Fish Oil May Be Dangerous for Some People

Fish oil rich in omega-3 fatty acids have long been encouraged by doctors as supplements to support heart and joint health, among other benefits. But the supplements have a dark side. Michigan State University Researchers found it induced severe colitis and colon cancer in mice.
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Jennifer Fenton, a food science and human nutrition researcher at MSU led the research that supported the need to establish a dose limit for docosahexaenoic acid (DHA), one of the omega-3 fatty acids present in fish oil, particularly for people suffering from chronic conditions such as inflammatory bowel disease (IBD).

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

The study findings, published in the October, 2010 issue of Cancer Research, support a growing body of literature implicating harmful effects of high doses of fish oil consumption in relation to certain diseases.

The MSU researchers found an increase in the severity and an aggressive progression of the cancer not only in the mice receiving the higher doses, but also in those receiving lower doses of DHA. The researchers observed the mice were prone to inflammatory-like bowel disease; inflammation is an important risk factor for many types of cancers, including colon cancer and prostate cancer.

The findings were surprising to the researchers who initially hypothesized DHA-enriched fish oil would decrease the cancer risk in the animal models. DHA has been shown in previous studies to have some anti-inflammatory properties.

“We actually found the opposite. These mice were less equipped to mount a successful immune response to bacteria that increased colon cancer tumors,” Fenton said.

Colon cancer rates in the United States are high compared to other nations. The National Cancer Institute estimates that one in 20 people of either sex will be diagnosed with colon cancer during their lifetime.