(HealthDay News) -- Fish oil supplements, and even certain fish, may hinder the effectiveness of chemotherapy, according to new research published online April 2 in JAMA Oncology.

For the study, a team led by Emile Voest, M.D., Ph.D., of the Netherlands Cancer Institute in Amsterdam, looked at fish oil use among 118 cancer patients undergoing chemotherapy. The researchers also assessed the levels of fatty acid in 50 healthy volunteers after they consumed either fish or fish oil supplements. Among the cancer patients, 35 said they took fish oil supplements regularly, and 13 used supplements containing omega-3 fatty acids.

Levels of the fatty acid 16:4(n-3) increased in the volunteers after they consumed 10 ml, the recommended amount of fish oil, Voest's group found. Blood levels returned to normal after 8 hours, but it took longer when the volunteers consumed 50 ml of fish oil. In addition, eating 3.5 ounces of herring and mackerel also increased blood levels of 16:4(n-3). Tuna, however, did not alter blood levels of the fatty acid, and salmon showed only a short spike, the researchers found.

"Taken together, our findings are in line with a growing awareness of the biological activity of various fatty acids and their receptors and raise concern about the simultaneous use of chemotherapy and fish oil," the authors write. "Until further data become available, we advise patients to temporarily avoid fish oil from the day before chemotherapy until the day thereafter."

Source

1. Daenen, L, et al. JAMA Oncol.Published online April 02, 2015. doi:10.1001/jamaoncol.2015.0388.

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