Research links fish oil to increased risk of colon cancer in mice

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Jennifer Fenton (view larger image)

Fish oil—long encouraged by doctors as a supplement to support heart and joint health, among other benefits—induced severe colitis and colon cancer in mice in research led by MABR food science and human nutrition researcher Jenifer Fenton and recently published in the journal Cancer Research.

The research results support establishing a dose limit for docosahexaenoic acid (DHA), one of the omega-3 fatty acids present in fish oil, particularly in people suffering from chronic conditions such as inflammatory bowel diseases.

“We found that mice developed deadly, late-stage colon cancer when given high doses of fish oil,” she said. “More importantly, with the increased inflammation, it took only four weeks for the tumors to develop.”

Specifically, the research team found an increase in the severity of the cancer and an aggressive progression of the cancer in not only the mice receiving the highest doses of DHA but those receiving lower doses as well. The mice used in the study were prone to inflammatory-like bowel disease; inflammation is an important risk factor for many types of cancers, including colon cancer.

The findings were surprising, specifically because DHA has been shown to have some anti-inflammatory properties, Fenton said.

“We hypothesized that feeding fish oil enriched with DHA to mice would decrease the cancer risk; we actually found the opposite,” she said. “These mice were less able to mount a successful immune response to bacteria that increased colon tumors.”

Fenton cautions people may not need to avoid fish oil—what the research shows is needed are guidelines on dosing. With any nutrient, there is a “bell curve” effect. On the left of the curve are those deficient in a nutrient; on the right are those in excess. The majority of the people fall in between the extremes.

She said that people already receiving enough omega-3 fatty acids through their normal diet have no need for added supplementation.

“With fish oil, we don’t yet know how much is appropriate,” said Fenton. “There are many examples of taking supplements, nutrients or chemicals in excess that can promote cancer (for example, beta-carotene supplementation in smokers). Supplementation is most useful when the person taking them is deficient in that specific nutrient.”

The research team’s findings could have an important preventive health impact, specifically in light of the high rates of colon cancer in the United States. Individuals with inflammatory bowel disease have an increased risk of developing colon cancer, and when the cancer metastasizes, it can be fatal.

The next step, Fenton said, is to test omega-3 fatty acid levels in people with inflammatory bowel disease. To that end, she is continuing to build relationships—via the MSU College of Osteopathic Medicine campus in Macomb County—with gastrointestinal specialists to develop a cohort of patients.

“To help develop guidelines, we need to see how these findings correlate to human populations,” she said.

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