A new analysis suggests that about 3.4 million Americans age 71
and older — one in seven people in that age group — have
dementia, and 2.4 million of them have Alzheimer's disease (AD).
The study, supported by the National Institutes of Health (NIH),
is the latest in a series of analyses attempting to assess the
prevalence of dementia and AD, the most common form of dementia.
Published online this week in Neuroepidemiology, the study
is the first to estimate rates of dementia and AD using a nationally
representative sample of older adults across the United States.
Brenda L. Plassman, Ph.D., of Duke University Medical Center,
with Kenneth M. Langa, M.D., Ph.D., and David R. Weir, Ph.D., of
the University of Michigan, Robert B. Wallace, Ph.D., of the University
of Iowa, and others, conducted the analysis as part of the Aging,
Demographics and Memory Study (ADAMS). ADAMS is a sub-study of
the larger Health and Retirement Study (HRS), the leading resource
for data on the combined health and economic circumstances of Americans
over age 50. ADAMS and the HRS are sponsored by the National Institute
on Aging, a component of NIH, under a cooperative agreement with
the University of Michigan.
The study highlights the nationwide reach of dementia, which affects
not only those with the disease, but their families and communities
as well. "As the population ages during the next few decades,
the prevalence of Alzheimer's disease will increase several-fold
unless effective interventions are discovered and implemented," said
NIA Director Richard J. Hodes, M.D. "These data underscore
the urgency of research in this area."
The study included 856 HRS participants age 71 and older from
42 states in 2001-2003. ADAMS interviewers from Duke University
Medical School conducted at-home evaluations to gather information
about each participant's cognitive and functional status and symptoms,
neuropsychiatric symptoms, current medications, medical history
and family history of memory problems. Prior neuroimaging and laboratory
results were also obtained.
A team of clinicians reviewed the evaluation information and made
a preliminary assessment of each person's cognitive status. A consensus
panel of other medical experts then used well-accepted diagnostic
criteria to determine if the participant had normal cognitive function,
cognitive impairment without dementia, or dementia. Such criteria
further were used to discern the type of dementia, including AD
or vascular dementia, the second most common cause of dementia
in older adults.
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.