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Type 1 Diabetes Shrinks the Brain

A loss that might explain why diabetics seem to have higher rates of cognitive impairment throughout life. It’s well known that people with juvenile-onset diabetes, or Type 1 diabetes, are more prone to a host of problems, including nerve damage in the extremities, kidney failure and stroke.

Less is understood about diabetes’ effect on the brain, says study author Dr. Richard K. Chan, an assistant professor of neurology and neurosurgery at the State University of New York at Buffalo. In fact, “there are a lot of people who believe diabetes does not affect the brain,” Chan says.

However, a growing body of research seems to say otherwise. People with Type 1 diabetes do not produce insulin, so they have to take daily insulin shots to stay alive.

Studies have shown children and adults with this form of diabetes are prone to subtle cognitive difficulties, including problems with memory, abstract reasoning and attention. Other studies suggest diabetes could be linked to dementia, including Alzheimer’s disease.

To learn more about the effect of diabetes on the brain, Chan and his colleagues did magnetic resonance imaging (MRI) brain scans on about 50 people aged 18 to 50 who had juvenile-onset diabetes for at least 10 years. The people in the study were otherwise healthy, meaning they had no evidence of heart disease or hypertension, and were in good control of their blood glucose levels.

The MRI scans, which can be used to measure the volume of the brain, were compared to brain scans of an equal number of people without diabetes.

When they controlled for age and sex, researchers found nearly 90 percent of the diabetic patients had a brain volume that was lower than the 50th percentile of the non-diabetic subjects.

“This is an indication that there is a loss of brain tissue, or brain atrophy,” Chan says.

The study also found about 10 percent to 20 percent of diabetics had stroke-like lesions in the brain, which are early indicators of stroke, while none of the non-diabetics did.

The study was presented April 1 at the American Academy of Neurology’s annual meeting in Honolulu.

The brain is made up of both tissue and fluid-filled cavities. Typically, as a person ages, the cavities grow and the brain tissue shrinks. “In diabetics, this process appears to be accelerated,” Chan says.

In the brains of the non-diabetics, the tissue accounted for about 90 percent of the volume, while the cavities accounted for 10 percent. In diabetics, the tissue made up 85 percent to 87 percent of the brain, while the cavities were 13 percent to 15 percent.

“What we are showing here is there are two kinds of anatomical changes related to diabetes,” Chan says. “The first are stroke-like lesions. The other is brain shrinkage. Both of them could possible explain the cognitive problems in diabetics.”

On the face of it, it sounds scary. However, some researchers say it is far too soon to worry.

The difference in brain volume is actually quite small, says Dr. Sami Harik, a professor of the department of neurology at the University of Arkansas College of Medicine in Little Rock.

“This is a statistically significant difference, but is it a biologically significant difference?” Harik says. “I don’t know. It seems like a mild amount of cerebral atrophy.”

Furthermore, it’s too soon to jump to the conclusion that a decrease in brain volume means brain atrophy. A brain can shrink in volume if it loses water, Harik explains. And it’s too soon to conclude that mild brain atrophy will have a significant effect on intelligence.

Still, Harik says, the study is significant. “This is a very important subject to study because of the prevalence of diabetes and the problems diabetics have with cognitive function,” he says. “It is well-known that diabetics have abnormalities of neurological function.”

The study is ongoing to determine if the diabetics with the decreased brain volume also had cognitive difficulties, Chan says.

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FACT: Patients on oral agents alone, only 5% of patients with type 2 diabetes test once per day; and 47% of patients with type 2 diabets and 21% of patients with type 1 diabetes do not test blood glucose levels at all. Am J Med. 2001;111:1-9