Middle-aged people with diabetes are nearly three times more likely to develop dementia in old age than people without diabetes.
Dr. Michal Schnaider Beeri, from Mount Sinai School of Medicine in New York, stated that in looking at a cross-section of the population, studies have "tied diabetes to Alzheimer’s disease or dementia. "Our study is special because it shows a strong association between these disorders over several decades."
The study involved 2600 subjects who participated in the Israeli Ischemic Heart Disease study in the 1960s and were still alive and available for follow-up in 1999. The subjects were between 40 and 65 years of age when the study began.
The mental status of 1892 participants was determined, and 652 were identified as possibly demented. This was confirmed in 309 subjects (16.3 percent).
Those with diabetes during the study were 2.83-times more likely to develop dementia than those without diabetes, the investigators report in the medical journal Neurology.
As for how diabetes might promote dementia, Beeri offered three possibilities.
First, excess glucose can create high levels of so-called "advanced glycation end products," and these have been linked to dementia and Alzheimer’s disease in several studies, she said.
"These end products seem to stick to beta-amyloid and prevent its degradation," the researcher explained, referring to the abnormal protein that accumulates in the brain of people with Alzheimer’s disease. Beeri noted that if glycation end products are involved this could be good news because recent reports suggest that these levels can be modified by diet.
Another possible explanation is that insulin competes for a degradation enzyme that also breaks down beta-amyloid, Beeri said. Therefore, with high insulin levels (as happens with type 2 diabetes), the enzyme is less able to clear away beta-amyloid.
Or, it may be that diabetes’ bad effect on the microcirculation could lead to dementia by interfering with the brain’s blood supply, she added.