Fasting C‐peptide at type 2 diabetes diagnosis is an independent risk factor for total and cancer mortality

Abstract Aims We assessed the association between insulin resistance and blood glucose concentrations at type 2 diabetes diagnosis and future development of diabetes‐related complications and mortality. Materials and Methods This retrospective cohort study included 864 individuals with type 2 diabetes (median age 60 years) whose fasting C‐peptide and HbA1c were measured at diabetes diagnosis. The median follow‐up time until death or study end was 16.4 years (interquartile range 13.3−19.6). The association between C‐peptide and mortality/complications was estimated by Cox regression adjusted for sex, age at diabetes diagnosis, smoking, hypertension, BMI, total cholesterol, and HbA1c. C‐peptide and HbA1c were converted to Z scores before the Cox regression analysis. Results An increase by one standard deviation in fasting C‐peptide at diabetes diagnosis was associated with all‐cause (hazard ratio [HR] 1.33; 95% confidence intervals [CI] 1.12–1.58; p = 0.001) and cancer mortality (HR 1.51; 95% CI 1.13–2.01; p = 0.005) in the fully adjusted model. An increase by one standard deviation in HbA1c at diabetes diagnosis was associated with all‐cause mortality (HR 1.24; 95% CI 1.07–1.44; p = 0.005), major cardiovascular events (HR 1.20; 95% CI 1.04–1.39; p = 0.015), stroke (HR 1.36; 95% CI 1.09–1.70; p = 0.006), and retinopathy (HR 1.54; 95% CI 1.34–1.76; p < 0.0001) in the fully adjusted model. Conclusions Fasting C‐peptide at type 2 diabetes diagnosis is an independent risk factor for total and cancer‐related mortality. Thus, treatment of type 2 diabetes should focus not only on normalising blood glucose levels but also on mitigating insulin resistance.