Aims Serum bilirubin concentration is associated with diabetic retinopathy in patients with type 2 diabetes. This study investigated the relationships between serum bilirubin concentration and the severity of diabetic retinopathy. In addition, the importance of bilirubin was compared with factors that were previously shown to be associated with the incidence of diabetic retinopathy. Methods A total of 674 patients with type 2 diabetes were investigated in this cross-sectional study. Serum total bilirubin concentration was compared between patients with and without diabetic retinopathy, and according to the severity of retinopathy. Univariate and multivariate analyses were performed to evaluate the association of retinopathy with total bilirubin concentration, duration of diabetes, body mass index, systolic blood pressure, and haemoglobin A1c. Results Serum total bilirubin concentration was significantly lower in patients with retinopathy than in those without. Patients with severer retinopathy showed lower total bilirubin concentration, longer diabetes duration, and higher systolic blood pressure. These three parameters were independent explanatory factors for diabetic retinopathy. Conclusions Total bilirubin concentration is lower in patients with type 2 diabetes complicated with severer retinopathy. Thus, bilirubin might protect against retinopathy in patients with type 2 diabetes.
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