A prospective study of body mass index, weight change, and risk of cancer in the proximal and distal colon.

BACKGROUND Body mass index (BMI) is an established risk factor for colon cancer, but risks may differ between genders and colon subsites. Moreover, whether weight change influences risk is not yet clarified. We investigated these issues in a large, Norwegian, population-based cohort study. METHODS Participants' weight was measured at examinations up to three times between 1974 and 1988. Hazard ratios (HR) and confidence intervals (CI) were estimated using Cox regression. RESULTS During follow-up of 38,822 men and 37,357 women, we identified 228 proximal and 174 distal colon cancer cases in men and 237 and 159 cases, respectively, in women. The association between BMI and colon cancer risk differed between subsites in men (P = 0.02) but not in women (P = 0.95). In men, HRs (95% CIs) per 5 kg/m(2) were 1.07 (0.86-1.33) and 1.49 (1.19-1.87) for proximal and distal colon, respectively. In women, corresponding HRs (95% CIs) were 1.15 (0.99-1.34) and 1.25 (1.05-1.49). Among overweight men (BMI > or = 25 kg/m(2)), weight gain > or = 10 kg gave higher colon cancer risk than weight maintenance (HR, 2.09; 95% CI, 1.21-3.63), whereas risks were similar among men with stable weight, weight loss, or gains <10 kg. Weight change was not associated with risk in women. CONCLUSIONS The influence of BMI on colon cancer risk differed between subsites in men. Weight gains <10 kg did not influence risk. IMPACT Our results support gender differences and the hypothesis of different etiologies for colon subsites. Whether weight loss in the overweight decreases risk of colon cancer warrants further study.