The association between green space around schools, screen time for entertainment, and adolescent depressive symptoms: A nationwide study from China

Background: Natural green environments are beneficial to people's mental health, while too much screen time may be harmful to adolescents' mental health. However, it is not clear how green spaces and screen time affect mental health together in adolescents. Methods: A total of 22,868 adolescents were recruited from October to December 2021 in eight cities in China, through multistage cluster sampling. The Patient Health Questionnaire (PHQ-9) was used to investigate adolescents' depressive symptoms, and the Normalised Vegetation Index for the 200m, 500m and 1000m buffer zones around the school represents the green cover around the school. We used binary logistic regression to analyse the association between green space, screen time and depressive symptoms. Results: In fully adjusted models, the highest quartile of NDVI in the 200m, 500m and 1000m buffer zones around the school was a protective factor for depressive symptoms. For less than 2 h of recreational screen time, the highest quartiles of the NDVI and the association with depressive symptoms were negatively correlated for the 200m, 500m and 1000m buffer zones (NDVI200: 0.904(0.848-0.964)), NDVI500: 0.863(0.808-0.921), NDVI1000: 0.862(0.808-0.920)). The highest quartiles of NDVI in all buffers were not associated with depressive symptoms when the screen time was >2 h. The association between green space and depressive symptoms at lower recreational screen time was observed to be stronger in the group of adolescents with a lower family economic status (NDVI200: 0.780(0.695-0.876), NDVI500: 0.838(0.748-0.938), NDVI1000: 0.783(0.698-0.879)). No potential gender differences were observed. Conclusions: For adolescents with less than 2 h of recreational screen time per day, the greenery around the school had a protective effect on their mental health, especially for adolescents from economically disadvantaged families. Green spaces around schools are significant in improving health inequities.