Associations of greenness surrounding schools and self-reported depressive and anxiety symptoms in Chinese adolescents

The effect of school-based greenness exposure on mental health among adolescents remains unclear. The study aimed to estimate the associations between school-based greenness and depressive and anxiety symptoms among adolescents and explore potential modifier and mediator between the associations.A cross-sectional survey involving 15,559 adolescents was conducted in China. The Chinese version of the Center for Epidemiologic Studies Depression 9-Item Scale and the Generalized Anxiety Disorder 7-Item Scale were used to assess the depressive and anxiety symptoms among adolescents. The Normalized Difference Vegetation Index within a 400 m and 800 m zone surrounding schools was used to indicate the adolescents' exposure to greenness. We estimated daily concentrations of PM1.0, PM2.5, and NO2 from the China High Air Pollutants dataset. Multiple logistic regression models were used.Higher exposure to greenness surrounding schools was negatively associated with depressive (OR: 0.774, 95%CI: 0.685-0.875) and anxiety symptoms (0.740, 0.669-0.818). We observed stronger associations between greenness and depressive and anxiety symptoms among girls, lower age group (11-15 years), and adolescents born to parents with lower education levels. PM1.0 (proportion mediated estimates: 14.3 %; 95 % CI: 4.2 %, 24.5 %) and PM2.5 (10.5 %; 95 % CI: 3.0 %, 17.9 %) mediated the associations between greenness exposure and depressive symptoms. The number of days adolescents attended physical education classes per week mediated -22.8 % (95 % CI: -38.5 %, -7.1 %) and -9.7 % (95 % CI: -15.5 %, -3.8 %) of the effects of greenness on depressive and anxiety symptoms.Increasing the greenness and improving the environment surrounding schools is effective in promoting the mental health of adolescents.