This systematic review of the literature evaluated research on the association between urban green space and human health. While other reviews have examined links between nature and human health, few have focused on the urban environment, and most such reviews have been limited to cross-sectional studies. This review represents a first step toward evaluating a possible causal relationship between nature and human health in urban settings.
Criteria for inclusion of studies in this review included research using experimental, quasi-experimental, or longitudinal approaches and published in the time frame January 1976 through December 2017. The main search terms were urban, greenspace and health. The search yielded 68 studies meeting the inclusion criteria, and all were included in this review. All of these studies measured human health in association with exposure to green space, and covered a wide array of age groups from infancy to old age. They were conducted in urban settings or with participants who were urban residents. Studies using perceived measures of the environment were not included nor were studies assessing health response to nature images. The majority of studies were experimental and assessed the impact of nature exposure in urban settings on different aspects of mental and/or physical health. Most of the studies (N=27) were conducted in the United States, with only a few (N=8) focusing on lower-income neighborhoods. Most of the studies used area-based measures to determine individual exposure to urban green space and were most often represented as quantity or density of residential green space. Some studies used proximity to parks and activity/leisure locations as measures of green space exposure.
In addition to presenting a comprehensive list of health-related outcomes in table format, the authors also devote separate sections of their paper to a discussion of nine specific areas: birth outcomes, cancer, cardiovascular, mental health, metabolic, mortality, physical activity, respiratory, and violence. They summarize their findings by noting a consistent negative association between greater urban green space exposure and decreased mortality, heart rate, and violence, and a positive association between greater urban green space exposure and increased attention, mood, and physical activity. They report mixed results or no association between urban green space exposure and general health, weight status, depression, and stress. Generalizations about birth outcomes, blood pressure, heart rate variability, cancer, diabetes, and respiratory symptoms could not be made. Positive nature-related outcomes for children included improved attention skills, decreased hyperactivity and peer-conduct problems, and lower body-mass index (BMI) scores.
The authors call for more research using rigorous study design to enable generalizations regarding nature-related health outcomes. They note, however, that the findings of this review support increased access to green space in urban environments as a way to promote human health. They suggest that urban managers, organizations, and communities might find this research helpful in their efforts to provide more green space for urban residents.