Dementia-free survival among centenarians: An evidence-based review

Background. The 2000 U.S. census identified 50,454 Americans older than 100 years (18 per 100,000). Increased longevity is only of benefit if accompanied by the maintenance of physical, social, and cognitive function into advanced age. The goal of this review was to identify research describing centenarians to find the prevalence of dementia-free survival. Methods. We reviewed 650 publications to find studies that described the prevalence of dementia in centenarians, were community-based, had data that were specific to persons older than 100 years, and were published in peer-reviewed journals. For each study, we identified the prevalence of dementia, the completeness of the sample, the number of study participants, the method used to diagnose dementia, and the duration of the study. Results. We identified 20 research groups from 14 countries with publications meeting our search criteria. The studies showed substantial variation in methods of assessing cognitive status, assuring a complete cohort, and sample size. Few studies reported longitudinal data or attempted diagnosis of the cause of dementia. The prevalence of dementia-free survival past 100 years of age varied between 0 and 50 percent. Conclusions. The methodology used in studies regarding dementia prevalence among centenarians is sufficiently varied that combination of existing studies into a meta-analysis is not possible. Suggestions for assuring quality in future centenarian research are presented.