July 17, 2006 -- Several new studies may help to clarify and strengthen the link between diabetesand Alzheimer's disease, according to researchers presenting their findings at the 10th International Conference on Alzheimer's Disease and Related Disorders in Madrid, Spain.
Affecting about 4.5 million Americans, Alzheimer's disease gradually destroys a person's memory and ability to learn, reason, make judgments, communicate, and carry out daily activities, according to the Alzheimer's Association.
'Excitement' Among Researchers
The most common type of diabetes, type 2 diabetes, occurs when either the body does not produce enough insulin or the cells ignore the insulin, according to the American Diabetes Association. The body needs insulin to be able to use sugar.
Exactly how diabetes and Alzheimer's are linked is not fully understood, but researchers are getting closer. One theory is that diabetes may cause blood sugar to accumulate in the brain, which could damage brain cells.
"The excitement in the field is twofold," John C. Morris, MD, director of the Alzheimer's Disease Research Center of Washington University in St. Louis, tells WebMD. "There have been a lot of observational studies in the field, but we don't yet understand how the link between Alzheimer's disease and diabetes works, and understanding it better will give us insight into the mechanisms of Alzheimer's disease," he says. "There are already effective treatments for type 2 diabetes and it would be great if there were this connection so we could take the drugs we use for type 2 diabetes to treat or reduce the risk of Alzheimer's disease."
Prediabetes Ups Risk of Developing Alzheimer's
In one new study, Swedish researchers report that people with borderline diabeteshave nearly a 70% increased risk of developing dementiaand Alzheimer's disease. Researchers tracked 1,173 people aged 75 and older who were free of dementia and diabetes at baseline. They identified borderline diabetes in 47 people. Borderline or prediabetes occurs if a person has higher than normal blood sugar levels that are not quite high enough to be diagnosed as type 2 diabetes.
What's more, this connection was present only among people who did not carry the APOE ¦Å4 gene that increases risk for the most common form of Alzheimer's. The risk for Alzheimer's was especially high when borderline diabetes occurred with severe systolic hypertension(¡Ý180 mm Hg in the top number of a blood pressure reading), the study showed.
Tight Control of Blood Sugar May Also Reduce Risk of Alzheimer's
Another new study presented here showed that people who already have type 2 diabetes have an increased risk of dementia and Alzheimer's disease. Researchers, including Rachel A. Whitmer, PhD, of Kaiser Permanente's division of research in Oakland, Calif., report that people with diabetes who had very poor blood sugar control had the greatest risk, but "effective blood sugar control may lower risk of another diabetes-associated complication -- dementia," they conclude in a written statement.
More good news is that a class of drugs commonly used to treat diabetes called thiazolidinediones may also influence inflammation and other brain cell processes that may be related to Alzheimer's disease. Drugs in this class include Avandia and Actos and they help insulin work better in the muscle and liver to use blood sugar and also reduce sugar production in the liver.
Donald Miller, ScD from Boston University School of Public Health and colleagues report that people with diabetes treated with these medications had lower rates of Alzheimer's disease than counterparts taking insulin. In fact, there were almost 20% fewer new cases of Alzheimer's among people taking thiazolidinediones compared with people who took insulin. Similar results were found in a separate comparison between thiazolidinediones users and people starting Glucophage, another drug used to treat diabetes.