Cancer patients who eat herring and mackerel or take omega-3 supplements may end up resistant to chemotherapy, a study has warned.
Researchers found these fish raised blood levels of a particular fatty acid in the blood. This, in turn, may reduce the effects of chemotherapy drugs, they say.
As a result those undergoing chemo should avoid oily fish or fish oil supplements in the day before and after treatment until further research had been carried out, scientists suggested.
Oily fish such as salmon, mackerel and sardines help against cardiovascular disease, prostate cancer, age-related vision loss and dementia. They are also a rich source of Vitamin D, some B vitamins, selenium and omega-3 fatty acids, a type of fat good for health. The research was carried out after concerns were raised over the increased use of supplements while taking anti-cancer drugs and the possible effect on treatments.
Dr Emile Voest, of the Netherlands Cancer Institute in Amsterdam, examined exposure to the fatty acid 16:4(n-3) after eating fish or taking fish oil. The study, published in the journal JAMA Oncology, examined the rate of fish oil use among patients undergoing cancer treatment.