In an agreement trumpeted as a “landmark,” major international diabetes organizations have endorsed new official guidelines for blood sugar targets during exercise for patients with Type 1 diabetes.
The new guidelines, published simultaneously in two leading research journals, were authored by an international constellation of experts with diverse backgrounds, including diabetologists, exercise physiologists, sports scientists, bioengineers and nutritionists. The recommendations were based both on the results of controlled studies and on the expertise of the authors and other authorities. Major organizations that have approved the position statement include the European Association for the Study of Diabetes (EASD), the International Society for Pediatric and Adolescent Diabetes (ISPAD), JDRF and the American Diabetes Association (ADA).
As Type 1 diabetes patients and caretakers already know, exercise can be a double-edged sword. While experts and patients alike agree that exercise can powerfully improve the health of people with diabetes, its outsized and sometimes unpredictable effect on blood sugar can be very challenging to manage. Different types of exercise, durations and intensity levels all impact blood sugar differently, and the effects can vary from one person to another and from one day to another. Hypoglycemia, in particular, can represent a very serious hazard during exercise for even the best-prepared people with diabetes. Many people with diabetes exercise less than they otherwise should or would like to, out of fear of the glycemic mayhem that can result.
The number of variables that can affect glycemic changes during exercise is bewilderingly large. A probably incomplete list would include: the nature of the exercise, exercise duration, exercise intensity, prior insulin usage, diet, time of day, medication use, health status, transient changes in insulin sensitivity, stress, anxiety, and even the weather.
No one rule of thumb could possibly consider all of those variables. But the image below offers a good summary of the expert panel’s recommendations:
It’s important to note that new guidelines assume that patients are using continuous glucose monitoring (CGM) technology. While CGM technology does allow exercisers to check their blood sugar with unmatched frequency, often without even having to halt exercise, CGM technology has one known flaw to contend with: lag time. CGM devices sample interstitial fluid, not blood, and as a result they actually give blood glucose values that were accurate five or more minutes ago. During intense exercise and periods of rapid glycemic change, lag time can be even longer, 20 minutes or more. All of the published recommendations take CGM lag time into account.
The exact guidelines, available in the original article, are very complex: a series of tables provide recommended actions before, during and after exercise based on hypoglycemia risk, blood sugar level, CGM trend arrow, and the “expected” effect of exercise. For example, a healthy adult with low hypo risk and a blood sugar level of 70-89 mg/dL that is about to perform a high-intensity exercise is asked to delay exercise and consume 20g of carbohydrates. An adult of moderate risk with a blood sugar level of 145-198 mg/dL that is about to perform cardio is recommended to proceed with exercise without consuming any carbohydrates.
The article also provides guidelines for children and adolescents. Glycemic targets in this population tend to be higher, given sharper fears of hypoglycemia.
The recommendations also place emphasis on post-exercise glucose levels, including what happens overnight. Studies have shown that exercise sessions late in the day or of unusual duration/intensity place patients at an increased risk of nocturnal hypoglycemia.
Some ASweetLife readers will likely find that they are less comfortable with mild hyperglycemia than the guidelines suggest users should be. Likewise, the recommendations may be of less relevance to patients that have already achieved outstanding glycemic control and that have already learned how to maintain steady glucose numbers during exercise. Potential issues that were not considered include the amount of insulin “on board” during exercise. Adjustments not considered include changing basal insulin rate in advance of exercise.
Experienced exercisers with Type 1 diabetes know that properly managing blood sugar during exercise is an art and a science, and that every individual’s experience is unique. Nevertheless, for patients newly diagnosed or just beginning exercise for the first time, the guidelines may provide a good starting point.