Chemotherapy and Fish Oil: Something Fishy Here?

Chemotherapy may be less effective in patients with high fish oil intake

(RxWiki News) Cancer patients often implement a variety of lifestyle changes, including the use of dietary supplements like fish oil. However, this may be a case in which a potentially healthy habit could also have negative effects.

A new study from the Netherlands found that taking fish oil supplements, as well as eating mackerel and herring, might raise blood levels of a certain fatty acid. Past experiments with mice indicated that these fatty acids could cause resistance to the chemotherapy used to treat cancer.

The authors of this study said people with cancer should avoid fatty fish and fish oils the day before and day after a chemotherapy treatment.

Emile E. Voest, MD, PhD, of the Netherlands Cancer Institute in Amsterdam, led this study.

“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," Dr. Voest and team wrote. "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.”

Dr. Voest and team recruited three different groups of patients. One group of healthy volunteers took fish oils. The second group ate fish. The third group responded to a survey on whether they took dietary supplements containing fish oils. The third group included only patients with cancer.

The first two groups submitted to blood testing to determine the effect of eating fish or taking fish oil supplements.

Past research in mice showed that fish oils may raise the blood levels of a fatty acid called 16:4(n-3). Three kinds of fish oils were found to have the same effect.

These tests in mice showed that this fatty acid could make chemotherapy less effective.

In the current study, Dr. Voest and colleagues found that the fish oil patient group had increased levels of 16:4(n-3) in their blood. Some patients had an increase of up to 20 times the normal level of 16:4(n-3).

After eight hours, these levels dropped back to normal. If patients took a higher dose of fish oil, their blood levels took longer to normalize.

Patients who ate 100 grams (about 3.5 ounces) of herring or mackerel also had increased blood levels of 16:4(n-3). Patients who ate tuna showed no changes, and those who ate salmon showed a smaller, short-lived increase.

In addition to their recommendation to hold the fish oil, Dr. Voest and colleagues said patients on chemotherapy should also avoid herring and mackerel for 48 hours prior to and after chemotherapy.

This study was published in the April issue of JAMA Oncology.

A Dutch Cancer Society grant funded this research. Dr. Voest and team disclosed no conflicts of interest.

Review Date: 
April 5, 2015