Incidence of dementia and associated risk factors in Japan: The Osaki-Tajiri Project.

The incidence of dementia and risk factors has not been fully investigated in Japan. Following a prevalence study in 1998, we investigated the incidence and associated factors in the same population in 2003 and 2005. Randomly selected 771 residents in Tajiri were targeted. The final participants included 204 (65.2%) healthy older adults (Clinical Dementia Rating, CDR 0) and 335 (73.1%) people with questionable dementia (CDR 0.5). We analyzed the incidence of dementia and dementing diseases, and possible risk factors. The risk factors included demographics, lifestyle-related factors, vascular risk factors, cognitive functions, and MRI findings. Overall, 3.9% of the CDR 0 and 37.0% of the CDR 0.5 participants developed dementia during the 5-year period, whereas 40.2% of the CDR 0.5 participants developed dementia during the 7-year period. Older adults had a higher incidence. Higher CDR Box scores had a higher incidence. Of the dementing diseases, 60.8% of participants developed Alzheimer' disease (AD), followed by vascular dementia (VaD), 17.9%. Logistic regression analyses showed that age, MMSE, cognitive functions such as recent memory, and generalized atrophy were significant predictors of progression to AD. Similarly, predictive factors for progression to VaD were age, MMSE, cognitive functions such as frontal function, and white matter lesions and cerebrovascular diseases. A comprehensive system including CDR, cognitive tests, and MRI, is recommended in community-based health policy planning.