How can exercise cause blood sugars to increase in a person with type 1 diabetes, instead of to decrease? I know that hormones play a role, but are there other reasons?

It is not uncommon for persons with type 1 diabetes in particular to observe a rise in blood sugar as a result of certain types of exercise. Stored sources of glucose in the liver (liver glycogen) combined with a lower level of basal insulin than is necessary allows for those rises in blood sugar levels. Hormones such as epinephrine, cortisol, and glucagon drive this liver “dumping” of glucose.

This response occurs most prominently with higher intensity, “anaerobic-type” intermittent exercise such as sprinting, power lifting, gymnastics. It is important to recognize that in people who do not have diabetes, the normal physiologic response to high intensity, anaerobic exercise is an increase in circulating insulin levels both during and immediately after exercise. Because today’s basal/bolus insulin regimens and insulin pumps are much more precise and much less likely to “over-insulinize”, we are more likely to observe these rises in blood sugar than we might have previously on some of the former insulin regimens. When correcting for highs after exercise, it is important to correct conservatively as insulin sensitivity and metabolism remain elevated as well.

Realize too, that we might also observe a rise in blood sugar from exercise when insulin levels are low to begin with, such as when an injection was omitted, or during times of stress or illness. It is important in these situations not to exercise when blood sugars are elevated and ketones are present.

DMW