Estimating the effect of reducing average annual ambient PM2.5 concentrations on allostatic load in children.

OBJECTIVE: Chronic exposure to environmental stressors may result in dysregulation across the body's adaptive stress-response systems, which can be conceptualized as allostatic load (AL). We estimated the effect of reducing annual average ambient fine particulate matter (PM2.5) on AL in children. METHODS: Cross-sectional data were collected from 279 participants, 1-12 years old. Recruitment occurred at the Benioff Children's Hospital in Oakland, California, during routine child wellness checks from March 2017-October 2018. Monthly ground-level ambient PM2.5 concentrations were mapped to each participant's residential address and averaged over the year prior to biospecimen collection. Inflammatory, metabolic, neurological, and cardiovascular plasma biomarkers related to hypothalamic-pituitary-adrenal (HPA) axis activation were measured to operationalize AL. Targeted maximum likelihood estimation paired with the Super Learner machine learning algorithm were used to estimate the effect of hypothetically reducing the observed ambient PM2.5 exposure distribution by 3, 4, 5, 6 and 7 μg/m3 on average AL score. RESULTS: Observed average annual ambient PM2.5 concentration was 10.93 μg/m3 (SD: 1.86) and observed average AL score was 1.46 (SD: 1.24). Shifting the sample's exposure distribution down by 4 and 5 μg/m3 resulted in an average exposure concentration of 7.94 (SD: 1.84) and 6.96 μg/m3 (SD:1.80). These reductions in exposure were associated with a -0.41 (95 % CI: -0.71, -0.12) and -0.6 (95 % CI: -1, -0.17) point decrease in average AL score, respectively. CONCLUSIONS: Reducing ambient PM2.5 concentrations to an annual average of 8 μg/m3 or below may reduce AL in children, prompting further consideration of the current PM2.5 national ambient air quality standard.