Asthma, but not allergic sensitization, is associated with impaired lung function in young adulthood - a longitudinal population based study

<bold>Background:</bold> Asthma is strongly associated with impaired LF, and allergic sensitization (AS) is a known risk factor for asthma, but the association between AS and LF is not clarified. <bold>Aim:</bold> To examine determinants of LF in adolescence, with special interest in allergic sensitization. <bold>Methods:</bold> In 1996, all schoolchildren in grade one and two, median age 8 years, in two municipalities in Northern Sweden was invited to a questionnaire survey of allergic diseases and skin prick tests (SPT) to 10 airborne allergens. Invitations were repeated at ages 12 and, at 19 years also including spirometry. Participating rate at all three occasions was 1495 (70% of participa age 8). Associations between exposures and spirometry indices were analysed by students t-test and linear regression. <bold>Results:</bold> AS was not associated with LF, irrespective of age at onset, type, or degree of sensitization. Early onset asthma, both persistent (β -0.35, 95% CI –0.60- -0.09) and in remission (β -0.43, 95% CI –0.74- -0.12) was associated with reduced FEV1. Persistent asthma was associated with reduced FEV1/FVC (β -0.81, 95% CI –1.07- -0.55), and remission with reduced FVC (β -0.37, 95% CI –0.67- -0.70). Maternal smoking in pregnancy was associated with lower FEV1/FVC, while own smoking was not. Underweight was associated with marked reduced FEV1 and FVC. Overweight was associated with slight increases in FEV1 and FVC. The results remained in analyses restricted to those without asthma. <bold>Conclusion:</bold> AS was not independently associated with LF, despite being an important risk factor for asthma. Early-onset asthma was associated with LF impairments also among those in remission.