Poor respiratory function is associated with greater incidence of depression

1. In a cohort of patients with varying lung function assessed through values of FVC and FEV1, and no previous depression, participants with the lowest lung function had increased depression levels, compared to individuals with better levels of lung function. 

Evidence Rating Level: 1 (Excellent) 

Depression is a mental health condition that contributes to disability-adjusted life years and may lead to an increased risk of developing negative health outcomes. Identifying a cost-effective strategy to prevent depression is needed, as the current ones are costly and have limited efficacy. Physical health is one modifiable protective factor for depression, with only some parts of it being understood. One aspect still not understood is the role of lung function in preventing depression. Due to the lack of previous evidence, researchers in this prospective cohort study investigated the association between lung function and depression, looking at the mechanisms behind the possible association. A large group of participants with complete lung function (N= 353,243) were taken from the UK Biobank (UKB). A spirometry test was performed on the eligible participants to assess their respiratory function. A normal lung function was considered to be FEV1 ≥ 80% and FEV1/FVC ≥ 0.70, while all individuals who did not meet this criteria had impaired lung function. To compare characteristics’ values at baseline, such as depression or lung function, Wilcoxon tests for continuous variables [mean (SD)] or chi-square tests for categorical variables [frequency (%)] were used. Also used were Cox proportional hazard models as these could estimate the risk of new-onset depression resulting from impaired lung function. There was a nonlinear dose-response relationship between depression risk and lung function (nonlinear P < 0.05 for FVC and FEV1). The hazard ratios (HRs) of depression for FVC (% predicted) were 0.874 (95% CI=0.827-0.924; P < 0.001) for the 2nd quartile, 0.888 (95% CI = 0.839-0.940; P < 0.001) for the 4th quartile, and 0.880 (95% CI = 0.830-0.933; P < 0.001) for the lowest quartile. The HRs of depression for FEV1 were done as well and were 0.903 (95% CI = 0.855-0.954; P < 0.001) for the 2nd quartile, 0.860 (95% CI = 0.813-0.911; P < 0.001) for the 4th quartile, and 0.854 (95% CI = 0.805-0.905; P < 0.001) for the lowest quartile. The risk of developing depression was 12.4% (HR = 1.124, 95% CI = 1.074-1.176) higher in participants with impaired lung function. Biomarkers involving systemic inflammation, erythrocytes, and liver function could be mediators for depression in those with impaired lung function. Overall, damaged lung function was associated with a higher risk of developing depression. Regular screening for lung function may have a role in identifying at-risk populations and then developing individualized interventions. 

Click to read the study in BMC Medicine

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