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Announcement on omega-3s suggests without evidence that fish oil prevents, treats breast cancer

Choose Omega-3s from fish over flax for cancer prevention, study finds

Our Review Summary

animal researchThis news release reports on a study of tumor growth in mice with an aggressive form of breast cancer who were fed varying types of omega-3s. The news release offers plenty of unwarranted medical advice such as “choose omega-3s from fish over flax for cancer prevention” while failing to caution about the limitations of using mouse studies to predict human outcomes.


Why This Matters

The study points out that previous research has focused on the protective role of eating fish and other marine life against breast cancer, with little evidence regarding the impact of plant sources of omega-3s. Yet there’s no conclusive evidence that eating fish reduces cancer risk, and no mouse study can prove otherwise. News releases shouldn’t extrapolate from the evidence as this one does by conferring benefits seen in a few unusual mice onto all humans looking to prevent any form of cancer. Such misleading news releases tend to produce misleading coverage such as the Daily Mail’s Salmon may help to prevent breast cancer more than flax seeds as scientists discover fish-source omega 3 fatty acids prohibit tumor growth by up to 70%.


Does the news release adequately discuss the costs of the intervention?

Not Satisfactory

The additional cost of adding fish and seafood to the diet aren’t discussed. 

Does the news release adequately quantify the benefits of the treatment/test/product/procedure?

Not Satisfactory

There aren’t benefits to quantify, only results, but the news release reports even those in confusing fashion. It states in the second paragraph that “marine-based omega-3s are eight times more effective at inhibiting tumor development and growth” without giving any sort of baseline for what’s being measured. Further down it states that “exposure to marine-based omega-3s reduced the size of the tumors by 60 to 70 percent and the number of tumors by 30 percent” without saying how much omega-3s the mice consumed or giving the sizes or frequency of tumors. Also, there’s no data on how many mice died.

The Cochrane Collaboration (a non-profit that researches and reports on evidence-based medicine) looked at many different human studies and says that so far there is no proof fish oil can treat or prevent cancer-related weight loss, depression, dementia and many other conditions.

Does the news release adequately explain/quantify the harms of the intervention?

Not Satisfactory

Some fatty and farm fish contain significant levels of mercury, PCBs, and other contaminants and experts recommend limiting their consumption and avoiding them entirely if you’re pregnant. That isn’t mentioned. The release also conveys an endorsement of fish oil tablets, which can have side effects such as heartburn, nosebleeds, hot flushes, leg cramps, nausea and bad breath.

Does the news release seem to grasp the quality of the evidence?

Not Satisfactory

Not until the fifth paragraph does this news release mention that this is a study of mice with an unusual form of breast cancer, not healthy humans. It doesn’t explain how those limit the usefulness of the results.

Does the news release commit disease-mongering?

Not Satisfactory

The news release states that the HER-2 form of breast cancer “affects 25 percent of women.” That number seems over-inflated according to other sources.

The Mayo Clinic website states “in about 1 of every 5 breast cancers, the cancer cells have a gene mutation that makes an excess of the HER2 protein.” And Cancer Investigation journal put the number of women with HER-2 positive at 19% for women under 49 years and 15% for those over 50 years old.

Does the news release identify funding sources & disclose conflicts of interest?

Not Satisfactory

Funding sources and conflicts of interest aren’t mentioned. According to the study, which is behind a paywall, funding came from the Public Health Agency of Canada, the Canadian Institutes of Health Research-Institute of Cancer Research, the Canada Foundation for Innovation, and the Ontario Research Fund, Ontario Graduate Scholarship. Canada is a world leader in both seafood and flax seed exports. The authors reported no competing interests.

Does the news release compare the new approach with existing alternatives?

Not Satisfactory

The news release doesn’t mention evidence-backed strategies to reduce breast cancer risk such as limiting alcohol consumption and getting exercise.

Does the news release establish the true novelty of the approach?


The news release notes in the seventh paragraph that it’s the first to compare the impact of different omega-3s on breast cancer tumor growth in mice.

Does the news release include unjustifiable, sensational language, including in the quotes of researchers?

Not Satisfactory

The news release gives premature medical advice to “choose omega-3s from fish over flax for cancer prevention” and “consume two to three servings of fish a week,” and suggests without evidence that “omega-3s will likely be beneficial for other types of cancer.” It veers even further astray by conveying a researcher’s view that “supplements and functional foods, such as omega-3 eggs or DHA milk, can offer similar cancer prevention effects.”

Total Score: 1 of 9 Satisfactory

Comments (1)

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Matthew E

February 23, 2018 at 3:06 pm

Awesome critique. Surprisingly (to many, I’d wager) Omega-3’s don’t seem to help with CHD (Coronary Heart Disease)*, so we may need to be more careful about tentative conclusions that it helps with cancer, etc. Thanks for encouraging that with reviews like this!

*Review article in JAMA Cardiology: