Long-term exposure to air pollution from road traffic and lung function in children and adolescents

Abstract

Lung function in early life is an important predictor of peak lung function and later decline in adults. However, lung development may also be influenced by factors later in childhood and adolescence. Identification of susceptible periods and modifiable factors affecting lung development already during infancy and childhood could help promote respiratory health later in life. The overall aim of this thesis was to investigate potential environmental determinants of lung function in children and adolescents, with particular focus on exposure to traffic-related air pollution.

The papers in this thesis were based on the BAMSE study, a longitudinal population-based birth cohort of children followed until adolescence. The parents of all children born in predefined urban and suburban areas of Stockholm County between February 1994 and November 1996 were invited to enroll their children. Symptoms of allergy-related disease, life-style factors and major exposures were assessed from questionnaires filled out at the ages of 1, 2, 4, 8, 12 and 16 years. Lung function was measured using spirometry at 8 and 16 years of age, with the addition of impulse oscillometry at age 16 years. The assessment of individual long-term exposure to traffic-related air pollution was based on dispersion modeling, using emission inventories and data on road traffic, meteorological conditions and topography, at relevant geographical locations. Time-weighted annual averages of nitrogen oxides (NOx) and particulate matter with an aerodynamic diameter of less than 10 μm (PM10) were assessed over the life course.

The influence of long-term exposure to traffic-related air pollution on lung function at 8 and 16 years of age was assessed, including life course analyses. Pollution exposure during the first year of life, but none of the other time periods examined, was significantly associated with reduced lung function at 8 and 16 years of age. No associations were observed for the change in lung function between the two time points for any of the time windows explored. This suggests that exposure in early life influences early lung growth and that lung function thereafter tracks with age. In addition, we observed that air pollution during the first year of life was associated with small but significant increase of small airways resistance. Associations appeared stronger in subjects with asthma at 16 years.

Exposure to air pollution and other environmental factors was investigated in relation to lung function growth between childhood and adolescence, using quantile regression on the 10th, 50th and 90th percentiles, corresponding to low, median, and high lung function growth. Out of 20 examined variables, birth weight, asthma heredity and environmental tobacco smoke exposure in infancy were the only independent predictors of lung function growth.

In summary, exposure to traffic-related air pollution during infancy was associated with decreased lung function, including in the small airways, in childhood and adolescence. Air pollution and other environmental factors assessed after infancy had little impact on lung function growth, supporting the notion of a susceptible period early in life with tracking of lung function thereafter.