The comprehensive study analyzed data from studies conducted over several decades and found that people who exercised the most were 24 percent less likely to develop the disease than those who exercised the least.

One of the lead study authors said:

"What's really compelling is that we see the association between exercise and lower colon cancer risk regardless of how physical activity was measured in the studies... that indicates that this is a robust association and gives all the more evidence that physical activity is truly protective against colon cancer."

"There is an ever-growing body of evidence that the behavior choices we make affect our cancer risk. Physical activity is at the top of the list of ways that you can reduce your risk of colon cancer."

The researchers found that the protective effect of exercise held for all types of physical activity, whether that activity was recreational, such as jogging, biking or swimming, or job related, such as walking, lifting or digging. It also had the same effect for both men and women.

Colorectal cancer is the third most common type of cancer, and two-thirds of cases occur in the colon, while the rest develop in the rectum. This study suggests that if people became more physically active, then less cases of this cancer would be seen.

Exercise is thought to cut the risk of the disease by keeping weight in check and increasing the speed at which cancer-causing chemicals in food pass through the gut. It may also reduce bowel inflammation and the level of hormones linked to the growth of tumors.

Details of study: Wolin KY, Yan Y, Colditz GA, Lee I-M. Physical activity and colon cancer prevention: a meta-analysis. British Journal of cancer. Feb. 10, 2009 (advance online publication).