Prevalence of dementia in old age: clinical diagnoses in subjects aged 95 years and older.

Epidemiologic studies have consistently shown an exponential increase in the prevalence of dementia in the very old, but different standards of the investigators and the instruments, as well as the selection of the samples, limit the comparison of these studies. They usually include only a small number of participants aged 90 years and older. This investigation focuses on whether there is an exponential increase in the prevalence of dementia in people aged 90 years and older. The Berlin Aging Study (BASE) consists of a representative sample of elderly aged 70 to 105 years stratified by age and gender. Analyses of a BASE first sample (N = 156) with 52 participants aged 90 years and older showed an exponential increase in dementia from age 70 up to age 94 years, but the group aged 95 years and older (N = 26) showed a plateau near 45%, with no further increase in dementia prevalence.