Long-term air pollution exposure and incident dementia in older adults in the Gingko Evaluation of Memory Study

Abstract

Introduction: Air pollution is associated with reduced cognitive performance and accelerated cognitive decline in older adults. Less is known regarding air pollution’s contribution to all-cause dementia, Alzheimer’s disease (AD), and vascular dementia (VaD). Methods: Over 3,000 adults aged 75 years and older residing in four communities in the United States participated in the Ginkgo Evaluation of Memory Study (GEMS) between 2000-2008. Rigorous evaluations of dementia occurred every six months, and cases were identified by expert panel based on neuropsychological battery, neurological examination, and magnetic resonance imaging results. Fine particulate matter (PM2.5) concentrations were predicted from a spatiotemporal model incorporating land-use regression and spatial smoothing approaches. Estimates were based on residential address histories obtained up to twenty years prior to study entry using the commercially available LexisNexis database. Cox models adjusted for age and date of randomization, site, gender, treatment assignment, education, smoking, and zip code level income were used to estimate hazard ratios (HRs) and 95% confidence intervals (CIs). Results: Mean follow-up time was 5.7 years for the 2,511 GEMS participants free of mild cognitive impairment and dementia at study entry who had information on exposure, dementia status, and relevant covariates. An approximate interquartile range (2 µg/m3) increase in mean PM2.5 exposure twenty years prior to study entry was associated with a 19% greater risk of all-cause dementia (HR: 1.19; 95% CI: 1.03, 1.37) in adjusted analyses. Risks appeared stronger for VaD and mixed VaD/AD (HR: 1.25; 95% CI: 0.96, 1.62) than for AD only (HR: 1.15; 95% CI: 0.97, 1.37). Conclusions: Preliminary results indicate a strong association between air pollution exposure and all-cause dementia and that PM2.5 exposure may be particularly important in dementia with vascular features. Findings provide evidence that air pollution exposure reductions may be a key target for reducing the burden of dementia in older adults.