Association of sustained extremely low income and income decrease with the risk of Parkinson's disease: A population-based nationwide cohort study in Korea

Objective: Previous studies on the association between income and Parkinson's disease assessed income status at a single time point, without considering changes over time. This study aimed to evaluate the longitudinal association between various income dynamics and the risk of Parkinson's disease. Methods: We used the Korean National Health Insurance Service data, enrolling 2,644,550 individuals who participated in the 2012 National Health Screening Program. The national health insurance premium was used as a proxy measure of income, with four levels (quartile 1 [low] to 4 [high]). Additionally, Medical Aid was classified as extremely low-income. Parkinson's disease was defined using the ICD-10 code (G20) and the rare intractable disease registration code (V124). Cox proportional hazards models were used to assess the longitudinal association between income status and Parkinson's disease rate. Results: During the study period, the incidence rate of Parkinson's disease was 27.13 per 100,000 person-years. A dose-response association between the cumulative number of years in the extremely low-income status and Parkinson's disease rate was identified (P for trend <0.001). A decrease in income from 2008 to 2012 to extremely low-income from quartile 1 (HR = 2.19, 95 % CI 1.55, 3.09), quartile 2 (HR = 2.56, 95 % CI 1.75, 3.74), or quartile 3 (HR = 2.20, 95 % CI 1.24, 3.88) was associated with more than a two-fold increased Parkinson's disease rate compared to individuals with sustained income status. Conclusions: Individuals with sustained extremely low income over 5 consecutive years and those who experienced a decrease in income to this status were at a significantly higher rate of developing Parkinson's disease.