Association of socioeconomic status with kidney function decline and mortality among older Korean adults: a nationwide cohort study

Chronic kidney disease (CKD) is common among older adults, and socioeconomic status (SES) is an important determinant of kidney health. However, evidence on socioeconomic differences in longitudinal kidney outcomes among older adults remains limited. We investigated the association of SES with kidney function decline and all-cause mortality in a nationwide cohort of older Korean adults. In this retrospective cohort study, we included 784,224 adults aged ≥ 60 years from the Korean National Health Insurance Service–Senior Cohort who had a baseline health screening examination and at least one follow-up examination between 2012 and 2023. SES was assessed using the NHIS insurance premium-based classification and categorized into five groups. The primary kidney outcome was a composite of a ≥ 40% decline in the estimated glomerular filtration rate (eGFR) or kidney failure. The secondary kidney outcome was a composite of a ≥ 30% eGFR decline or kidney failure; all-cause mortality was also evaluated. Fine–Gray competing-risk models were used to analyze kidney outcomes, and Cox proportional hazards models were used for all-cause mortality. During a median follow-up of 8.33 years (IQR, 5.15–10.67), higher SES was associated with a lower incidence of the primary kidney outcome. Compared with the lowest SES group, the highest SES group had a lower incidence of the primary kidney outcome (adjusted subdistribution hazard ratio [sHR], 0.85; 95% CI, 0.82–0.88). A similar association was observed for the secondary kidney outcome (adjusted sHR, 0.86; 95% CI, 0.85–0.88). The highest SES group also had lower all-cause mortality than the lowest SES group (adjusted HR, 0.77; 95% CI, 0.76–0.79). A graded association was observed across SES categories (P for trend < 0.001), and the findings remained consistent across analyses of individual kidney outcome components and multiple sensitivity analyses. Among older Korean adults, lower SES was associated with a higher incidence of kidney function decline and all-cause mortality. These findings underscore socioeconomic disadvantage as an important contextual factor in kidney health and support further efforts to understand and reduce socioeconomic disparities in kidney outcomes.