Depressive symptoms and chronic lung disease in middle-aged and older Chinese adults: Prospective bidirectional association and mediation analysis.

Abstract Background We investigated the prospective bidirectional association between depressive symptoms and chronic lung disease (CLD) and explored biologically and behaviorally relevant mediators in this bidirectional association among Chinese middle-aged and older population in the China Health and Retirement Longitudinal Study. Methods Multivariable-adjusted Cox proportional hazard models were used to examine baseline depressive symptoms in relation to incident CLD risk among 12,546 adults and examine CLD condition in association with incidence of elevated depressive symptoms among 6,929 participants from 2011 to 2018. Elevated depressive symptoms were assessed with the 10-item Center for Epidemiologic Studies Depression scale and CLD was determined by self-reported physician diagnosis. Causal mediation analysis was performed to examine the direct and indirect effects of a priori selected nine blood biomarkers and four lifestyle factors in the bidirectional association. Results Elevated depressive symptoms significantly increased CLD risk by 68% (HR=1.68, 95%CI=1.46–1.93) after a mean follow-up of 5.9 years and the strong positive association was consistently shown in almost all the subgroups. Having positive CLD status at baseline was associated with 17% increased risk of developing elevated depressive symptoms (HR=1.17, 95%CI=1.01–1.35) during an average of 4.6 years follow-up period. Significant inflammatory, metabolic or pulmonary function related mediators were not identified. Limitations Inadequate follow-up time and limited mediator variable information may reduce chance of identifying significant mediators. Conclusions Elevated depressive symptoms and CLD were mutual risk factors in middle-aged and older Chinese adults. Early screening and treatment of depression is needed to reduce CLD risk and related comorbidities including new-onset depression so as to relieve substantial disease burdens of CLD and depression in China.