Relationship of Neighborhood Greenness to Alzheimer's Disease and Non-Alzheimer's Dementia Among 249,405 U.S. Medicare Beneficiaries.

BACKGROUND Neighborhood greenness (vegetative presence) has been linked to multiple health outcomes, but its relationship to Alzheimer's disease (AD) and non-Alzheimer's (non-AD) dementia has been less studied. OBJECTIVE This study examines the relationship of greenness to both AD and non-AD dementia in a population-based sample of Medicare beneficiaries. METHODS Participants were 249,405 US Medicare beneficiaries aged >  65 living in Miami-Dade County, FL, from 2010 to 2011. Multi-level analyses examined the relationship of greenness, assessed by mean Census block level Normalized Difference Vegetation Index (NDVI), to odds of each of AD, Alzheimer's disease and related dementias (ADRD), and non-AD dementia, respectively. Covariates included age, gender, race/ethnicity, number of comorbid health conditions, and neighborhood income. RESULTS Higher greenness was associated with reduced risk of AD, ADRD, and non-AD dementia, respectively, adjusting for individual and neighborhood sociodemographics. Compared to the lowest greenness tertile, the highest greenness tertile was associated with reduced odds of AD by 20%(odds ratio, 0.80; 95%CI, 0.75-0.85), ADRD by 18%(odds ratio, 0.82; 95%CI, 0.77-0.86), and non-AD dementia by 11%(odds ratio, 0.89; 95%CI, 0.82-0.96). After further adjusting for number of comorbidities, compared to the lowest greenness tertile, the highest greenness tertile was associated with reduced odds of AD (OR, 0.94; 95%CI, 0.88-1.00) and ADRD (OR, 0.93; 95%CI, 0.88-0.99), but not non-AD dementia (OR, 1.01; 95%CI, 0.93-1.08). CONCLUSION High neighborhood greenness may be associated with lower odds of AD and ADRD. Environmental improvements, such as increasing neighborhood vegetation, may be a strategy to reduce risk for AD and possibly other dementias.