Trends in dementia-free life expectancy among elderly members of a large health maintenance organization

Background This study examined the secular trends of life expectancy withou t dementia among elderly American members of a health maintenance organizat ion, and observed if an increased life expectancy is accompanied by an incr ease in the duration of life with dementia. Methods The data derived from two chronological 9-year prospective cohort s tudies of members of the Kaiser Permanente Medical Care Program of Northern California. The first and second cohorts included 2702 and 2926 people age d greater than or equal to 65 years free from dementia at baseline. Life ex pectancy without dementia or dementia-free life expectancy (DemFLE) is defi ned as the average number of years a person is expected to live without dem entia. Total life expectancy is equal to the sum of DemFLE and life expecta ncy with dementia. Estimations of DemFLE were based on mortality data and i ncidence of dementia, using double-decrement life tables. Results Between the first and second cohorts, all-cause mortality rates dec lined, while the incidence of dementia remained constant in both men and wo men. Among the males, total life expectancy increased at a higher rate than DemFLE. Consequently, the duration of life with dementia was extended in t he second cohort. Conversely, among the females DemFLE increased at a highe r rate than total life expectancy, thus the duration of life with dementia decreased in the second cohort. The median age of dementia onset was postpo ned by 2-3 years in the second cohort for females, and did not show any spe cific difference between the two cohorts in males. Conclusion The trends of health expectancies suggest an extension of the du ration of Life with dementia for males and a compression of dementia for fe males. A decreased incidence of risk factors for dementia among females in the second cohort such as stroke may explain these trends.