Fish oil linked to increased risk of colon cancer in mice

October 5, 2010, Michigan State University

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 Michigan State University and published this month in the journal Cancer Research.

Jenifer Fenton, a food science and human nutrition researcher at MSU, led the research that supports establishing a dose limit for (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 when given high doses of fish oil," she said. "More importantly, with the increased inflammation, it only took 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.

"Our findings support a growing body of literature implicating harmful effects of high doses of fish oil consumption in relation to certain diseases," Fenton said. "Currently, there is a call by academics and the food industry to establish dietary guidelines for omega-3 consumption. This is primarily motivated by the fact that most Americans are deficient in omega-3 fatty acids, and there is substantial evidence supporting the beneficial effects of the consumption."

The findings were surprising, specifically because DHA has been shown to have some anti-inflammatory properties, according to Fenton: "We hypothesized that feeding fish oil enriched with DHA to mice would decrease the cancer risk; we actually found the opposite. These mice were less equipped 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.

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

"With , we don't yet know how much is appropriate," said Fenton, also a researcher with the Michigan Agricultural Experiment Station. "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 MSU's 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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sstritt
5 / 5 (1) Oct 05, 2010
"We found that mice developed deadly, late-stage colon cancer when given high doses of fish oil,"
What was the dose and how does that translate to human dosage? Just about anything can be shown to cause cancer in a high enough dose.
darkchild
not rated yet Oct 05, 2010
wow it would be so much better if they gave us some numbers and data to work with. this is definitely something I will be following being that I know a lot of people that take this daily including my mother.
nanotech_republika_pl
not rated yet Oct 07, 2010
@George
Here is the link (but only the abstract is free):
http://cancerres....ubmit=Go
nanotech_republika_pl
not rated yet Oct 07, 2010
@sstritt
Here is the quote from the abstract, but not sure if it helps:
"Mice were fed isocaloric diets modified to include corn oil, safflower oil, or DFO (doses ranging from 0.75% to 6.00%) as the fatty acid source for 8 weeks."
nanotech_republika_pl
not rated yet Oct 07, 2010
DFO means dietary fish oil
Shootist
not rated yet Oct 10, 2010
doses ranging from 0.75% to 6.00%


If of diet, then the amounts were not absurdly high.
SkiSci
not rated yet Oct 12, 2010
Yeh...because mice evolved eating fish and everything...pointless, ultra specific nonsense. "Lemur shows unhealthy complications when given high doses of barracuda blood"...fish must be bad

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