Ambient PM_2.5 exposure and salivary cortisol output during pregnancy in a multi-ethnic urban sample

Objectives: Evidence from murine research supports that fine particulate matter (PM_2.5) may stimulate the hypothalamic-pituitary-adrenal axis, leading to elevated circulating glucocorticoid levels. Epidemiologic research examining parallel associations document similar associations. We examined these associations among a diverse sample of pregnant individuals exposed to lower levels of ambient PM_2.5. Materials and Methods: Participants included pregnant individuals enrolled in the PRogramming of Intergenerational Stress Mechanisms (PRISM) pre-birth cohort. Daily residential PM_2.5 exposure was estimated using a satellite-based spatial-temporal hybrid model. Maternal 3rd trimester salivary cortisol levels were used to calculate several features of the diurnal cortisol rhythm. We used multivariable linear regression to examine PM_2.5 during the pre-conception period and during each trimester in relation to cortisol awakening rise (CAR), slope, and area under the curve relative to ground (AUC_G). Results and Discussion: The average PM_2.5 exposure level across pregnancy was 8.13 µg/m³. PM_2.5 in each exposure period was positively associated with AUC_G, a measure of total cortisol output across the day. We also observed an inverse association between PM_2.5 in the 3rd trimester and diurnal slope, indicating a steeper decline in cortisol throughout the day with increasing exposure. We did not detect strong associations between PM_2.5 and slope for the other exposure periods or between PM_2.5 and CAR for any exposure period. Conclusions: In this sample, PM_2.5 exposure across the preconception and pregnancy periods was associated with increased cortisol output, even at levels below the U.S. National Ambient Air Quality Annual Standard for PM_2.5 of 12.0 µg/m³.