Undiagnosed dementia and mortality among older adults in the United States and Brazil: A cross-national cohort study.

INTRODUCTION: Cross-national evidence on undiagnosed dementia and its prognostic implications remains limited. We compared the proportion of undiagnosed dementia, associated factors, and mortality in the United States and Brazil. METHODS: This population-based cohort study included adults aged ≥ 65 years from the 2016 US Health and Retirement Study (n = 9,539) and the 2015-2016 Brazilian Longitudinal Study of Aging (n = 3603), followed for mortality through 2020. Dementia was classified as no dementia, undiagnosed dementia, or diagnosed dementia using harmonized cognitive, functional, and informant measures. RESULTS: The proportion of undiagnosed dementia was higher in Brazil (76.1%) than in the United States (45.1%). Undiagnosed dementia was associated with increased 4-year mortality compared with no dementia in both countries. It was linked to younger age and absence of memory complaints, with marked socioeconomic and healthcare disparities in Brazil. DISCUSSION: Undiagnosed dementia is common and associated with increased mortality, identifying a vulnerable population missed by current diagnostic pathways.