The influence of physical activity in 1,2 dimethylhydrazine induced colon carcinogenesis in the rat.

Recent epidemiologic findings indicate that relative risk of colon cancer is augmented with increasing proportion of time spent on sedentary occupations, and reduced with occupations requiring high levels of work-related physical activity. Therefore, the influence of exercise on experimental colon carcinogenesis was investigated. Spontaneous running wheel activity was related to incidence of 1,2 dimethylhydrazine (DMH) colon tumor induction. Colon tumor incidence was significantly reduced in animals that were allowed spontaneous wheel activity throughout the period of DMH tumor induction vs standard housed controls (p less than 0.05), indicating that, in the rat, physical activity protects against colon tumorigenesis. Further comparisons reveal a mild positive association (p = 0.07) between activity and incidence of tumors in the left colon. These results are in accord with epidemiologic findings indicating reduced colon cancer risk with increased physical activity. Possible mechanisms for the protective influence of physical activity on tumorigenesis include reduction in fecal pH, body weight and increased antioxidant enzyme activity. To the extent that epidemiologic associations between colon cancer and activity are inclusive of the multidimensional nature of physical activity, animal models such as that utilized in this experiment can be utilized for investigating the etiologic potential, or strength of association in variables that have been epidemiologically associated with colon cancer risk.