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Life sciences · Journal article
Neurology · November 6, 2026
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Background and objectives. Dementia underdiagnosis is a major barrier to public health strategies, particularly in low- and middle-income countries. Although Brazil has a high prevalence of dementia, data on underdiagnosis remain scarce. We aimed to investigate the prevalence and sociodemographic profile of individuals with undiagnosed dementia in Brazil over 5 years.Methods. We analyzed 2 waves of the Brazilian Longitudinal Study of Aging, a nationally representative study of community-dwelling adults, comparing samples from wave 1 (W1; 2015-2016) and wave 2 (W2; 2019-2021) aged 60 years or older. Dementia was defined by an algorithm combining cognitive testing, functional status, and informant report; undiagnosed dementia was algorithm-positive dementia without a prior physician diagnosis of Alzheimer disease. We estimated survey-weighted population prevalences and design-based within-wave and wave-to-wave differences (in percentage points, pp), applying the Benjamini-Hochberg false discovery rate (FDR) correction.Results. The samples included 5,432 participants (mean age 70.3 ± 7.97 years, 60.0% female) in W1 and 6,929 (mean age 71.0 ± 8.28, 59.5% female) in W2. The prevalence of undiagnosed dementia decreased from 5.53% (95% CI 4.46-6.59) in W1 to 3.86% (3.11-4.61) in W2 (-1.66 pp; p = 0.013), whereas total dementia prevalence did not differ significantly between waves (6.21% vs 5.02%; p = 0.104). Among people with dementia, the undiagnosed proportion fell from 89.66% to 77.17% (p = 0.002). Declines were concentrated among historically underserved groups: women (-2.57 pp), non-White individuals (-2.72 pp), adults with ≤4 years of education (-2.71 pp), and residents of the Northeast (-4.68 pp; all FDR q = 0.010).Discussion. Although undiagnosed dementia in Brazil remains high, its prevalence decreased significantly over the 5 years, particularly among vulnerable groups, individuals with low education, women, non-White populations, and in the Northeast. These findings suggest that the expansion and continuity of primary care are beginning to reach historically underserved populations. However, substantial regional inequalities persist, highlighting the need for targeted public health policies and active case finding to bridge diagnostic gaps in isolated territories.