Fish Oils and Prostate Cancer: The Australian Expert’s Response

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ONA_fish oils“Moderation in all things is good, including data crunching,” – Professor Ian Davis, Chair of ANZUP

We recently reported on a research paper published in the Journal of the National Cancer Institute that concluded men who consume omega-3s / fatty acids regularly could have  a 71 per cent increased risk of developing prostate cancer. The findings were based on an analysis of specimens and data from the SELECT trial, (Selenium and Vitamin E Cancer Prevention Trial).  Users of the supplements have rightly been alarmed by the new research findings as many take fish oil/Omega 3 supplements and include oily fish in their diet for its ‘wonder benefits’ including anti-inflammatory effects, increasing cognitive function and reducing the risks of both heart disease and Diabetes.

As so many Australians could potentially be affected, we asked Professor Ian Davis, chair of the ANZUP clinical trials group and Professor of Medicine at Monash University for his expert analysis, which we are delighted to publish in full:

“There are confusing messages in the media coverage of this paper. Briefly, it was a retrospective unplanned subgroup analysis of the SELECT trial. This very large trial showed no benefit in terms of cancer-specific or overall survival by supplementation with selenium and/or vitamin E, and in fact worse outcome for prostate cancer with vitamin E supplementation. The current report confirms previous work by the same group in a different trial population indicating an association between high serum levels of certain long chain omega-3 fatty acids and risk of developing high grade prostate cancer.

The authors indicate that serum levels are mainly associated with dietary intake including supplements and conclude a cause-and-effect relationship although this has not been proven. There are also some study design issues that can affect the data and their interpretation. They then make an understandable logical but unproven leap to the conclusion that omega-3 supplements or even diets containing fatty fish increase the risk of developing prostate cancer. Nowhere in the study is the confounding effect of study treatment accounted for in these findings and numerically more people in this subpopulation received vitamin E, although the previous study involved a different intervention.

The bottom line is:

  • An association has been confirmed between serum levels of certain omega-3 fatty acids and risk of developing high grade prostate cancer.
  • It is possible but unproven that intake of omega-3 supplements or of fatty fish might therefore increase the risk of developing these cancers.
  • A safe or unsafe level of intake has not been defined in these studies.
  • Any other health benefits or adverse effects of normal or supplemented levels of intake have not been considered in this work.
  • The hypothesis should probably be tested in a properly designed trial.
  • Moderation in all things is good, including data crunching.

What does this mean for consumers of Omega 3 supplements and men who include a lot of oily fish in their diets?

Professor Davis’ take-home messages for users of fish oil supplements who have been alarmed by the recent media coverage are:

  • Everything you take into your body can have unexpected effects. You’re taking these things because they thought they would have potent actions to improve your health; why be surprised if there are other effects as well?
  • Before making decisions about treating yourself with any sort of supplement, ask yourself how strong the evidence is that it is useful and whether there might be reasons not to take it. if in doubt, talk to your doctor.
  • Remember that media coverage is for the 15 second grab and complex issues can’t be covered easily. Don’t take everything you see or hear at face value!”

The ONA thanks Professor Davis for his valued contribution to this story. For more information, please visit:

About Author

Ian Davis

Ian Davis is Professor of Medicine, Monash University and Eastern Health Head, Eastern Health Clinical School and Medical oncologist, Eastern Health Chair. He is also Chair of the ANZUP Cancer Trials Group.

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