PURPOSE OF THE STUDY.
Exposure to elevated concentrations of ambient air pollutants is associated with increases in the prevalence of bronchitic symptoms in children. The authors hypothesized that reductions in measured air pollutants over the periods studied would be associated with an improvement in respiratory symptoms in children with or without asthma.
Data were collected from 3 successively recruited cohorts involving 4602 children (48% female subjects, age range of 5–18 years, mean age of 8 years, 45% Hispanic) from 8 Southern California communities during the years 1993 to 2001, 1996 to 2004, and 2003 to 2012.
This was a longitudinal study with data from the 3 separate but overlapping cohorts. Regional levels of air pollution (measuring average concentrations of nitrogen dioxide, ozone, and particulate matter with an aerodynamic diameter of <10 μm [PM10] and <2.5 μm [PM2.5]) were collected with consistent methods over the study periods. Bronchitic symptoms were assessed by using a baseline and annual questionnaires evaluating symptom recall over the previous 12 months. Bronchitic symptoms were defined as parental or child report of “daily cough for 3 months in a row, congestion or phlegm other than when accompanied by a cold or bronchitis.” The subjects were categorized as having asthma or not on the basis of a questionnaire. Air pollution exposure levels were lagged by 12 months for alignment with bronchitic outcomes data. Additional covariates from questionnaires included annual information on tobacco smoke exposure or pets in the home, sex, race and/or ethnicity, and housing conditions. A multilevel logistic model was used to estimate the association of changes in pollution levels with bronchitic symptoms.
Overall, air pollution levels declined (especially after 2001) across the 3 cohorts. For nitrogen dioxide, the odds ratio (OR) for bronchitic symptoms among children with asthma at age 10 years (n = 892, 19.4%) was 0.79 (95% confidence interval [CI], 0.67–0.94) for a median reduction of 4.9 ppb, with an absolute decrease in prevalence of 10.1%. For ozone, the OR was 0.66 (95% CI, 0.50–0.86) for a median reduction of 3.6 ppb, with an absolute decrease in prevalence of 16.3%. For PM10, the OR was 0.61 (95% CI, 0.48–0.78) for a median reduction of 5.8 µg/m3, with an absolute decrease in prevalence of 18.7%. For PM2.5, the OR was 0.68 (95% CI, 0.53–0.86) for a median reduction of 6.8 µg/m3, with an absolute decrease in prevalence of 15.4%. Among children without asthma (n = 3710), there was an absolute decrease in the prevalence of bronchitis symptoms of 1.8% for nitrogen dioxide, 1.7% for ozone, 2.2% for PM10, and 2.3% for PM2.5.
Decreases in ambient pollution levels were associated with statistically significant decreases in bronchitic symptoms in children with and without asthma. Although the authors do not establish causality with their study design, their findings support the potential benefit of air pollution reduction for asthma control.
With this study, the authors confirm the association of air pollution with impaired respiratory health in children, both with and without asthma. Regulations for clean air are good policy for children’s health.
- Copyright © 2017 by the American Academy of Pediatrics