Outdoor Time Could Regulate the Effects of Green Environment on Myopia in Chinese Children and Adolescents

To explore the relationship between myopia and green space, and the mediation effects of outdoor time. We used large-scale, cross-sectional observational data from Shanghai, China. Participants were aged 3~20 years and underwent visual acuity and non-cycloplegic refraction in 2021. Using GIS-based data on environments surrounding participants' schools and kindergartens, we examined the association between green space (measured by NDVI) and myopia. We employed a logistic mixed-effects model to assess the impact of school-level green environments on individual myopia, reporting odds ratios (OR) and their 95% confidence intervals. Mediation analysis was conducted to explore whether outdoor activity time mediates the relationship between green environments and myopia. Additionally, we conducted age- and gender-stratified analyses and validated the robustness of the model through sensitivity analysis. Complete case sample sizes were 1,727,709 from 3,399 schools and kindergartens [899,817 (52.082%) boys; mean age 10.065 years (SD: 3.633)]. NDVI within 1000 m of schools was independently associated with lower odds of myopia (OR: 0.299, 95% CI: 0.249 ~ 0.357, p < 0.001), with 2.7% of the total effects attributed to the mediation effects of outdoor time. The effect sizes for NDVI were comparatively more protective in boys and those aged 7~12 years (OR: 0.223, 95% CI:0.156 ~ 0.319, p < 0.001). Sensitivity analysis with a 500-meter NDVI radius and alternative outcome variable of wearing glasses confirmed consistency with the previous results. This study demonstrates a significant impact of green environments on myopia in children and adolescents aged 3~20 years, revealing the potential mediating effect of outdoor activities. Policymakers should consider implementing intervention measures to enhance green spaces in schools to promote eye-health-friendly environments.