Prevalence of dementia after age 90: results from the 90+ study.

BACKGROUND: Although the prevalence of dementia increases with age from ages 65 to 85, whether this increase continues after age 90 is unclear. Most studies reporting on dementia prevalence do not have sufficient participants to estimate prevalence for specific ages and sexes above age 90. Here, we estimate age- and sex-specific prevalence of all-cause dementia in the oldest-old, those aged 90 and older. METHODS: Participants are 911 elderly from The 90+ Study, a population-based study of aging and dementia in people aged 90 and above. Dementia was diagnosed using in-person examinations as well as telephone and informant questionnaires. RESULTS: The overall prevalence of all-cause dementia was higher in women (45%, 95% CI = 41.5-49.0) than men (28%, 95% CI = 21.7-34.2). Among women, prevalence increased with age after age 90, essentially doubling every 5 years. A lower prevalence of dementia was significantly associated with higher education in women but not in men. CONCLUSIONS: In a very large sample of participants aged 90 and older, prevalence of all-cause dementia doubled every 5 years for women but not men.