Low Blood Glucose Doesn’t Affect Long-Term Brain Function

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A study published in the May 3 issue of The New England Journal of Medicine shows that episodes of severe hypoglycemia (very low blood glucose) do not seem to have any lasting effects on cognitive function in teenagers and adults with Type 1 diabetes.

The study, which was led by researchers at the Joslin Diabetes Center and conducted through 28 additional medical centers around the United States, involved 1,144 people with Type 1 diabetes. These people had all been participants in the Diabetes Control and Complications Trial (DCCT), a landmark study that began in the 1980’s and proved that intensive, or “tight,” blood glucose control lowers a person’s risk of developing diabetes complications, such as retinopathy (eye disease), nephropathy (kidney disease), and neuropathy (nerve disease). The DCCT participants in the intensive therapy group achieved HbA1c levels (a measure of blood glucose control over time) nearly 2 percentage points lower than those in the conventional therapy group and developed fewer complications. However, they were also three times as likely to experience episodes of severe hypoglycemia, which can lead to coma or seizure.

Because severe hypoglycemia can cause nerve cell death, experts wondered whether severe hypoglycemic events might have any long-term effects on people’s cognitive function. To answer this question, researchers tested the cognitive abilities of DCCT participants from both the intensive and conventional therapy groups at the beginning of the DCCT and an average of 18 years later. They also recorded incidences of hypoglycemic coma or seizure in the participants over that period of time.

After adjusting for age, sex, education, length of follow-up, and number of cognitive tests taken through the years, the researchers found that episodes of severe hypoglycemia did not have any effect on participants’ cognitive abilities. They did find, however, that people who had higher blood glucose levels (or HbA1c levels above 8.8%) experienced some decline in two measures of cognitive ability.

These results show that consistently higher blood glucose levels appear to be more of a threat to long-term brain function than occasional episodes of severe hypoglycemia. However, it is important to remember that hypoglycemia, when not recognized in time, can result in serious injury and even death, which is why it is important for people who use insulin or a diabetes drug that can cause hypoglycemia to monitor their blood glucose levels regularly. This is especially true in people who have developed hypoglycemia unawareness, a condition in which they do not experience early warning signs of hypoglycemia (such as shakiness, dizziness, or sweating).

Also, the effects of severe hypoglycemia on the developing brains of children are still unclear, since the youngest participants in the DCCT were 13 years old at the time the trial started. Further study of hypoglycemia and cognitive function over time in people younger than 13 is needed.

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