Both regular physical activity and physical fitness have been associated with lower mortality from cancer. Although data for most specific cancers are limited, studies of occupational and leisure time activity indicate that physical activity is protective against colon cancer. Several studies suggest a reduced risk of breast cancer in regularly active women, but a nearly equal number of studies have failed to demonstrate this relationship. The protective effects may be mediated by reduced intestinal transit time (colon cancer) and altered endocrine function.
