Low
Blood Sugar's Effect on the Brain Studied
Persons with type 1 diabetes do not need to worry that they
may have brain function problems in the future if they have severe hypoglycemia
(low blood sugar) on occasion, according to a report in the New
England Journal of Medicine (NEJM).
Researchers found that while serious hypoglycemic episodes
did sometimes occur as a result of aggressive diabetes control, those low blood
sugar events did not have any effect on cognitive function.
"Hypoglycemia did not seem to predict the advent of worsening
cognitive function," says the study's lead author, Dr. Alan Jacobson, director
of the behavioral and mental health research program at the Joslin Diabetes
Center in Boston.
"Of course, it goes without saying that hypoglycemia can
be a serious problem," he adds. "But, if you've had a more severe hypoglycemia
event, at least it appears that you don't have to worry that 10 years later
you may have trouble doing your job or thinking.”
Persons with type 1 diabetes - the inherited form of the
disease, which affects about 5 percent of diabetics - have to maintain a difficult
balancing act. They have to try to get their blood sugar to as near-normal
levels as possible, but they cannot go too low, or they will have problems
with hypoglycemia.
Adding to that difficulty is that while persons without
diabetes experience clear warning symptoms that their blood sugar is dropping
too low, such as shakiness, dizziness, or sweating, some people with type 1
diabetes eventually stop receiving those warning signs from their bodies.
Instead, they may not know that their blood sugar is too
low until it is so dangerously low that they have signs such as seizure or
coma. This is known as hypoglycemia unawareness, and it is one of the reasons
persons with type 1 diabetes are advised to monitor their blood sugar levels
often.
Experts have been concerned that repeated episodes of severe
hypoglycemia might affect cognitive function because it can cause nerve cell
death.
To assess whether or not several bouts of severe hypoglycemia
could have any effect on long-term cognition, Dr. Jacobson and his colleagues
tested the cognitive abilities of 1,144 people with type 1 diabetes enrolled
in the Diabetes Control and Complications Trial (DCCT).
That clinical trial was set up to assess the effect of intensive
management of type 1 diabetes on the long-term complications of the disease.
The team measured the participants' cognitive performance
at the start of the study and then again an average of 18 years later.
Those participating in this study were between the ages
of 13 and 39 years old at the start of the study, which commenced in the mid-to-late
1980s.
The DCCT trial randomized participants into
one of two treatment options. The first were sent to "standard" diabetes
treatment, with no long-term blood sugar goal provided.
The second group was part of an "intensive management" regimen
that the researchers hoped would reduce the risk of long-term diabetes complications,
such as blindness, kidney failure, and cardiovascular disease.
Those in the intensive management part of the trial were
asked to try to attain a near-normal A1C level - a measure of blood sugar over
a long term - of less than 6 percent.
During the six-and-a-half-year trial, those in the intensive
management portion lowered their A1C to 7.1 percent, while those in the standard
management group kept their blood sugar at 9 percent.
A1C levels were measured again in 1994, several years after
the active treatment portion of the trial ended, and those that had been in
intensive management had an average A1C of 8 percent, while those who had been
in the standard treatment group were at 8.2 percent.
The standard management group was given training in intensive
management at the end of the treatment portion of the study.
By the end of the whole study period, 18 years, there were
a total of 1,355 episodes of coma or seizure due to hypoglycemia. Three of
the more than 1,100 people in the trial also died during the study period due
to hypoglycemia.
Not surprisingly, there were more incidences of low blood
sugar in those in the intensive management portion of the trial.
The good news from this study is that those occasional hypoglycemic
events did not appear to have any effect on long-term cognition.
However, the researchers did note that the opposite might
be true - higher average blood sugars might also negatively affect cognition.
The study found a small, subtle decrease in certain measures
of cognitive function for those who failed to manage their diabetes well, as
defined by an A1C above 8.8 percent.
On the whole, the study results are "reassuring for people
with type 1 diabetes," says Dr. Maria Ramos-Roman, a diabetes specialist at
the University of Texas Southwestern Medical Center at Dallas.
But, she says, it is important for people with type 1 diabetes
to know that their care must be individualized. Not everyone can safely reach
a goal of an A1C under 6 percent.
"We have to individualize care and set a goal of glycemic
control on a patient by patient basis," says Dr. Ramos-Ramon.
Always consult your physician for more information.
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