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Item #8
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.
===============================
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
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