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EAST LANSING, Mich. — 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
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 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 fish oil, 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. |
