The finding comes from an analysis of 41 past studies on the link between fish in the diet and new diagnoses and deaths from colorectal cancer.
“People who rarely eat fish may experience health benefits in a variety of areas — heart disease, reproductive and now colon cancer — by increasing their fish consumption somewhat,” said Dr. Michael Gochfeld, a professor of environmental and occupational medicine at University of Medicine and Dentistry of New Jersey-Robert Wood Johnson Medical School.
“If you eat fish very frequently, it’s not clear whether your benefit continues to go up (by eating even more),” he told Reuters Health.
And although the new study focused specifically on fresh fish, the authors noted they were unable to pinpoint what types of fish people ate or the manner in which fish was prepared in the prior studies.
“Cooking temperatures might affect the risk of colorectal cancer,” Dr. Jie Liang of Xijing Hospital of Digestive Diseases in Xi’an, China, who worked on the study, wrote in an email to Reuters Health.
Liang cited recent evidence that suggests eating lots of meat and fish barbecued or grilled over high heat may actually be tied to an increased cancer risk.
According to the Centers for Disease Control and Prevention, approximately 143,000 Americans were diagnosed with colorectal cancer in 2007, the most recent year with available data. The disease affects the large intestine and is one of the leading causes of cancer-related deaths in the United States.
For the new report, Liang and his colleagues combined results from 41 studies published between 1990 and 2011 that measured fish consumption and tracked cancer diagnoses. That included research from the U.S., Norway, Japan, Finland and elsewhere.
Overall, regularly eating fish was tied to a 12 percent lower risk of developing or dying of colon or rectal cancer, the researchers found.
That was after taking into account study participants’ age, alcohol and red meat intake, family history of cancer and other risk factors.
The protective effect tied to fish consumption was stronger for rectal cancer than colon cancer.
People who ate the highest amounts of fish had a 21 percent lower risk of getting rectal cancer than those who ate the least. That compared to just a four percent lower risk of colon cancer — which was so small, it could have been due to chance.
“Rectal cancer is much rarer, so we’d rather have a larger reduction (in risk) for colon cancer,” Gochfeld said.
The study, published in the American Journal of Medicine, was partially funded by the National Natural Science Foundation of China.
Liang’s team did not investigate why eating fish may have a positive effect on colorectal cancer risk. The study also can’t prove that it’s the fish, itself, that was responsible for a lower cancer risk in some participants.
“It doesn’t tell us whether the benefit you get from fish has to do with specific nutrients in the fish, or with the fact that people who tend to eat fish tend to adopt other healthful lifestyles, such as avoiding red meat or processed meats,” said Gochfeld, who was not involved in the research.
If fish indeed are behind the lower colorectal cancer risk, the added benefit could be coming from the omega-3 essential fatty acids found in certain fish such as salmon and sardines, Gochfeld said.
But even if the high omega-3 levels in fatty fish have a protective effect, it’s unclear whether or not the same benefit extends to supplements such as fish-oil capsules.