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Fish Oil Increases Risk of Colitis, Colon Cancer in Mice


It seems contradictory: fish oil supplements are often recommended because they contain omega-3 fatty acids associated with a reduction in inflammation. Now, however, researchers at Michigan State University have found that fish oil increases the risk of severe colitis and colon cancer in mice prone to inflammatory-like bowel diseases.

DHA in fish oil is linked to cancer risk

Although most people are deficient in omega-3 fatty acids and are encouraged to include more foods rich in this essential fat and to take fish oil supplements, there is a caveat. According to Jenifer Fenton, a food science and human nutrition researcher at Michigan State University, “our findings support a growing body of literature implicating harmful effects of high doses of fish oil consumption in relation to certain diseases.”

This concern has led some academics to work on establishing intake guidelines for omega-3 fatty acids. Excessive intake of the omega-3 DHA could be especially harmful for people who have chronic conditions such as inflammatory bowel diseases, according to the new study.

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Researchers discovered that mice given high doses of fish oil developed lethal, late-stage colon cancer, and that the increased inflammation associated with DHA use caused the tumors to develop in only one month. Even low doses of the fatty acid resulted in an increase in the severity of the cancer and in aggressive progression of the disease.

Fenton noted that the results of this study do not mean people should not take fish oil, but that healthful amounts need to be identified. “With fish oil, we don’t yet know how much is appropriate,” said Fenton. Currently, numerous scientific and other authoritative bodies, ranging from the Institute of Medicine to the World Health Organization and the Council for Responsible Nutrition, have voiced their opinions about the optimal amount of omega-3 fatty acids, including DHA, people should consume. These can be seen on the Purdue Research Foundation website.

Fenton explained that they had expected to see a decreased risk of cancer when giving the mice DHA because the omega-3 has been shown to possess anti-inflammatory abilities. However, “these mice were less equipped to mount a successful immune response to bacteria that increased colon tumors.”

The increased risk of colitis and colon cancer related to use of fish oil seen in this study may serve as a warning to individuals with inflammatory bowel disease, who have an increased risk of developing colon cancer. Since this study was conducted using mice, Fenton noted that the next step is to test levels of omega-3 fatty acids in people who have inflammatory bowel disorders.

Mayo Clinic
Michigan State University
Purdue Research Foundation