Exposure to moderate air pollution and associations with lung function at school-age: A birth cohort study

Background: Adverse effects of higher air pollution levels before and after birth on subsequent lung function are often reported in the literature. We assessed whether low-to-moderate levels of air pollution during preschool-age impact upon lung function at school-age.

Methods: In a prospective birth cohort of 304 healthy term-born infants, 232 (79%) completed lung function at follow-up at six years. Using spatial-temporal models, levels of individual air pollution (nitrogen dioxide (NO₂) and ozone (O₃), particulate matter with a diameter <10 μm (PM₁₀)) were estimated for the time windows pregnancy, first up to the sixth year of life separately, and birth until follow-up at six years. Time window means were compared to World Health Organization (WHO) guideline limits. Associations of exposure windows with spirometry and body plethysmography indices were analyzed using regression models, adjusting for potential confounders. For subgroup analysis, air pollution exposure was categorized into quartiles (four groups of 52 children).

Results: Mean NO₂ level from birth until follow-up was [mean (range)] [11.8 (4.9 to 35.9 μg/m³)], which is almost 4-times lower than the WHO suggested limit of 40 μg/m³. In the whole population, increased air pollution levels from birth until follow-up were associated with reduced lung function at six years. In the subgroup analysis, the 52 children exposed to NO₂ levels from the highest quartile during pregnancy, the first and second years of life and from birth until follow-up, had a significant decrease in forced expiratory volume in 1 s (FEV₁). Per interquartile range increase of NO₂, FEV₁ decreased by [z-score change (95% confidence interval)] [-1.07 (-1.67 to -0.47)], [-1.02 (-1.66 to -0.39)], [-0.51 (-0.86 to -0.17)] and [-0.80 (-1.33 to -0.27)], respectively. Air pollution exposure during pregnancy and childhood resulted in a non-significant decrease in lung volume at six years, as assessed by functional residual capacity measured by body plethysmography (FRC_pleth).

Conclusion: Our results suggest that exposure to higher NO₂ levels, which are still much lower than WHO guideline limits, especially during the sensitive period of early lung development, may be associated with reduced lung function at school-age. These findings support the concept of age and dose-dependent pollution effects on lung function in healthy school-aged children and underline the importance of pollution reduction measures.