is a major cause of blindness, kidney damage, heart disease,
and loss of sensation leading to limb amputation. Few parts
of the body seem to be immune from the ravages of chronically
high blood sugar (glucose) that characterizes diabetes—including,
it appears, the brain. Some studies suggest that older people
with diabetes tend to suffer more from impairments in memory
and thinking. Scientists have also uncovered some intriguing
possible connections between diabetes and Alzheimer’s
Fundamentally, diabetes is an inability to make or use insulin
normally. Insulin is the hormone
that regulates the level of glucose
in the blood and helps our bodies use the food we eat. Food
must be converted into glucose before our cells can use it
as fuel, but glucose can’t enter the cells without insulin.
In lock-and-key fashion, insulin enters structures on the
cell surface called receptors.
Only when insulin “docks” with the receptors does
the cell allow glucose to enter. Cells use glucose to produce
In type 1 diabetes, which typically develops by young adulthood,
the pancreas stops making insulin altogether and the person
must inject the hormone daily to survive. In type-2 diabetes,
which typically strikes in middle age and is by far the most
common form of the disease, cells gradually become “resistant”
to insulin. Glucose cannot enter the cells as readily, so
the amount of it in the blood rises. Left unchecked, chronically
high blood sugar damages the blood vessels, kidneys, eyes,
You’ve probably heard about the current “epidemic”
of diabetes (type 2), driven by rising rates of obesity and
sedentary lifestyles. Media reports dramatize the trend with
anecdotes about 14-year-old children who are developing the
disease. But strictly in terms of the numbers, it’s
older people who are most affected, says Edward Gregg, Ph.D.,
an epidemiologist with the Division of Diabetes Translation
at the Centers for Disease Control and Prevention (CDC). “There’s
a lot of concern these days with diabetes and youth, but in
terms of the total numbers it’s really the older segment
of the population where the diabetes actually occurs and it’s
going to be more so. In people 65 and older, about 20 percent
have diabetes, and a third don’t know it.”
Diabetes and the brain
As if loss of limb, vision, and kidney function weren’t
bad enough, a number of studies suggest that diabetes may
be associated with memory loss and other cognitive impairments.
Indeed, in a study reported in the February 18, 2003, Proceeding
of the National Academy of Sciences, scientists linked “pre-diabetic”
problems with controlling blood sugar to changes in a part
of the brain important to memory.
The study, involved 30 healthy middle-aged and elderly people
ranging in age from 53 to 89. All had a condition called impaired
glucose tolerance (IGT). This means their blood sugar
remains elevated after eating, although not elevated enough
for a diagnosis of diabetes. People with IGT often go onto
develop type 2, or adult onset, diabetes eventually.
Brain scans showed that an area of the brain called the hippocampus,
which is important to creating new memories, tended to be
smaller than average in these “pre-diabetic” people.
They also scored lower than average on standard memory tests.
Previous research has found that people with diabetes sometimes
show impairments in certain kinds of memory tasks, such as
the ability to repeat a short story from memory (i.e., verbal
memory). This may be because in diabetes, cells in the body—including
brain cells—aren’t able to obtain sufficient glucose
to fuel memory tasks. As a result, levels in the blood remain
high even as cells “starve” for energy. Or, high
blood sugar may have some direct damaging effect on brain
cells. Nobody knows.
Another thing that remains unclear is whether these impairments
even matter in the real world. From a scientific point of
view, it’s interesting that the brains of diabetics
may be different, or that people with diabetes score slightly
lower on “pencil and paper” tests of memory and
other thinking skills. However, “whether because of
that, somebody can’t go out and get their groceries,
or deal with their bills and mail, there’s no direct
evidence,” Gregg says.
Diabetes and dementia
Researchers have also discovered possible links between diabetes
and dementia. Particularly as it relates to Alzheimer’s
disease—the most common form of dementia
in older people—this could be very important. It could,
for example, reveal something about Alzheimer’s disease
that would point to a new treatment. Or at the very least,
it might motivate people with diabetes to achieve “tight
control” of blood sugar, keeping it neither too high
nor too low with a combination of diet, exercise, and (if
needed) medication. Tight blood sugar control is proven to
prevent the major complications of the disease.
