Traffic-related air pollution correlates with adult-onset asthma among never-smokers

BACKGROUND: Traffic-related pollution is associated with asthma onset in children. Its effect on adult-onset asthma is poorly investigated. OBJECTIVE: We used the SAPALDIA cohort study to investigate associations between the 11-year change (1991-2002) in home outdoor traffic-related particulate matter up to 10 micrometers in diameter (TPM10) and asthma incidence. METHODS: Never-smokers without asthma at baseline (ages: 18-60 years in 1991) were eligible. Subjects reporting doctor's diagnosed asthma at follow-up were considered incident cases. TPM10 at baseline and follow-up was predicted and interpolated to subject's residences by dispersion models using emission and meteorological data. Cox proportional hazard models for time to asthma onset were adjusted (age, gender, baseline atopy, BMI, bronchial reactivity, maternal allergies). RESULTS: Among 2725 never-smokers, 41 reported asthma onset in 2002. Home outdoor TPM10 concentrations improved during the interval (mean: -0.6; range -9 to +7.2; IQR 0.6 microg/m3). Asthma incidence was associated with change in TPM10. The hazard ratio (1.30; 95%CI: 1.05 - 1.61) per 1 microg/m3 change in TPM10 (IQR) was not sensitive to further adjustments (education, workplace exposure, passive smoking, parental asthma or allergies, random area effects, lung function, or co-pollutants such as regional, secondary, total PM10, or proximity to busy roads). CONCLUSION: The data suggest a role for traffic-related pollution in adult-onset asthma. Space, time, and source-specific individual assignment of exposure to traffic-related pollution is a key strength of SAPALDIA. It may explain why findings were statistically significant despite the limited number of new cases. As traffic-related pollution prevails, the finding may be of substantial public health relevance.