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

Abstract

This study examined the secular trends of life expectancy without dementia among elderly American members of a health maintenance organization, and observed if an increased life expectancy is accompanied by an increase in the duration of life with dementia. The data derived from two chronological 9-year prospective cohort studies of members of the Kaiser Permanente Medical Care Program of Northern California. The first and second cohorts included 2,702 and 2,926 people aged > or =65 years free from dementia at baseline. Life expectancy without dementia or dementia-free life expectancy (DemFLE) is defined as the average number of years a person is expected to live without dementia. Total life expectancy is equal to the sum of DemFLE and life expectancy with dementia. Estimations of DemFLE were based on mortality data and incidence of dementia, using double-decrement life tables. Between the first and second cohorts, all-cause mortality rates declined, while the incidence of dementia remained constant in both men and women. Among the males, total life expectancy increased at a higher rate than DemFLE. Consequently, the duration of life with dementia was extended in the second cohort. Conversely, among the females DemFLE increased at a higher rate than total life expectancy, thus the duration of life with dementia decreased in the second cohort. The median age of dementia onset was postponed by 2-3 years in the second cohort for females, and did not show any specific difference between the two cohorts in males. The trends of health expectancies suggest an extension of the duration of life with dementia for males and a compression of dementia for females. A decreased incidence of risk factors for dementia among females in the second cohort such as stroke may explain these trends.