May 5, 2009
Researchers continue to explore the link between diabetes and Alzheimer's disease, and two recent studies provide new clues about the connection between the two diseases. In one, Scottish researchers showed that people with diabetes who fail to keep their blood sugar levels under control may experience long-term damage to the brain. In another, researchers at Mount Sinai School of Medicine in New York found a gene that is defective in both diabetes and Alzheimer's disease.
Researchers at the University of Edinburgh studied more than a thousand men and women, ages 60 to 75, who had diabetes. Of those, 113 had experienced episodes of severe hypoglycemia, in which blood sugar levels drop dangerously low. During these periods, insufficient blood sugar, or glucose, is present to "fuel" the brain.
Hypoglycemia typically occurs when people with diabetes do not manage the disease well. Typically, they do not eat at regular intervals, or neglect to take insulin and other diabetes medicines. Symptoms of hypoglycemia include sweating, feeling tired, hungry or dizzy, a high heart rate and blurred vision. If severe, it can result in coma or death.
In the study, people with diabetes who had experienced hypoglycemic episodes scored lower on tests of thinking and memory than those who had not experienced such symptoms. They performed poorly on tests of thinking and vocabulary. The findings were presented at an Alzheimer's conference by the charity Diabetes, UK.
Earlier studies have shown that poorly controlled diabetes may damage the brain, and that diabetes increases the risk of Alzheimer's disease. The researchers are conducting additional tests to determine how the hypoglycemic episodes affect the brain. It is also possible that people with memory problems may be less likely to remember to eat and take their medications.
In the Mount Sinai study, researchers found that a gene associated with type 2 diabetes, the most common form of diabetes in older people, was also defective in people with Alzheimer's disease. The gene, known as proliferator-activated receptor coactivator 1, or PGC-1, plays a critical role in regulating blood sugar. The findings appeared in the medical journal Archives of Neurology.
Activity of the gene is diminished in both those with diabetes and those with Alzheimer's. And the lower the gene activity, the higher the levels in the brain of beta-amyloid, a protein that in its toxic form builds up in the brains of those with Alzheimer's disease, according to the researchers.
"This new evidence is of extreme interest," said study leader Giulio Maria Pasinetti, M.D., Ph.D., "especially because of the evidence that approximately 60 percent of Alzheimer's disease dementia cases have at least one serious medical condition primarily associated with type-2 diabetes."
The relationship between diabetes and Alzheimer's remains elusive, Dr. Pasinetti said. Not everyone with type-2 diabetes has Alzheimer's disease. And not all people with Alzheimer's disease have diabetes. However, population studies continue to show that, relative to their healthy peers, seniors affected by diabetes are twice as likely to develop Alzheimer's disease.
Unraveling the link between diabetes and Alzheimer's is important, since better understanding of the underlying mechanisms of both diseases could lead to new, more effective treatments. While diabetes can often be controlled for decades with a healthy diet and medications, drugs for Alzheimer's provide only temporary relief and do nothing to stop the downward progression of disease.
Groups like the Fisher Center for Alzheimer's Research Foundation continue to fund vital research into the underlying causes of Alzheimer's. Such basic research is considered vital to one day finding a cure for the disease.
Weiping Qin, Vahram Haroutunian, Pavel Katsel, Christopher P. Cardozo; Lap Ho; Joseph D. Buxbaum; Giulio M. Pasinetti: "PGC-1-Alpha Expression Decreases in the Alzheimer Disease Brain as a Function of Dementia." Archives of Neurology, Volume 66 (3), 2009, pages 352-361.