There really seems to be a difference in colon cancer risk between the most physically active individuals and the least, a 27% reduction in proximal colon cancer (closer to the small intestine) and a 26% reduction in distal colon cancer (closer to the rectum) for people who are in the category "most" physically active. In the meta-analysis of 21 studies that resulted in these figures, the most physically active would get the equivalent of 5-6 hours of moderate exercise per week and the least physically active would get the equivalent of 30 minutes of moderate exercise per week or less.
However, the benefits of getting 4 hours a week instead of 3 or 45 minutes a week instead of 30 are less clear.
What does the research literature tell us?
- Most studies find a trend in the relationship between exercise and colon cancer risk. The more you exercise, the lower your risk. Any exercise is better than no exercise.
- Exercise reduces the risk of proximal colon cancers, which are "higher" in the colon and harder to detect. Death rates are higher for proximal colon cancer than for distal colon cancers.
- Exercise doesn't guarantee you won't get colon cancer, and only a minority of people ever actually get the disease. But if colon cancer runs in your family, a mild to moderate consistent exercise program is surely a good idea.
Wolin KY, Yan Y, Colditz GA, Lee IM. Physical activity and colon cancer prevention: a meta-analysis. Br J Cancer. 2009 Feb 24;100(4):611-6. doi: 10.1038/sj.bjc.6604917. Epub 2009 Feb 10.