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Fish and Omega-3s May Reduce Colon Cancer Risk
Harvard study links higher fish and omega-3 intake to lower rates of colorectal cancer; may slow prostate cancer, too
11/30/2006By Craig Weatherby
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The study we’re reporting today was co-authored by researchers from the Harvard School of Public Health, which in 2001 honored former Today Show host Katie Couric (pictured at left) for her colon-cancer awareness work.

Couric’s “Confronting Colon Cancer” series spread public awareness of colorectal cancer and prevention strategies, including the critical step of undergoing a colon exam every three years after age 50.

It only makes sense to adjust our diets to minimize the risk. Fortunately, it's looking more and more like fish can help prevent colon cancer.

Hard on the heels of a Swedish team’s finding that salmon cuts prostate cancer rates (click here for that story) come new research results that represent more good news for fish-lovers... especially men.

A new data analysis reported by researchers from Harvard University shows that fishy diets may reduce risk of colorectal cancer in men substantially (Phillips MN et al 2006).

Compared to men who ate fish less than once a week:
  • Men who ate fish five times a week or more were 40 percent less likely to develop colorectal cancer.
  • The risk was 20 percent lower among men who ate fish two to five times a week.
The findings flow from a new analysis of diet and health survey data from the 22,071 male medical doctors who participated in the famed Physicians' Health Study (PHS): a huge, rigorously designed clinical trial designed to determine the effects, if any, of aspirin and beta-carotene supplements on development of cancer and cardiovascular disease.

The trial began in 1982 and ended in 1995, and in the end, aspirin proved itself preventive against both diseases, while beta-carotene failed to produce comparable benefits.

Harvard findings add to preventive potential of fish versus colon cancer

Separate Harvard study reports prostate-prevention findings
The Harvard team that performed the colon cancer study analyzed the same data to see if fish had a preventive effect on prostate cancer (Chavarro J et al 2006).

As they said "...although fish intake may not reduce the risk of developing prostate cancer, it may improve prostate cancer survival. Whether this is due to early cancer detection and treatment or a true benefit of fish intake on cancer progression deserves further investigation."

We already have some evidence that fish and omega-3s can help prevent colon cancer (see “Fish Oil May Curb Onset of Colorectal Cancer” and “Fish Cuts Risk of Colorectal Cancer, Red Meat Raises It”).

But the investigators who performed the new analysis were also trying to determine if fish consumption had a different effect on men who received aspirin for five years compared to men who didn’t use aspirin.

According to lead author Megan Phillips, “We thought that maybe for men who received aspirin, it wouldn't matter whether they ate fish or not.”

The PHS participants filled out a one-time food questionnaire 12 months after starting the study. It asked how often they ate fish, and divided seafood consumption into four different categories, including a fatty "dark meat" category (salmon, sardines, etc.) to make estimates of omega-3 intake as accurate as possible.

About 11 percent reported eating fish five times or more a week, 48 percent ate fish less than five times a week, 31 percent ate it less than two times a week, and about 10 percent ate fish less than once a week.

The Harvard team then compared these figures with rates of colorectal cancer that later developed in each group at an average of 19.4 years after the beginning of the study.

Omega-3s seen as the key factor
The researchers also estimated the participating men's omega-3 intake, based on their reported consumption of various kinds of fish.

The scientists found that colon cancer risk fell as omega-3 intake rose: results that seem to confirm the notion that fatty fish like salmon, sablefish, and sardines are the oceans' leading anti-cancer candidates.

The Harvard team did not find a significant additional risk-reduction advantage among the men randomized to take aspirin for five years. They speculated that it may take more time for aspirin use to reduce the risk of colorectal cancer.

Although the authors controlled for risk-increasing and risk-reducing factors such as cigarette smoking, vigorous exercise, and multivitamin use, we should note two possible confounding factors:
  • The pattern of fish consumption reported in the one food questionnaire each participant submitted might not reflect the diets that the men followed later.
  • Fish intake was strongly associated with markers of health consciousness, including less smoking, more exercise, lower meat and dairy intake, and higher intake of tomato products (which contain the anti-cancer carotenoid-class antioxidant called lycopene) and vitamin supplements.
The Harvard-based authors included Meir Stampfer, M.D., who is the number one most cited scientist in clinical medicine for the past decade, and Walter Willett, M.D., who ranks as the second most cited scientist in the field.

Their findings add considerably to the existing evidence indicating that omega-3s from fish can help prevent colon cancer, or at least slow its progress substantially. Thanks are due all those volunteer docs, for helping shed light on diet and health.


Sources
  • Phillips MN, Chavarro J, Stampfer M, Willett W, Ma J. A prospective study of fish, n-3 fatty acid intake, and colorectal cancer risk in men. Poster B165, Poster Session B (Biomarkers and Early Detection: Cancer Surveillance and Screening). Fifth Annual International Conference on Frontiers in Cancer Prevention Research, Boston, MA November 12 – 15 2006. Accessed online November 22, 2006 at http://www.aacr.org/Uploads/DocumentRepository/pdf_files/ 2006Prevention/prev06_posterb.pdf
  • Chavarro J, Stampfer M, Phillips MN, Sesso H, Willett W, Ma J. A prospective study of fish intake in relation to prostate cancer risk and survival. Poster A158, Poster Session A (Biomarkers and Early Detection: Premalignant Lesions). Fifth Annual International Conference on Frontiers in Cancer Prevention Research, Boston, MA November 12 – 15 2006. Accessed online November 22, 2006 at http://www.aacr.org/ Uploads/DocumentRepository/pdf_files/ 2006Prevention/prev06_postera.pdf

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