Study population
We included 318,950 unique individuals with asthma during the study period 1999-2018, contributing with a total of 1,731,632 years of observation time. Demographic characteristics at time of inclusion including frequency of asthma-related comorbidities are summarized in Table 1 . The majority were women (57%) and the median age at cohort entry was 29 years (IQR 20-38 years). The annual asthma cohort from 1999-2018 consisted of 68,799 individuals with active asthma (median, IQR 67,414-70,277), corresponding to an annual asthma prevalence of 3.4% among 18-45-year-olds in Denmark.