The Cog-Aging: a 15-year cohort study of cognition in Brazilian older adults

Prevalence of dementia is higher in low- and middle-income countries (LMICs). However, longitudinal studies characterizing cognitive decline and its clinical and epidemiological predictors remain scarce in Brazil.

Participants were enrolled from 2011 to 2025 and followed through May 2026. A total of 887 participants were classified as cognitively unimpaired (CU) (n = 274), mild cognitive impairment (MCI) (n = 378), or dementia of the Alzheimer's type (DAT) (n = 235). CU and MCI participants were followed until dementia conversion, which was analyzed under competing risks using cumulative incidence functions and Fine-Gray models.

Overall, annualized dementia conversion rate in the MCI group was 10.72 per 100 person-years (95% confidence interval [CI]: 8.54% to 13.29%). In addition, 40.39% of participants progressed to dementia during a mean follow-up time of 3.75 years (standard deviation: 3.28), with an estimated cumulative incidence of 29.85% at 3 years (95% CI: 22.74% to 36.96%), accounting for death as a competing event.

This study adds valuable information for LMICs. However, estimates should be interpreted considering attrition and competing mortality.