Long-Term Exposure to Residential Greenness and Neurodegenerative Disease Mortality Among the Elderly: A 13-Year Follow-Up Cohort Study

Abstract

Background Living in greener areas is associated with slower cognitive decline and reduced dementia risk among the elderly, but the evidence with neurodegenerative disease mortality is scarce. We studied the association between residential surrounding greenness and neurodegenerative disease mortality in an elderly population. Methods We used data from the 2001 Belgian census linked to mortality register data during 2001-2014. We included individuals aged 60 years or older and residing in the five largest Belgian urban areas at baseline (2001). Exposure to residential surrounding greenness was assessed using the Normalized Difference Vegetation Index (NDVI) within 500-m from residence. We considered all neurodegenerative diseases and four specific outcomes: Alzheimer’s disease, vascular dementia, unspecified dementia, and Parkinson’s disease. We fitted Cox proportional hazard models to obtain hazard ratios (HR) and 95% confidence intervals (CI) of the associations between one interquartile range (IQR) increment in surrounding greenness and neurodegenerative disease mortality outcomes. Furthermore, we conducted mediation analyses to assess potential mediation by air pollution (PM2.5), and stratification analyses to explore effect modification by sociodemographic characteristics. Results From 1,134,502 individuals included at baseline, 6.1% died from neurodegenerative diseases during follow-up. After full adjustment, one IQR (0.22) increment of surrounding greenness was associated with a 4-5% reduction in premature mortality from neurodegenerative diseases, Alzheimer’s disease, vascular and unspecified dementia [e.g., for Alzheimer’s disease mortality: HR 0.95 (95%CI: 0.93, 0.98)]. No association was found with Parkinson’s disease mortality. Reductions in air pollution concentrations could potentially mediate 58% (95%CI: 31.7%, 95.7%) of the observed effect with all neurodegenerative disease mortality. Associations were strongest in the lower educated and residents from most deprived neighbourhoods. Conclusions Living near greener spaces may reduce the risk of neurodegenerative disease mortality among the elderly, partly mediated by a reduction in air pollution concentrations. Socioeconomically disadvantaged groups may experience the greatest beneficial effect.