Summary: A meta-analysis of nine longitudinal studies reveals urban green spaces are significantly associated with a reduction in premature mortality. A 4% reduction in premature mortality was linked to each increment of 0.1 in vegetation score within 500 meters of residential buildings.
Residential greenness can protect against premature all-cause mortality, according to a systematic review and meta-analysis conducted by the Barcelona Institute for Global Health (ISGlobal), an institution supported by “la Caixa”, in collaboration with Colorado State University and the World Health Organization (WHO), and published in The Lancet Planetary Health.
The analysis, which included nine longitudinal studies involving seven countries and a total of over eight million people, provides strong evidence on the impact of increasing green areas on mortality.
Half of the world’s population lives in cities, where there is often a lack of green space. Many studies suggests that green spaces in cities have a positive health effect, including less stress, improved mental health, and lower risk of cardiovascular disease, metabolic syndrome and premature death, among others. However, many of these studies look at only one specific point in time and use different ways to measure exposure to greenness.
This is why the research team decided to summarize the available evidence and focus on studies that were longitudinal -studies that follow the same cohort of individuals during several years-, used a simple measure of exposure to green space -the NDVI (Normalised Difference Vegetation Index) based on satellite images-; and looked at premature all-cause mortality as a health outcome. They identified nine cohort studies worldwide that included over eight million individuals in total, from seven different countries (Canada, United States, Spain, Italy, Australia, Switzerland and China).
The meta-analysis of these studies found that an increment in greenness around homes is significantly associated with reduced premature mortality. More specifically, the study provides an estimate for the protective effect: a 4% reduction in premature mortality per each increment of 0.1 in vegetation score, within 500 meters of the residence.
“This is the largest and most comprehensive synthesis to date on green space and premature mortality”, says David Rojas, researcher at ISGlobal and Colorado State University and first author of the study, “and the results support interventions and policies to increase green spaces as a strategy to improve public health”. Furthermore, this study “provides important information that can already be used in future Health Impact Assessment (HIA) studies”, explains Rojas.
Indeed, Rojas and colleagues are currently applying the results of the above meta-analysis to estimate the number of premature deaths that could be prevented in cities around the world if the city achieved its ambitious goal of increasing green infrastructures.
“Urban greening programmes are not only key to promoting public health, but they also increase biodiversity and mitigate the impacts of climate change, making our cities more sustainable and livable” concludes Mark Nieuwenhuijsen, director of the Urban Planning, Environment and Health Initiative at ISGlobal.
Marta Solano – ISGLOBAL
The image is in the public domain.
Original Research: Closed access
“Green spaces and mortality: a systematic review and meta-analysis of cohort studies”. Rojas-Rueda D, Nieuwenhuijsen M, Gascon M, Perez-Leon D, Mudu P.
The Lancet Planetary Health doi:10.1016/S2542-5196(19)30215-3.
Green spaces and mortality: a systematic review and meta-analysis of cohort studies
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.