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Diabetes and Exercise: Preventing Low Blood Sugar

You and your child may become frustrated with the ups and downs of blood sugar levels when your child exercises. But it is important to remember that your child needs to put up with the changes in blood sugar levels in return for a healthier heart and blood vessels. You and your child can avoid problems by keeping good exercise records and being prepared.

How does exercise affect my child's blood sugar level?

Exercise usually helps lower your child's blood sugar. This is because insulin is more effective during exercise. The number of insulin receptors, the places where insulin attaches to cell membranes to allow sugar to pass into the cell, increases as a result of regular exercise. This makes the body more sensitive to insulin and the insulin can work more efficiently. This means a lower daily dose is needed. Exercising can be a very good way to lower a high blood sugar (as long as ketones are not present).

Sometimes blood sugars go up with exercise. This may be because your child is excited and is releasing a hormone called adrenaline. This is a normal response in people with or without diabetes. The adrenaline causes sugar to be released from stores in the muscle and liver and raises the blood sugar for awhile. This usually happens in the first hour of exercise.

How can I help prevent low blood sugar (hypoglycemic) reactions during exercise?

Check blood sugars before, during, and after the exercise.

The best way to know how any exercise affects your child is to check blood sugars before, during (when possible), and after the exercise. Keeping good records is important so that when your child does a similar exercise at a similar time of the day (with the usual insulin dose) and with a similar starting blood sugar level, you will already know how to adjust your child's insulin and snacks.

Exercise record chart

Eat before heavy exercise.

If your child is going to exercise around mealtime, your child should eat the meal first. When it is possible to choose the exercise time, try to begin the exercise 30 to 60 minutes after a meal or snack.

  • Liquids are absorbed most rapidly and generally prevent low blood sugar reactions for the next 30 to 60 minutes.
  • Solid foods, such as those eaten at mealtime, are digested more slowly and usually keep the blood sugar level up for at least 2 to 3 hours.

Have extra snacks available during exercise.

Your child must always have a source of sugar available.

  • You can sew pockets in basketball shorts, jogging pants, and other clothes to hold a sugar packet, sugar cube, or a glucose tablet for an emergency. Joggers' wallets on shoes work nicely.
  • A sandwich or similar snack should be available nearby, as a sugar packet may last only a few minutes.
  • It is helpful for the coach or instructor to have a tube of instant glucose or some other emergency source of sugar.

It is often difficult to guess the amount of a snack necessary for a particular activity. If the exercise is in the hour after a meal, an extra snack may not be needed. If your child is not physically fit, his blood sugar may drop more rapidly than if he is physically fit. It is very useful to monitor the blood sugar to figure out what the correct snack is for each child. If the blood sugar is low (for example, below 100 mg/dl or 5.5 mmol/L), a larger snack is needed than when the blood sugar is high. The type of snack can vary depending on the expected length of the activity.

  • Snacks such as milk or juice are used for short-term (30 to 60 minutes) activities because they are rapidly absorbed carbohydrates. Add more food, such as crackers or bread, if the activity is to last longer.
  • Snacks that include protein and fat along with carbohydrate are good for long-term activities. This might be a cheese or meat sandwich with a glass of juice.

It is wise to check the blood sugar after the activity to help decide what to use for a snack the next time. Experience is the best teacher!

Extra water is also important, particularly during hot weather. A general rule is to drink 8 ounces of fluid for every 30 minutes of vigorous activity. Liquids such as milk, Gatorade, and fruit juices help replace water, salts, and carbohydrates. It is a good idea to keep packets of cheese and crackers in the glove box of your car for your child to eat before or after an activity. This is especially important if the distance is far between home and the activity.

Reduce the insulin dosage.

Before trying an activity for the first time, discuss any changes that might be needed in insulin dosage with your diabetes care provider. The insulin dose is easy to decrease if you know which insulin is having its main effect during the time of exercise. Your child should reduce the insulin that is most active during the period of heavy exercise. People reduce insulin by different amounts.

If extra morning exercise is planned, you can reduce or leave out the morning Humalog/NovoLog or Regular insulin. If late afternoon exercise is planned, you can reduce the morning NPH or Lente insulin by 10% to 50%. NPH or Lente insulin is never left out entirely. Lantus insulin in the evening may be reduced by a few units when heavy exercise occurs after dinner.

For example: If your child gets 30 units of NPH insulin in the morning and he has a soccer game in the afternoon. You might reduce the dose by 10% to 20% (3 to 6 units). He would then receive 24 to 27 units of NPH insulin.

If strenuous exercise is planned for all day, the morning NPH, the Lantus, and the short-acting insulins can all be reduced. The evening insulin dose may also need to be reduced to prevent a delayed low blood sugar reaction. If strenuous exercise is planned for the evening, the dinner short-acting insulin or Regular insulin can be reduced or not given. One reason the evening NPH or Lantus might be decreased is for overnights at friends' homes, when a child may be staying up later than usual. More activity and excitement burn more sugar, and less insulin may be needed. You may have to try a few times before you find the best way to reduce the insulin for your child's activities. Keep careful records and discuss them at clinic visits. Blood sugar tests before and after exercise can help you make these decisions.

Change the injection site.

Where you inject the insulin can help prevent low blood sugar. Exercise increases blood flow into the part of the body that is moving. The increased blood flow takes up more insulin.

  • If you inject insulin into an arm or leg that will be used heavily during exercise, your child's body may absorb the insulin too fast. If your child is going to run, don't inject insulin into the leg. If your child is going to play tennis, avoid injecting into the tennis arm.
  • The abdomen is a good site for most strenuous exercise days.

Make sure others know.

It is important that coaches and teammates are aware of your child's diabetes. A team manager may be a good person to carry extra sugar snacks. It is helpful if the coach can have at least some awareness of the diabetes and know the symptoms and treatment of low blood sugar. Remember that when a low blood sugar occurs during a sporting event, it is important for your child rest for at least 10 minutes to let the blood sugar rise. The coach should be aware of this.

What is delayed hypoglycemia?

Delayed hypoglycemia means your child has low blood sugars several hours after the exercise is over. It may occur 3 to 4 hours or up to 12 hours after exercise. This can sometimes cause an insulin reaction in the middle of the night. It may happen because extra sugar in the blood goes back into storage in the muscle. Hormone changes with sleep (for example, lower adrenaline levels) may also cause the delayed reaction. It is best prevented by:

  • Eating extra carbohydrate at the next meal or snack (even when the blood sugar is above-range)
  • Eating a longer-lasting snack (including solid carbohydrate, protein, and fat) at bedtime
  • Reducing the insulin dose.

If your child is having this problem, you should discuss it with your health care provider.

Abstracted from the book, "Understanding Diabetes," 10th Edition, by H. Peter Chase, MD (available by calling 1-800-695-2873).
Published by McKesson Provider Technologies.
Last modified: 2005-04-14
Last reviewed: 2005-12-05
This content is reviewed periodically and is subject to change as new health information becomes available. The information is intended to inform and educate and is not a replacement for medical evaluation, advice, diagnosis or treatment by a healthcare professional.
Copyright 2006 McKesson Corporation and/or one of its subsidiaries. All Rights Reserved.
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