Prevalence and risks of dementia in the Japanese population: RERF's Adult Health Study Hiroshima subjects

OBJECTIVES: To study the prevalence rate of dementia and its subtypes in Ja pan and to investigate the relationship of risk factors, such as demographi c features and disease history, to the prevalence of Alzheimer's disease or vascular dementia. DESIGN: A prevalence study within a longitudinal cohort study. SETTING: The original Adult Health Study (AHS) cohort consisted of atomic-b omb survivors and their controls selected from residents in Hiroshima and N agasaki using the 1950 national census supplementary schedules and the Atom ic Bomb Survivors Survey. Since 1958, the AHS subjects have been followed t hrough biennial medical examinations. PARTICIPANTS: Subjects were 637 men and 1585 women aged 60 years or older i n the AHS cohort. Forty-eight subjects resided in hospitals and institution s. MEASUREMENTS: In addition to the biennial medical examinations ongoing sinc e 1958, a screening test for cognitive impairment (CASI) was conducted by t rained nurses between September 1992 and September 1996. The prevalence of dementia and its subtypes was assessed in 343 subjects suspected to have de mentia and in 272 subjects with high CASI scores who were selected randomly . RESULTS: The prevalence of dementia based on DSM III/R criteria, using neur ological examination, the IQCODE, and CDR greater than or equal to 1, was 7 .2%. The prevalence of Alzheimer's disease was 2.0% in men and 3.8% in wome n, and the prevalence of vascular dementia was 2.0% in men and 1.8% in wome n. The relationship of risk factors to Alzheimer's disease or vascular deme ntia was investigated by the multivariate logistic linear regression analys is. Odds ratios of Alzheimer's disease for age (in 10-year increments), att ained education (in 3-year increments), history of head trauma, and history of cancer are 6.3, 0.6, 7.4, and 0.3, respectively. Odds ratios of vascula r dementia for age, history of stroke, and history of hypertension are 2.0, 35.7, and 4.0, respectively. Neither type of dementia showed any significa nt effect of sex or radiation exposure. CONCLUSION: This study is the first study of Japanese dementia rates carrie d out with a protocol similar enough to that of a US study to allow meaning ful comparisons. The prevalence rates demonstrated are more similar to US r ates than were found in many previous reports in Japan.