Fish Oil Makes Chemotherapy Less Effective, Study Finds, So What Does That Mean For People With Cancer?

LONDON - JUNE 06: Health supplements fill the shelves of Whole Food Market's new flagship store on June 6, 2007 in London. The US firm of natural and organic food outlets have opened their flagship store to Londoners today in Kensington. (Photo by Bruno Vincent/Getty Images)
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A recent study published in JAMA Oncology has shown that a specific omega-3 fatty acid found in fish oil may make chemotherapy less effective for cancer patients. The study specifically cites 16:4(n-3), a lipid that is found in fish oil supplements as well as in fish like herring and mackerel as the primary culprit. The study is four years in the making and came about after Netherlands Cancer Institute medical director Emile Voest had published a study linking fatty acids produced by stem cells in mice with cancer to a marked reduction in chemotherapy's effects.

The new study picks up where Voest left off. In 2011, Voest began studying 118 cancer patients at the University Medical Center Utrecht, who responded to a survey on whether they regularly took fish oil supplements or supplements in general. Just 11 percent of respondents indicated they were taking fish oil. A little over a third of the patients surveyed indicated that they were taking general vitamins and supplements during treatment.

Voest then tested healthy patients to determine fatty acid levels after those patients had either ingested fish or 10 milliliters or 50 milliliters of fish oil. Understandably, the lower milliliter supplement caused fatty acid levels to spike but for a shorter period of time than the higher milliliter supplement. He found that, of the fish ingested, the aforementioned herring and mackerel produced far higher levels of 16:4(n-3) than, say, salmon and tuna, whose 16:4(n-3) levels were negligible.

Though specific dosages of fish oil was doled out for this particular study, Voest does remind those taking fish oil supplements that dosages do vary from product to product. In that regard, he says cancer patients shouldn't blame themselves for taking fish oil supplements during chemotherapy treatment.

I don’t want patients who had chemotherapy in the past and it didn’t work to think that it was their fault because they took fish oil. Obviously there is a balance between how sensitive a tumor is to chemo versus the resistance-causing effect of fatty acids.

Voest said testing people undergoing chemotherapy was unethical, even if it was for the intent of testing fish oil's effects. That's why he returned to mice to determine whether an increase in fatty acids would produce the same effect as in his previous study. Once again, the mice showed lower success rates in chemotherapy treatment when measured with higher levels of 16:4(n-3). So, what course of action do doctors recommend when taking supplements and undergoing chemotherapy? Fish oil isn't necessarily out of the question, but Voest recommends that patients refrain from taking the supplement or ingesting omega-3 fatty acid-rich fish the day before, the day of, and the day after chemotherapy treatment.

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