Association of greenness surrounding schools and homes with adiposity levels in children and adolescents
方法 2016—2018年，在中国珠三角地区3个城市52316名5~18岁儿童青少年中开展了一项横断面研究，通过问卷调查获得基本社会人口学特征和肥胖水平。应用陆地遥感卫星（Landsat）数据和中分辨率成像光谱仪（MODIS）产品评估研究对象所在学校和家庭周围的植被水平，计算家庭或学校所在500 m和1 000 m缓冲区半径内的归一化植被指数（NDVI）、植被覆盖率（VCF）、土壤调整植被指数（SAVI）、增强型植被指数（EVI）。应用二水平广义线性模型评估不同植被暴露水平下的儿童青少年相对于最低植被暴露水平下的体重指数z分值（zBMI）变化和相对超重风险，并采用限制性立方样条评估暴露-反应关系。采用反事实框架模型评估PM2.5和NO2，以及体育锻炼水平在其关联上的中介作用。
结果 研究最终纳入的52316名儿童中， 8406人（16.1%）为超重。植被水平与儿童青少年的zBMI呈现出非线性的暴露-反应关联，当植被达到一定水平时，儿童青少年zBMI降低。按照植被水平四分位数分组，调整协变量后，与处于NDVI500 m和VCF500 m最低四分位组的儿童青少年相比，处于最高四分位组的儿童青少年zBMI和超重风险更低：家庭处于NDVI500 m第四四分位组的儿童青少年zBMI值相对于第一四分位组的变化量 ( b) 为−0.07（95%CI：−0.10~−0.04），超重OR 为0.92（95%CI：0.85~0.99）。当使用1000 m缓冲半径和SAVI、EVI时，观察到了与500 m缓冲半径植被暴露对儿童肥胖水平类似的负相关关联。中介分析结果显示：调整协变量后，最高NDVI500 m四分位组中，家庭和学校周围空气污染分别介导了NDVI500 m与儿童青少年zBMI负向关联的50%（95%CI：20%~80%）、90%（95%CI：50%~160%），未观察到体育锻炼水平的中介效应。
Background Evidence on the association between greenness and adiposity in children and adolescents is inconsistent and mostly from developed countries. Relatively limited evidence is from China.
Objective To assess the association between greenness and adiposity in children and adolescents based on satellite remote sensing data.
Methods From 2016 to 2018, a cross-sectional study was conducted among 52316 children and adolescents aged 5-18 years in three cities in the Pearl River Delta region of China. Basic sociological and demographic characteristics of the population and adiposity levels were collected through questionnaires. Land Remote-Sensing Satellite (Landsat) data and moderate-resolution imaging spectroradiometer (MODIS) products were used to quantify the greenness around the schools and homes, including normalized difference vegetation index (NDVI), vegetation continuous field (VCF), soil-adjusted vegetation index (SAVI), and enhanced vegetation index (EVI) calculated within 500 m and 1000 m buffers centered around the participants' homes or schools. A restricted cubic spline function was used to assess the exposure-response relationship. After categorizing greenness levels into quartiles with the first quartile as the reference, two-level generalized linear models were applied to assess the change in body mass index z-scores (zBMI) and the risk of overweight of children and adolescents in higher quartiles relative to the lowest quartile. In addition, counterfactual framework modelling was applied to assess the potential mediation effects of PM2.5 and NO2, and physical activity levels on the associations between greenness and adiposity levels.
Results Of the 52316 children included, 8406 (16.1%) were overweight. A non-linear negative association of the level of greenness around the homes or schools and zBMI was found, with a significant lower zBMI in children and adolescents when a certain level of greenness was reached. After adjusting for confounders, the participants in the highest quartile had a significantly lower level of zBMI and a significantly lower risk of overweight compared with those in the lowest quartile of NDVI500 m and VCF500 m. The estimate change ( b) for zBMI was −0.07 (95%CI: −0.10-−0.04) and the odds ratio (OR) for overweight was 0.92 (95%CI: 0.85-0.99) for the students in the highest NDVI500 m quartile based on home address compared to those in the lowest quartile. Significant negative associations were also observed when 1000 m buffer, SAVI, and EVI were used. The mediation analysis showed that PM2.5 and NO2 partially mediated the negative association of NDVI500 m with zBMI , and the proportions of mediation were 50% (95%CI: 20%-80%) and 90% (95%CI: 50%-160%), respectively while no significant mediation effect was observed for physical activity level.
Conclusion Higher levels of greenness surrounding homes or schools may be associated with a reduced risk of overweight and decreased zBMI in children and adolescents, and such associations may be partially mediated by reducing air pollutant concentrations.