Abstract
<title>Abstract</title> <p> <bold>Background:</bold> Population-based cohorts with repeated clinical assessments and long-term linkage to national health registers are essential for understanding the trajectories of asthma. We describe the design, data collection, participant characteristics, and future research potential of the Asthma in Middle Sweden (ASTHMID) cohort. <bold>Methods:</bold> ASTHMID is a population-based prospective cohort initiated in 1990. A postal questionnaire was sent to 12,648 individuals in three age groups. A subset underwent clinical examination. Follow-up questionnaires were administered in 1993 to the youngest age group and in 2003 to all. The cohort was linked to Swedish national registers, including the National Patient Register, Cause of Death Register, Prescribed Drug Register, and sociodemographic registers. A matched reference population from the general Swedish population was included for comparison. <bold>Results:</bold> In the study, 11,213 responded in 1990. The baseline population included 3,287 participants in the youngest, 4,201 in the middle, and 3,725 in the oldest age group. Physician-diagnosed asthma was reported by approximately 5–6% across all age groups. In the clinical examination, 721 (28.3%) of 2,544 participants were classified as having confirmed asthma. In 2003, 8,066 participants responded to the follow-up questionnaire. From 1990 to 2023, outpatient visits among cases were highest in the oldest age groups, with 15,586 visits among 1,974 women and 14,824 visits among 1,879 men. Comorbidity burden increased with age, with the highest mean values observed among the oldest men. <bold>Conclusions:</bold> ASTHMID participants have been followed for over 30 years, enabling investigations of long-term asthma outcomes in individuals with and without asthma. </p>