Dementia-free life expectancy among elderly Japanese.

A 3-year prospective cohort study was conducted to estimate the life expectancy free of dementia (dementia-free life expectancy) in a representative sample of older persons living in an urban Japanese community. For the persons aged 65 years and older, who were not demented at the baseline survey in 1988, mortality and incidence rates of dementia were calculated. At the age of 65 years, males showed a total life expectancy of 18 years, including 16 years free of dementia, and females showed a total life expectancy of 23 years, including 18 years without dementia. At 65 years, the dementia-free life expectancy represented 89% of the total life expectancy for males and 79% for females. Total life expectancy and dementia-free life expectancy were longer among females than among males. However, the life-years with dementia were longer among females. This result would be attributable to a higher incidence of dementia and a lower mortality among females.