Long-term exposure to residential green and blue spaces and anxiety and depression in adults: A cross-sectional study

Background: Although exposure to natural outdoor environments has been consistently associated with improved perceived general health, available evidence on a protective association between this exposure and specific mental health disorders such as depression and anxiety is still limited. Objective: The aim of this study was to evaluate the effects of long-term exposure to residential green and blue spaces on anxiety and depression and intake of related medication. Additionally, we aimed to explore potential mediators and effect modifiers of this association. Methods: The study was based on an existing adult cohort (ALFA - Alzheimer and Families) and includes 958 adult participants from Barcelona recruited in 2013-2014. For each participant residential green and blue exposure indicators [surrounding greenness (NDVI), amount of green (land-cover) and access to major green spaces and blue spaces] were generated for different buffers (100m, 300m and 500m). Participants reported their history of doctor-diagnosed anxiety and depressive disorders and intake of related medication. Logistic regression models were applied to assess the corresponding associations. Results: Increasing surrounding greenness was associated with reduced odds of self-reported history of benzodiazepines [e.g. Odds ratio - OR (95%CI) = 0.62 (0.43, 0.89) for 1-interquartile range (IQR) increase in NDVI in a 300m buffer] and access to major green spaces was associated with self-reported history of depression [OR (95%CI) = 0.18 (0.06, 0.58)]. No statistically significant associations were observed with blue spaces. Air pollution (between 0.8% and 29.6%) and noise (between 2.2% and 5.3%) mediated a proportion of the associations observed, whereas physical activity and social support played a minor role. Conclusion: Our findings suggest a potential protective role of green spaces on mental health (depression and anxiety) in adults, but further studies, especially longitudinal studies, are needed to provide further evidence of these benefits and of the mediation role of exposures like air pollution and noise.