I am 15 (16 in three months) and have type 1 diabetes. I eat pretty healthy, and I take Ultralente with Humalog. Whenever I exercise my blood sugar raises to about 300 mg/dl [16. 7 mmol/L], and I don’t know why.

Exercise can sometimes cause a rise in blood sugar, for a variety of reasons. You don’t say if you notice this at particular times during the day, and where that might be in relation to your pre-exercise blood sugar levels, to insulin injection and peak action timing, or to a meal or snack. Blood sugars can rise due to a reduction in the amount of circulating insulin necessary to prevent this.

Realize that the liver also is a significant source of glucose and can release sugar in conditions of low insulin or low carbohydrate levels. This also occurs naturally during high intensity (anaerobic/power types) of exercise.

Are you observing this rise regardless of which type of exercise you are doing? Or is it specific to a particular workout? If the exercise training is new for you, you may observe this effect as well. Continued training will often correct this, as your body because more used to the effort and more efficient at blood sugar management. There are some “tricks” that can be used to better manage this, if it continues to be a problem. The Diabetic Athlete (by Sheri Colberg PhD, Edward Horton, MD) is an excellent resource in this regard.

DMW