Correlation between C-peptide and diabetic retinopathy in patients with type 2 diabetes mellitus: a cross-sectional study

This study aimed to investigate the relationship between C-peptide levels, specifically 180-min postprandial C-peptide levels, and diabetic retinopathy (DR) in individuals with type 2 diabetes. This cross-sectional study involved 1545 participants divided into two groups: one with diabetic retinopathy (742 individuals) and one without (803 individuals). To assess the connection between C-peptide levels and DR, multivariate logistic regression and Spearman correlation analysis were performed, including subgroup analyses to ensure robustness of the results. Compared with individuals without DR, individuals with DR had significantly lower postprandial C-peptide levels. Additionally, these postprandial C-peptide levels were inversely correlated with Haemoglobin A1c (HbA1c), fasting blood glucose, and duration of diabetes but positively correlated with body mass index (BMI) and triglyceride levels. Logistic regression analysis revealed a strong inverse association between postprandial 180-min C-peptide levels and the risk of DR. Specifically, higher C-peptide levels were linked to a lower prevalence of DR, a relationship that persisted even after adjusting for potential confounding factors. Furthermore, when different subgroups were analyzed based on sex, age, BMI, and HbA1c levels, individuals without DR consistently had higher C-peptide levels than those with DR. A stratified analysis further confirmed that the inverse relationship between C-peptide levels and DR risk was consistent across most subgroups. In conclusion, the results of this study suggest that higher postprandial 180-min C-peptide levels are inversely related to the risk of diabetic retinopathy, implying that elevated C-peptide levels could offer some protection against the retinal damage associated with diabetes.