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 mellitus (T2DM). This study examined the longitudinal association of income changes with ESKD risk among nonelderly adults with T2DM in South Korea.

Study design: Population-based retrospective cohort study.

Setting & participants: 1,481,371 adults aged 30 to 64 years with T2DM represented in the South Korean National Health Insurance Service database in 2015 and 2016 and followed to 2020.

Exposure: Sustained income levels, income variability, and income changes over 5 years before entry into the study cohort.

Outcome: The 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% CI, 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 T2DM, findings that may inform health care policies that address the economic factors potentially contributing to kidney disease progression in South Korean adults with diabetes.

Plain-language summary: Managing diabetes can be expensive, and financial challenges may affect access to proper care. This study investigated the association between changes in income over time with the risk of end-stage kidney disease (ESKD) in adults with type 2 diabetes in South Korea. Using a large national health database, we examined the relationship between income levels, income changes, and the likelihood of developing ESKD. We found that remaining in the lowest income group or experiencing a decline in income was associated with a higher risk of ESKD. Conversely, maintaining a high income was associated with a lower risk. These findings suggest that stable financial resources are associated with a lower risk of ESKD progression in individuals with diabetes, highlighting the potential relationship between economic factors and health outcomes.

Keywords: End-stage kidney disease; income dynamics; risk factor; type 2 diabetes.