Smoking and the incidence of asthma during adolescence: results of a large cohort study in Germany

Background: The association between smoking and asthma or wheeze
has been extensively studied in cross sectional studies, but
evidence from large prospective cohort studies on the incidence of
asthma during adolescence is scarce.Methods: We report data from a
cohort study in two German cities, Dresden and Munich. The study
population (n = 2936) was first studied in 1995/6 at age 9--11
years as part of phase II of the International Study of Asthma and
Allergies in Childhood (ISAAC II) and followed up in 2002/3. At
baseline the parents completed a questionnaire and children
underwent clinical examination and blood sampling. At follow up the
young adults completed questionnaires on respiratory health,
living, and exposure conditions. Incidence risk ratios (IRR) were
calculated and adjusted for potential confounders using a modified
Poisson regression approach.Results: The adjusted IRR for incident
wheeze for active smokers compared with non-smokers was 2.30 (95%
confidence interval (CI) 1.88 to 2.82). The adjusted IRR was
slightly higher for incident wheeze without a cold (2.76, 95% CI
1.99 to 3.84) and the incidence of diagnosed asthma (2.56, 95% CI
1.55 to 4.21). Analysis of duration and intensity of active smoking
indicated dose dependent associations. Stratified analyses showed
that the risk of incident wheeze without a cold in atopic smokers
increased with decreasing plasma \textgreeka1-antitrypsin levels at
baseline (1.64, 95% CI 1.22 to 2.20 per interquartile
range).Conclusions: Active smoking is an important risk factor for
the incidence of asthma during adolescence. Relatively lower plasma
levels of \textgreeka1-antitrypsin, although well above currently
accepted thresholds, may increase susceptibility to respiratory
disease among atopic smokers.