Background: Incidence of asthma increases during early adulthood. We aimed to estimate the contributions of sex and early life factors to asthma diagnosed in young adults. Methods: 1246 healthy newborn babies were enrolled in the Tucson Children's Respiratory Study. Parental characteristics, early-life wheezing phenotypes, airway function, and bronchial hyper-responsiveness to cold dry air and sensitisation to Alternaria alternata were determined before age 6 years. Physician-diagnosed asthma, both chronic and newly diagnosed, and airway function were recorded at age 22 years. Findings: Of 1246 babies enrolled, 849 had follow-up data at 22 years. Average incidence of asthma at age 16-22 years was 12·6 per thousand person-years. 49 (27%) of all 181 cases of active asthma at 22 years were newly diagnosed, of which 35 (71%) were women. Asthma remittance by 22 years was higher in men than in women (multinomial odds ratio [M-OR] 2·0, 95% CI 1·2-3·2, p=0·008). Age at diagnosis was linearly associated with the ratio of forced expiratory volume at 1 s to forced vital capacity at age 22 years. Factors independently associated with chronic asthma at 22 years included onset at 6 years (7·4, 3·9-14·0) and persistent wheezing (14·0, 6·8-28·0) in early life, sensitisation to A alternata (3·6, 2·1-6·4), low airway function at age 6 years (2·1, 1·1-3·9), and bronchial hyper-responsiveness at 6 years (4·5, 1·9-10·0). Bronchial hyper-responsiveness (6·9, 2·3-21·0), low airway function at 6 years (2·8, 1·1-6·9), and late-onset (4·6, 1·7-12·0) and persistent wheezing (4·0, 1·2-14·0) predicted newly diagnosed asthma at age 22 years. Interpretation: Asthma with onset in early adulthood has its origins in early childhood. Funding: National Heart Lung and Blood Institute.
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