School-based Greenness and its Association with Overweight and Obesity in Children and Adolescents: a National Cross-Sectional Study in China

Abstract

Background: Prior investigations on the associations of greenness exposure, which is generally assessed at participants’ home addresses, with obesity are still controversial. Furthermore, few documented evidences have focused on the association between childhood obesity and school-based greenness exposure.Objective: This study aimed to assess the associations between school-based greenness and markers of adiposity in children and adolescents in China.Method: We performed a national cross-sectional analysis of a representative sample including 56,620 children and adolescents aged 6-18 years in seven municipalities/provinces across China. We utilized the Normalized Difference Vegetation Index (NDVI) and Soil Adjusted Vegetation Index (SAVI) within 100-, 500-, and 1,000m circular buffers around each school’s address to evaluate greenness exposures. We estimated the associations of greenness with changes in BMI z-scores and waist circumference as well as odds ratio of overweight and/or obesity using two-level logistic and generalized linear mixed regression models. We also took consideration of the modifying effects of ambient air pollution and physical activity into the greenness-adiposity associations. Result: We found that BMI z-scores (-0.13, 95%CI:-0.13, -0.07) and waist circumference (-0.63, 95%CI:-1.2, -0.06) were decreased when NDVI-1000m per interquartile (IQR, 0.13 unit) increase in adjusted model. And an IQR increase in NDVI of three different buffers was associated with 10-21% lower odds ratio (OR) of overweight and/or obesity. We also found that the associations were more pronounced in boys, urban dwellers and children with lower parental education levels. Air pollution mediated 9.8-56.9% of the greenness-obesity associations, but no mediating effects were observed for physical activity.Conclusion: Higher school-based greenness exposure was associated with decreased BMI z-scores and lower relative prevalence of overweight and/or obesity in children and adolescents. Ambient air pollutants may partially mediate the greenness-adiposity associations.