Bidirectional Associations Between Asthma and Types of Mental Disorders

Background: Asthma and mental disorders frequently co-occur. Studies of their comorbidity have generally focused on associations related to a subset of mental disorders. Objective: To estimate bidirectional associations between asthma and 10 broad types of mental disorders. Methods: In a population-based cohort study, including all individuals born in Denmark between 1955 and 2011 (N = 5,053,471), we considered diagnoses of comorbid mental disorders among those with asthma, and vice versa, between 2000 and 2016. We used Cox regression models to calculate overall and time-dependent hazard ratios for mental disorder-asthma pairs and competing-risks survival analyses to estimate absolute risks. Results: Altogether, 376,756 individuals were identified as having an incident mental disorder and 364,063 incident asthma during follow-up. An increased risk was seen for all bidirectional mental disorder-asthma pairs. Following an asthma diagnosis, adjusted hazard ratios for different subsequent mental disorders ranged from 1.75 (95% CI, 1.64-1.87) for organic disorders to 2.75 (95% CI, 2.69-2.81) for personality disorders. Following a prior mental disorder diagnosis, hazard ratios for asthma ranged from 1.06 (95% CI, 1.00-1.12) for developmental disorders to 2.33 (95% CI, 2.28-2.39) for substance use disorders. Risks varied with time since prior disorder diagnosis but remained elevated. Cumulative incidence of (1) asthma after a mental disorder and (2) a mental disorder after asthma was higher in those with prior disorders than in matched reference groups. Conclusions: Our findings provide evidence of bidirectional associations between asthma and each of the mental disorder types, suggesting possible shared etiological factors or pathophysiologic processes