Relation of impaired glucose tolerance and diabetes mellitus to colorectal adenomas in Japan

Objective: Because a link between hyperinsulinemia and colorectal carcinogenesis has been hypothesized, we explored the relation between glucose tolerance status and colorectal adenomas. Methods: We conducted a case–control study of 560 cases of histologically confirmed colorectal adenomas and 829 controls of normal total colonoscopy in Japanese middle-aged men. Subjects were classified into normal, impaired fasting glucose (IFG), impaired glucose tolerance (IGT), newly diagnosed type 2 diabetes mellitus (DM), and known DM based on fasting blood glucose, 75 g glucose tolerance test, and medical history. Odds ratios (ORs) and 95% confidence intervals (CIs) were obtained from logistic regression analysis with subjects with normal glucose tolerance and IFG as a referent group. Results: IGT, new type 2 DM, and known DM were each associated with a modest increase in the risk of colorectal adenomas after adjustment for possible confounding factors. An increased risk of large, but not small, adenomas was observed among men with IGT and new type 2 DM. An increased risk associated with new type 2 DM was observed for proximal adenomas only. Conclusions: Not only type 2 DM but also IGT is associated with increased risk of colorectal adenomas. Hyperinsulinemia may be involved in colorectal carcinogenesis.