Association between neighbourhood green space and biological markers in school-aged children. Findings from the Generation XXI birth cohort

Background: There is considerable literature on the psychological and behavioural benefits of green space. However, less is known about its health-promoting effects, as expressed on biological markers. Additionally, incorporating biomarkers into pediatric research may help elucidate the links between exposures to environmental stressors and lifelong health. Objective: To measure the association between geographical accessibility to green spaces and allostatic load (AL), a measure of biological multi-system dysregulation. Methods: We used data from 3108 7-year old children enrolled in Generation XXI, a population-based birth cohort from the Porto Metropolitan Area (Portugal). We computed an AL index based on seven biomarkers representing four regulatory systems: immune/inflammatory system (high sensitivity C-reactive protein); metabolic system (high density lipoprotein; total cholesterol; glycated hemoglobin; waist-hip ratio) and cardiovascular system (systolic and diastolic blood pressure). Accessibility to green spaces was calculated using a Geographic Information System and crude and adjusted associations were estimated using mixed-effects regression models. Results: Among the 3108 children (51.7% male; mean age 87.3 months), the mean AL index was 0.00 (standard deviation 2.94). Adjusted models showed that having a green space within 400m and 800m from the child's school was inversely associated with AL (400 m: beta -0.29 95% CI -0.54 to -0.02; 800 m: -0.29 95% CI -0.51 to -0.07). Also, there was a 12% (0%; 23%) increase in the AL index for every 1 km increase in distance to the nearest green space. No significant associations with AL were observed with residential accessibility to green space or with the presence of a garden at home. Conclusion: We found a cross-sectional negative association between accessibility to green space near schools and AL in children, suggesting that the provision of green space may contribute to improvements in population health beginning early in life.