Effects of greenness, public parks, and blue space on neurodegenerative disease hospitalizations in the US Medicare cohort

Abstract

Background and Aim: Exposure to natural environments has been associated with health outcomes that are related to neurological disorders. However, the few studies that examined associations of natural environments with neurological disorders reported mixed findings. Our goal was to evaluate associations of multiple features of natural environments with Alzheimer’s disease and related dementia’s (ADRD) and Parkinson’s disease (PD) hospital admissions. Methods: We created an open cohort including all fee-for-service Medicare beneficiaries aged 65+, who lived in the contiguous US January 1, 2000 through December 31, 2016 (~63 million individuals). Zip code level greenness (Normalized Difference Vegetation Index, NDVI), percent public park cover, and percent blue space cover (≥1 % cover vs. <1% cover) were assessed. We examined associations of these exposures with first ADRD or PD hospitalizations based on primary or secondary discharge diagnosis, using a novel Cox-equivalent Poisson model. We also assessed if associations varied by demographics and area-level socioeconomic status. Results: We observed 7,910,111 and 1,196,981 first ADRD and PD hospitalizations, respectively. After adjustment for potential individual- and area-level confounders, NDVI was negatively associated with ADRD hospitalization (HR=0.95, 95%CI: 0.94-0.96, per IQR increase). Percent public park cover and blue space cover were not associated with ADRD hospitalization. For PD hospitalization, we observed negative associations of NDVI (HR=0.94, 95%CI: 0.93-0.95, per IQR), percent public park cover (HR=0.97, 95%CI: 0.97-0.98, per IQR), and blue space cover (HR=0.97, 95%CI: 0.96-0.98, ≥1% v. <1%). Patterns of effect modification by demographics differed between the exposures. For example, for PD hospitalization, negative associations of NDVI were strongest in the mid and high SES neighbourhoods, while negative associations of percent public park cover were strongest in the low SES neighbourhoods. Conclusions: Features of natural environments are associated with a decreased risk of ADRD and PD hospitalization in this cohort of US-based older adults.