Previous studies have suggested that diabetes increases the risk of Parkinson disease (PD); however, this has not been conclusively established. We analyzed the risk of PD based on baseline glucose tolerance status in a large-scale cohort representative of the general Korean population. RESEARCH DESIGN AND METHODS This analysis was performed in a cohort of 15,168,021 adults aged ‡40 years who underwent health checkups under the National Health Insurance Service between January 2009 and December 2010. The clinical course of subjects was monitored until December 2016. Subjects were classified into the following groups: no diabetes, impaired fasting glucose (IFG), diabetes duration <5 years, and diabetes duration ‡5 years. We analyzed the adjusted hazard ratio of PD for each group. RESULTS During the observation period of 49,076,148.74 person-years, PD occurred in 31,577 patients. Compared with the nondiabetes group, the adjusted hazard ratio was 1.038 (95% CI, 1.009-1.067) in the IFG group, 1.185 (95% CI, 1.143-1.229) in the diabetes duration <5 years group, and 1.618 (95% CI, 1.566-1.672) in the diabetes duration ‡5 years group. These results were consistent with those of the subgroup analysis, and the presence of diabetes further increased the risk of PD regardless of comorbidities such as cardiovascular, cerebrovascular, and chronic kidney diseases. CONCLUSIONS This population-based cohort study suggests that diabetes is an independent risk factor for PD. The prevalence of diabetes and related complications is increasing worldwide (1,2). Accordingly, the burden on global health care related to diabetes continues to increase (1,3). Meanwhile, various therapeutic interventions for diabetes have been developed, and the clinical course and quality of life of people with diabetes have improved (4). However, it remains impossible to completely prevent the development of diabetes-related complications. Rather, the clinical significance of previously overlooked atypical complications has paradoxically increased (5). Parkinson disease (PD) is also a major chronic disease, and its clinical significance is increasing worldwide. Damage to the dopaminergic neurons of the substantia nigra is known to be a major cause of PD, which is clinically characterized by a variety of
