Green space, air pollution, traffic noise and saliva cortisol in children aged 12 years

Abstract

OPS 43: Noise, stress and mental health, Room 217, Floor 2, August 27, 2019, 4:30 PM - 5:30 PM Background: Green space, air pollution and traffic noise may be associated with stress levels in children. Secretion of the stress hormone cortisol is characterized by a peak in the early morning, followed by declining cortisol levels throughout the day. A slower rate of decline in cortisol across the day has been related to chronic psychosocial stress. Aim: To examine the associations of green space, air pollution and traffic noise with the diurnal change in saliva cortisol levels in children aged 12 years. Methods: We used data of 1061 participants aged 12 years of the Dutch PIAMA birth cohort. Children collected saliva samples during a single day: 30 minutes after awakening and at 20.00hr (in the evening). We calculated the change between evening and morning saliva cortisol levels (in ng/ml per hour). We estimated residential exposure to green space (i.e. the average Normalized Difference Vegetation Index (NDVI) and percentages of green space in circular buffers of 300m and 3000m), air pollution and traffic noise. Associations of these exposures with the diurnal cortisol change were assessed by multiple linear regression, adjusted for potential confounders. Associations are presented for an interquartile range (IQR) increase in exposure. Results: The average NDVI, total percentage of green space and percentage of agricultural green space in a buffer of 3000m were associated with a stronger diurnal decrease in cortisol levels (adjusted difference -0.05ng/ml/hr [95%CI -0.08, -0.01ng/ml/hr] per IQR (0.13) increase in the average NDVI; adjusted difference -0.05ng/ml/hr [95%CI -0.09, -0.01ng/ml/hr] per IQR (31.1%) increase in the total percentage of green space). We found no associations of air pollution or traffic noise with the diurnal cortisol change. Conclusions: This study indicates that residential exposure to green space may be associated with lower stress levels in children aged 12 years.