Context: In spite of numerous studies on the occurrence of dementia, many questions remain, such as the relation between age, aging, and dementing disorders. This question is relevant both for understanding the pathogenetic mechanism of the dementias and for the public health prospective because of the increasing number of 85-year-old or older persons in our population.
Objective: To estimate the occurrence of dementia in the very old, including nonagenarians, in relation to age, gender, and different dementia types.
Design: An epidemiological survey where all participants were clinically examined by physicians, assessed by psychologists, and interviewed by nurses. The Diagnostic and Statistical Manual of Mental Disorders, Revised Third Edition (DSM-III-R) criteria for dementia were followed. A category of "questionable dementia" was added when all criteria were not fulfilled. A double diagnostic procedure was used for all subjects.
Setting: Community-based population, including all inhabitants of 2 areas in central Stockholm, Sweden (N = 1848).
Participants: Of the 1848 subjects in the study population, 168 (9.1%) had died and 56 (3%) moved before examination. Of the remaining subjects, 1424 (87.7%) were examined, and the refusal rate was 12.3%.
Main outcome measures: Age- and gender-specific prevalence figures, and gender- and education-adjusted odds ratios were used.
Results: At the end of the diagnostic procedure, 358 clinically definite cases of dementia and 101 questionable cases of dementia were identified. Alzheimer disease (AD) contributed to 76.5%, and vascular dementia (VaD) to 17.9%. The prevalence of dementia increases from 13% in the 77- to 84-year-old subjects to 48% among persons 95 years and older (from 18% to 61% when questionable cases were included). The odds ratio for subjects 90 to 94 years and 95 years and older in comparison with 77- to 84-year-old subjects was 3.7 (95% confidence interval [CI], 2.7-5.1) and 6.5 (95% CI, 3.9-10.8) for dementia, 4.8 (95% CI, 3.3-7.0) and 8.0 (95% CI, 4.6-14.0) for persons with AD, 2.3 (95% CI, 1.3-4.2) and 4.6 (95% CI, 1.9-11.2) for VaD, respectively.
Conclusions: Dementia prevalence continues to increase even in the most advanced ages. This increase is especially evident among women and is more clear for AD. We believe that our prevalence data reflect the differential distribution of dementia risk.