Associations between sleep duration with depression and the mediating role of physical activity in patients with chronic respiratory diseases: evidence from three nationwide population-based studies

Chronic obstructive pulmonary disease (COPD), asthma, and asthma-COPD overlap (ACO) are common chronic respiratory diseases that could cause severe mental disorders. Sleep duration and physical activity (PA) are related to depression in various diseases. However, their roles in patients with chronic respiratory diseases remain unknown. This study was designed to investigate the potential relationship among sleep duration, PA, and depression in patients with respiratory disorders. Data from CHARLS, KNHANES, and NHANES were collected. Generalized linear model (GLM) was applied to investigate the link among sleep duration, PA, and depression. Subgroup analyses were performed. Restricted cubic splines (RCS) were applied to investigate possible nonlinear correlations between sleep duration and depression. Additionally, mediation analysis assessed whether PA mediated the association between sleep duration and depression. Network analysis were performed to explore the core symptoms. Sleep duration was significantly associated with depression. Gender-stratified analyses showed a stronger association with depression in males in CHARLS and NHANES. Subgroup analysis by respiratory disease subtypes (COPD, asthma, and ACO) revealed consistent inverse associations between sleep duration and depression across all cohorts. RCS revealed that sleep duration exhibited a nonlinear association with depression severity in three cohorts. Mediation analysis demonstrated that PA accounted for 24.1 % (CHARLS), and 25.5 % (KNHANES) of the sleep duration - depression relationship. According to strength centrality, node CESD3 ‘Felt sadness’ and node CESD2 ‘Trouble focus’ represented the most central positions of the network in CHARLS. In KNHANES and NHANES, node PHQ2 ‘Feeling down, hopeless’ and node PHQ6 ‘Guilt’ as the core symptoms. This study confirms that sleep duration is consistently linked to depression in COPD, asthma, and ACO patients across three countries. PA partially mediates this connection. Key depressive symptoms (e.g., sadness, guilt) were most strongly tied to sleep and activity patterns. Clinicians should consider both sleep and physical activity when managing depression in these patients. Further research is needed to confirm causality and refine interventions. Chronic respiratory diseases, including COPD, asthma, and ACO usually bring severe mental damage Pioneering study of the relation between sleep and depression in patients with COPD, asthma, and ACO, and reveal the mediating effect of physical activity between sleep duration and depression Investigating the dose-response association of sleep duration with depression severity, and explore the core symptoms using network analysis which could be vital intervention targets