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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...

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.

Bernstein and colleagues published a study in 2010 about the dramatic effects of "sitting time" on the likelihood of dying.

The study was led by Bernstein's former doctoral student, Alpa Patel, PhD, now an epidemiologist with the American Cancer Society. They found the likelihood of dying during the 14-year follow-up was higher in those who spent six or more hours a day sitting, compared to those who spent less than three hours. The risk was 37% higher for women sitting six or more hours and18% for men.

The link was strongest for death from heart disease. The sitting time was linked with death risk, regardless of the amount of physical activity, Bernstein tells WebMD. The study is published in the American Journal of Epidemiology.

"All our messages before [to reduce disease risk] were 'exercise, exercise, exercise,''' Bernstein says. Now, growing evidence suggests it is also important to avoid prolonged periods of sitting, she says.

Tips for Office Workers

Bender says it's possible even for a commuting, desk-bound office worker to avoid long periods of sitting.

Her tips:

  • Set the timer on your computer to alert you every 60 minutes to take a break. A short walk down the hall is enough.
  • Ask a colleague to walk with you to talk about a problem instead of sitting.
  • During a phone call in your office, stand up and walk around if possible.
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