Fish Oil Should Not Be Consumed During Cancer Chemotherapy, New Study Suggests

A new study found that patients who take fish oil supplements while undergoing cancer chemotherapy may be doing more harm than good.

The authors of the study published in the journal JAMA Oncology indicated that "fish oil contains substantial levels of 16:4(n-3)," which is "a fatty acid with potent chemotherapy-negating effects" seen in preclinical models and the "intake of low doses of fish oil interferes with chemotherapy activity in mice."

The researchers asked 20 volunteers to eat mackerel or herring, and the results showed increased levels of 16:4(n-3) in their blood. However, salmon or tuna consumption did not have the same effect, but closer to none.

In another part of the study, the researchers then had 30 volunteers without cancer take 10 or 50 milliliters (mL) of the three fish oil supplements. Levels of 16:4(n-3) peaked in their blood about four hours after taking the 10 mL supplements; levels returned to normal after about eight hours. Levels of the fatty acid remained elevated longer among those taking 50 mL.

"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.

"In general, when giving chemotherapy, we discourage the use of additional supplements," said Brown, who wasn't involved with the study. "It's very well known that some supplements affect the metabolism of chemotherapy."

People should not avoid all omega-3 fatty acids though because they are an essential part of the diet that the body can't make on its own, said Stacy Kennedy, an expert on oncology nutrition at the Dana-Farber Cancer Institute in Boston.

Flaxseed, chia seeds and walnuts are also sources of omega-3 fatty acids.