Long-term exposure to air pollution from road traffic and development of airway and allergic diseases in children

Abstract

Allergic diseases are of great public health concern and constitute one of the most prevalent childhood illnesses. Air pollution exposure is related to several types of adverse health effects. There are, however, limited prospective data on long-term exposure to air pollution and effects on childhood respiratory and allergic morbidity, particularly concerning the role of timing of exposure, and susceptible groups. The aim of this thesis was to investigate effects of long-term exposure to air pollution on the development of airway disease in children, focusing on allergic sensitization, asthma-related symptoms and lung function. It is based on two epidemiologic materials, the Swedish birth cohort BAMSE and the ESCAPE study, which included five European birth cohorts.

Over 4000 children in the BAMSE cohort were followed with repeated questionnaires, blood samples and lung function tests until 12 years of age. Outdoor concentrations of nitrogen oxides (NOx), and particles with an aerodynamic diameter of <10 μm (PM10) from traffic, were assigned to residential, day care, and school addresses by dispersion models. Air pollution exposure during the first year of life was related to an increased risk of sensitization to pollen allergens at 4 years (OR, 1.83; 95% CI, 1.02–3.28) for a 46.7 μg/m3 increase in exposure to NOx, but no consistent association was seen at 8 years of age. Our results suggested possible associations between exposure to air pollution during infancy and asthma in children up to 12 years of age. Risks appeared particularly elevated in children aged 8-12 years (OR, 2.0; 95% CI, 1.1–3.5) and for nonallergic asthma (3.8; 0.9–16.2), for a 7.2 μg/m3 increase in PM10. Furthermore, early-life exposure to air pollution seemed to have long-term negative consequences on lung function, particularly in atopic children, with a reduction of forced expiratory volume in one second (FEV1) of -136.9 mL; 95% CI, -224.1 to -49.7, for a 7.0 μg/m3 increase in PM10. Exposure after the first year of life appeared to have less impact on the respiratory outcomes under study.

In five European birth cohorts participating in the ESCAPE project, land-use regression models were applied to assess the individual exposures to several air pollution components. Blood samples drawn at 4 and/or 8 years from more than 6500 children were analyzed for specific IgE against common inhalant/food allergens. A meta- analysis did not reveal any clear association between air pollution exposure and development of allergic sensitization in children up to 10 years of age.

In conclusion, our results suggest that the infancy period might be critical for the influence of air pollution exposure on the development of asthma, allergy and lung function in children. Furthermore, our results suggest that current air quality standards do not fully protect children against adverse respiratory effects.