Income-Related Disparities in Mortality Among Young Adults With Type 2 Diabetes.

Importance: Previous studies have indicated an inverse association between income and mortality. However, differences in health outcomes according to the income level of young adults with type 2 diabetes (T2D) compared with older adults with T2D have not been elucidated. Objective: To estimate the overall and cause-specific mortality risks among patients with T2D according to income and age. Design, Setting, and Participants: This retrospective nationwide cohort study in South Korea included adults aged 20 to 79 years who were diagnosed with T2D between January 1, 2008, and December 31, 2013, and followed up until December 31, 2019, and age- and sex-matched controls without diabetes. Data were analyzed between January 1, 2023, and August 27, 2024. Main Outcomes and Measures: Risks of all-cause, cardiovascular, and cancer mortality were estimated according to participants' income, which was categorized into 3 levels (low, middle, and high) based on the health insurance premium. Logistic regression analyses and Cox proportional hazard regression analyses were performed according to age groups (20-39, 40-59, and 60-79 years). Results: A total of 1 240 780 adults (604 975 patients with T2D and 635 805 age- and sex-matched controls without diabetes) were included in the analyses. Their mean (SD) age was 56.9 (11.8) years, and 626 176 (50.5%) were men. Overall, the risk of mortality increased with lower income among patients with T2D, as well as in comparison with controls without diabetes. There was an inverse association between income and mortality risk in younger individuals (adjusted hazard ratios of all-cause mortality in the low income vs high income subgroups with T2D were 2.88 [95% CI, 2.25-3.69] in those aged 20 to 39 years, 1.90 [95% CI, 1.81-2.00] in those aged 40 to 59 years, and 1.26 [95% CI, 1.23-1.29] in those aged 60 to 79 years; P < .001 for comparing risk ratios between age groups). The pattern of income-related disparities in younger individuals was observed in cardiovascular mortality but less in cancer mortality. Conclusions and Relevance: In this cohort study of 1 240 780 individuals aged 20 to 79 years, the risk of mortality with low income was most prominent among individuals with T2D aged 20 to 39 years. These findings highlight the need for socioeconomic support to reduce income-related health disparities in younger individuals.