Incidence and risk factors of dementia in a defined elderly Japanese population: the Hisayama study.

Vascular dementia (VaD) is more common than Alzheimer's disease (AD) in Japan, while AD is much more frequent in Western countries. The Hisayama study, an epidemiological study on dementia in a Japanese elderly population aged 65 years or older, has shown that the prevalence of VaD decreased for men, while AD remained unchanged in both sexes during a 7-year follow-up period (1985-1992). Decreased prevalence of VaD seems to be due to decreased incidence of stroke in recent years, resulting from the management of hypertension. The age-adjusted incidence of total dementia was approximately 20 per 1000 person-years in either sex; VaD was more frequent for men and AD for women. Risk factors for VaD were age, hypertension, previous stroke, and alcohol consumption, while age was only a significant risk factor for AD. Although the Hisayama study failed to demonstrate the relationship of vascular factors to AD, the previously reported studies suggest that either hypertension per se or blood pressure changes appear to partially participate in the pathogenesis of AD.