Many studies conducted during the last decade suggest the mental health benefits of green and blue spaces. We aimed to systematically review the available literature on the long-term mental health benefits of residential green and blue spaces by including studies that used standardized tools or objective measures of both the exposures and the outcomes of interest. We followed the PRISMA statement guidelines for reporting systematic reviews and meta-analysis. In total 28 studies were included in the systematic review. We found limited evidence for a causal relationship between surrounding greenness and mental health in adults, whereas the evidence was inadequate in children. The evidence was also inadequate for the other exposures evaluated (access to green spaces, quality of green spaces, and blue spaces) in both adults and children. The main limitation was the limited number of studies, together with the heterogeneity regarding exposure assessment. Given the increase in mental health problems and the current rapid urbanization worldwide, results of the present systematic review should be taken into account in future urban planning. However, further research is needed to provide more consistent evidence and more detailed information on the mechanisms and the characteristics of the green and blue spaces that promote better mental health. We provide recommendations for future studies in order to provide consistent and evidence-based recommendations for policy makers.

A number of studies have associated natural outdoor environments with reduced mortality but there is no systematic review synthesizing the evidence. We aimed to systematically review the available evidence on the association between long-term exposure to residential green and blue spaces and mortality in adults, and make recommendations for further research. As a secondary aim, we also conducted meta-analyses to explore the magnitude of and heterogeneity in the risk estimates. Following the PRISMA statement guidelines for reporting systematic reviews and meta-analysis, two independent reviewers searched studies using keywords related to natural outdoor environments and mortality. Our review identified twelve eligible studies conducted in North America, Europe, and Oceania with study populations ranging from 1645 up to more than 43 million individuals. These studies are heterogeneous in design, study population, green space assessment and covariate data.We found that the majority of studies show a reduction of the risk of cardiovascular disease (CVD) mortality in areas with higher residential greenness. Evidence of a reduction of all-cause mortality is more limited, and no benefits of residential greenness on lung cancer mortality are observed. There were no studies on blue spaces. This review supports the hypothesis that living in areas with higher amounts of green spaces reduces mortality, mainly CVD. Further studies such as cohort studies with more and better covariate data, improved green space assessment and accounting well for socioeconomic status are needed to provide further and more complete evidence, as well as studies evaluating the benefits of blue spaces.

A growing number of quantitative studies have investigated the potential benefits of outdoor blue spaces (lakes, rivers, sea, etc) and human health, but there is not yet a systematic review synthesizing this evidence. To systematically review the current quantitative evidence on human health and well-being benefits of outdoor blue spaces. Following PRISMA guidelines for reporting systematic reviews and meta-analysis, observational and experimental quantitative studies focusing on both residential and non-residential outdoor blue space exposure were searched using specific keywords. In total 35 studies were included in the current systematic review, most of them being classified as of "good quality" (N=22). The balance of evidence suggested a positive association between greater exposure to outdoor blue spaces and both benefits to mental health and well-being (N=12 studies) and levels of physical activity (N=13 studies). The evidence of an association between outdoor blue space exposure and general health (N=6 studies), obesity (N=8 studies) and cardiovascular (N=4 studies) and related outcomes was less consistent. Although encouraging, there remains relatively few studies and a large degree of heterogeneity in terms of study design, exposure metrics and outcome measures, making synthesis difficult. Further research is needed using longitudinal research and natural experiments, preferably across a broader range of countries, to better understand the causal associations between blue spaces, health and wellbeing.

Green spaces have been proposed to be a health determinant, improving health and wellbeing through different mechanisms. We aimed to systematically review the epidemiological evidence from longitudinal studies that have investigated green spaces and their association with all-cause mortality. We aimed to evaluate this evidence with a meta-analysis, to determine exposure-response functions for future quantitative health impact assessments. We did a systematic review and meta-analysis of cohort studies on green spaces and all-cause mortality. We searched for studies published and indexed in MEDLINE before Aug 20, 2019, which we complemented with an additional search of cited literature. We included studies if their design was longitudinal; the exposure of interest was measured green space; the endpoint of interest was all-cause mortality; they provided a risk estimate (ie, a hazard ratio [HR]) and the corresponding 95% CI for the association between green space exposure and all-cause mortality; and they used normalised difference vegetation index (NDVI) as their green space exposure definition. Two investigators (DR-R and DP-L) independently screened the full-text articles for inclusion. We used a random-effects model to obtain pooled HRs. This study is registered with PROSPERO, CRD42018090315. We identified 9298 studies in MEDLINE and 13 studies that were reported in the literature but not indexed in MEDLINE, of which 9234 (99%) studies were excluded after screening the titles and abstracts and 68 (88%) of 77 remaining studies were excluded after assessment of the full texts. We included nine (12%) studies in our quantitative evaluation, which comprised 8 324 652 individuals from seven countries. Seven (78%) of the nine studies found a significant inverse relationship between an increase in surrounding greenness per 0·1 NDVI in a buffer zone of 500 m or less and the risk of all-cause mortality, but two studies found no association. The pooled HR for all-cause mortality per increment of 0·1 NDVI within a buffer of 500 m or less of a participant's residence was 0·96 (95% CI 0·94-0·97; I2, 95%). We found evidence of an inverse association between surrounding greenness and all-cause mortality. Interventions to increase and manage green spaces should therefore be considered as a strategic public health intervention. World Health Organization.

Research into the potential health and well-being benefits from exposure to green spaces such as parks and woodlands has led to the development of several frameworks linking the different strands of evidence. The current paper builds on these to provide a model of how exposure to aquatic environments, or blue spaces such as rivers, lakes and the coast, in particular, may benefit health and well-being. Although green and blue spaces share many commonalities, there are also important differences. Given the breadth of the research, spanning multiple disciplines and research methodologies, a narrative review approach was adopted which aimed to highlight key issues and processes rather than provide a definitive balance of evidence summary. Novel aspects of our framework included the inclusion of outcomes that are only indirectly good for health through being good for the environment, the addition of nature connectedness as both a trait and state, and feedback loops where actions/interventions to increase exposure are implemented. Limitations of the review and areas for future work, including the need to integrate potential benefits with potential risks, are discussed.