Income Gradient in Renal Disease Mortality in the United States

Background: Non-communicable diseases and associated mortality follow a social gradient and chronic kidney disease is not an exception to this rule. Intermediate behavioral and medical factors that may explain such social gradients are, however, still unknown.

Objectives: Using nationally representative data in the United States, this study was conducted to investigate the mediating effect of medical and behavioral risk factors on the association between socioeconomic status (SES) and renal disease mortality.

Patients and methods: Americans' Changing Lives Study (ACL), 1986-2011, is a 25-year nationally representative prospective cohort study. ACL followed 3,361 adults for up to 25 years. Income, education, and unemployment were the main predictors of interest. Death due to renal disease was the main outcome. Health behaviors (smoking, drinking, and exercise) and medical risk factors (diabetes, hypertension, and obesity) were the mediators. Cox proportional hazards models were used for data analysis.

Results: Higher income (HR = 0.75; 95% CI = 0.62-0.89) was associated with lower risk of death due to renal disease over the 25-year follow-up period. Although health behaviors and medical risk factors at baseline were also predictors of the outcome, they failed to explain the effect of income on death due to renal disease. That is, income was associated with death due to renal disease above and beyond all potential mediators including behavioral and medical risk factors.

Conclusion: Socioeconomic inequalities in the United States cause disparities in renal disease mortality; however, such differences are not due to health behaviors (smoking and drinking) and medical risk factors (hypertension and diabetes). To reduce disparities in renal disease mortality in the United States, policies should go beyond health behaviors and medical risk factors. While programs should help low-income individuals maintain exercise and avoid smoking, reduction of income disparities should be regarded as a strategy for reduction of disparities in renal disease mortality. By increasing minimum pay and minimizing the income gap, we may reduce disparities in renal disease mortality.