Green spaces and cognitive development at age 7 years in a rome birth cohort: The mediating role of nitrogen dioxide*,**

Introduction There is evidence of improvement on mental health and well-being due to contact with green spaces, through various mechanisms and with potentially differential impacts in different populations. Many of these studies have been conducted among adults, while children have not been sufficiently investigated. This study aimed to evaluate the association between residential exposure to greenness and cognitive development at age 7 and to evaluate nitrogen dioxide (NO2) as a potential mediator of this association.Methods This longitudinal study was based on a cohort of newborns enrolled at delivery in two large obstetric hospitals in Rome. We assessed cognitive development at 7 years of age through the Wechsler Intelligence Scale for Children-III edition (WISC-III). We estimated residential surrounding greenness, using satellite derived Normalized Difference Vegetation Index (NDVI), within 300m and 500m buffers around each residential address at birth. We applied weighted multiple linear regression analyses to study the association between NDVI and the WISC-III cognitive scores, using the inverse probability weighting methodology to correct for potential selection bias. We performed a mediation analysis to evaluate the mediating role of NO2 in the association under study.Results We enrolled 719 children at birth and performed our analyses only on 465 children with data on exposure and outcome. The results were not consistent for the average residential surrounding greenness in 300m buffer. For an IQR increase in greenness within 500m buffer around home addresses at birth we found a progress in Arithmetic subtest (?:0.39; 90% CI: 0.11?0.6), a test concerning with attention, concentration and numerical reasoning, apart from an indication of the positive association with Full scale IQ and Verbal IQ. This association was partly mediated by reduction in NO2, since adding this pollutant in our model explained 35% (90% CI: 7%?62%) of our estimate. Conclusions Our findings showed an association between residential surrounding greenness within 500m and better scores on attention tests at 7 years of age. The observed association between Arithmetic subtest and NDVI was mediated, in part, by a reduction in NO2. This topic has important public health implications in supporting green urban planning policies and promoting children?s well-being.