Air pollution exposure during pregnancy and child attention deficit and hyperactivity disorder symptoms in eight European cohort studies.

Abstract

Background: Some studies have suggested that exposure to air pollution during pregnancy may increase attention deficit and hyperactivity disorder (ADHD) symptoms in young children, but findings have not been consistent. We aimed to study this association in about 27,000 European children. Methods: In a collaborative study including 8 European population-based birth/child cohorts, mother-child pairs were recruited from 1992 to 2008. Air pollution concentrations (nitrogen oxides and particulate matter) at birth addresses were estimated by land-use regression models based on monitoring campaigns performed between 2008 and 2011. Concentrations were extrapolated back in time to the pregnancy periods. ADHD symptoms were assessed between 3 and 12 years of age by teachers or parents. Children were classified with ADHD symptoms within the borderline/clinical range and within the clinical range using validated cut-offs. Adjusted area-specific effect estimates were combined using random-effects meta-analysis. Results: Between 6% and 22% of children were classified as having ADHD symptoms within the borderline/clinical range, while between 3% and 11% were classified as having ADHD symptoms within the clinical range. Median air pollution levels ranged from 14.08µg/m3 (the French cohort of Poitiers) to 43.4µg/m3 (the Spanish cohort of Sabadell) for NO2 and from 8.4µg/m3 (the Swedish cohort) to 22.4µg/m3 (the Italian cohort) for PM2.5. Exposure to air pollutants during pregnancy was not associated with a higher risk of ADHD symptoms (e.g., OR with ADHD symptoms in the borderline/clinical range was 0.93, 95%CI 0.88-0.99 per 10µg/m3 increase in NO2 and 0.98, 95%CI 0.82-1.18 per 5µg/m3 increase in PM2.5). We observed similar results when ADHD symptoms were assessed within the clinical range. Conclusions: There was no evidence of an association between air pollution during pregnancy and ADHD symptoms in children aged 3 to 12 years.