The Association between Residential Green Space in Childhood and Development of Attention Deficit Hyperactivity Disorder: A Population-Based Cohort Study

BACKGROUND: Access to green space has been hypothesized to have a beneficial impact on children’s mental well-being and cognitive development. The underlying mechanisms of the mental health benefits of green space are not fully understood, but different pathways have been suggested, such as the psychologically restoring capacities of green space, the ability to facilitate physical activity and social cohesion, and the mitigation of exposure to air pollution. OBJECTIVES: In this nationwide cohort study, we investigated associations between residential green space in early childhood and a clinical diagnosis of attention deficit hyperactivity disorder (ADHD). METHODS: The cohort included individuals, who were born in Denmark between 1992 and 2007 ([Formula: see text]) and followed for a diagnosis of ADHD from age 5, during the period 1997–2016. We used the normalized difference vegetation index (NDVI) as a measure of vegetation greenness surrounding each residential address in a quadratic area of [Formula: see text] in which the residence was located in the center of the quadrate. Individual exposure to green space was calculated as the average of NDVI surrounding each individual’s residential address (or addresses if more than one) between birth and the fifth birthday. Multilevel modeling was used to estimate the incidence rate ratios (IRRs) with 95% confidence intervals (CI) for ADHD, according to exposure level and adjusted for calendar time, age, sex, parental socioeconomic status, neighborhood level socioeconomic status, and urbanicity. RESULTS: Individuals living in areas defined by sparse green vegetation (lowest decile of NDVI) had an increased risk of developing ADHD, compared with individuals living in areas within the highest decile of NDVI ([Formula: see text]; 95% CI: 1.46, 1.65). Adjusting for the known confounders attenuated the result, but the association remained ([Formula: see text]; 95% CI: 1.13, 1.28). CONCLUSION: Our findings suggest that lower levels of green space in residential surroundings, during early childhood, may be associated with a higher risk of developing ADHD. https://doi.org/10.1289/EHP6729