The challenge is to find indicators -- physical, mental or lifestyle factors -- that can single out people with mild thinking impairment who can benefit from preventive treatment, says study leader Frederick Unverzagt, associate professor of psychology at the Indiana University School of Medicine.
"It's a mixed bag, a heterogeneous group," says Unverzagt. "We had five different subsets. Some had medically unexplained memory loss, some were heavy alcohol users, some had medical conditions such as stroke. Now that we can describe the scope and nature of these categories, the next step is to look at predictors or triggers of cognitive decline."
The study, in the issue of Neurology, the journal of the American Academy of Neurology, included more than 2,200 African-American residents of Indianapolis. It is a joint American-Nigerian, cross-cultural comparison of the incidence of Alzheimer's disease and other forms of dementia in the two countries.
The incidence of what the researchers call Cognitive Impairment No Dementia (CIND), a loss of mental function short of Alzheimer's disease, was similar to those found in other, more limited studies, and is applicable to ethnic groups other than African-Americans, Unverzagt says. For example, a smaller Canadian study whose participants were predominantly Caucasian also found a 25 percent incidence of
CIND is "a transition stage from normal aging to dementia," Unverzagt says. While only 2 percent of persons with normal mental function developed Alzheimer's disease during the follow-up period, the rate for those with CIND was 26 percent.
Why an equal percentage recovered normal mental function is not clear, Unverzagt says. It was not the result of treatment. One possibility explored by the researchers was that depression caused the poor results, and that thinking improved as the subjects' outlooks brightened. But that did not prove out. The researchers still are investigating the possibility that the first poor results were due to physical conditions that improved over time.
The results are valuable because "this is really the first one to get a handle on the incidence of CIND in the general population," says Neil Buckholtz, chief of the Dementias of Aging branch at the National Institute on Aging.
"It is increasingly important to learn more about how to measure and characterize this condition. We are not sure what factors lead some people to develop Alzheimer's disease and others not," he says.
The study found that the Americans were twice as likely to develop Alzheimer's as the Nigerians.
While there now is no proven treatment to prevent Alzheimer's disease, one may be on the horizon, Buckholtz says. A large-scale clinical trial of vitamin E and donepezil hydrochloride (Aricept), a drug used to treat Alzheimer's disease, is underway. Results are expected in two to three years.
What To Do
The warning signs of CIND that indicate a need to consult a physician are "major changes in cognitive ability and function -- someone who wants to balance a checkbook and can no longer do it," Buckholtz says.
The National Institute of Neurological Diseases and Stroke and the Alzheimer's Association offer information about Alzheimer's disease.