Prevalence of dementia in centenarians.

Above age 65, the prevalence of dementia rises exponentially from 1 to 15% at age 85. Despite many studies concerning dementia, little is known about the prevalence of dementia in the 'oldest old'. Whether the prevalence levels off around age 95 is yet unanswered. This question is important because it addresses whether dementia is an inevitable consequence of ageing or a disorder occurring within a specific age range. All 17 persons aged 100 or more in three Dutch towns with 250 000 inhabitants were examined by means of cognitive tests, informant questionnaires, clinical interviews and anamneses. Fifteen out of 17 Dutch centenarians in a complete population sample of 250 000 were found to be demented. Two could not be examined.