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.

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