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

Abstract

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. 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. 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. 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.