Physical Activity and Risk of Colon Cancer in Diabetic and Nondiabetic US Adults

Objective: To determine whether moderate to vigorous physical activity is associated with a decreased risk of colon cancer in diabetic patients. Patients and Methods: We evaluated the association between physical activity and colon cancer in 25,753 patients with a self-reported history of diabetes and in 274,965 nondiabetic individuals from the National Institutes of Health-AARP Diet and Health Study who were aged 50 to 71 years in 1995-1996. Moderate to vigorous physical activity was assessed at baseline using a self-administered questionnaire. Follow-up for colon cancer incidence extended to December 31, 2011. Results: During 13.0 years of follow-up, 480 diabetic patients and 4151 nondiabetic individuals had development of colon cancer. Among diabetic patients, compared with never/rarely engaging in physical activity, more than 7 h/wk of physical activity exhibited a reduced risk of colon cancer in the age-and sex-adjusted model (hazard ratio [HR], 0.74; 95% CI, 0.56-0.996; P =.16 for trend). This association was attenuated and no longer statistically significant after additional control for other covariates (HR, 0.78; 95% CI, 0.58-1.05; P =.29 for trend). By comparison, physical activity was inversely related to colon cancer risk in nondiabetic individuals (multivariate-adjusted HR, 0.81; 95% CI, 0.73-0.89; P<. 001 for trend). Conclusion: In this investigation of the relationship between physical activity and colon cancer in diabetic patients, we found a statistically significant inverse relationship in the age-and sex-adjusted model, which was no longer statistically significant in the multivariate-adjusted model. A reduced risk was noted among nondiabetic individuals, irrespective of other covariates. Future studies with a larger number of participants are required to explore whether physical activity beneficially affects colon cancer risk among diabetic patients. (C) 2016 Mayo Foundation for Medical Education and Researc