More than 173,000 cancer cases diagnosed each year may be due to physical inactivity and prolonged periods of sitting, USA Today reported.

A new analysis blames physical inactivity for about 49,000 cases of breast cancer and 43,000 cases of colon cancer each year, as well as an estimated 37,200 cases of lung cancer, 30,600 cases of prostate cancer, 12,000 cases of endometrial cancer and 1,800 cases of ovarian cancer.

"This gives us some idea of the cancers we could prevent by getting people to be more active," said epidemiologist Christine Friedenreich of Alberta Health Services in Calgary, Canada. “This is a conservative estimate. The more physical activity you do, the lower your risk of these cancers."

The estimations were based on national physical activity data and cancer incidence statistics, as well as a review of more than 200 cancer studies worldwide.

The numbers suggest that regular physical activity can reduce the risk of breast, colon and endometrial cancers by 25 to 30 percent.

Experts have long known that physical activity decreases the risk of chronic diseases including cancer, heart disease and diabetes, Friedenreich said, but the new data gives more concrete estimates on how many cases may actually be prevented by being more active.

James Levine, a professor of medicine at Mayo Clinic in Rochester, Minn., said many people sit an average of seven to 9½ hours a day. "If you've sat for an hour, you've probably sat too long," he said.

Friedenreich is also looking into why exercise reduces cancer risk. In a study of 320 post-menopausal women, she found that physical activity appears to decrease the risk of cancer by increasing insulin sensitivity and reducing body fat, inflammation, metabolic hormones and sex steroids hormones.

The data was presented Thursday at the annual conference of the American Institute for Cancer Research (AICR) in Washington, D.C.

Click here to read more from USA Today.

MyHealthNewsDaily contributed to this report.