Fish oil (omega-3) supplements are taken by many patients receiving chemotherapy. A team of researchers in The Netherlands and Japan identified specific platinum-induced fatty acids (PIFAs) that activate splenic macrophages, which in turn led to resistance to chemotherapy in mouse models. Fish oil contains PIFA 16:4(n-3), and when given to mice along with chemotherapy, inactivated the chemotherapy that had been administered.
Four hundred patients with cancer undergoing treatment were surveyed to determine their use of fish oil supplements, and 118 patients responded to the questionnaire. The researchers analyzed the 16:4(n-3) content of 6 fish oils and 4 types of fish, and measured 16:4(n-3) plasma levels in healthy volunteers after ingesting 3 different brands of fish oil or 4 different fish species. Thirty healthy volunteers were randomly selected for the fish oil study, and 20 were randomly selected for the fish study.
Eleven percent of the patients reported using omega-3 supplements. All fish oils tested contained relevant amounts of 16:4(n-3). Mouse experiments showed that the addition of 1 µL of fish oil to cisplatin was sufficient to induce chemoresistance. When the recommended daily amount of 10 mL of fish oil was administered to healthy volunteers, rises in plasma 16:4(n-3) levels were observed, and reached up to 20 times the baseline levels. The researchers concluded that 16:4(n-3) is rapidly taken up in the plasma after ingestion of fish or fish oils. Until further data become available, fish oil and fish containing high levels of 16:4(n-3) may best be avoided on the days surrounding chemotherapy.
Daenen LGM, Cirkel GA, Houthuijzen JM, et al. Increased plasma levels of chemoresistance-inducing fatty acid 16:4(n-3) after consumption of fish and fish oil. JAMA Oncology. April 2, 2015. [Epub ahead of print] doi:10.1001/jamaoncol.2015.0388.