The findings, from the Rush Alzheimer's Disease Center's Religious Orders Study, add to a developing body of research on a possible link between diabetes, AD, and cognitive decline. The results reported are among the first to examine how certain cognitive "systems" - memory for words and events, the speed of processing information, and the ability to recognize spatial patterns -- may be affected selectively in people with diabetes.
The research, by Dr. Zoe Arvanitakis, Dr. David Bennett, and colleagues at the Rush University Medical Center in Chicago, appears in the May 2004 issue of the Archives of Neurology. The investigators are part of the institution's Rush Alzheimer's Disease Center, headed by Bennett. The AD Center is one of 30 across the U.S. supported by the National Institute on Aging to study and care for Alzheimer's patients.
Some 824 Catholic nuns, priests, and brothers participating in the Religious Orders Study were followed for an average of 5.5 years. They received detailed clinical evaluations annually, including neuropsychological testing of five cognitive "systems" commonly affected by aging, AD, and other dementias - episodic memory (memory of specific life events), semantic memory (general knowledge), working memory (ability to hold and mentally rearrange information), perceptual speed (the speed with which simple perceptual comparisons can be made, such as whether two strings of numbers are the same or different), and visuospatial ability (the ability to recognize spatial patterns). Over the study period, 151 of the participants developed AD, including 31 who had diabetes. The researchers found a 65 percent increase in the risk of developing AD among those with diabetes compared with people who did not have diabetes.
In measures of cognitive function, only in the area of perceptual speed was there an association with an increased rate of decline over time, by about 44%, when comparing the diabetes and non-diabetes groups. Since stroke-related changes in the brain were found in a previous study to be tied to a decline in perceptual speed, the researchers could not say whether the link between cognitive decline and diabetes appeared because of the changes in the brain associated with Alzheimer's disease or those of some other common age-related condition like stroke or other vascular complications. In other areas of cognition, the rate of change over the time period of the study was no different in the two groups. However, at the start of the study, the baseline cognitive function scores of people with diabetes were lower than those of people without diabetes.
"We found that diabetes was related to decline in some cognitive systems but not in others," says Arvanitakis, the lead author of the report. "Since all participants have agreed to organ donation, we will have the opportunity to examine the pathologic basis of the association of diabetes to cognitive decline." The Rush researchers also expressed their indebtedness to the more than 1,000 nuns, priests, and brothers from across the U.S. participating in the Religious Orders Study.
"The research on a possible link between diabetes and increased risk of AD is intriguing, and this study gives us important additional insights," says Neil Buckholtz, Ph.D., head of the Dementias of Aging Branch in the NIA's neurosciences program. "Further research, some currently underway, will tell us whether therapies for diabetes may in fact play a role in lowering risk of AD or cognitive decline." Diabetes mellitus is a common condition affecting about 20 percent of people over age 65 years. Diabetes is known to be associated with various health effects including heart disease, kidney failure, and impaired cognitive function.
"This study represents a continuation of our research on possible risk factors for Alzheimer's disease," Arvanitakis said. "Researchers have not yet found a cure for Alzheimer's disease, but if we can identify factors that influence one's risk of developing Alzheimer's disease, this may allow us to make progress towards identifying factors that decrease the risk of Alzheimer's disease."
Previous work based done by Rush researchers on the Religious Orders Study, the Memory and Aging Project, and other large population studies, have shown that remaining intellectually active and eating a diet high in Vitamin E may be important ways to decrease the risk of AD, according to Bennett, director of the Rush Alzheimer's Disease Research Center. By contrast, depression and the tendency to be stressed may increase risk of the disease.
For more information on aging and Alzheimer's disease, readers can visit the Rush Alzheimer Disease Center's website at www.rush.edu, the NIA's Alzheimer's Disease Education and Referral (ADEAR) Center at www.alzheimers.org or call toll free 1-800-438-4380. Information on aging generally may be viewed at the NIA's general website at www.nia.nih.gov or by calling the NIA Information Center at 1-800-222-2225.