Fasting blood glucose was linearly associated with colorectal cancer risk in the population without self-reported diabetes mellitus history

Fasting plasma glucose level was linearly associated with colorectal cancer (CRC) risk. However, the dose–response relationship between fasting blood glucose (FBG) and CRC risk was still uncertain. A total of 11,632 patients without self-reported diabetes mellitus and colorectal polyps’ history were identified in the Korean Multicenter Cancer Cohort (1993–2005). The nonlinear relationship was estimated through a restricted cubic spline regression, and a two-piece-wise Cox proportional hazards model was further performed to calculate the threshold effect. Multiple imputation was used to control the bias from missing data. Overall, 1.1% (n = 132) of participants were diagnosed with CRC in the follow-up duration. With a median follow-up duration of 12.0 years, participants with FBG ≥126 mg/dL were associated with higher CRC risk (adjusted hazard ratio [HR], 1.67; 95% confidence interval [CI]: 1.01, 2.76). Landmark analyses limited to long-term survivors demonstrated increased CRC risk with FBG ≥ 126 mg/dL in all subsets (≥3years: HR,1.93 (95% CI: 1.13–3.29); ≥5years: HR, 2.04 (95% CI: 1.–3.63); ≥10years: HR, 2.50 (95% CI: 1.19–5.25)). With FBG smoothly increasing before, the latter increased dramatically after the turning point (P for nonlinearity = 0.283). When FBG was increasing per mmol/L, HR was 1.07(95% CI: 0.90, 1.29) for FBG < 126 mg/dL and 1.27 (95% CI: 1.06, 1.53) for FBG ≥ 126 mg/dL. Besides, HR was 1.09 (95% CI: 1.02, 1.16) for the CRC risk. In the population without self-reported diabetes mellitus and colorectal polyps’ history. FBG was linearly associated with CRC risk, especially for FBG over 126 mg/dL.