Sustained low income, income changes, and risk of all-cause mortality in individuals with type 2 diabetes: a nationwide population-based cohort study

Objective: There is limited evidence on the association between sustained low-income status, income changes, and all-cause mortality risk in individuals with type 2 diabetes(T2D). 

Research Design and Methods: Using the Korean Health Insurance Service database, we studied 1,923,854 adults with T2D (aged≥30 years) without cardiovascular disease and cancer, who were enrolled from 2009 through 2012 and followed to the end of 2020 (median of 10.8 years of follow-up). We defined income levels based on the amount of health insurance premiums and categorized them into quartiles, the first being the low-income group and assessed the income status annually in the preceding five years. Cox proportional hazards models were used to quantify the association of low-income status and income changes with mortality, adjusting for sociodemographic factors, comorbidities, and diabetes duration and treatment.

Results: Participants who consecutively had low income showed a higher risk of mortality(hazard ratio(HR), 1.19; 95% confidence interval(CI), 1.16-1.22), compared with those who had never been in the low-income group. This association was much stronger for consecutive recipients of Medical Aid, reflecting very low-income status(HR, 2.26; 95%CI, 2.16-2.36), compared with those who had never been Medical Aid beneficiaries. Sustained low- and very low-income status was associated with increased risk of mortality, specifically for younger adults(aged<40 years) and males. Those who experienced declines in income between the first(preceding five years) and the last(baseline) time points had an increased risk of mortality, regardless of baseline income status. 

Conclusions: Among Korean adults with T2D, sustained low-income status and declines in income were associated with increased risk of mortality.