Type 1 Diabetes and Exercise
Physical exercise is not without risks to individuals with IDDM. The principal risk is low blood glucose, but some IDDM patients with high initial blood glucose levels can raise them even more with exercise. There is also the potential that diabetic complications (e.g., heart disease, foot problems, retinal disease, etc.) can be worsened if the patient does not take the appropriate precautions.
The ADA has urged that “safe participation in all forms of exercise, consistent with an individual’s lifestyle, should be a primary goal for people with IDDM.” However, the ADA adds that “physical exercise is not without risks to IDDM individuals.”
While nondiabetic individuals usually experience little change in blood glucose levels during exercise, patients with IDDM may see an increase (i.e., hyperglycemia) or a decrease (hypoglycemia) depending on their initial levels.
Patients with IDDM who have very high blood glucose levels (above 250 mg/dl) with ketones in their urine can experience a rapid rise in blood glucose upon starting exercise, as well as the development of ketosis. For this reason, people with IDDM should postpone exercise until they have gotten their blood glucose under control through proper diet and insulin therapy.
For most IDDM patients who begin exercising, the principal risk is hypoglycemia. The ADA cautions that “many variables, including fitness, duration and intensity of exercise, and time of exercise regarding insulin administration and meals will affect the metabolic response to exercise.” Hypoglycemia is most likely to occur when the exercise is prolonged and/or intense, when the blood glucose prior to exercise was near normal, and when the exercise takes place shortly after insulin injection into a muscle used during the bout.
To avoid hypoglycemia during or after exercise, a regular pattern of exercise and diet should be adopted, with frequent blood glucose measurements to test the body’s response. Each individual with IDDM is unique, and each will need to discover for him or herself the best schedule to follow to keep the blood glucose under tight control. Exercise should be performed at the same convenient time every day, at approximately the same intensity and for the same amount of time. Morning appears to be preferable to evening for most persons with IDDM because episodes of delayed hypoglycemia may occur during sleep following late-day exercise.
Exercise should not be performed at the time of peak insulin effect (i.e., within one hour after an injection of short-acting insulin). Because of the insulin-like effect of exercise, the person with IDDM initiating an exercise program will have to reduce insulin dosage (by about one-third) and/or increase food intake. Insulin injections should not be at sites of the body that will be exercised soon thereafter (e.g., thighs that will be used in running or cycling).
During prolonged physical activity, 60 to 120 calories of carbohydrate (i.e., the amount found in one to two cups of most sport drinks) is recommended for each 30 minutes. A meal one to three hours before exercise is recommended, and fluids should be taken during and after exercise to avoid dehydration. A carbohydrate snack is recommended soon after unusually strenuous exercise.
Several of the long-term complications of diabetes may be worsened by exercise. Vigorous exercise may precipitate heart attack when there is underlying coronary heart disease, a common medical problem in diabetics. Patients with IDDM who are over 40 years of age, individuals who have had diabetes for 10 years or more, or those with established complications should first undergo a thorough medical exam that includes a graded exercise stress test.
There is some concern that large and sustained increases in blood pressure during heavy exertion may accelerate the development of eye or kidney problems in persons with IDDM. Until more is known, IDDM patients with these complications are cautioned to avoid sustained heavy exercise such as vigorous weight lifting or prolonged, intense aerobic activity.
Patients with IDDM who have nerve and blood vessel damage in their feet and legs should be particularly careful to avoid cuts, blisters, and pounding exercises of the lower extremities (e.g., running, high-impact aerobic dance, etc.). Good footwear, careful foot hygiene, and regular inspection are necessary.