Outdoor air pollution, road traffic noise, and allostatic load in children aged 6-11 years: evidence from six European cohorts.

Emerging evidence suggests that exposure to air pollutants and road traffic noise triggers stress responses, which mediate physiological responses in multiple organs and tissues. However, epidemiological study in children is sparse. We aimed to evaluate whether outdoor air pollution and road traffic noise are associated with physiological response measured by allostatic load in children. We studied 919 children aged 6-11 years from the HELIX (Human Early Life Exposome) cohort in 6 European countries with 19 biomarkers assessed in four physiological systems-cardiovascular, metabolic, immune/inflammation, and neuroendocrine systems. We then calculated both count-based and continuous scores for each physiological system and generated allostatic load scores (range 0-19). Exposure to air pollution (NO, PM, PM, PMabsorbance) and road traffic noise (L) based on participants' home, school, and commuting route addresses were estimated for the year prior to outcome assessment. Higher exposure to all air pollutants was associated with a higher allostatic load, although only the association of PM survived correction for multiple testing (for count-based allostatic load score: RR = 1.27, 95%CI: 1.08, 1.48; for continuous allostatic load score: β = 0.56, 95% CI: 0.27-0.84, per each 10 µg/m increase in PM). Examining physiological systems separately, higher exposure to air pollution was mainly associated with higher allostatic load in the immune/inflammatory and metabolic systems. No associations between road traffic noise and allostatic load were observed. Our findings suggest that air pollution act as a chronic stressor in manifesting multi-systemic physiological dysregulation in childhood, which may be a precursor of air pollution-related diseases.