Severe Low Blood Sugar Won't Harm Brain

Type 1 diabetics shouldn't worry about past hypoglycemic episodes, study suggests

WEDNESDAY, May 2, 2007 (HealthDay News) -- People with type 1 diabetes don't need to worry that they may have brain function problems in the future if they've had a bout or two of severe hypoglycemia (low blood sugar), a new study suggests.

Researchers found that while serious hypoglycemic episodes did sometimes occur as a result of aggressive diabetes control, those low blood sugar events didn't have any effect on cognitive function.

"Hypoglycemia did not seem to predict the advent of worsening cognitive function," said 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 added. "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," he said.

Results of the study were published in the May 3 New England Journal of Medicine.

People 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 can't go too low, or they'll have problems with hypoglycemia.

Adding to that difficulty is that while normal people 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's so dangerously low that they have signs such as seizure or coma. This is known as hypoglycemia unawareness, and it's one of the reasons people 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, 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 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 long-term blood sugar -- 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 9.0 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 8.0 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.

However, the good news from this study is that those occasional hypoglycemic events didn't 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," said Dr. Maria Ramos-Roman, a diabetes specialist and an assistant professor of internal medicine at the University of Texas Southwestern Medical Center at Dallas.

But, she said, it's 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," said Ramos-Ramon.

More information

To learn more about hypoglycemia, visit the American Diabetes Association.

SOURCES: Alan Jacobson, M.D., professor, psychiatry, Harvard Medical School, and director, behavioral and mental health research program, Joslin Diabetes Center, Boston; Maria Ramos-Ramon, M.D., assistant professor, internal medicine, University of Texas Southwestern Medical Center at Dallas; May 3, 2007, New England Journal of Medicine
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