Longitudinal Income Dynamics and Risk of End-Stage Kidney Disease in Type 2 Diabetes: A South Korean Population-Based Cohort Study.

Abstract

RATIONALE & OBJECTIVE The prevalence of end-stage kidney disease (ESKD) continues to rise, with socioeconomic status (SES), particularly income, having associations with ESKD risk among individuals with type 2 diabetes (T2D). This study examined the longitudinal association of income changes with ESKD risk among non-elderly adults with T2D in South Korea. STUDY DESIGN Population-based retrospective cohort study. SETTING & PARTICIPANTS 1,481,371 adults aged 30 to 64 years with T2D represented in the South Korean National Health Insurance Service (NHIS) database in 2015 and 2016, followed to 2020. EXPOSURE Sustained income levels, income variability, and income changes over five years prior to entry into the study cohort. OUTCOMES Primary outcome was progression to ESKD, defined as initiation of dialysis or kidney transplantation. ANALYTICAL APPROACH Cox proportional hazards models were used to assess the risk of ESKD, adjusting for demographic, behavioral, and clinical variables. RESULTS Compared with those who never reached the lowest income quartile, individuals who spent any time (1-5 years) in the lowest quartile had a higher risk of ESKD (P for trend < 0.001). Conversely, spending 2-5 years in the highest quartile was significantly associated with a lower ESKD risk (P for trend < 0.001), whereas spending only 1 year in the highest quartile was not associated with ESKD risk. Income that dropped from a higher quartile to the lowest quartile was associated with higher risk, and even those moving from the lowest to the highest quartile had a higher ESKD risk than those who remained consistently in the highest quartile. Individuals with the highest income variability exhibited an increased risk of ESKD (hazard ratio 1.14, 95% confidence interval 1.01-1.29, P for trend = 0.02). LIMITATIONS Residual confounding, lack of data on medication adherence, and missing laboratory results. CONCLUSIONS Dynamic changes in income were associated with ESKD risk among adults with T2D, findings that may inform healthcare policies that address the economic factors potentially contributing to kidney disease progression in South Korean adults with diabetes.