Published: Mar. 17, 2008
Updated: Mar. 18, 2008
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By Duke Medicine News and Communications
DURHAM, NC – More than a third of people over age 70 have some form of memory loss according to a national study by a team of researchers at Duke University Medical Center, the University of Michigan, the University of Iowa, the University of Southern California and the RAND Corporation. The group performed the first population-based study to determine the number of people who have some form of cognitive impairment, with and without dementia.
While an estimated 3.4 million Americans have dementia, defined as a loss of the ability to function independently, the researchers estimate that another 5.4 million over age 70 have memory loss that disrupts their regular routine but is not severe enough to affect their ability to complete daily activities.
"These findings illustrate that nearly every family will be faced with the challenges of caring for a family member with some form of memory impairment," said Brenda Plassman, Ph.D., associate research professor of psychiatry at Duke and the study's lead author. "Even among the people age 71-79, a sizeable number had cognitive impairment. This is an age at which most people expect to have many productive years ahead."
The frequency of memory loss without dementia increased with advancing age and with fewer years of education -- similar to the trends seen in dementia.
Plassman explained that throughout the course of the study, individuals with cognitive impairment without dementia progressed to dementia at a rate of about 12 percent per year. On average, the mortality rate for the study group was 8 percent annually but varied across the subtypes of cognitive impairment without dementia.
"While the overall rate of progression to dementia is in line with findings from other studies, the surprising finding here is that some subtypes of cognitive impairment without dementia progressed to dementia at much higher rates, around 20 percent, within one year," Plassman said.
Nearly a quarter of those with memory loss without dementia also had a chronic medical condition, such as diabetes or heart disease, that appeared to be the cause of the cognitive impairment. The researchers speculate that this group is one of the most underdiagnosed subtypes of cognitive impairment because doctors are likely focusing on the primary health issue.
"Given how common cognitive impairment without dementia is, physicians should be alert to this problem as they evaluate and treat the patient for other medical problems," said Robert B. Wallace, MD, the study's senior author from the University of Iowa. "This may have significant ramifications because it means that patients may not be able to accurately portray their symptoms and may not retain important information about their treatment."
The data, published in the Annals of Internal Medicine, is from the Aging, Demographics and Memory Study, which is part of the larger Health and Retirement Study conducted by the University of Michigan Institute for Social Research and funded by the National Institute on Aging.
"As the population ages and works longer, understanding the extent of cognitive impairment in the older population is critically important," notes Richard Suzman, PhD, director of the NIA's Behavioral and Social Research Program. "Research is now beginning to suggest that interventions -- such as controlling hypertension and diabetes or perhaps cognitive training -- might help maintain or improve mental abilities with age. As such interventions are tested and widely applied, we should be able to track their impact through this type of research."
A total of 856 study participants were assessed by a health care team in their home. During the assessment, the participants completed a neuropsychological examination and family members were asked to evaluate their loved one's memory, ability to complete daily activities and medical history.
A team of experts reviewed the information and assigned a diagnosis based on the general pattern and severity of the symptoms. This information was used to group patients together into subtypes for further analysis. Participants were followed from July 2001 through March 2005.
"With such a sizable number of Americans with some form of cognitive impairment, many of whom will get dementia; it's imperative to increase research funding that could lead to breakthroughs in Alzheimer's diagnosis, prevention and treatment," said William Thies, PhD, vice president of Medical and Scientific Relations for the Alzheimer's Association.
Co-authors on the study include Kenneth M. Langa, Gwenith C. Fisher, Steven C. Heeringa, David R. Weir, Mary Beth Ofstedal, James R. Burke, Michael D. Hurd, Guy C. Potter, Willard L. Rodgers, David C. Steffens, John McArdle and Robert J. Willis.