Physical activity and reduced risk of incident sporadic colorectal adenomas: observational support for mechanisms involving energy balance and inflammation modulation.

To investigate the role of physical activity, energy balance, and inflammation on the risk of incident sporadic colorectal adenoma, the authors conducted a community- and colonoscopy-based case-control study (n = 177 cases, n = 228 controls) in Winston-Salem and Charlotte, North Carolina, from 1995 to 1997. Participants reported energy intake by a semiquantitative food frequency questionnaire, daily physical activity levels by a standardized questionnaire, and anthropometrics by self-assessment. The odds ratios for adenomas comparing the highest and lowest quantiles of exposure were 0.63 (95% confidence interval (CI): 0.34, 1.17) for physical activity, 0.80 (95% CI: 0.37, 1.73) for total energy intake, 0.70 (95% CI: 0.37, 1.34) for body mass index, 1.46 (95% CI: 0.73, 2.92) for waist/hip ratio, and 2.40 (95% CI: 1.24, 4.63) for height. For the combined effects of these factors, risk was particularly low for those with higher physical activity and low waist/hip ratio (odds ratio = 0.37, 95% CI: 0.18, 0.75) or shorter stature (odds ratio = 0.32, 95% CI: 0.16, 0.62). The inverse effect of physical activity was apparent only among those not taking nonsteroidal antiinflammatory drugs (odds ratio = 0.49, 95% CI: 0.25, 0.94). These findings add further evidence that physical activity and overall patterns indicating positive energy balance increase the risk of adenoma. Furthermore, the results suggest indirectly that biologic mechanisms related to inflammation may play a role in the beneficial effect of physical activity on the risk of incident adenoma.