# Association between depressive symptom and respiratory health in two prospective cohort studies

## TL;DR

This study found that fluctuating, increasing, or consistently high depressive symptoms are linked to a higher risk of chronic lung diseases and worse lung function.

## Contribution

The study introduces a novel analysis of dynamic depressive symptom trajectories and their specific associations with respiratory health outcomes.

## Key findings

- Fluctuating, increasing, and consistently high depressive symptoms were linked to higher chronic lung disease risk.
- These depressive symptom patterns were also associated with lower peak expiratory flow values.
- Total and somatic depressive symptoms showed stronger associations with adverse respiratory outcomes.

## Abstract

The association between depressive symptoms and respiratory health remains inconclusive, with limited research exploring dynamic changes in overall and symptom-specific depression. This study aimed to investigate the relationship between depressive symptom trajectories and the risk of chronic lung diseases (CLDs) as well as pulmonary function. We used data from two prospective cohorts: the China Health and Retirement Longitudinal Study (CHARLS) and the Health and Retirement Study (HRS). Depressive symptoms were assessed using the 10-item and 8-item CES-D scales, respectively, at three time points (CHARLS: wave1-3; HRS: wave 5–7), and classified into five trajectories: consistently low, decreasing, fluctuating, increasing, and consistently high. Incident CLDs were identified by self-reported physician diagnoses (CHARLS: wave 4–5; HRS: wave 8–12), and pulmonary function was evaluated by peak expiratory flow (PEF, CHARLS: wave 3; HRS: wave 8). Cox proportional hazards and linear regression models were used to estimate hazard ratios (HRs), beta coefficients (β), and 95% confidence intervals (CIs), adjusting for potential confounders. At baseline, individuals with depressive symptoms had a higher risk of Incident CLDs and lower PEF values. Compared to the consistently low group, the fluctuating (CHARLS: HR = 1.56, 95% CI: 1.33, 1.84; HRS: HR = 1.52, 95% CI: 1.30, 1.77), increasing (CHARLS: HR = 2.39, 95% CI: 1.86, 3.07; HRS: HR = 1.62, 95% CI: 1.13, 2.31), and consistently high (CHARLS: HR = 2.59, 95% CI: 2.16, 3.11; HRS: HR = 1.66, 95% CI: 1.30, 2.13) trajectories were associated with significantly increased CLDs risk. These trajectories were also significantly associated with lower PEF. The decreasing trajectory showed no significant association with CLDs risk or PEF. Total and somatic depressive symptoms demonstrated stronger associations with adverse respiratory outcomes. Depressive symptom trajectories characterized by fluctuation, increase, or persistent elevation are associated with higher CLDs risk and poorer pulmonary function. In contrast, symptom remission appears unrelated to respiratory outcomes. Total and somatic symptoms may serve as more sensitive indicators for predicting respiratory health.