Exercise May Not Shield Women from Colorectal Cancer

Study finds no link, but more research could still show a benefit, experts say

By E.J. Mundell
HealthDay Reporter

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FRIDAY, Feb. 17 (HealthDay News) -- Although it's proven to have a protective effect for men, regular physical activity may not lower a woman's risk for colorectal cancer, a new study suggests.

But the study's authors caution that more rigorous research might yet reveal a benefit for women.

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"We shouldn't close the door on this," said senior researcher Dr. Michael F. Leitzmann, an investigator with the U.S. National Cancer Institute in Bethesda, Md.

His team published its findings Friday in the online edition of the International Journal of Cancer.

According to Leitzmann, basic biology supports the notion that being active cuts colorectal cancer risk.

"One of the main hypotheses is that physical activity speeds gastrointestinal transit -- in other words, bowel transit time," he said. "It's also very effective in weight control and weight maintenance, and we know that [increased] body weight is related to an increased risk for colon cancer." Exercise may also enhance the body's natural cancer-fighting abilities by preventing insulin resistance and improving immune function.

In fact, numerous studies of varying quality have consistently shown a real benefit to men from regular exercise, in terms of helping to prevent colon cancer, Leitzmann said.

"The results have been less consistent for women, however," he said.

In their study, the researchers examined data from a prospective study of nearly 32,000 postmenopausal women followed for more than 10 years as part of the Breast Cancer Detection Demonstration Project Follow-Up Study. For that effort, women were asked to provide information on their rate of daily physical activity.

"Somewhat to our surprise, we found that there was no association between our measure of physical activity at that time and [the women's] subsequent risk for colon cancer," Leitzmann said.

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