Incidence of dementia, Alzheimer disease, and vascular dementia in a Japanese population: Radiation Effects Research Foundation adult health study.

OBJECTIVE: To determine the age-, sex-, and subtype-specific incidence of dementia and to assess the effect of education level on the incidence in a Japanese population. METHODS: 2,286 dementia-free subjects, aged > or =60 years, were followed for 5.9 years through biennial two-phase examinations. RESULTS: 206 cases of dementia were newly diagnosed based on DSM IV. The incidence per 1,000 person-years was 12.0 for men and 16.6 for women. Based on NINCDS-ADRDA criteria, 80 cases of probable Alzheimer disease (AD) and 50 cases of possible AD were diagnosed. Based on NINDS-AIREN criteria, 36 cases of probable vascular dementia (VaD) and 40 cases of possible VaD were diagnosed. Age and education showed the most statistically significant effects for all dementia. Probable AD showed the most remarkable increase with age and decreased with increasing education level (p = 0.001). Probable VaD showed significant effects of sex (p = 0.033) and sex-age interaction (p = 0.048), but not education (p = 0.26). CONCLUSION: AD was the predominant type of dementia in this recent incidence study conducted in Japan, suggesting a reduction in VaD and an increase in AD. Age, sex, and education effects differed by dementia subtype.