Urban green spaces and suicide mortality in Belgium (2001-2011): a census-based longitudinal study

Abstract

BACKGROUND Exposure to green spaces is associated with improved mental health and may reduce the risk of suicide. Here, we investigate the association between long-term exposure to residential surrounding greenness and suicide mortality. METHODS We used data from the 2001 Belgian census linked to mortality register data (2001-2011). We included individuals aged 18 years or older at baseline (2001) and residing in the five largest urban areas in Belgium (n=3,549,514). Suicide mortality was defined using ICD-10 codes X60-X84, Y10-Y34, and Y870. Surrounding greenness was measured using the Normalized Difference Vegetation Index (NDVI) within 300m and 1,000m buffers around the residential address at baseline. To assess the association between residential surrounding greenness and suicide mortality, we applied Cox proportional hazards models with age as the underlying time scale. Models were adjusted for age, sex, marital status, migrant background, educational attainment, neighbourhood socio-economic position. We additionally explored potential mediation with residential outdoor nitrogen dioxide (NO2) concentrations. Associations are expressed as hazard ratios (HR) and their 95% confidence intervals (CI) for an interquartile range (IQR) increase in residential surrounding greenness. RESULTS Between 2001 and 2011, 8,577 suicide deaths were registered. We observed a 7% (95%CI 0.89-0.97) and 6% (95%CI 0.90-0.98) risk reduction of suicide mortality for an IQR increase in residential surrounding greenness for buffers of 300m and 1,000m, respectively. Furthermore, this association was independent of exposure to NO2. After stratification, the inverse association was only apparent among females, and residents of Belgian origin, and that it was stronger among residents aged 36 or older, those with high level of education, and residents living in socio-economic deprived neighborhoods. CONCLUSION Our results suggest that urban green spaces may protect against suicide mortality, but this beneficial effect may not be equally distributed across all strata of the population. KEYWORDS Suicide mortality; surrounding greenness; longitudinal study