Scientists are on the verge of painting a new and dramatically detailed portrait of Americans who have Alzheimer's disease and related dementias. The first brush strokes on the canvas came with the November publication of new data on the prevalence of dementia collected by teams of nurses and neuropsychology technicians from Duke University. They traveled to homes, apartments, assisted living facilities and nursing homes, collecting blood and DNA samples and videotaping interviews.
The study, published in the journal Neuroepidemiology (29: 1-2, 2007), is the first to include people from all regions of the United States, a sample of 856 individuals in 42 states that represents a cross-section of the U.S. population. Prior studies were based on extrapolations from data collected in only a few communities. Besides the researchers at Duke, study coauthors represented the universities of Michigan and Iowa, as well as RAND Corporation in Santa Monica, Calif.
RISK FOR BOOMERS
Brenda Plassman and coauthors calculated that 3.4 million people in the United States, or 13.9% of the population age 71 or older, had some degree of dementia in 2002. The prevalence rose dramatically with age, with dementia affecting 37.4% of those ages 90 and older.
"We should be upset; the problem is an enormous one, but it seems tiny today compared to what it's going to be in 20 or 30 years as the baby boomers reach the age of greatest risk," said Richard Suzman, director of the National Institute on Aging (NIA) Behavioral and Social Research Program. NIA funded the study.
The American medical system has done a good job of helping people forestall the ravages of some diseases, especially cardiovascular disease, that might have killed them before they reached advanced old age. Thus, more people can now expect to survive to ages when they are much more likely to develop Alzheimer's disease and other dementias.
The new study reveals the levels at which age brings increased risk:
In the U.S. population ages 71 through 79, 5% have dementia (5.3% for men and 4.8% for women). From ages 80 through 89, the prevalence of dementia soars to 24.2%, with a dramatic gender gap: the disease affects 17.7% of men and 27.8% of women in this age group. At ages 90 and beyond, the gender balance shifts as dementia affects 37.4% of the population, including 44.6% of men and 34.7% of women.
The 2002 population figures for those with dementia included 712,000 people between ages 71 and 79; another 1,996,000 people between 80 and 89; and 699,000 people over the age of 90.
Dementia means a "decline in memory or other cognitive function [that] leads to a loss of independence. That has a wide-ranging impact on individuals, families and healthcare systems," according to the study, titled "Prevalence of Dementia in the United States: The Aging, Demographics and Memory Study."
A TROVE OF DATA
The effects of dementia range from someone living at home who can no longer be allowed to cook because he or she might forget to turn off the stove to a person who lies helpless and incontinent in a nursing home bed, unable to recognize family members.
The national total of 3.4 million people with dementia includes 2.4 million people with Alzheimer's disease. Other forms of dementia may be caused by such factors as vascular dementia, Parkinson's disease, alcoholism or traumatic brain injury.
In addition to age, fewer years of education puts individuals at higher risk, as does the genetic factor, the presence of a gene called the Apo-E allele.
The new study is especially noteworthy because it will provide much more than figures on the occurrence of the disease. Interviews the authors conducted also will provide a trove of data about the income, education and family structure of people with dementia, about whether they live alone at home or with caregivers, and about …