Intrauterine and postnatal exposure to outdoor NO2 and lung function at school age

Lungs are highly vulnerable to permanent harmful effects of environmental factors during their in-utero and early life development. The detrimental effects of air pollution on lung development are well known although studies mainly focused on the postnatal exposure period. We investigated the windows of susceptibility during pregnancy and first 7 postnatal years on the association between nitrogen dioxide (NO2) and lung function at the age of 7 years in the INMA cohort in Spain. We estimated monthly average exposure to NO2 for the prenatal and postnatal period at home address of 1230 children with temporally-adjusted land use regression models. Spirometry was performed at age 7. We estimated the change in lung function associated with 10 µg/m3 increase in NO2 concentrations with distributed lag models, which consider the association at a specific time point while controlling for exposure at all other periods. Mean NO2 concentration was 30.3 (±15.2) µg/m3 and the average interquartile range was 19.9 µg/m3. Results on complete cases (n=856) identified two sensitive exposure periods associated with a reduction of the FVC: (i) from the half of the second trimester until the end of pregnancy (e.g. prenatal month 7: -3.3 [95% CI: -5.4, -1.2] ml for 10 µg/m3 increase in NO2) and (ii) at 3 years old (e.g. postnatal month 46: -1.9 [95%CI: -3.5, -0.3] ml). Moreover, a sensitive window when the children turn 3 years old was identified with a decrease on FEV1 of -1.7 [95% CI: -3.0, -0.3] ml for each 10 µg/m3 increase of NO2 (in postnatal month 36). Exposure to NO2 at sensitive periods including pregnancy and first years of life is associated with a lower lung function at 7 years.