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Fish Consumption Reduces Colon Cancer Risk by 40%

With cancer, researchers don’t believe “you are what you eat” - that disease is always a direct result of what is, or what isn’t, on your dinner plate. But studies into the association between diet and cancer show that food can have an impact in preventing cancer, or in reducing the aggressiveness of the disease. At the American Association for Cancer Research’s Frontiers in Cancer Prevention Research meeting in November 2006, investigators have found that eating fish regularly as an adult can help to protect against development of colon cancer. The researchers say these studies provide some of the strongest links found to date between diet and cancer.

Men who ate fish five times a week or more had a 40 percent lower risk of developing colorectal cancer compared to men who ate fish less than once a week, according to a new analysis of data from 22,071 participants in the Physicians’ Health Study (PHS).
The researchers say the reduction in colorectal cancer risk is substantial in comparison to other dietary components, and while they don’t suggest that everyone starts eating fish daily simply because of these results, they say the health benefits of fish consumption have already been proven.

“We already know that eating fish can reduce the risk of sudden cardiac death, and this might provide another reason to add fish to your diet,” said Megan Phillips, a doctoral student at the Harvard School of Public Health and the lead author of this study.
The researchers believe the health effects of fish consumption in relation to colorectal cancer may lie in their content of the omega-3 fatty acids that can inhibit the cyclooxygenase-2 (COX-2) enzyme. This enzyme acts as a mediator of inflammatory responses thought to be associated with cancer development. Neptune krill oil is another important source of Omega-3 DHA and EPA.

The Physicians’ Health Study was designed as a randomized, double blind, placebo-controlled clinical trial to examine the effect of aspirin and beta-carotene supplements on development of cancer and cardiovascular disease, and the participants filled out a one-time food questionnaire 12 months after starting the study. In this analysis, investigators were also trying to determine if fish consumption had a different effect on men who received aspirin for five years compared to men who weren’t randomized to use aspirin, which is also a COX-2 inhibitor. “We thought that maybe for men who received aspirin, it wouldn’t matter whether they ate fish or not,” Phillips said.

The researchers looked at four different categories of fish consumed - tuna fish, dark meat fish (salmon, sardines, bluefish, etc.), a general fish category, and shellfish including shrimp, lobster and scallops - and asked how many times the participants ate them on average during the previous year. They found almost 10 percent ate fish less than once a week, 31 percent ate it less than two times a week, 48 percent ate fish less than five times a week, and about 11 percent ate it five times or more a week. They then compared these figures with incidence of colorectal cancer that later developed in the men. (The average follow-up was 19.4 years).

They found that compared to men who ate the least amount of fish, the risk of developing colorectal cancer was 40 percent lower in men who ate the most fish, was 20 percent lower in men who ate fish 2-5 times a week, and 13 percent lower among participants who ate fish less than two times a week.

The relationship between fish consumption and colorectal cancer was similar for men randomized to aspirin and those who weren’t, possibly because the researchers only had information on aspirin use during the first five years in the trial, and “it may take more years of aspirin use to see an effect,” Phillips said.

While she said the results are promising, Phillips also noted that they are based on the assumptions that the pattern of fish consumption observed in the sole food questionnaire represented a diet that the men subsequently followed for many years.

In addition, men who consumed more fish may also have a healthier lifestyle perhaps including better cancer screening. Although this study controlled for some of these factors such as cigarette smoking, vigorous exercise, and multivitamin use, the investigators do not have information on colorectal endoscopies. Thus, these findings need additional confirmation through other prospective studies with more complete information and a definitive answer might require a randomized trial, said senior author Jing Ma, M.D., Ph.D., a researcher at the Brigham and Women’s Hospital-based Channing Laboratory and associate professor of medicine at Harvard Medical School.


American Association for Cancer Research’s Frontiers in Cancer Prevention Research meeting, November 2006.

The mission of the American Association for Cancer Research is to prevent and cure cancer. Founded in 1907, AACR is the world’s oldest and largest professional organization dedicated to advancing cancer research. The membership includes more than 24,000 basic, translational, and clinical researchers; health care professionals; and cancer survivors and advocates in the United States and more than 70 other countries. AACR marshals the full spectrum of expertise from the cancer community to accelerate progress in the prevention, diagnosis and treatment of cancer through high-quality scientific and educational programs. It funds innovative, meritorious research grants. The AACR Annual Meeting attracts over 17,000 participants who share the latest discoveries and developments in the field. Special Conferences throughout the year present novel data across a wide variety of topics in cancer research, diagnosis and treatment. AACR publishes five major peer-reviewed journals: Cancer Research; Clinical Cancer Research; Molecular Cancer Therapeutics; Molecular Cancer Research; and Cancer Epidemiology, Biomarkers & Prevention. Its most recent publication, CR, is a magazine for cancer survivors, patient advocates, their families, physicians, and scientists. It provides a forum for sharing essential, evidence-based information and perspectives on progress in cancer research, survivorship and advocacy.

Key concepts: Omega-3 fatty acids, colon cancer