[The cohort study of dementia: the Hisayama study].

An accurate population-based cohort study of dementia was begun in 1985 in the town of Hisayama, Japan. To examine secular trends in the prevalence of dementia and its subtypes, four cross-sectional surveys were conducted among Hisayama residents aged 65 years or older in 1985, 1992, 1998, and 2005. The prevalence of Alzheimer's disease (AD) significantly increased with time, while the prevalence of vascular dementia (VaD) decreased from the 1985 survey to the 1998 survey and then increased in the 2005 survey. In a 17-year prospective study of a total of 668 elder residents without dementia, elevated midlife and late-life blood pressure were significant risk factors for the late-life onset of VaD, but not for that of AD. A 15-year prospective study of 1,017 elder subjects, who underwent a 75-g oral glucose tolerance test, revealed that the age- and sex-adjusted incidence of VaD and AD significantly increased in subjects with diabetes than in those with normal glucose tolerance. Moreover, 2-hour post-load plasma glucose levels were closely associated with increased risk of VaD and AD. In a pathological study of Hisayama residents, higher levels of 2-hour post-load plasma glucose, fasting insulin, and HOMA-IR were significantly associated with increased likelihood of neuritic plaques.