Cross-sectional evaluation of the association between greenness and cognitive performance in Mexican pre-pubertal boys.

Background: Evidence shows that greenspace exposure benefits children's health and cognitive development. However, evidence assessing this association in young children in low- and middle-income economies is scarce.

Objective: To assess the association between exposure to greenness and cognitive performance in pre-pubertal boys living in Mexico City.

Methods: Cross-sectional study using data from 144 boys aged 6-11 years living in Mexico City in 2017 and enrolled in the "MetCog" study. Cognitive performance was evaluated through selected Wechsler Scale for Intelligence in Children Fourth Edition (WISC-IV) and Neuropsychological Assessment of Children (Evaluación Neuropsicológica Infantil, ENI) tests. Exposure to greenness was assessed through Normalised Difference Vegetation Index (NDVI) at 300, 500, 1500, 2000, and 3000 m buffer zones from children's residences. Multiple linear regression analysis was undertaken to assess associations between cognitive performance and greenness (aβ) with 95% confidence intervals (CI) and adjusted for potential confounding variables. Significance was set at q < 0.05 after False Discovery Rate (FDR) correction.

Results: A positive association was found between the NDVI Interquartile Range (IQR) at 2000 m and the WISC-IV block design test score (aβ  = 1.18, 95% CI = 0.31, 2.06; q < 0.05), which assesses perceptual reasoning. Positive associations were found with NDVI IQR at 1500 m and WISC-IV block design (aβ = 1.00, 95% CI = 0.14, 1.86) and matrix reasoning (aβ = 0.83, 95% CI = 0.06, 1.61) scores, but neither survived FDR correction. No significant associations were found between NDVI IQR at any buffer size with other WISC-IV and ENI task scores.

Conclusions: Greater exposure to greenness was associated with higher perceptual reasoning skills in 144 pre-pubertal boys living in Mexico City. Thus, urban planning should consider increasing vegetation in megacities, especially in neighbourhoods with high percentages of young children.