Association between Diabetic Retinopathy and Parkinson Disease: The Korean National Health Insurance Service Database

Context: Studies have shown an association between diabetes and Parkinson disease (PD). The retina is a part of the central nervous system; it was proposed that diabetic retinopathy (DR) and PD share common pathophysiology of dopamine deficiency. However, no epidemiologic studies have investigated the relationship between these two diseases. Objective: We assessed the association between DR and incident PD using a populationbased database. Design/Setting/Participants: Using the Korean National Health Insurance Service database, 14,912,368 participants who underwent regular health checkup from 2005 to 2008 were included. Subjects were classified into non-diabetes, diabetes without DR, and diabetes with DR groups at baseline and followed up until the date of PD incidence, death, or 31 December 2013. Cox proportional hazards regression analysis was used to evaluate the association between DR and incident PD. Results: During the period, 34,834 subjects were newly diagnosed with PD. The incidence of PD was 2.74, 8.39, and 15.51 per 10,000 person-years for the non-diabetes, diabetes without DR, and diabetes with DR groups, respectively. In multivariate Cox proportional hazard models, DR groups were associated with significantly higher risk of PD than non-diabetes or diabetes without DR groups even after adjusting for age, sex, fasting plasma glucose level, insulin usage, and other possible risk factors. Conclusion: Concurrent DR was associated with an increased risk of incident PD. Future studies are necessary to investigate the mechanism of increased risk of PD in DR including dopamine deficiency in the central nervous system and long-lasting poor glycemic control.