Exposure to Air Pollution from Traffic and Childhood Asthma Until 12 Years of Age

Background: There are limited prospective data on long-term exposure to air pollution and effects on childhood respiratory morbidity. We investigated the development of asthma and related symptoms longitudinally over the first 12 years of life in relation to air pollution from road traffic. Methods: The Swedish birth cohort BAMSE (Children, Allergy, Milieu, Stockholm, Epidemiological Survey) includes 4089 children who were followed up with repeated questionnaires and blood samples for up to 12 years of age. Residential, daycare, and school addresses, time-activity patterns, emission databases, and dispersion models were used to estimate individual exposure to particulate matter with aerodynamic diameter <10 mu m (PM10) and nitrogen oxides (NOx) from traffic. Results: Overall, the data suggested possible associations between exposure to air pollution during the first year of life and asthma and wheezing in children up to 12 years of age. Asthma risks seemed to be particularly increased in children age 8 to 12 years; the overall odds ratio was 2.0 (95% confidence interval = 1.1-3.5), and for nonallergic asthma, the odds ratio was 3.8 (0.9-16.2) for a 5th to 95th percentile increase in time-weighted average exposure to PM10 (corresponding to 7.2 mu g/m(3)). Results were similar using exposure to traffic-NOx. Conclusions: We found modest positive associations between air pollution exposure from traffic during infancy and asthma in children during the first 12 years of life, with stronger effects suggested for nonallergic asthma. (Epidemiology 2013;24: 54-61)