Health professionals almost always advise their patients to eat plenty of fish because fish oil is good for you. But now researchers say they have found fish oil may hinder treatment for cancer patients by making their chemotherapy less effective.
Researchers say it appears that some fish-oil supplements interfere with chemotherapy metabolism, in such a way that allows cancer cells to reassemble after treatment ends.
For that reason, experts say patients probably should avoid taking any fish oil on the day before and the day after any chemotherapy session. They also advised against eating oily fish such as herring or mackerel during the same 48-hour period.
A recent study in the Netherlands, published by the journal JAMA Oncology, looked at blood levels of a particular type of fatty acid suspected of interfering with cancer treatment — one of the so-called omega-3 oils found in fish.
Blood tests performed on healthy volunteers who took fish-oil supplements showed elevated levels of the specific fatty acid persisted for at least eight hours and sometimes much longer, depending on the amount of fish oil that was consumed.
Fish-oil supplements are commonly taken by many cancer patients in the U.S. and other countries as part of a lifestyle change in the interest of their health. And, of course, many more people regularly take fish oil as a dietary supplement for other reasons.
Two years ago, research in the Journal of the National Cancer Institute reported a link between omega-3 fish oils and an elevated risk of prostate cancer.