A Tide of Evidence Washes Away Flawed Fish Oil Prostate Cancer Study

by DailyHealthPost Editorial

flawed fish oil prostate cancer study

We hear about omega fatty acids all the time. The one thing everyone agrees on is that they are required nutrients and must be balanced with one another to have a positive health benefit; imbalance causes problems.

In a 2013 study that initiated a furor over the potential harmful effects of omega-3 fatty acid as it relates to prostate cancer, media took up the flag and ran, saying the study showed a direct correlation between high concentrations of omega-3 and the incitement of prostate tumors.


flawed fish oil prostate cancer study

Several medical experts have reviewed this singular study and found a great many flaws in its premise, execution, and conclusions.

The foundation:

“This case–cohort study examines associations between plasma phospholipid fatty acids and prostate cancer risk among participants in the Selenium and Vitamin E Cancer Prevention Trial.”[1]

We don’t want to pick apart the study point by point.

Here are the highlights that you should consider when a) hearing about omega-3 fats and their health implications, b) reviewing any study that results in something contradictory to multiple previous studies performed by others, and c) the consequences of dietary supplements.

  • None of the subjects were asked if they were taking omega-3 supplements nor were their diets evaluated at the outset or during the study.
  • The study was to review the effects of vitamin E and selenium, individually and together, in treating prostate cancer.
  • Fish oil was implicated in the study but not actually tested.
  • Fatty acid levels were tested in the subjects at the beginning of the study and they were compared in subjects who did and did not develop prostate cancer.
  • Findings reported that men with the highest levels of omega-3 fatty acids were at substantially higher risk for prostate cancer.
  • The correlation was assumed to be as the result of omega-3 supplementation. (Assumptions are a normal part of any empirical research, however, this is an invalid assumption because there was no established basis.)
  • The subjects of this particular study were a sub-group of a larger study of the effects of vitamin E and/or selenium supplementation for the prevention of prostate cancer. It is unclear whether the researchers considered the interactions of these nutrients with fatty acids in the individuals or any other dietary or lifestyle factors:

“Prostate cancer expert Anthony Victor D’Amico, MD, PhD, points out that the authors failed to adjust their calculations for the main risk factors associated with prostate cancer. Key factors such as ethnicity, age, body mass index (BMI) and prostate specific antigen (PSA) level were not accounted for, despite being listed in the table of baseline patient characteristics and SELECT trial [the larger study] cancer outcomes. Prof D’Amico has commented: ‘The study really cannot make the conclusion that it’s trying to. These types of studies are not cause and effect. These studies are simply associations…They didn’t account for the known predictors of prostate cancer when they were making the calculation. You’re left with a weak association’.”[2]

Gerald Chodak, MD of the Midwest Prostate and Urology Health Center carefully reviewed the study (as did many others) and summarizes his review:


“The bottom line is that we cannot determine from this study design whether the intake of omega-3 fatty acids will cause prostate cancer and raise a man’s risk for high-grade disease. The media has taken this and sensationalized the risk associated with omega-3 fatty acid intake, but I believe that the attention is overplayed and the concerns about the study design were not mentioned at all. At the end of the day, this study does not prove that intake of omega-3 fatty acids causes prostate cancer or increases a man’s risk for high-grade disease. We would need better-designed trials that are prospective and randomized to be able to make such a claim. Until that is done, we will have to weigh the pros and cons of taking omega-3 fatty acids in terms of its other potential health benefits to decide what to do.”[3]

The take-away for us:

  • Since its publication, numerous medical experts have spoken out against the findings.
  • Every scientific study must be scrutinized for possible bias.
  • A subsequent study by the same group of researchers was published in 2014, obviously as a result of the original study’s backlash. Its premise:

“Individual studies have suggested that some circulating fatty acids are associated with prostate cancer risk, but have not been large enough to provide precise estimates of associations, particularly by stage and grade of disease.”

The new study concluded:

“There was no strong evidence that circulating fatty acids are important predictors of prostate cancer risk. It is not clear whether the modest associations of stearic, eicosapentaenoic, and docosapentaenoic acid are causal.”[4]

Can you say “retraction”?

OD on O3

On a related topic, is it possible to get too much omega-3 fatty acid? Sure, if you supplement. That’s the danger of self-supplementation. It is possible to get too much of a good thing if you don’t consider the details of your individual diet and lifestyle.

Do your research to determine the right supplement for you. Keep in mind that you probably get plenty of omega-6 in your diet–probably too much–and balance of the two is key. The optimal range is 1:1 to 4:1 omega-6 to omega-3; in North America, the average proportion is around 15:1, which is a big cause for concern.

Fish oil is rich in two critical fatty acids that your body needs but doesn’t produce: EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid). (“Omega-3” is the scientific term given to this type of fatty acid due to the position of the first carbon double-bond atom that occurs from the end of the molecule—in this case, it’s third; “omega” is the last letter of the Greek alphabet.)

These omega-3s have been shown to reduce and manage inflammation in the body, reduce the risk of heart disease, support brain function and memory, protect cells from degeneration, improve bone health, ameliorate arthritis symptoms, and more.


The North American diet is lacking in these essential fatty acids due, in part, to cooking methods (like frying) and the availability of cheap, processed foods that are high in omega-6.

Omega-6 isn’t a bad thing in and of itself; the body needs this fatty acid, too. The issues are the sources and amounts that we eat. Vegetable oils like canola, corn, and soybean have high omega-6 with little nutritional value (not to mention that they are among the top crops using genetically-modified organisms).

Better sources are seeds, nuts, poultry, and eggs (organic, free range). The GLA (gamma linolenic acid) in omega-6 is what the body uses and is essential to regulating inflammation, the immune system, and metabolism.

As a result from all of the studies and hype over fish oils, many have come to market in various forms.

Be wary: not all fish oils are the same.

Potency and bioavailability are paramount. High-quality fish oil will have the full chains of EPA and DHA. These will be readily absorbed by the body, delivering the full effect of the nutrients. Keep in mind that the cost of the oil may or may not be indicative of its efficacy.

Consider additional nutrients present in the oil. Oil extracted from the fish liver, for example, adds vitamins as well as the fatty acids you’re looking for. As for DHA versus EPA content, DHA promotes brain health while EPA has anti-inflammatory properties; select the supplement that contains the appropriate ratio to address your needs.


There are international standards for purity: GOED (Global Organization for EPA and DHA Omega-3s, a non-profit trade association) and IFOS (International Fish Oil Standards Program, a third-party testing and certification program) are the primary overseers.

Fresh is best. Omega-3 oils are sensitive to oxidation (interaction with oxygen), causing spoilage. Rancid fish oil won’t give you the benefits you paid for and may cause adverse effects, like inflammation. Check the date on the bottle, use it right away, buy small bottles rather than large ones (unless others in your household will share it), and refrigerate after opening.

Make sure the oil is coming from wild fish, harvested in a sustainable context.

Don’t over-supplement. Know the nutrition of the other foods you’re eating if you do take any supplement for anything.

[1] https://jnci.oxfordjournals.org/content/early/2013/07/09/jnci.djt174.abstract
[2] https://anh-europe.org/news/a-tide-of-evidence-washes-away-flawed-fish-oil-prostate-cancer-study
[3] https://www.medscape.com/viewarticle/808402
[4] https://jnci.oxfordjournals.org/content/106/9/dju240.abstract