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

Dr. Fran Cogen Health Pro
  • 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).

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    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?


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    I repeat: there were no differences in task accuracy. However, the time it took to complete the task was longer (seconds, not minutes or hours). The information that both hypo and hyperglycemia may cause difficulties is especially significant. This reinforces the need to decrease blood glucose variability and to blunt those peaks and valleys that are noted on blood glucose downloads. Of course, this is easier to recommend than actually execute. However, simple changes may help to decrease blood glucose variability.

    1. Try to bolus before meals and snacks as much as possible (even 15 minutes before to match the carbohydrate excursion).
    2. Carbohydrate count as carefully as possible.
    3. Check blood glucose levels frequently; especially 2-3 hours after eating. Studies have demonstrated, that post-prandial blood sugars play a major role in those children, teens, and adults that have lower hb A1c.
    4. Pay attention to the physical signs of lows or highs as you may be feeling the rapid drop or increase of glucose levels rather than the actual blood glucose in mg/dl.
    5. Pay close attention to the need to change insulin/carbohydrate ratios or insulin sensitivity factors during times of rapid growth, stress, illness, exercise, etc.
    6. Monitor blood sugars overnight periodically to observe for the dawn phenomenon or post-exercise induced hypoglycemia.
    7. Consider use of a continuous glucose sensor for diagnostic purposes or if you are extremely motivated to monitor trends in glucose levels. A compromise would be to wear a sensor for a week (every month or so...for example) when major fluctuations are noted so that changes in insulin dosing may be made. This is of particular importance in children that are undergoing rapid growth spurts or going through puberty.
    8. Download meters at home and observe the peaks and valleys. Contact your diabetes team for advice.
    9. Consider a change in your current insulin regime if your blood sugars are all over the place.
    10. Bolus before eating carbs ... always.

    Keep in mind that these are the results of one field study. More research needs to be conducted to verify and enhance these findings. However, based on this information, much of what we know by fact and feel has been verified and we should act accordingly.


    We can now use this study as a reference for testing accommodations to provide extra time for our students (But we knew that already per the Americans with Disability Act.)


    I will continue to keep watch for further studies.


Published On: June 30, 2009