MONDAY, May 17, 2004 (HealthDayNews) -- Having diabetes appears to be linked to a 65 percent higher risk of developing Alzheimer's disease.
While previous research has looked at the association between dementia and diabetes, results were often inconclusive.
The current study, appearing in the May issue of the Archives of Neurology, not only looks specifically at Alzheimer's, but it is also the first to look at how different cognitive "systems" might be affected differently in people with diabetes.
"I think it strengthens the link," said Dr. Sam Gandy, vice president of the Medical and Scientific Advisory Council of the Alzheimer's Association.
It also means there may be things people can do to stave off Alzheimer's. "This strengthens the evidence that tight control of diabetes may be important not only to manage vascular complications but to lower your risk for Alzheimer's," Gandy added. "It's now possible with oral agents and insulin and relatively painless glucometers to monitor and maintain your blood sugar in a very tight range."
The issue of an association between diabetes and Alzheimer's is an important one as the prevalence of type 2 diabetes increases dramatically throughout the world. Currently, about 20 percent of Americans over the age of 65 have the disease. If left unchecked, diabetes can lead to heart problems, kidney problems, cognitive impairment and more.
This study used data from the Religious Orders Study, an ongoing study of Catholic nuns, priests and brothers, to analyze the relationship between Alzheimer's and diabetes. Some 824 participants were followed for about five and a half years, undergoing periodic neuropsychological testing of five cognitive "systems." Those systems were general knowledge, working memory, perceptual speed (the speed with which simple comparisons can be made, such as whether two groups of numbers are the same), and the ability to recognize spatial patterns.
Over the study period, 151 of the participants developed Alzheimer's, including 31 who had diabetes. This amounted to a 65 percent increase in the risk of developing Alzheimer's among people who had diabetes compared with people who did not.
People with Alzheimer's and diabetes had an increased rate of decline in their perceptual speed (44 percent lower) compared to people who had Alzheimer's but not diabetes. The other systems declined at a similar rate.
The difference in perceptual speed may be due to strokes, which are more common in people with diabetes.
Other underlying mechanisms are still not clear, nor were they specifically addressed in this study.
"One of the first thoughts that comes to mind is that it would be through a vascular process, because we know that diabetes is associated with vascular diseases that affect the brain and thinking ability," said study author Dr. Zoe Arvanitakis, a neurologist with the Alzheimer's Disease Center at Rush University Medical Center in Chicago.
It's also not certain whether this is a cause-and-effect relationship or simply an association, although a cause-and-effect scenario would make a certain amount of sense. "We know, for example, that diabetes increases atherosclerosis and high cholesterol, and high cholesterol can aggravate Alzheimer's," Gandy said. "The other thing is it appears the same enzyme that degrades insulin also decreases amyloid peptide [which is important in Alzheimer's]." In a person with diabetes, different systems may be competing for the same enzyme.
All the study participants have agreed to donate their organs after they die, so researchers will have an opportunity to explore some of these hypotheses at that time.
More information means more hope for prevention and treatment of Alzheimer's. "The overall goal of this and other studies is to better understand the factors that either increase or decrease the risk of Alzheimer's disease," Arvanitakis said. "If we can identify those factors and understand what mechanisms underlie the relationship, we might be able to influence a person's risk of having Alzheimer's disease."
The National Institute on Diabetes and Digestive and Kidney Diseases has more on the blood-sugar disorder.