The Cog-Aging cohort study found an annualized dementia conversion rate of 10.72 per 100 person-years in Brazilian MCI patients, with 40.39% progressing to dementia over a mean follow-up of 3.75 years, adding valuable longitudinal data for low- and middle-income countries.
The annualized dementia conversion rate in the MCI group was 10.72 per 100 person-years.
40.39% of MCI participants progressed to dementia during the follow-up period.
The study enrolled 887 total participants classified into three cognitive groups.
Prevalence of dementia is higher in low- and middle-income countries (LMICs), yet longitudinal studies characterizing cognitive decline remain scarce in Brazil.
The authors caution that study estimates should be interpreted in the context of attrition and competing mortality.
This research describes a large Brazilian study called Cog-Aging that followed nearly 900 older adults over up to 15 years to track how their memory and thinking abilities changed over time. Participants were grouped at the start as either having normal cognition, mild cognitive impairment (MCI — a condition where memory problems are noticeable but not severe enough to interfere greatly with daily life), or Alzheimer's-type dementia. The researchers then tracked how many of those with MCI eventually developed dementia. The study found that among people with MCI, roughly 10 to 11 out of every 100 developed dementia each year. Over the course of the study, about 40% of MCI participants converted to dementia, with nearly 30% doing so within just 3 years. These findings are important because they provide concrete estimates of how quickly cognitive decline progresses in a Brazilian population, filling a significant gap in knowledge about dementia in lower- and middle-income countries, where dementia rates tend to be higher but long-term studies are rare. This research suggests that MCI in Brazilian older adults carries a substantial risk of progressing to dementia over relatively short time periods, which has implications for healthcare planning and early intervention efforts in Brazil and similar countries. The authors note that the results should be interpreted carefully given that some participants dropped out over the lengthy follow-up period and that death itself was a competing outcome — meaning some participants died before they could develop dementia, which was statistically accounted for in the analysis.
Engelmann G, de Alvarenga J, Moro G, Bolaños Burgos I, Miranda M, Miranda M, et al.. (2026). The Cog-Aging: a 15-year cohort study of cognition in Brazilian older adults.. Alzheimer's & dementia : the journal of the Alzheimer's Association. https://doi.org/10.1002/alz.71780