There is growing evidence that urban green space (UGS) can promote human health, but our research suggests there is still inadequate knowledge to direct planning and design of UGS for improved health outcomes. Given the urgency brought about by global urban health challenges, future research should progress from those that merely document the evidence of UGS benefits on health, to those that directly inform UGS planning and design. To guide such research, a holistic framework that clarifies the multiple determinants of health, multiple cause-effect pathways between UGS and health, and methodological challenges is needed. Through a review of 70 studies published between 2001 and 2015 across 40 cities and a review of current frameworks on the impacts of UGS on health, we developed a framework centered on the concept of ‘dose–response’. Dose refers to the exposure to certain UGS provision, and response refers to health outcomes arising from the exposure. There may be dose thresholds beyond which health response increases or even decreases. We also identified a range of moderators and mediators which can be used to explain the causal mechanisms leading to health responses. Using this framework, we identified four research needs, which are focused on improving methods measuring quantitative and qualitative attributes of UGS and health responses, the need to evaluate the multiple pathways in which UGS lead to improved health, the need to recognize scale effects on outcomes of studies, and the need to consider disservices from UGS and evaluate net benefits rather than positive benefits alone.

Although the benefits from exposure to urban green spaces (UGS) are increasingly reported, there are important knowledge gaps in the nature of UGS-health relationships. One such unknown area is the dependence of UGS-health associations on the types of UGS studied, the way they are quantified, and the spatial scale used in the analysis. These knowledge gaps have important ramifications on our ability to develop generalizations to promote implementation and facilitate comparative studies across different socio-cultural and socio-economic contexts. We conducted a study in Singapore to examine the dependence of UGS-health associations on the metrics for quantifying UGS (vegetation cover, canopy cover and park area) in different types of buffer area (circular, nested and network) at different spatial scales. A population-based household survey (n = 1000) was used to collect information on self-reported health and perception and usage pattern of UGS. The results showed that although all three UGS metrics were positively related to mental health at certain scales, overall, canopy cover showed the strongest associations with mental health at most scales. There also appears to be minimum and maximum threshold levels of spatial scale at which UGS and health have significant associations, with the strongest associations consistently shown between 400 m to 1600 m in different buffer types. We discuss the significance of these results for UGS-health studies and applications in UGS planning for improved health of urban dwellers.