The role of exercise in cancer is the subject of many studies and considerable debate at present. The cancer most studied for its relationship to cancer is colorectal cancer.  In fact, at least 30 studies have examined the association between physical activity and developing colon cancer.

Colon Cancer

At least 29 studies have focused on the relationship between colon cancer and exercise. These studies were conducted in diverse population groups in various countries including China, Denmark, Japan, New Zealand, Sweden, Switzerland, Turkey and the United States.  Of these, 14 reported a significant relationship between exercise and colon cancer.  Specifically, increase in activity led towards a decrease in colon cancer risk.  Four of the studies showed no relationship.

Just looking at a couple of the studies highlights some interesting observations.  For example, Lee and his colleagues (Lee et al., 1991) looked at over 17,000 Harvard alumni, aged 30-79 years who were followed prospectively for the occurrence of colon cancer and rectal cancer.  They found that physical activity based on self-reported stair climbing, walking and sports play was not associated with a change in risk for colon cancer.  On the other hand, highly active individuals (energy expenditure of > 2500 kilocalories per week) had half the incidence of those that expended less than 1000 kilocalories per week.  As a matter of clarification for the reader,  what most lay people call a calorie is technically a kilocalorie, or Kcal.  Bottom line: in this large study, vigorous activity was associated with a significant decrease in the risk of developing colon cancer. 

Another study, this one from Stanford University (Whittemore et al. 1990), looked at colon cancer risks among Chinese men and women living both in the People's Republic of China, and the Western United States.  This study looked at exercise and diet as risk factors for colon cancer.  The findings indicate that the group that spent the most time sitting (reflecting sedentary lifestyles and occupations) had the highest incidence of colon cancer.  Other interesting findings were that a diet high in saturated fat was also a risk factor, and that those who were most sedentary and consumed the most saturated fat had a four fold higher incidence of colon cancer than those who were the least sedentary and consumed the least saturated fat. 

Rectal Cancer

Rectal cancer does not appear to be associated with a lack of exercise, at least in most studies.  For example, of 13 studies that looked at occupational activity and rectal cancer, 10 reported no relationship.  Two others found a decrease in incidence with increased physical activity, and 1 found an increase in incidence with increased activity.  The conclusion of the CDC is that there does not appear to be a relationship between exercise and rectal cancer.

It must be pointed out that the benefits of exercise in lowering the risk of cardiovascular disease are well established, and there definitely appears to be a decrease in risk of colon cancer.  Once again, we come to some basics.  You can optimize your chances of living a long and healthy life by maintaining a consistent exercise program, maintaining an optimal weight, and eating a diet rich in a variety of fruits and vegetables and a minimal amount of red meat and saturated fat. 

Article By Michael Guthrie, R.Ph.

 

Lee, I.M., Paffenbarger, R.S. Jr., Hsieh, C. (1991). Physical activity and the risk of developing colorectal cancer among college alumni. Journal of the National Cancer Institute 1991 Sep18;83(18):1324-9

Whittemore, A.S. Wu-Williams, A.H., et al. (1990). Diet, physical activity, and colorectal cancer among Chinese in North America and China. Journal of the National Cancer Institute 1990 June 6;82(11):915-26