Cancer Treatment News Update 2015: Fish Oil Reduces Chemotherapy's Effectiveness, Study Indicates

Contrary to popular beliefs, fish oil supplements will not help cancer patients if they are undergoing chemotherapy, according to a recent study published on Saturday.

A specific fatty acid contained in all six of the fish oil supplements that researchers examined has been found to lessen the effectiveness of chemotheraphy in mice, Reuters said, citing a report in JAMA Oncology.

Dr. Emile Voest, the study's lead author from the Netherlands Cancer Institute in Amsterdam, advised people undergoing chemotherapy to avoid taking fish oil supplements. He also recommended discussing supplements with doctors.

"I'm always discussing it with my patients," Voest said. "Please have an open relationship with me and tell me what you're taking."

Omega-3 fatty acid is taken by about a fifth of Americans with cancer usually though fish oil, which is sold in capsules with price tags ranging from about $10 to $11 for a bottle containing 100 pills, according to Voest.

Researchers previously observed that even a small amount of two fatty acids decreased chemotherapy's effectiveness in tested mice, although these fatty acids may enable cancer cells to repair themselves faster after the procedure.

Voest and his team looked for two fatty acids in all of the six fish oil supplements. The fatty acid called 16:4(n-3) was found in all of them. One was not detected.

They also surveyed 400 people undergoing chemotherapy in November 2011. Thirty-five percent of the 118 people who returned the surveys said they used nutritional supplements and 11 percent said they specifically use omega-3 fatty acid supplements.

Researchers also had 30 volunteers without cancer take 10 or 50 milliliters (mL) of the three fish oil supplements, in another part of their study. Levels of 16:4(n-3) were found to be in the highest levels in their blood about four hours after taking the 10 mL supplements. Levels normalized again after about eight hours. Levels of the fatty acid remained elevated longer among those taking 50 mL.

Also, when 20 volunteers consumed herring or mackerel, levels of 16:4(n-3) in their blood rose, but salmon or tuna had little or no effect.

Researchers said people on chemotherapy should avoid fish oil the day before and after their treatments, until more information has been found.

The Dutch Cancer Society and the Dutch National Working Group for Oncologic Dieticians, they noted, are already advising people undergoing chemotherapy to keep away from taking fish oil around the time of treatment.

"Although further evidence on the relation between fish consumption and chemotherapy activity is desired, we would currently also recommend to avoid herring and mackerel in the 48 hours surrounding chemotherapy exposure," the researchers said.

However, Voest clarified that the study's findings are a little circumstantial, saying it is hard to prove the findings. One stumbling block is that it would be unethical to give patients fish oil during chemotherapy on a random manner to examine if it makes the treatment less effective.

"It's an intriguing observation, which warrants further investigation," said Dr. Powel Brown, chairman of the Department of Clinical Cancer Prevention at the University of Texas M.D. Anderson Cancer Center in Houston. Brown is not a part of the study.

"In general, when giving chemotherapy, we discourage the use of additional supplements," said Brown. "It's very well known that some supplements affect the metabolism of chemotherapy."

Meanwhile, an expert on oncology nutrition warned people against going the extreme route in avoiding all omega-3 fatty acids. Stacy Kennedy from Dana-Farber Cancer Institute in Boston, who is not part of the research, said such fatty acids are an importnat part of the diet that the body cannot produce on its own.

"I think it's important to have those detailed conversations with your doctors and dieticians to weigh the risk and benefits of any over-the-counter medication, supplements and powders," she said.