Type 1 Diabetes Mellitus and Intensive Exercise

In today’s New York Times, there is an article entitled “Diabetic and Determined” written by Abby Ellin (New York Times. Thursday July 26, 2007, p E1). The article is all about type 1 diabetes and “ultra-athletes.” The basic message is that having type 1 diabetes shouldn’t keep a person from being an ultra-athlete if that’s what they want to do. I would agree and I was a bit surprised by the article as I thought this subject a non-issue in 2007. I guess I was wrong?

The effects of exercise on blood glucose

We will start with the assumptions that a person with type 1 diabetes can do any physical activities that a person without diabetes can do and at as as high a level of performance. This has been demonstrated many times in the laboratory and “on the field.” But, to achieve optimal performance, a person with diabetes must learn how to keep his blood glucose level in a reasonable range throughout the activity. This can be quite a challenge and requires much “trial and error” in figuring out what to do about the insulin dosing and caloric intake.

When a person exercises, the metabolic rate increases in proportion to the intensity and or duration of the exercise. This requires enegy which comes from stored carbohydrates, fats, and proteins. Initially, the major share of the stored energy comes from glucose in the blood stream. Unfortunately, there is only a very small amount of glucose in the blood and hypoglycemia (low blood glucose) would develop quickly unless the body could match, molecule for molecule, production of glucose to equal that used up for energy. Initially, that glucose comes from stored glucose in the form of glycogen (long chains of glucose molecules) in the liver and in muscle. As the exercise continues, the body converts stored fats and proteins into energy to fuel the exercising msucles while leaving enough to maintain the blood glucose level in a normal range (proteins can be converted into glucose through a process called gluconeogenesis). This is quite a feat and involves many hormonal and neuronal mechanisms. The key to all of these adaptations is insulin. With exercise and increased glucose utilization, the body decreases insulin secretion which allows stored glucose and other nutrients to be used for energy and to maintain the blood glucose level.

If I go out and jog 10 kilometers (6.2 miles), my blood glucose level will be well maintained or even may go up a bit and I don’t even need to think about it- my body has figured out just how much to lower my insulin level to allow the required amounts of glucose to be made available for the exercise while maintaining my blood glucose level. But, what if I had diabetes and took insulin injections or used an insulin pump and couldn’t count on my body to figure things out? That’s the challenge for a person with type 1 diabetes who wants to exercise.

Getting down to specifics

Today, I do not want to go into great detail on how a person with diabetes figures out how to keep his blood glucose level from falling too low (or climbing too high) while providing enough metabolic fuels for the exercise. Obviously, it involves some combination of adjusting insulin doses and caloric intake. Sometimes, people with diabetes can anticipate the exercise and lower the insulin doses before and during the exercise. Such an adjustment in insulin may allow the normal mechanism of releasing stored glucose into the blood to work as in people without diabetes. Sometimes, taking in calories to mimic the release of stored glucose is necessary (e.g, ingestion of glucose-containing liquids or solids). For very long periods of exercise, ingestion of foods containing protein and fat may also be necessary. My point is that with some practice in figuring out the insulin/calorie factors, anyone with type 1 diabetes can expect to do as much exercise as they choose and do it well.

Most physicians who specialize in managing patients with type 1 diabetes should be quite experienced in helping their patients develop exercise plans. Particularly with the introduction of insulin infusion pumps and multiple injection insulin regimens over the past 25 years, the task is much easier than it used to be. In 2007, no one should be telling people with type 1 diabetes that they can’t do this or can’t do that, and that includes vigorous exercise programs.

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