Ambient air pollutants are associated with morning serum cortisol in overweight and obese Latino youth in Los Angeles

Abstract

Background

Hypothalamic-pituitary-adrenal (HPA)-axis dysfunction has been associated with a variety of mental health and cardio-metabolic disorders. While causal models of HPA-axis dysregulation have been largely focused on either pre-existing health conditions or psychosocial stress factors, recent evidence suggests a possible role for central nervous system activation via air pollutants, such as nitrogen dioxide (NO₂), ozone (O₃) and particulate matter (PM). Therefore, in an observational study of Latino youth, we investigated if monthly ambient NO₂, O₃, and PM with aerodynamic diameter ≤ 2.5 (PM_2.5) exposure were associated with morning serum cortisol levels.

Methods

In this cross-sectional study, morning serum cortisol level was assessed after a supervised overnight fast in 203 overweight and obese Latino children and adolescents (female/male: 88/115; mean age: 11.1 ± 1.7 years; pre-pubertal/pubertal/post-pubertal: 85/101/17; BMI z-score: 2.1 ± 0.4). Cumulative concentrations of NO_2, O₃ and PM_2.5 were spatially interpolated at the residential addresses based on measurements from community monitors up to 12 months prior to testing. Single and multi-pollutant linear effects models were used to test the cumulative monthly lag effects of NO₂, O_3, and PM_2.5 on morning serum cortisol levels after adjusting for age, sex, seasonality, social position, pubertal status, and body fat percent by DEXA.

Results

Single and multi-pollutant models showed that higher O₃ exposure (derived from maximum 8-h exposure windows) in the prior 1–7 months was associated with higher serum morning cortisol (p < 0.05) and longer term PM_2.5 exposure (4–10 months) was associated with lower serum morning cortisol levels (p < 0.05). Stratification by pubertal status showed associations in pre-pubertal children compared to pubertal and post-pubertal children. Single, but not multi-pollutant, models showed that higher NO₂ over the 4–10 month exposure period associated with lower morning serum cortisol (p < 0.05).

Conclusions

Chronic ambient NO_2, O₃ and PM_2.5 differentially associate with HPA-axis dysfunction, a mechanism that may serve as an explanatory pathway in the relationship between ambient air pollution and metabolic health of youth living in polluted urban environments. Further research that uncovers how ambient air pollutants may differentially contribute to HPA-axis dysfunction are warranted.