Based on the experts' classifications, Drs. Plassman and Langa and co-authors estimated the national prevalence and total numbers of people age 71 and older, by age group, with any dementia and with AD or vascular dementia in 2002. According to their calculations, 13.9 percent of Americans age 71 and older have some type of dementia, 9.7 percent of Americans in that age group have AD, and 2.4 percent have vascular dementia. AD accounted for about 70 percent of all dementia cases among people 71 and older.

As in other studies, the ADAMS analysis showed that the prevalence of dementia increases significantly with age. Five percent of people ages 71 to 79, 24.2 percent of people 80 to 89, and 37.4 percent of those 90 years or older were estimated to have some type of dementia. The estimated rate of Alzheimer's also rose greatly with older age - from 2.3 percent of people ages 71 to 79 to 18.1 percent of people 80 to 89 to 29.7 percent of those age 90 and older. The ADAMS investigators found fewer years of education and the presence of at least one APOE e4 allele, a genetic risk factor for AD, to be strong predictors of AD and other dementias.


Richard Suzman, Ph.D., director of NIA's Behavioral and Social Research Program, which jointly directs the HRS, said the ADAMS data will prove particularly valuable not only in assessing the prevalence of dementia, but also its impact. "ADAMS, with its link to the data about the health, economic, and family resources of individuals in the study, will help us to characterize more fully the burden of dementia on individuals, caregivers and the nation's health care system," he says.

The ADAMS report is the latest published study to estimate the prevalence of dementia and AD among older Americans. "These assessments have provided a range of estimates, based on differing methodologies and approaches," explains Dallas Anderson, Ph.D., program director for population studies in NIA's Dementias of Aging Branch. For example, some studies have included lower age ranges than ADAMS or broader characterizations of dementia, or have sampled participants in a specific community as a base for national extrapolations. A study reported in 1998 (Brookmeyer et al., 1998) combined incidence data from four community-based studies, estimating that national Alzheimer's prevalence among individuals age 60 years or older would rise from 2.3 million in 1997 to 8.6 million in 2047. Widely cited estimates based on the prevalence of Alzheimer's disease in a Chicago-based community (Hebert et al., 2003), and an earlier comparable study using data from East Boston (Evans et al., 1990) forecast the number of those age 65 or older with AD to be 5.1 million in 2010.

More Industry Headlines