Your doctor can tell you more about how to manage
diabetes or IGT. Certified diabetes educators
(CDEs) can also help you to find a way to combat
diabetes and win. Here's how to find one:
-Contact the American Diabetes
Association (ADA) to find a diabetes education
program in your area recognized by the organization.
Call 800-DIABETES or visit the ADA web
-Call the American Association
of Diabetes Educators (AADE) at 800-TEAMUP4 or
go to the AADE web
page and click on "Find an Educator."
The findings on diabetes
and dementia are contradictory, however. In 1999, scientists
reported the findings of a large study involving about 8,000
people, average age 69, living near the Dutch city of Rotterdam.
At the beginning, they were tested for dementia (Alzheimer’s
and other types) and other health factors, including diabetes.
After an average of about two years, 126 of the participants
in the study had developed dementia. Most of the cases were
Alzheimer’s disease (88 people). The rest was diagnosed
dementia, related to damage to the brain caused by repeated
small strokes (“ministrokes”). The people with
diabetes were found to be at nearly twice the risk of developing
dementia, compared to people without diabetes.
Protection from Alzheimer’s?
On the other hand, another study reported in 1999—this
one of nursing residents—suggested that people with
Alzheimer’s had diabetes at a much lower rate than people
without Alzheimer’s: 6 percent (people with Alzheimer’s)
compared to 20 percent (non-Alzheimer’s). On the other
hand, nearly half of the people in the home with vascular
dementia had diabetes.
The association of diabetes and vascular dementia makes sense.
Diabetes is known to harm the cardiovascular system, which
is why it is a major risk factor for heart attacks and heart
disease in general. But it’s more difficult to account
for why people with Alzheimer’s disease had such a low
rate of diabetes (6 percent).
One possible explanation centers on a protein called insulin
degrading enzyme, or IDE. The body makes this protein to break
down “used” insulin in the bloodstream. As diabetes
develops and the body grows ever more resistant to insulin,
the pancreas must crank out more and more insulin in order
to get blood sugar into the cells. High levels of insulin,
then, mean higher levels of IDE.
IDE also happens to break down beta-amyloid,
the abnormal protein that collects in the brains of people
with Alzheimer’s disease. Thus, as the person develops
diabetes, high levels of IDE in the brain could, in theory,
help to slow down the accumulation of beta-amyloid deposits.
The result would be to delay symptoms of Alzheimer’s.
However, this is all speculation based on a handful of studies.
It is still not clear whether diabetes is a risk factor for
memory loss, dementia, or other cognitive impairments. The
reason researchers study these connections is because they
may lead to a more fundamental understanding of the causes
of disease and possibly suggest innovative treatments.
For the average person, the message of all this is clear:
Diabetes, if left undiagnosed or inadequately treated, can
have a number of serious complications down the road—possibly
including damage to the brain. To avoid such complications,
have your blood sugar checked by middle age and, if it’s
high, take serious steps to lower it.
“Complications of diabetes in elderly people,”
by Edward W. Gregg, Michael M. Engelgau, and Venkat Narayan.
(British Medical Journal, October 26, 2002, Volume
325, Number 7370, pp. 916-917).
“Diabetes mellitus and the risk of dementia: The Rotterdam
Study,” by A. Ott and others. (Neurology, Volume
53, Number 9, pp. 1937-42).
American Diabetes Association
This large membership organization for people with diabetes
provides news coverage and health information about diabetes.
Members receive a subscription the organizations helpful monthly
magazine, “Diabetes Forecast.”
National Institute of Diabetes and Digestive and
Kidney Diseases (NIDDK)
NIDDK conducts research and provides a wealth of health information
to the general public about diabetes and its treatment. Browse
the NIDDK web site for information and publications you can
receive free of charge.