Physical Activity

This chapter discusses epidemiologic studies of physical activity and cancer prevention. There is a large body of epidemiologic data on the relation between physical activity and the risk of developing cancer. Although the direct evidence on this relation comes only from observational studies, randomized clinical trials have provided indirect evidence by examining the association of physical activity with markers of cancer risk, such as body weight and hormone levels. Moreover, several plausible biological mechanisms support the hypothesis that higher levels of physical activity decrease the incidence of various cancers. The data are clearest for colon and breast cancer, with case-control and cohort studies supporting a moderate, inverse relation between physical activity and the development of these cancers.