Research has shown that diabetes increases the risk of Alzheimer's disease and the risk of memory loss in people who don't have Alzheimer's disease. But it hasn't been clear whether people with Alzheimer's disease and diabetes have more rapid memory loss than those who have Alzheimer's disease but no diabetes.
New research published in the October 27, 2009, print issue of Neurology®, the medical journal of the American Academy of Neurology, suggests that those with both diseases actually have a slower rate of memory loss than people who had only Alzheimer's disease.
"This result was surprising," said study author Caroline Sanz, MD, of INSERM, the French National Institute for Health and Medical Research in Toulouse. "Our initial hypothesis was that diabetes would increase the rate of cognitive decline in people with Alzheimer's disease."
For the study, researchers followed 608 people with mild to moderate Alzheimer's disease for four years and tested their memory and thinking skills twice a year. A total of 63 people, or 10.4 percent, had diabetes.
At the beginning of the study, both those with and without diabetes had average scores of 20 points on the cognitive test. Over each six-month testing period, the overall group declined by an average of 1.24 points on the test. However, those without diabetes declined by 0.38 points more per six-month period than those with diabetes.
Researchers say it is not clear yet why the rate of memory loss was slower for people with diabetes. "One possible explanation is that diabetes in the elderly differs from that in younger people and in addition, elderly people with diabetes may be more likely to receive cardiovascular medications such as drugs for high blood pressure than people who don't have diabetes," Sanz said. "These drugs have been reported to decrease the risk of developing Alzheimer's disease and also the rate of cognitive decline in people with Alzheimer's disease. Other possible explanations for these findings may relate to differences in brain lesions in those people with diabetes compared to those without diabetes."
The study was supported by the French Ministry of Health and the Toulouse University Hospital.
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