Comparison of the impact of school environment on body mass index, physical fitness, and mental health among Chinese adolescents: Correlations, risk factors, intermediary effects

Schools offer prospects to enhance adolescent health by encouraging physical activity. This study contributes to the understanding of adolescent health research, drawing on data from physical fitness and mental health surveys conducted in 2015. The participants included 8,967 seventh-grade students across 45 junior high schools in Dalian, China. By employing multilevel analytical models, this research explores the effects of both the school environment and school neighbourhood environment on adolescents' body mass index (BMI), physical fitness (PF), and mental health (MH). Additionally, we delve into how physical activities (PA) affect these relationships through stepwise regression analysis. The findings indicate that the school setting significantly affects adolescents' health outcomes. Specifically, BMI is positively correlated with distance to the nearest amusement park. Conversely, it negatively relates to the extent of school green space and playground, the diversity of land use, and sidewalk density. In terms of PF, positive associations were observed with land use mix and the normalised difference vegetation index (NDVI). However, PF demonstrates negative associations with distance to the nearest parks and beaches. Concerning MH, there is a positive relationship with the proportion of playground, land use mix, sidewalk density, NDVI, and the green view index (GVI). On the contrary, MH is negatively correlated with the distance to park, amusement park, and beach. PA, as an intermediary factor, moderates the relationship between the school environment and both adolescent PF and MH, with mediation effects of 3.713% and 25.193%, respectively. These insights offer valuable theoretical guidance for designing health-promoting schools and urban planning strategies.