摘要：Objectives. We estimated dementia incidence rates, life expectancies with and without dementia, and percentage of total life expectancy without dementia. Methods. We studied 3605 members of Group Health (Seattle, WA) aged 65 years or older who did not have dementia at enrollment to the Adult Changes in Thought study between 1994 and 2008. We estimated incidence rates of Alzheimer’s disease and dementia, as well as life expectancies with and without dementia, defined as the average number of years one is expected to live with and without dementia, and percentage of total life expectancy without dementia. Results. Dementia incidence increased through ages 85 to 89 years (74.2 cases per 1000 person-years) and 90 years or older (105 cases per 1000 person-years). Life expectancy without dementia and percentage of total life expectancy without dementia decreased with age. Life expectancy with dementia was longer in women and people with at least a college degree. Percentage of total life expectancy without dementia was greater in younger age groups, men, and those with more education. Conclusions. Efforts to delay onset of dementia, if successful, would likely benefit older adults of all ages. The number of people with dementia worldwide will rise with population aging, especially as the population of oldest adults increases. Understanding dementia risk and survival with dementia in older, community-dwelling adults is essential for health policymakers. Previous studies have produced somewhat conflicting estimates of trends in dementia and Alzheimer’s disease incidence for persons aged 85 years or older. Most studies found an increase in dementia incidence 1–3 and Alzheimer’s disease incidence 1,3,4 with each successive age group. However, some studies found a decrease in dementia incidence 5,6 and Alzheimer’s disease incidence 5 in the oldest people in the population. Others found a decrease in dementia incidence for women only 4,7 or a decrease in dementia incidence 8 and Alzheimer’s disease incidence 7 for men only. Few studies have estimated the effect of dementia on survival of the total population, which consists of those with dementia, those who will develop dementia, and those who will not develop dementia. Life expectancy with dementia quantifies the effect of dementia on the survival of the total population. This metric is defined as the average number of years one is expected to live with dementia. 9 This measure incorporates both risk of dementia incidence and expectation of life based on population-level trends rather than the trends of only those with dementia. A related measure is percentage of total life expectancy without dementia, which relates the proportion of life expectancy in a healthy state. The few studies that used these types of metrics found that older age was associated with shorter life expectancy with dementia compared with younger age and that women had a longer life expectancy with dementia than did men. 9–12 These studies also found that percentage of total life expectancy without dementia decreased with increasing age and was higher among men than among women at each age. 9–12 Studies of dementia incidence 1,8 and Alzheimer’s disease incidence 1 are often limited by small sample sizes in the oldest ages and therefore combine ages 85 years and older into a single group. Studies that included more detailed age groups past 85 years had small sample sizes in these oldest age groups, which might have limited the precision and stability of incidence estimates for both dementia 2,3,7 and Alzheimer’s disease. 3,7 A few studies estimated life expectancy with and without dementia but primarily used cross-sectional data with prevalence estimates of dementia. 10,12,13 This study design is not ideal for understanding dementia incidence and mortality in the general population, which is the information that is the most useful for informing health policy. In addition, no study, to our knowledge, has yet examined the association between educational attainment and life expectancy with and without dementia. We used data from a long-running, population-based cohort study to estimate incidence of dementia and Alzheimer’s disease, and to calculate life expectancy with and without dementia and percentage of life expectancy without dementia. We tested the following hypotheses: Incidence of dementia and Alzheimer’s disease increases with age. Life expectancy with dementia decreases with age. Women have a longer life expectancy with dementia than do men but a smaller percentage of total life expectancy without dementia than do men. Higher levels of education are related to longer life expectancy without dementia and greater percentage of total life expectancy without dementia.
