Background: Depression has been associated with unhealthy behaviors, which may lead to a higher risk of respiratory ill-health. However, little is known about the association between childhood depression and respiratory health outcomes in young adults.

Methods: A prospective study was conducted based on the 24-year follow-up of the Swedish BAMSE cohort. We identified clinically diagnosed depression through the dispensation of antidepressants using national register data confirmed by self-reported diagnosis. At age 24, respiratory symptoms were assessed via questionnaires and clinical evaluation. Metabolic and inflammatory profiles were analyzed to explore potential mechanisms.

Results: Among the 2994 participants who provided study data, 403 (13.5%) had depression at any time point from age 11 to 24. Depression was associated with higher risks of chronic bronchitis (odds ratio, OR=1.58, 95% confidence interval = [1.21, 2.06]) and respiratory symptoms (OR=1.41, [1.11, 1.80]) in early adulthood, independent of body mass index and smoking status. Compared to individuals without depression, those with depression had a higher fat mass index (FMI, ?=0.48, [0.22, 0.74]) and increased blood levels of fibroblast growth factor 21 and Interleukin-6 in early adulthood. These markers together with FMI were found to partly mediate the association between depression and respiratory symptoms (total mediation proportion: 19.8% and 15.4%, respectively, p<0.01).

Conclusions: Childhood depression was associated with an increased risk of respiratory ill-health in early adulthood, independently of smoking. Links to metabolic and inflammatory dysregulations were suggested.