The influence of residential greenness on mortality in the Asia-Pacific region: a systematic review and meta-analysis

Aims: To critically appraise the evidence of the impact of exposure to salutogenic green environment on mortality, which is an important endpoint in epidemiological and clinical studies. Methods: We searched for studies published and indexed in three databases (PubMed, AMED, and CINAHL Plus) from inception until 31 March 2020, complemented with a search of cited literature for articles describing the effects of greenness on mortality in Asia-Pacific region. Eligible articles were screened and data were extracted independently by two reviewers. A random-effects model was utilised to obtain pool hazard ratio (HR) and risk ratio of all-cause mortality outcome. Results: The search identified 3239 studies, of which 20 studies reporting 133,363 participants from longitudinal cohort studies and 202 million people from population-based prevalence studies were included in the review. The majority of the studies (60%) were conducted in high-income countries in Asia-Pacific. All participants of the longitudinal cohort studies were aged 60 years or older, whereas the prevalence studies involved people of all age groups. A significant protective association of green environment exposure with all-cause mortality was reported in 18 studies. Pooled results from five studies showed increased level of greenness exposure was associated with a significant decrease in all-cause mortality (pooled HR = 0.97; 95% confidence interval (CI) = 0.93 to 1.02; p < 0.01; I²= 87.8%). Meta-analysis of total number of deaths in different quartiles of green spaces noted decreased risks of mortality with all causes of death with increased surrounding greenness. Conclusions: Some limited evidence suggests that populations exposed to the greener environment have a lower risk of mortality, implying the potential role of greenness in increasing longevity. Further studies with standardised design and outcome reporting should be conducted in low- and middle-income countries and in populations of low socioeconomic status to glean more generalisable and complete evidence for public health policy implications.