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Objective: To investigate secular trends in the prevalence, incidence, and survival rate of dementia in a Japanese elderly population in a comprehensive manner. Methods: Five cross-sectional surveys of dementia were conducted among residents of a Japanese community, aged ≥65 years, in 1985, 1992, 1998, 2005, and 2012. We also established 2 cohorts consisting of the residents of this age group without dementia in 1988 (n = 803) and 2002 (n = 1,231), and each was followed for 10 years. Results: The age-standardized prevalence of all-cause dementia and Alzheimer disease (AD) increased with time (for all-cause dementia: 6.8% in 1985, 4.6% in 1992, 5.3% in 1998, 8.4% in 2005, and 11.3% in 2012, p for trend p for trend p for trend = 0.59). The age- and sex-adjusted incidence of all-cause dementia and AD, but not VaD, increased from the 1988 cohort to the 2002 cohort (for all-cause dementia: adjusted hazard ratio aHR 1.68, 95% confidence interval CI 1.38–2.06; for AD: aHR 2.07, 95% CI 1.59–2.70; for VaD: aHR 1.18, 95% CI 0.83–1.69). The 5-year survival rate of all-cause dementia and AD improved from the 1988 cohort to the 2002 cohort (for all-cause dementia: 47.3% to 65.2%; for AD: 50.7% to 75.1%; all p Conclusions: The increased incidence and improved survival rate of AD could have resulted in the steep increase in AD prevalence in the Japanese elderly.
Ohara et al. (2017) studied this question.