Rancidity: The Link Between Fish, Fish Oil and Prostate Cancer?

Woman holding capsule

July 11th, 2013, national media reported that a study out of Ohio State University found that men consuming the most omega-3 (fish or fish oil) also had the highest risk of getting prostate cancer.

The study’s results and the news attention left a firestorm of worry about fish oil, and a lot of questions. How can omega-3 from fish and fish oil, which has been lauded in tens of thousands of research studies for its health benefits, promote cancer?

In the aftermath, the Ohio State University study received a torrent of criticism from the omega-3 research and academic community for its hastily drawn conclusions and poorly designed research protocol. (The study had, amongst other strange conclusions, also found that smokers had a lower risk of developing prostate cancer than non-smokers!).

In addition, the study’s conclusion contradicts the results of numerous other studies that reveal omega-3 helps reduce the risk of developing cancer. In fact, an Australian review on omega-3 and cancer published in January found that a daily dose of up to 3 grams of EPA/DHA per day had positive outcomes as an anti-cancer treatment, and worked as an effective adjunct treatment to chemotherapy.

So what exactly is going on, and why are studies finding such drastically different results? We believe part of the answer has to do with a little-discussed quality issue – namely rancidity.

When looking at omega-3 research to date, it is important to note that the quality of the oil used is rarely described – namely  the rancidity or oxidation levels of the oil.

A graph of the oxidation levels of omega-3 fish oils on the Norwegian market.

Oxidation levels in omega-3 oils can vary by 100 fold, and can be distinguished by taste and odor. Omega-3s with the lowest oxidation values have no smell or taste. On the other end of the spectrum, omega-3s with the highest oxidation values may smell or taste so bad that the manufacturer has to conceal the oil in gelatin capsules or add large amounts of flavoring.

While oxidation levels are almost never recorded by the researchers who use the oil in their studies, scientists are slowly starting to voice their concern over giving patients rancid oil on a daily basis.

While the long term effect of rancid fish oil has never been researched on humans, animal studies indicate that rancid fish oil may promote cancer and increase inflammation. So when a government study from Norway concluded two years ago that an overwhelming majority of fish oil capsules are rancid, the findings from Ohio State University should at least bring up the discussion of using oxidized omega-3.

For the consumer, the rancidity test is simple: Cut open the capsule. If the oil smells or taste fishy or makes you burp, it is likely rancid. Truly fresh fish oil has no taste or smell.

Get the Facts on Freshness, Omega-3 and Your Health. Read the Rancid Truth about Omega-3 Fish Oil.

For more information, download our whitepaper on “The Rancid Truth about Omega-3 Fish Oil.”

So does omega-3 really promote or prevent prostate cancer? With any study, we have to be wary before jumping to conclusions. We know that Japanese men, who consume vast amounts of omega-3 from fish and fish oil supplements, also have among the lowest prostate cancer rates in the world. Clearly the Ohio State University study has to be redesigned before they can explain their explain their results. A simple explanation for their findings may be that patients diagnosed with prostate cancer would likely start consuming more fish or omega-3 since it is reputed to be beneficial and healthy.  An elevated blood sample reflecting diet from a single day does not mean that fish or fish oil caused the cancer.

Omega Cure fresh liquid fish oilStill, the study’s findings should serve as a wake-up call to all fish oil consumers: Rancid fish oil has no place in human nutrition.

On the other hand, removing pure, fresh fish and fish oil from the diet would be a health disaster. Omega Cure is the freshest fish oil in the world.


1. Albert, Benjamin B. “Oxidation of Marine Omega-3 Supplements and Human Health.” BioMed Research International. Hindawi Publishing Corporation, 9 Apr. 2013. Web. 13 July 2013.

2. Brasky, TM. “Result FiltePlasma Phospholipid Fatty Acids and Prostate Cancer Risk in the SELECT Trial.” National Center for Biotechnology Information. U.S. National Library of Medicine, 10 July 2013. Web. 13 July 2013.

3. Gray, Nathan. “Experts Slam Omega-3 Link to Prostate Cancer as Overblown ‘Scaremongering'” NutraIngredients.com. William Reed Business Media SAS, 12 July 2013. Web. 13 July 2013.

4. Lysvold, Susanne. “Slår Alarm of Dårlige og Harske Produkter.” NRK. NRK, 22 Sept. 2010. Web. 13 July 2013.

5. Vaughan, VC. “Marine Polyunsaturated Fatty Acids and Cancer Therapy.” National Center for Biotechnology Information. U.S. National Library of Medicine, 8 Jan. 2013. Web. 13 July 2013.

Bo Martinsen, MD

Bo Martinsen is the co-founder and CEO of Omega3 Innovations. Born and raised in Norway, Dr. Martinsen received medical training at the University of Bordeaux in France and at the University of Oslo. He is ECFMG-certified in the United States. Dr. Martinsen has extensive experience practicing psychiatry, general medicine, neurology and preventive medicine, in addition to training in epidemiology (Ph.D program at the University of Oslo) and business administration. He has served as medical consultant to large international corporations focusing on stress management and synergistic medicine.

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2 Responses

  1. deborah@firstfriendsmeeting.org' deborah suess says:

    hi – I can’t exactly tell from the bottle how many calories are in 2 t of omega cure fish oil? I just need to count it in my diet … thanks for the info. Deborah Suess

    • admin says:

      Great question! Each teaspoon holds about 5 ml of oil. Therefore, if you take 2 teaspoons of Omega Cure, you’re consuming 10 mL of fish oil – which translates into roughly 80 calories. Hope that helps!

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