Income Volatility and Risk of All-Cause Mortality and Cause-Specific Hospitalization Among Adults With Depression: A Nationwide Cohort Study.

BACKGROUND: Depression and personal income volatility are associated with adverse health outcomes through both shared and distinct pathways. However, their combined impact on long-term health outcomes remains poorly understood. METHODS: This nationwide cohort study used the National Health Insurance Service claims database of South Korea, including 735,922 adults aged 19-80 years newly diagnosed with depression in the pre-observation period (2008-2012). Depression was identified using International Classification of Diseases, Tenth Revision codes F32, F33, and F34.1. Personal income volatility was measured using the intraindividual standard deviation of annual percent income change from the same period and categorized into tertiles (low, medium, and high). Individuals were followed from the index date (January 1, 2013) through December 31, 2023 for all-cause mortality and hospitalizations across 15 major disease categories and 80 specific conditions. We estimated mortality using Cox proportional hazards regression and hospitalization using negative binomial regression, using overlap propensity score weighting across tertiles in a 1:1:1 ratio. RESULTS: Among 735,922 adults with a recorded diagnosis of depression (mean age 46.08 years; 499,404 [67.9%] women), a total of 1,770,856 hospitalizations and 90,087 deaths were observed over 7,622,456 person-years of follow-up (mean duration, 10.3 years). Higher income volatility was associated with increased risk of all-cause mortality (high vs. low tertile: hazard ratio [HR], 1.18 [95% confidence interval, 1.16-1.19]) and hospitalization (incidence rate ratio [IRR], 1.07 [1.06-1.08]). The associations between high income volatility and all-cause mortality were more pronounced among men (HR, 1.26 [1.24-1.28]) than women (HR, 1.12 [1.10-1.14]), and among adults aged 30-49 years (HR, 1.17 [1.14-1.21]). The associations with hospitalization were also more pronounced among men (IRR, 1.08 [1.07-1.10]) than women (IRR, 1.07 [1.06-1.08]), and among those aged 50-80 years (IRR, 1.09 [1.08-1.10]). Among the 15 disease categories, hospitalization risks associated with high income volatility were greatest for blood disorders (IRR, 1.47 [1.36-1.59]), endocrine diseases (IRR, 1.40 [1.34-1.46]), respiratory diseases (IRR, 1.35 [1.27-1.43]), and mental disorders (IRR, 1.26 [1.23-1.30]), and lowest for cancer and neoplasms (IRR, 0.96 [0.92-0.99]). Among the 80 conditions, hospitalization risks associated with high income volatility were greatest for hypertensive heart disease (IRR, 1.74 [1.50-2.02]), epilepsy/seizures (IRR, 1.58 [1.46-1.71]), malnutrition (IRR, 2.08 [1.34-3.22]), and nutritional anemia (IRR, 1.85 [1.60-2.13]), among others. CONCLUSION: Income volatility is a risk factor for increased mortality and hospitalization among individuals with depression, separable from baseline income. These findings underscore income volatility as a critical but overlooked determinant of health in this population.