Exercise curbs precancerous changes in the colon

By Anne Harding

NEW YORK (Reuters Health) - Regular, moderate-to-vigorous aerobic exercise can reduce cellular changes in the tissue lining the colon that can lead to the formation of colon polyps and colon cancer, a study suggests.

"This shows that you can see a biological effect at the tissue level of exercise," Dr. Anne McTiernan of the Fred Hutchinson Cancer Research Center in Seattle told Reuters Health. "This supports the observational studies that people who exercise have a lower risk of colon cancer."

However, the effects of exercise were only seen among men in the current study. This may have been because women just didn't exercise as hard, McTiernan offers, or because their workouts reduced their levels of estrogen, which protects against colon cancer.

McTiernan and her team looked at the structure of colonic crypts, microscopic pits in the lining of the colon that help to absorb water and nutrients. People with colon cancer show increased cell growth within these crypts, she explained. Specifically, the area of rapid cell growth, or proliferation, extends higher from the bottom of the crypt in patients' tissue than in healthy individuals.

To investigate whether exercise might affect these structures, the researchers randomly assigned 202 healthy men and women aged 40 to 75 years to an exercise program with the goal of working out moderately to vigorously for one hour a day, six days a week, for a year, or a control group who did not exercise. All study participants had undergone a colonoscopy within three years before the study, and then had another colonoscopy after the study ended.

Men exercised for 370 minutes each week, on average, compared to 295 minutes for the women.

Men who exercised for 250 to 300 minutes each week had a 1.7 percent reduction in the extent of cellular proliferation within their colonic crypts, while the men who exercised more than 300 minutes weekly reduced it by 2.4 percent, the researchers found.

The men who exercised for less than 250 minutes a week showed a 0.3 percent increase in the height of cellular proliferation, while those who didn't exercise had no change.

Among men who increased their cardiovascular fitness by more than 5 percent, the reduction in colon crypt cell proliferation height was 2 percent, compared to 0.9 percent for those who exercised but showed lower gains in cardiovascular fitness.

The findings support studies linking regular aerobic exercise to lower colon cancer risk, and suggest that exercise may cut this risk by reducing cell proliferation in the colon, the investigators conclude.

SOURCE: Cancer Epidemiology, Biomarkers & Prevention, September 2006.