Residential exposure to green space and early childhood neurodevelopment

Background: A few studies reported that exposure to high levels of residential surrounding green spaces was associated with better cognitive development in primary school children. However, no studies have been conducted to examine such association in early childhood. Objectives: We investigated the association between residential exposure to green space and early childhood neurodevelopment, and further explored the mediation effects of traffic-related air pollution and maternal physical activity on this association. Methods: We enrolled 1312 pregnant women between January 2012 and October 2015 and their children were followed up until an age of 2 years. We measured residential exposure to green space by calculating averaged normalized difference vegetation index (NDVI) within a 300 meter buffer area surrounding residential address at birth. The neurodevelopment, which included mental development index (MDI) and psychomotor development index (PDI), was assessed using Bayley Scales of Infant Development for each child at about 24 months. The associations of residential exposure to NDVI with early childhood MDI score and PDI score were evaluated using multiple linear regression models. The mediation effects of traffic-related air pollution and maternal physical activities on those associations were estimated by causal mediation analyses. Results: Exposure to higher levels of residential surrounding green spaces was associated with increased early childhood PDI score (adjusted changes for one SD increment of NDVI: 3.28 (95% CI: 2.15, 4.41)) and MDI score (adjusted changes for one SD increment of NDVI: 1.97 (95% CI: 0.63, 3.30). These associations were more pronounced in children of mothers whose pre-pregnancy BMI were lower than 24 kg/m(2). Further mediation analyses indicated that reduced levels of traffic-related air pollution explained 13.6% to 28.0% of the association between exposure to green space and early childhood PDI score. Conclusion: Exposure to higher levels of residential surrounding green spaces was associated with better early childhood neurodevelopment. The association between exposure to green space and early childhood psychomotor development might be partly explained by reduced levels of traffic-related air pollution.