High and Low Blood Sugars: How Do They Affect Cognitive Performance?

David Mendosa recently posted a blog about "glycemic variability." Most people have come to expect that their diabetes control is primarily evaluated by the hb A1C level. Indeed, the hb A1c is correlated with a three-month estimated average glucose level, which is very helpful to know in terms of the effectiveness in medical (insulin or oral) therapy. However, what is less often discussed is the importance of glycemic variability: the ups and downs of glucose values that occur naturally and as a result of medication. How does glycemic variability play a role in the management of diabetes? The latest information to date indicates that glycemic variability is extremely crucial in blood vessel inflammation and in physical/emotional well-being. The rate of those glucose excursions (highs and lows) profoundly effect how one feels emotionally, physically, and now cognitively, according to a recent article in Diabetes Care (a journal associated with the American Diabetes Association).

As a member of a pediatric diabetes healthcare team, we are always concerned about quality of life in our young patients. Upon review of the article "Cognitive Function is Disrupted by Both Hypo- and Hyperglycemia in School-Aged Children with Type 1 Diabetes: a Field Study" previous suspicions about the disruption of learning due to highs and lows were demonstrated to be true based on the tasks described in the research study. In this field study conducted by the Behavioral Medicine Center and the Department of Psychiatry and Neurobehavioral Sciences at The University of Virginia and The Joslin Diabetes Center at Harvard University it was demonstrated that a decrease in mental efficiency occurs with naturally occurring hypo- and hyperglycemic glucose fluctuations in children with type 1 diabetes. This can be detected with a field procedure using PDA technology. Most surprisingly, the authors (Gonder-Frederick, Zrebiec and Bauchowitz et. al.), noted that with marked hyperglycemia (blood glucose >403.6 mg/dl), cognitive deterioration approximates that which is associated with significant hypoglycemia. It appears that the anecdotal evidence described multiple times by our patients and families has been proven true with evidence-based medicine.

The study was quite simple. Children (aged 6-11) were given a PDA with two simple thinking tests (mental math and choice reaction time), which were completed before testing blood sugars at home. The computer recorded the time to complete each test and the number of correct responses. The children also were asked to complete a questionnaire asking how they thought they performed on the tasks. Interestingly enough, the results demonstrated that the time to complete both mental math and reaction time was significantly longer during hypoglycemia. During hyperglycemia, time to complete math was significantly longer and reaction time only barely significant. There were no differences on task accuracy. The decline in mental math performance was the same for blood sugars <54.5 mg/dl and > 403.6 mg/dl. What do these results signify?