Fish oil supplements, which contain omega-3 fatty acids thought to offer a variety of health benefits, can be bad news for cancer patients. According to a study published in Cancer Cell, fish oil can induce resistance to chemotherapy drugs in cancerous cells.
Emile Voest of the University Medical Centre Utrecht and her colleagues found that blood stem cells from mice started producing two fatty acids also found in fish oil, KHT and 16:4(n-3), which somehow enabled tumor cells to evade treatment with the chemotherapy drug cisplatin. Indeed, giving the mice off-the-shelf fish oil supplements had a similar effect. Blocking the production of these fatty acids, on the other hand, improved the effectiveness of the chemotherapy.
"We show that the body itself secretes protective substances into the blood that are powerful enough to block the effect of chemotherapy,” Voest told BBC News. "These substances can be found in some types of fish oil. Whilst waiting for the results of further research, we currently recommend that these products should not be used whilst people are undergoing chemotherapy."