Associations of Income Variability and Incident ESKD in Diabetes: A Population-Based Cohort Study

Background: Studies analyzing the association between income variability and incident end-stage kidney disease(ESKD) among individuals with type 2 diabetes(T2D) are limited. Methods: Based on data from the Korean National Health Insurance Service, 1,481,371 adults aged 30-64 with no history of kidney disease were identified among individuals with T2D who underwent health checkups from 2015 to 2016. Annual income levels from the preceding 4 years to the baseline year were categorized into four quartiles. Income parameters were analyzed in three aspects: (1) cumulative number of years belonging to a specific income status quartile, (2) income volatility, and (3) changes in income status between the initial and end points during the observation. The primary outcome was defined as the first occurrence of incident ESKD, followed up until December 31, 2020. Cox proportional hazard models were used to estimate hazard ratios(HRs) and 95% confidence intervals(CIs). Results: Persistent low income status over 5 years was associated with an increased risk of ESKD (HR 5years vs. 0years: 1.54, 95% CI 1.33-1.78; Ptrend<0.0001). High income volatility was associated with an increased risk of ESKD (HR highest vs. lowest quartile: 1.43, 95% CI 1.27-1.60; Ptrend<0.001). Irrespective of initial income status, individuals whose income status declined during the 5 years of observation, comparing between the initial and end points, had an increased risk of ESKD. The increase in ESKD risk was most pronounced among those whose income status declined steeply from the highest to the lowest quartile (HR steepest decline vs. unchanged: 1.58, 95% CI 1.19-2.09; Ptrend=0.0025). Conclusion: Among adults aged 30–64 with T2D, individuals with more persistent low income status, higher income volatility, and steeper income decline had a significantly increased risk of ESKD. Funding: Government Support – Non-U.S.