Children with more green space around their home, school, and neighborhood have better neuropsychological and mental health outcomesThis study is a systematic review of observational research examining the effects of exposure to green space on children’s neurological development and mental health. The primary aim was to analyze and synthesize the existing evidence base of observational studies to support evidence-based policies and interventions to increase green spaces that enhance children’s neurological development and mental health. In addition, the study aimed to address two limitations of other reviews of observational evidence. First, most reviews have analyzed the cognitive benefits of green space exposure throughout life, including adulthood—not the neuropsychological benefits for children. Second, reviews that analyzed the effects of green space exposure on children’s mental health have not assessed the quality of those observational studies. Thus, these authors designed a systematic review that would both synthesize and assess observational studies that examine correlations between green space measures and neuropsychological and mental health outcomes for children.
The Spain-based research team followed the Navigation Guide methodology for systematic literature reviews. They developed explicit inclusion and exclusion criteria to restrict the review to original research articles published in English or Spanish that (1) focused on primary school children (age 6-12), (2) assessed greenness via approved objective or subjective measures, (3) compared levels of green space exposure, (4) had valid outcome measures for neuropsychological development or mental health, (5) and observational study designs. Researchers systematically searched four databases for relevant studies and then screened selected studies with group-approved protocols to evaluate the eligibility of each study. Then, they used the Navigation Guide protocol to assess the risk of bias for individual studies, rating each one as low, probably low, probably high, or high risk of bias. Based on these protocols, the research team identified 34 observational studies that met all eligibility criteria. The review comprised 17 longitudinal, 12 cross-sectional, and 5 ecological study designs. The researchers then analyzed, synthesized, and evaluated the methods and findings of these 34 studies.
Nearly all of the included studies established beneficial relationships between green space exposure and children’s neuropsychological development and mental health. Outcomes within the neuropsychological domain included brain volume, visual and working memory, intelligence, cognitive development, academic performance, and self-discipline. Outcomes in the mental health domain included well-being, ADHD symptoms, and behavior. The review reported main findings by the area where greenness was measured: by residential area, school, or neighborhood. Children living in residences surrounded by more greenness had larger volumes of brain tissue, improvements in cognitive development and well-being, fewer ADHD symptoms, and higher scores for self-discipline, attention, and intelligence. Children who attended schools surrounded by more greenness demonstrated fewer ADHD symptoms and better well-being, working memory, attention, cognitive development, and academic performance compared to children attending schools with less tree cover. Children living in greener neighborhoods demonstrated fewer behavior problems and emotional problems, more prosocial behavior, and better spatial working memory, intelligence, test scores, academic performance, and well-being. In addition, the strongest associations were linked to the widest green space buffers (>2000 meters) – highlighting the importance an neighborhood greenery – and tree cover surrounding school, not shrubs or grassland. Finally, most correlations between exposure to greenspace and neuropsychological development and mental health remained significant after adjusting for socioeconomic status. Several studies also confirmed that children living in disadvantaged neighborhoods had inequitable access to green space.
This was the first systematic review that analyzed how children’s neuropsychological development and mental health were related to exposure to green space. Overall, the current scientific evidence is promising— children with more green space surrounding their home, school, and neighborhood have better neuropsychological and mental health outcomes. However, the diversity and quality of the studies make it difficult to develop clear conclusions and recommendations for researchers, policymakers, health care workers, and urban planners. The researchers also found that a majority of studies had a high or probably high risk of bias, especially cross-sectional studies. Plus, they noted the limitations of the most commonly used tool to measure green space, the Normalized Difference Vegetation Index. To address these limitations, the authors call for stronger research designs to assess the most beneficial types of green space and the mechanisms by which these spaces support neuropsychological development and mental health. Their recommendations include (1) more longitudinal studies to infer causality, (2) measures and study designs that differentiate between vegetation types, and (3) designs which examine the specific pathways by which green spaces contribute to positive health outcomes.
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