Prevalence and Environmental Correlates of Small Airways Dysfunction in a Rural Swiss Cohort

Introduction: Small airways dysfunction (SAD) is increasingly recognized as an early marker of respiratory disease. Recent cohort studies have reported wide variability in SAD prevalence across countries, suggesting a possible role of air pollution as a contributing factor. This study aimed to assess SAD prevalence in a general population from rural Switzerland, compare it to existing cohorts, and identify associated factors.

We analysed data from the Swiss Longitudinal Cohort Study (SWICOS), conducted in two neighbouring rural villages in Southern Switzerland (Cama and Lostallo). All participants underwent spirometry, with SAD defined as a maximal mid expiratory flow below the lower limit of normal. Air pollution data were obtained from official monitoring stations located within 10 km of the study site.

The study included 423 participants (mean age 50.4 ± 16.3 years; 43.7% male). SAD prevalence was 2.60% (95% CI: 1.46-4.60), significantly associated with active smoking but not with age, BMI, or respiratory symptoms. Exposure to particulate matter was lower than in other international cohorts.

In this rural Swiss population study, SAD prevalence was slightly lower than in the Swiss urban cohort and markedly lower than in other recent studies, which involved populations exposed to higher levels of air pollution. These findings support growing evidence that air pollution exposure may contribute to early small airways impairment.