Of all the benefits associated with exercise, the one least investigated until recently was the association of exercise and cancer.

A number of studies in the past have suggested an association with people who exercise regularly and decreased rates of cancer.

The two cancers which seemed most dramatically affected were cancer of the breast and colon.

These two cancers, breast cancer and colon cancer, have recently been studied in several well done randomized studies. The results seem indisputable: women who exercise regularly most definitely reduce their risk of breast cancer. In fact, the risk of breast cancer seems inversely proportional to the amount of exercise. Women who exercise between one and three hours per week reduce their risk by approximately 30 percent; those exercising more than four hours per week seem to have 55 percent lower rate of breast cancer. Although this study was done in the University of California, there is no reason to believe that this population is in any way different than the general population of America. In addition, among men with desk jobs, there is a direct relationship between the number of years spent at a desk job, in a sedentary fashion, and the cumulative risk of colon cancer. Those men who are up and around have approximately one-half the risk of colon cancer in their lifetime.

Other tumors in which there seems to be a definite reduction of cancer risk with increasing exercise level include uterus, cervix, prostate, and lungs.

Several explanations have been offered for these apparent relationships. First with,atleast some cancers, notably breast cancer, increasing obesity is statistically related with development of breast cancer. To what extent this is because of late diagnosis (due to increased fatty tissue) versus actual decreased cancer, has been clarified only in the last several years. Scientific studies have a higher rate of breast cancer. It seems logical, then, that people who exercise regularly would be less likely to be obese and therefore more likely to "ward off" breast cancer.