OBJECTIVE: To estimate the lifetime cumulative incidence of dementia and its subtypes from a community-dwelling elderly population in Japan. METHODS: A total of 1,193 community-dwelling Japanese individuals without dementia, aged 60 years or older, were followed up prospectively for 17 years. The cumulative incidence of dementia was estimated based on a death- and dementia-free survival function and the hazard functions of dementia at each year, which were computed by using a Weibull proportional hazards model. The lifetime risk of dementia was defined as the cumulative incidence of dementia at the point in time when the survival probability of the population was estimated to be less than 0.5%. RESULTS: During the follow-up, 350 participants experienced some type of dementia; among them, 191 participants developed Alzheimer disease (AD) and 117 developed vascular dementia (VaD). The lifetime risk of dementia was 55% (95% confidence interval, 49%-60%). Women had an approximately 1.5 times greater lifetime risk of dementia than men (65% [57%-72%] vs 41% [33%-49%]). The lifetime risks of developing AD and VaD were 42% (35%-50%) and 16% (12%-21%) in women vs 20% (7%-34%) and 18% (13%-23%) in men, respectively. CONCLUSION: Lifetime risk of all dementia for Japanese elderly was substantial at approximately 50% or higher. This study suggests that the lifetime burden attributable to dementia in contemporary Japanese communities is immense.
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