Exposure to green-blue spaces and mental health: a retrospective e-cohort study in Wales

Abstract

BackgroundGrowing cross-sectional evidence links access to green-blue spaces with mental health benefits, but studies at an individual level and at a national population scale are scarce. This gap can be addressed through the Secure Anonymised Information Linkage (SAIL) Databank, which allows household-level green-blue spaces access and exposure data to be linked to individual-level health-care use. MethodsWithin the SAIL Databank, an e-cohort of the population of Wales (2008–19) was created from green-blue space metrics and the Welsh Longitudinal General Practice database. Green-blue spaces metrics (derived from satellite imagery and planning data) included average ambient greenness within 300 m of the home (designated as the Enhanced Vegetation Index) and average access to green-blue spaces (designated as the number of green-blue spaces within 1600 m of the home). A validated algorithm was applied to create a common mental health disorder flag and linked to green-blue spaces exposure (ambient greenness and access) recorded for individuals not affected by common mental health disorders. We used multivariate logistic regression models to test the hypothesis that greater green-blue spaces exposure is associated with a reduced likelihood of a flagged common mental health disorder. Subgroup analyses were done for socioeconomic deprivation. FindingsThe e-cohort comprised 2 341 591 individuals (1 193 240 men and 1 148 351 women), aged 16 or over and registered with a general practice in the SAIL Databank. After adjusting for individual and area-level covariates, a unit increase in ambient greenness around the home and access to green-blue spaces within 1600 m were associated with lower odds of a common mental health disorder (adjusted odds ratio 0·11 [95% CI 0·11–0·12] for ambient greenness around the home and 0·47 [0·46–0·48] for access to green-blue spaces within 1600 m). A unit increase in ambient greenness was associated with reduced odds of a common mental health disorder for residents of the most deprived areas (n=473 410; 0·22 [0·20–0·24]) and of the least deprived areas (n=480 424; 0·07 [0·07–0·08]). InterpretationPeople with greater exposure to green-blue spaces were less likely to develop a common mental health disorder and the effect is modified by socioeconomic deprivation. This finding has implications for both public health policy and urban planning. This large, adult-population cohort provides sufficient power to examine variations between subgroups to investigate inequalities. FundingThe project was developed as part of independent research funded by the National Institute for Health Research (study number 16/07/07).