The Association Between Depression and Survival in Asthma: The Mediating Role of Income.

Background: Depression is common among individuals with asthma and is linked to increased mortality. However, whether socioeconomic factors contribute to this association remains unclear. We explored whether income may partially account for the association between depressive symptoms and reduced survival in adults with asthma. Methods: A total of 4945 asthma patients were included using baseline data from the National Health and Nutrition Examination Survey (NHANES) 2005-2018 linked to the National Death Index (NDI) mortality follow-up through December 31, 2019. Depression was assessed using the Patient Health Questionnaire-9 (PHQ-9), and mortality was identified through linkage to the NDI. Cox proportional hazards models were used to evaluate the association between depression symptoms and all-cause mortality, and restricted mean survival time (RMST) analysis quantified survival differences over 15 years. Exploratory mediation analysis with quasi-Bayesian simulation was conducted to evaluate whether the poverty-income ratio (PIR) may partially account for the observed association, adjusting for demographic, behavioral, and clinical covariates. Results: Depression was associated with all-cause mortality in asthma patients, and the strength of this association decreased after adjustment for demographic, behavioral, and clinical factors. Over a 15-year period, patients with depression symptoms (PHQ-9 ≥ 10) had markedly shorter survival, losing 9.89 months in RMST (155.2 vs. 165.1 months; Conclusion: Depressive symptoms were associated with reduced survival among adults with asthma, and income may partially account for this observed relationship. These findings should be interpreted cautiously because depressive symptoms and income were measured at baseline, limiting causal interpretation of the mediation analysis. Further longitudinal studies are needed to confirm these findings and clarify temporal relationships.