Optimal glycaemic control and the reduced risk of colorectal adenoma and cancer in patients with diabetes: a population-based cohort study

Objective Whether varying degrees of glycaemic control impact colonic neoplasm risk in patients with diabetes mellitus (DM) remains uncertain. Design Patients with newly diagnosed DM were retrieved from 2005 to 2013. Optimal glycaemic control at baseline was defined as mean haemoglobin A1c (HbA1c)<7%. Outcomes of interest included colorectal cancer (CRC) and colonic adenoma development. We used propensity score (PS) matching with competing risk models to estimate subdistribution HRs (SHRs). We further analysed the combined effect of baseline and postbaseline glycaemic control based on time-weighted mean HbA1c during follow-up. Results Of 88 468 PS-matched patients with DM (mean (SD) age: 61.5 (±11.7) years; male: 47 127 (53.3%)), 1229 (1.4%) patients developed CRC during a median follow-up of 7.2 (IQR: 5.5–9.4) years. Optimal glycaemic control was associated with lower CRC risk (SHR 0.72; 95% CI 0.65 to 0.81). The beneficial effect was limited to left-sided colon (SHR 0.71; 95% CI 0.59 to 0.85) and rectum (SHR 0.71; 95% CI 0.57 to 0.89), but not right-sided colon (SHR 0.86; 95% CI 0.67 to 1.10). Setting suboptimal glycaemic control at baseline/postbaseline as a reference, a decreased CRC risk was found in optimal control at postbaseline (SHR 0.79), baseline (SHR 0.71) and both time periods (SHR 0.61). Similar associations were demonstrated using glycaemic control as a time-varying covariate (HR 0.75). A stepwise greater risk of CRC was found (P trend <0.001) with increasing HbA1c (SHRs 1.34, 1.30, 1.44, 1.58 for HbA1c 7.0% to <7.5%, 7.5% to <8.0%, 8.0% to <8.5% and ≥8.5%, respectively). Optimal glycaemic control was associated with a lower risk of any, non-advanced and advanced colonic adenoma (SHRs 0.73–0.87). Conclusion Glycaemic control in patients with DM was independently associated with the risk of colonic adenoma and CRC development with a biological gradient.