The impact of greenspace and air pollution exposure on incident dementia in the Ginkgo Evaluation of Memory Study

BACKGROUND AND AIM: While long term exposure to fine particulate matter (PM₂.₅) has been linked to all-cause dementia, less is known about potential modification of these effects by greenspace exposure. METHODS: The Ginkgo Evaluation of Memory Study (GEMS) was a randomized trial in four US sites (Hagerstown MD, Pittsburgh PA, Sacramento CA, and Winston-Salem NC) from 2000-2008 with rigorous neuropsychological assessments for dementia every six months. Minimum age at enrollment was 75 years. Mean residence-specific PM₂.₅ concentrations were estimated using a novel spatiotemporal model and reconstructed from residential address histories for a 20-year period (1980-1999). Greenspace exposure was measured by averaging standardized 1) normalized difference vegetation index (NDVI), 2) reverse coded distance to nearest park, and 3) percentage of park overlap within a 10km buffer of residence. We evaluated modification by greenspace of the effects of PM₂.₅ on dementia risk by including an interaction term in Cox proportional hazards models adjusted for age, study site, year of randomization, gender, treatment assignment, neighborhood deprivation index, and education. RESULTS:For 2,549 participants who were free of mild cognitive impairment (MCI) at enrollment, preliminary analyses indicate that an interquartile range (2 µg/m³) increase in 20-yr mean PM₂.₅ exposure was associated with a 19% (HR: 1.19: CI: 1.04, 1.37) greater risk of dementia. Relative to participants in the first tertile of greenspace, those in the second tertile had a 17% reduction (HR: 0.83; 95% CI: 0.63, 1.09) in dementia risk and those in the third tertile had a 25% reduction (HR: 0.75; 95% CI: 0.54, 1.03); however, these estimates included the null. Greenspace exposure did not modify the impact of PM₂.₅ on dementia risk (interaction term p-value=0.57). CONCLUSIONS:Greenspace exposure may be a promising protective factor against dementia but does not appear to modify the impact of PM₂.₅ on dementia in this cohort of older adults. KEYWORDS: Greenspace, Air pollution, All-cause dementia, Fine particulate matter, Long-term exposure