is no reliable study to date that proves that omega 3 supplements will increase the incidence or aggressiveness of prostate cancer.
  • There is a lot of research and information indicating that inflammation is a cause of cancer and cardio-vascular events. The non-steroidal anti-inflammatory drugs (NSAIDS) have been shown to decrease the incidence of colon, breast and prostate cancer. Since omega-3 fatty acids do have an anti-inflammatory effect there is the possibility that omega-3 fatty acids could actually decrease the incidence of cancer. But at this point there are no studies suggesting taking NSAIDs to decrease the probability of developing prostate cancer.
  • The studies on the effectiveness of omega 3 supplements in preventing cardio-vascular events vary from research indicating that this supplement is effective to research that indicates no effect in preventing cardio-vascular events such as heart attacks and strokes.
  • You should consult your internist or cardiologist about their understanding of the research and take their advice.