Is Sitting Too Long a Major Cancer Risk?

Nov. 3, 2011 -- Here's a new risk for cancer a lot of us can relate to -- simply sitting too long.

"It seems highly likely that the longer you sit, the higher your risk," Neville Owen, PhD, of Australia's Baker IDI Heart and Diabetes Institute, says in a news release.

Owen presented the research at a news conference today at the American Institute for Cancer Research annual conference in Washington, D.C.

Regular exercise has long been linked with reducing the risk of certain cancers.

Now, experts say they have a better strategy. Get regular exercise and avoid prolonged periods of sitting.

Higher activity could prevent nearly 100,000 cases of breast and colon cancer in the U.S. each year, says Christine Friedenreich, PhD, research scientist and epidemiologist at Alberta Health Services in Canada. "These are just estimates," she tells WebMD.

Friedenreich presented the estimates at the news conference today.

Being sedentary has been linked with an increase in inflammation and other indicators of cancer risk. More recently, so has prolonged sitting.

"We'd like Americans to think about physical activity in a different way," Alice Bender, RD, a dietitian for the American Institute for Cancer Research, said at the news conference. 

The focus, Bender says, should be on finding time for regular exercise while also reducing prolonged sitting. "We would like people to think about 'make time' and 'break time' and that equals cancer protection."

The American Institute for Cancer Research now recommends that adult Americans who sit most of the day take one- or two-minute ''activity'' breaks every hour.

Sitting Time and Cancer Risk

"Sitting time is emerging as a strong candidate for being a cancer risk factor in its own right," Owen says. The link is not dependent, he says, on body weight or the level of exercise done.

In his research, Owen measured waist circumference, inflammation, and other indicators of heart disease and cancer risk. "We found that even breaks as short as one minute can lower these biomarkers."

The study is published in the European Heart Journal.

Along with less sitting, Friedenreich updated the evidence linking physical activity with reduced cancer risk by reviewing more than 200 studies.

"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.