MONDAY, April 9, 2007 (HealthDay News) -- Adults with diabetes may be at higher risk for developing mild cognitive impairment, a condition that is often seen as a precursor to Alzheimer's disease, new research found.
"There is mounting evidence that diabetes is bad for cognition," said Dr. Jose A. Luchsinger, the lead author of the study and an assistant professor of medicine at Columbia University. "The mechanisms need to be elucidated. Type 2, or adult-onset diabetes, which the study refers to, is increasing in the U.S. and in the world. The consequences of the potential cognitive complications of diabetes could be devastating from a public health standpoint."
Still, there are perhaps more questions than answers in the new study, which was published Monday in the April issue of Archives of Neurology.
"What is the real message for diabetes control?" asked Dr. Larry Deeb, president of medicine and science for the American Diabetes Association. "If the message is that you're at greater risk for MCI (mild cognitive impairment) no matter what, that's one thing. If taking good care of blood sugar makes a difference, as seems to be the case for most other complications of diabetes, that's another thing. One would hope this might be another argument for controlling diabetes."
Health experts already knew that type 2 diabetes can be a risk factor for Alzheimer's disease. The evidence has been less clear on whether diabetes is related to a higher risk of mild cognitive impairment, often considered a bridge state between normalcy and Alzheimer's.
"There are few studies looking at the outcome of mild cognitive impairment," Luchsinger said.
More than 10 percent of the elderly population of the United States has diabetes. And the prevalence is twice as high among black Americans and Hispanics as it is among non-Hispanic whites.
For this study, Luchsinger and his colleagues looked at 918 men and women older than 65 (average age 75.9) who did not have mild cognitive impairment or dementia at the start of the study. The participants, all from northern Manhattan in New York City, were assessed every 18 months with an in-person interview as well as physical and neurological examinations.
Almost one-quarter -- 23.9 percent -- of the participants had diabetes, 68.2 percent had high blood pressure, 33.9 percent had heart disease, and 15 percent had suffered a stroke.
During follow-up that averaged 6.1 years, 334 of the participants developed mild cognitive impairment. And people with diabetes had a higher risk of having mild cognitive impairment, especially amnestic MCI, which affects memory more than non-amnestic MCI.
Overall, 8.8 percent of cases of mild cognitive impairment among the study participants could be attributable to diabetes. And the rates were higher for black Americans (8.4 percent) and Hispanics (11 percent) than for non-Hispanic whites (4.6 percent). This makes sense, given that minority populations in the United States have a higher prevalence of diabetes.
What explains the possible link between diabetes and impairment?
Diabetes could contribute to plaque build-up in the brain, with such a build-up a hallmark of Alzheimer's, the study authors said.
But, they added, more research is needed.
"Studies are needed to see if preventing diabetes prevents cognitive impairment and how diabetes treatment affects cognition," Luchsinger said. "We also need to see how cognitive impairment in persons with diabetes affects their ability to follow their treatment, which is usually complex and involves several medications."
Other experts applauded even the tentative findings.
This type of research may help target populations who could one day benefit from drugs, said Maria Carrillo, director of medical and scientific relations at the Alzheimer's Association.
"This supports the idea that risk factors are real," Carrillo added. "The field has now matured to a point where we can start looking at earlier and earlier aspects of the disease. It makes sense to look even earlier than that and try to tease out what the risk factors look like in that population, in case we have a disease-modifying drug coming up in near future."
"This is documenting what we know a little bit better and emphasizing that patients should control their blood sugar as well as they can early in the disease," added Dr. Joel Zonszein, director of the Clinical Diabetes Center at Montefiore Medical Center in New York City. "This is another piece of information, more wood to the fire."
The Alzheimer's Association has more on mild cognitive impairment.