Growing interest in the benefits of urban greening is evident in a number of different areas including public health. Some related studies have shown a positive association between neighborhood greenness and children's physical activity levels and weight, however the evidence has been mixed, perhaps due to the use of different measures of greenness. Some of the studies measured greenness around schools; others greenness around homes. Measures have also included distance to greenery, street greenness and satellite measures of area greenness. The aim of this study was to determine the impact of urban greenery on individual body mass index (BMI), a commonly-used weight-status indicator, using three urban greenness measures.
The study was conducted in Hong Kong with 1,148 students from 40 primary schools participating. The schools were selected by stratified random sampling, a method used to include schools in neighborhoods with different socio-economic and built environment contexts. The three different methods used to measure various dimensions of urban greenery around the schools were: the number of nearby parks; the Normalized Difference Vegetation Index (NDVI) based on satellite imagery; and street greenness based on Google Street View images. Street greenness represents the eye-level greenness perceived by commuters and thus provides an objective estimate of the daily greenery exposure of urban residents. Information gathered about the students (age 11-13) included weight, height, demographic information, household information, and active school transport (AST) record. AST (walking, biking) is a major source of physical activity for children and youth. Data analysis focused on determining the direct impact of urban greenery on individual BMI and the indirect impact of urban greenery on individual BMI via AST.
Over one-third of the participants walked or rode a bicycle to school four or five days a week. Slightly less than one-third of the students never walked or rode a bicycle to school. A slightly higher percentage of girls walked or rode a bicycle to school than boys. Students attending schools with greener surrounding areas (within 800 meters) were more likely to engage in active transport behavior than students attending schools with less greenery. They were also more likely to have a lower BMI. Street greenness and the number of parks near school (within 400 meters) were both positively associated with the odds of students engaging in AST. Greater school connectivity (density of street intersections near the school) and fewer bus stops increased the odds of engaging in AST.
This study found that street greenery in the area surrounding a school was significantly associated with children's active school transport and body weight status. These findings highlight the importance of greenery around urban schools (as opposed to residential neighborhoods more generally) for promoting physical activity and positively impacting the health of children and youth. This study also found that street greenness was a superior measure of exposure to greenery compared to the NDVI measure used in many similar studies.
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