Consuming certain types of fish and taking fish oil supplements may induce chemoresistance, according to research published in JAMA Oncology.
Researchers found that herring and mackerel, as well as 6 different types of fish oil supplements, raised blood levels of the fatty acid 16:4(n-3).
And experiments in mice showed that small amounts of either purified 16:4(n-3) or fish oil induced resistance to the chemotherapy drug cisplatin.
Emile E. Voest, MD, PhD, of the Netherlands Cancer Institute in Amsterdam, and his colleagues conducted this multi-part study.
In one part, the team conducted a survey to determine the rate of fish oil use among patients undergoing cancer treatment (n=118). Thirty-five patients (30%) reported regular use of nutritional supplements, and 13 (11%) said they used supplements containing omega-3 fatty acids.
For another part of the study, the researchers evaluated 6 types of fish oil supplements. All of them contained relevant amounts of 16:4(n-3), ranging from 0.2 µM to 5.7 µM.
The team also recruited healthy volunteers to examine blood levels of 16:4(n-3) after the ingestion of fish oil supplements (n=30) and fish (n=20).
Volunteers had increased blood levels of 16:4(n-3) after the recommended daily amount of 10 mL of fish oil and after a 50 mL dose. Subjects had an almost-complete normalization of blood levels 8 hours after a 10 mL fish oil dose, but they had a more prolonged elevation of fatty acid levels after a 50 mL dose.
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,
which resulted in a small, short-lived peak.
Finally, experiments in mice showed that as little as 2.5 pmol of purified 16:4(n-3) or 1 µL of fish oil was sufficient to induce resistance to the chemotherapy drug cisplatin.
The fish oil/cisplatin combination had no significant impact on mouse tumors when compared to vehicle control treatment. The estimated tumor volume difference was 44.1 mm3 (P >0.99).
When the researchers compared cisplatin alone to cisplatin plus 16:4(n-3), the estimated tumor volume difference was 95.5 mm3 (P=0 .04). When they compared vehicle control to cisplatin alone, there was an estimated tumor volume difference of 142.4 mm3 (P=0.001).
The team said these results suggest that simultaneous exposure to chemotherapy and fish oil may be detrimental to cancer patients. So until further data become available, patients should avoid consuming fish oil from the day before chemotherapy until the day after.
