Exercise is beneficial for all people with diabetes because it helps lower blood glucose levels. As a result, people with type 1 diabetes may need less insulin, and people with type 2 diabetes may be able to control their diabetes without medication. Exercise has other benefits as well. It helps improve cardiovascular fitness and provides a sense of psychological well-being.
However, exercise requires careful planning and monitoring, particularly for people who take oral medication or insulin to control their diabetes. These individuals may need to make adjustments to their medication and food intake to prevent blood glucose levels that are too low (hypoglycemia) or too high (hyperglycemia) during exercise.
If you have diabetes, be sure to talk to your doctor before beginning an exercise program or making any changes to your medication or diet. Getting in the habit of exercising regularly may be difficult at first, but the benefits can be great for people with diabetes.
How Exercise Affects Glucose Levels
In most cases, exercise lowers blood glucose levels. As muscles do their work, they obtain energy from glucose stored in the muscle cells as glycogen. When these supplies of glycogen run low, glucose from the bloodstream is used as an energy source. After exercise, the body replaces the stores of glycogen in the muscle cells and liver, which lowers blood glucose levels even more. This drop can take place many hours after exercising.
Exercise can also have the opposite effect and raise blood glucose. This usually occurs when blood glucose levels are too high (usually over 250 mg/dL) before exercising, which indicates that insulin activity is too low. In addition, very strenuous exercise can stimulate the liver to release extra glucose into the bloodstream, due to an increase in adrenaline.
The Best Time To Exercise
To prevent hypoglycemia, workouts should be timed in relation to meals and medication. A general rule is to exercise one to three hours after eating something. People with diabetes who take insulin should not exercise when their insulin is at its peak. Since exercise can lower blood glucose hours later, avoid exercising just before bedtime to prevent hypoglycemia in the middle of the night.
Before Exercising
If you have diabetes, you should always check your blood glucose levels twice before exercising: once 30 minutes in advance, and again just before starting. This routine will let you know whether your blood glucose is stable, rising, or dropping.
A safe pre-workout blood glucose level is between 100 mg/dL and 250 mg/dL. If the level is less than 100 mg/dL, have a carbohydrate snack (such as a piece of fruit or three graham crackers) before starting to exercise to prevent hypoglycemia.
People with type 2 diabetes should limit snacking, however, especially if they are exercising to lose weight. If this is the case, your doctor may recommend lowering the dose of your medication on the days that you exercise. If your blood sugar is above 250 mg/dL and you have type 1 diabetes, test your urine for ketones; delay exercise if ketone levels are moderate or high. Regardless of your type of diabetes, do not exercise if your blood glucose levels are 300 mg/dL or higher.
While Exercising
When you exercise for more than an hour, check your glucose every 30 minutes. If blood glucose starts to fall, have a snack. Testing your blood glucose while exercising is also important if you are trying a new exercise or changing the intensity or duration of your workout. If you start to experience symptoms of low blood glucose such as faintness, palpitations, or weakness during your workout, stop immediately. Test your blood glucose and, if necessary, have a fast-acting carbohydrate snack such as fruit juice or hard candies.
After Exercising
Blood glucose can continue to drop for hours after exercising, so test your levels at least twice: once immediately after, and again a few hours later. Since more intense exercise prolongs the glucose-lowering effect, be extra careful after strenuous workouts.
Safety Precautions
People with diabetes need to take a few extra safety measures when exercising:
- If you take medication to control your diabetes, always carry a fast-acting source of carbohydrates (glucose tablets, hard candies, or raisins) with you while exercising in case of a hypoglycemic reaction.
- Carry your identification and diabetes information with you. Include your name, address, phone number, doctor’s name and phone number, and type and dose of insulin or other medications.
- Skip exercise if you feel ill. Pushing yourself too hard could make your diabetes worse.
- Exercise with a friend whenever possible. When going out alone, tell someone where you will be and what time you plan to return.
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Posted in Diabetes on February 7, 2006
Reviewed March 2010
