Exposure to different types of residential greenness during pregnancy and early childhood and attention-deficit/hyperactivity disorder diagnosis: A nested case-control study

Abstract

Background

Epidemiological studies suggest that exposure to greenness may protect children attention-deficit/hyperactivity disorder (ADHD) diagnosis. However, evidence to date is limited while no previous research has independently investigated exposure to prenatal greenness.

Objective

We conducted a nested case-control study with data from Born in Bradford (BiB) and INfancia y Medio Ambiente (INMA) birth cohorts to investigate the association between exposure to various types of residential greenness and ADHD diagnosis, considering both pregnancy and early childhood exposure periods independently. PM_2.5 was tested as a potential mediator of the association.

Methods

Children with ADHD were identified based on a confirmed medical diagnosis. Pregnancy and early childhood exposure to residential greenness were estimated through Normalized Difference Vegetation Index (NDVI) within 300-m, urban green space and natural green space percentages within 300-m, and the linear distance to the closest green space in meters. We performed a conditional logistic regression to analyze the association between the included greenness metrics and ADHD.

Results

We found no statistically significant associations between any of the pregnancy and early childhood greenness metrics and ADHD diagnosis in the BiB cohort. Further analysis on the INMA cohort found that higher urban green space percentage slightly increased the risk of ADHD diagnosis during both pregnancy (total effects: OR 1.04, 95 % CI 1.01 to 1.07, p = 0.012; direct effects: OR 1.06, 95 % CI 1.03 to 1.10, p < 0.001) and early childhood (total effects: OR 1.03, 95 % CI 1.00 to 1.07, p = 0.042; direct effects: OR 1.04, 95 % CI 1.00 to 1.07, p = 0.033). However, these associations were not supported by the sensitivity analyses.

Conclusions

This study found both null and inconsistent associations between the included greenness metrics and ADHD. Further research is warranted to elucidate the potential role of exposure to different types of greenness in ADHD diagnosis.