Bidirectional Associations Between Asthma and Types of Mental Disorders

Abstract

Asthma and mental disorders frequently co-occur. Studies of their comorbidity have generally focused on associations related to a subset of mental disorders. To estimate bidirectional associations between asthma and 10 broad types of mental disorders. 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. 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. Our findings provide evidence of bidirectional associations between asthma and each of the mental disorder types, suggesting possible shared etiological factors or pathophysiologic processes.