Change in physical activity and colon cancer incidence and mortality.

BACKGROUND Although data on the association of physical activity and colon cancer risk is convincing, little research has examined whether change in physical activity alters risk of cancer incidence and mortality. METHODS We examined the association of 10- and 15-year change in physical activity with risk of colon cancer incidence and mortality in the Cancer Prevention Study II. Endpoints were verified through medical record abstraction or registry or National Death Index linkage. Ten-year physical activity analysis included 1,863 incident and 826 fatal cases, whereas the longer-term exposure analysis included 1,386 incident and 602 fatal colon cancer cases. Age and multivariable-adjusted hazard ratios were estimated using Cox proportional hazards models. RESULTS Neither measure of physical activity change was associated with colon cancer incidence. Fifteen-year change was not associated with colon cancer mortality. However, consistently high physical activity over 10 years was associated with a decreased risk of colon cancer mortality as compared with those with consistently low activity. The association attenuated to borderline significance with adjustment for body mass index. Those consistently at or above sample median physical activity levels over 15 years had half the risk of colon cancer death as those consistently below the median. CONCLUSIONS Regular long-term physical activity was associated with a lower risk of colon cancer mortality. IMPACT This study suggests that long-term participation in physical activity provides the greatest reduction in risk of colon cancer death.