Associations between Ultrafine Particles and Incident Dementia in Older Adults.

Fine particulate matter (PM) is linked to dementia risk, but ultrafine particles (UFPs, <100 nm) may be even more toxic due to their distinct physicochemical properties. However, evidence on UFPs and dementia remains limited. This study assessed the association between UFP exposure and Alzheimer's disease (AD) and related dementias (ADRD) among U.S. older adults. Using Medicare data, we analyzed ZIP code-level UFP exposure in 2017 for beneficiaries aged 65 and older residing in the contiguous U.S., applying Cox proportional hazard models to estimate AD and ADRD incidence (2018-2020) while considering comorbidities. Among ∼21 million participants for AD and ∼20 million for ADRD, each interquartile range increase in UFP exposure (3701.6 and 3668.5 particles/cm, respectively) was associated with higher AD (HR: 1.026, 95% CI: 1.014-1.038) and ADRD (HR: 1.016, 95% CI: 1.008-1.023) risks. The association was linear within typical exposure levels and stronger in individuals with comorbidities. Geographically, the UFP-associated dementia risk was higher in rural areas than in urban areas, possibly due to different pollution sources. These findings underscore UFPs as neurotoxicants and highlight the need for targeted public health interventions to protect vulnerable populations.