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Cancer Health Center

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Is Sitting Too Long a Major Cancer Risk?

Study Shows Inactivity and Excess Sitting Linked to an Estimated 100,000 Cancer Cases a Year

Sitting Time and Cancer Risk continued...

"We can now say there is convincing evidence that activity reduces the risk of colon and breast cancer and probably endometrial," she tells WebMD.

There is weaker evidence for the effect of exercise on lung, prostate, and ovarian cancer risk, she says.

For colon cancer, studies showed that people who exercised the most (and the amount varied from study to study) had a 30% or 35% risk reduction compared to people who were least active, she says.

In studies on exercise and breast cancer, the most active people reduced their risk 20% or 30%, compared to the least active.

For endometrial cancer, the risk reduction was also 30% to 35% for the most active.

Because each study had different categories of most or least activity, "we can't say, 'this is how many hours [of activity are needed],'" she says. She is addressing that in a current study.

To calculate the effect of activity on cancer risk, Friedenreich turned to the SEER Program (Surveillance, Epidemiology and End Results) database of the National Cancer Institute.

A total of 141,210 colon cancers and 230,480 breast cancers were reported for 2011. She estimated that about 30% of the colon cancers, or nearly 43,000, could be prevented with activity. About 21% of breast cancers, or about 49,000, might be avoided.

In her research, Friedenreich recently found that women who began to exercise had much lower levels of C-reactive protein, an indicator of inflammation and possibly cancer risk, than those who did not.

She randomly assigned half of 320 women, ages 50 to 74, to the exercise group. They worked up to exercise five days a week for at least 45 minutes. The program lasted a year. The study is published in Cancer Prevention Research.

Second Opinion

The bottom line for reducing health risks, including cancer? "Exercise is good, but you can't sit all the time," says Leslie Bernstein, PhD, professor and director of the division of cancer etiology at the City of Hope Comprehensive Cancer Center, Duarte, Calif. She reviewed the findings for WebMD.

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