New-onset of adult asthma: Gender differences in the SAPALDIA cohort

In adulthood, a higher incidence of asthma is reported in women compared to men, but evidence on gender differences in later adulthood is limited. We aimed to determine new onset of asthma in adult men and women over 20 years of follow-up in the Swiss Study on Air Pollution and Lung and Heart Disease in Adults (SAPALDIA). Methods: We calculated incidence of asthma (self-report of doctor diagnosed asthma) between SAPALDIA1 (S1, 1991/92) and SAPALDIA3 (S3, 2010/11) in 2,434 men and 2,681 women without asthma and aged 20-62 at baseline. The age-related probability of new onset of asthma was analysed by logistic regression adjusting for sex, smoking status, parental asthma, BMI, early life respiratory infections, education and area. Analyses were also stratified by sex and atopic status in S1. Results: Over 20 years of follow-up, 135 men (5.01%) and 218 women (7.33%) newly reported doctor diagnosed asthma. In the adjusted analyses, the OR for female sex was 1.87 (95%CI 1.41-2.47) overall and 3.6 (95%CI 2.25-5.78) among non-atopic subjects and 1.2 (95%CI 0.83-1.74) in atopic subjects. The probability of new onset of asthma decreased with increasing baseline age in women but not in men. A higher probability of new asthma was present in atopic compared to non-atopic men, unrelated to age. In women, a higher probability was seen particularly in younger atopic than in older atopic women. These differences decreased with increasing age. Conclusions: Gender differences in asthma incidence over 20 years of follow-up in subjects initially aged 20-60 years were limited to non-atopic subjects. A decline of incidence and of differences between atopic and non-atopic subjects with increasing age was seen only in women.