The impact of green space and biodiversity on health

Urban green spaces are associated with many health outcomes, but the mechanisms underlying these links remain unclear. One explanation is that biodiverse microbiomes in green spaces affect human health by modifying immune function. Our systematic review included studies that investigated the relationship between green space and either health or biodiversity. Reported effects of green space on health were generally positive, but 22% of the papers identified either no effect or negative effects. We also found that although green space was commonly associated with biodiversity, few green-space health studies simultaneously examined biodiversity. Overreliance on cross-sectional studies, various definitions of green space, and a lack of research in tropical and developing nations limit the conclusions that can be drawn. A better understanding of the biological aspects of contact with nature is required before city planners can optimize green spaces for health gains.