Effects of school neighborhood food environments on childhood obesity at multiple scales: a longitudinal kindergarten cohort study in the USA

Background: School neighborhood food environment is recognized as an important contributor to childhood obesity; however, large-scale and longitudinal studies remain limited. This study aimed to examine this association and its variation across gender and urbanicity at multiple geographic scales. Methods: We used the US nationally representative Early Childhood Longitudinal Study-Kindergarten cohort data and included 7530 kindergarteners followed up from 1998 to 2007. The Census, road network, and Dun and Bradstreet commercial datasets were used to construct time-varying measurements of 11 types of food outlet within 800-m straight-line and road-network buffer zones of schools and school ZIP codes, including supermarket, convenience store, full-service restaurant, fast-food restaurant, retail bakery, dairy product store, health/dietetic food store, candy store, fruit/vegetable market, meat/fish market, and beverage store. Two-level mixed-effect and cluster-robust logistic regression models were performed to examine the association. Results: A higher body mass index (BMI) in 2007 was observed among children experiencing an increase of convenience stores in school neighborhoods during 1998-2007 (beta=0.39, p<0.05), especially among girls (beta=0.50) and urban schoolchildren (beta=0.41), as well as among children with a decrease of dairy product stores (beta=0.39, p<0.05), especially among boys (beta=1.86) and urban schoolchildren (beta=0.92). The higher obesity risk was associated with the increase of fast-food restaurants in urban schoolchildren (OR=1.27 [95% CI=1.02-1.59]) and of convenience stores in girls (OR=1.41 [95% CI=1.09-1.82]) and non-urban schoolchildren (OR=1.60 [95% CI=1.10-2.33]). The increase of full-service restaurants was related to lower obesity risk in boys (OR=0.74 [95% CI=0.57-0.95]). The decrease of dairy product stores was associated with the higher obesity risk (OR=1.68 [95% CI=1.07-2.65]), especially boys (OR=2.92 [95% CI=1.58-5.40]) and urban schoolchildren (OR=1.67 [95% CI=1.07-2.61]). The schoolchildren exposed to the decrease of meat/fish markets showed the lower obesity risk (OR=0.57 [95% CI=0.35-0.91]), especially urban schoolchildren (OR=0.53 [95% CI=0.32-0.87]). Results from analyses within 800-m straight-line buffer zones of schools were more consistent with our theory-based hypotheses than those from analyses within 800-m road-network buffer zones of schools and school ZIP codes. Conclusions: National data in the USA suggest that long-term exposure to the food environment around schools could affect childhood obesity risk; this association varied across gender and urbanicity. This study has important public health implications for future school-based dietary intervention design and urban planning.