Scimex: Dutch and Japanese scientists have found that people consuming herring and mackerel fish, as well as three kinds of fish oils, actually raised their blood levels of a certain chemo-counteracting fatty acid, indicating that chemotherapy patients should avoid them during treatment. Previous studies in mice have indicated that certain fatty acids in fish oils may actually counteract the tumour-fighting effects of chemotherapy, a finding which has implications for the growing use of supplements by cancer patients during their treatments.
Researchers found that consuming the fish herring and mackerel, as well
as three kinds of fish oils, raised blood levels of the fatty acid
16:4(n-3), which experiments in mice suggest may induce resistance to
chemotherapy used to treat cancer, according to a study published online
by JAMA Oncology.
Patients with cancer often adopt lifestyle changes and those changes
often include the use of supplements. But there is growing concern about
the use of supplements while taking anticancer drugs and the possible
effect on treatment outcomes, according to the study background.
Emile E. Voest, M.D., Ph.D., of the Netherlands Cancer Institute,
Amsterdam, and coauthors examined exposure to the fatty acid 16:4(n-3)
after eating fish or taking fish oil.
The authors examined the rate of fish oil use among patients undergoing
cancer treatment, while researchers also recruited healthy volunteers to
examine blood levels of the fatty acid after ingestion of fish oils and
fish. The fish oil portion included 30 healthy volunteers and the fish
portion included 20 healthy volunteers.
Among 118 cancer patients who responded to a survey about the use of
nutritional supplements, 35 (30 percent) reported regular use and 13 (11
percent) used supplements containing omega-3 fatty acids, according to
The study found increased blood levels of the fatty acid 16:4(n-3) in
healthy volunteers after the recommended daily amount of 10 mL of fish
oil was administered. An almost complete normalization of blood levels
was seen eight hours after the 10-mL fish oil dose was given, while a
more prolonged elevation resulted after a 50-mL dose, according to the
Eating 100 grams of herring and mackerel also increased blood levels of
16:4(n-3) compared with tuna, which did not affect blood levels, and
salmon consumption, which resulted in a small, short-lived peak.
"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.
Based on our findings, and until further data become available, we
advise patients to temporarily avoid fish oil from the day before
chemotherapy until the day thereafter," the study concludes.