According to a new research, published online April 2 in JAMA Oncology, fish oil supplements, and even certain fish, may hinder the effectiveness of chemotherapy.

In order to carry out the study, a team led by Emile Voest, M.D., Ph.D., of the Netherlands Cancer Institute in Amsterdam, checked out the use of fish oil among 118 cancer patients undergoing chemotherapy.

Further, the researchers assessed fatty acid levels in 50 healthy volunteers after they consumed either fish or fish oil supplements.

There were 35 among the cancer patients, who said that they took fish oil supplements regularly, whereas 13 used supplements containing omega-3 fatty acids.

Voest's group found that the levels of the fatty acid 16:4(n-3) showed an increase in the volunteers after they consumed the recommended amount of fish oil, 10 ml. Their blood levels returned to normal after eight hours, but in the case of 50ml consumption of fish oil, it took longer.

Further they found that intake of 3.5 ounces of herring and mackerel also led to the increased blood levels of 16:4(n-3). But, Tuna did not alter blood levels of the fatty acid, and salmon showed only a short spike.

The authors wrote, “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”.

Researchers have advised the patients to temporarily avoid the consumption of fish oil from the day before chemotherapy until the day thereafter, before the availability of further data.

Dr. David Nanus, chief of hematology and medical oncology at Weill Cornell Medical College and New York Presbyterian Hospital, said that if the fish and fish oil proves deleterious effects on chemo, then also it would affect the patients only if they were consuming them while undergoing chemo treatments.