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Diabetes: Preventing Low Blood Sugar During Exercise

Exercise has many benefits, including a healthier heart and healthier blood vessels. In addition, it usually helps lower blood sugar by helping the body burn more sugar. This is because insulin works better during exercise.

Exercise can usually be a good way to lower a high blood sugar. However, sometimes it may lower the blood sugar too much. You and your child can avoid problems with changing levels of blood sugar if you keep good records of exercise and blood sugar.

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

If your child is taking insulin or other diabetes medicines that can lower blood sugar, you need to take precautions against the blood sugar getting too low when your child exercises. You can avoid problems by keeping good exercise records and learning:

  • When to check the blood sugar
  • How to adjust your child’s medicine, what your child eats, and the exercise schedule

Check blood sugars before, during, and after exercise.

The best way to know how exercise affects your child’s blood sugar is to do a blood sugar test before, during, and after exercise. This is especially important if your child has just been recently diagnosed with diabetes or if your child is starting an exercise program. Keep good records of your child’s exercise and the results of blood tests. If your child does the same exercise at the same time of day and with the usual insulin dose and a similar starting blood sugar level, you will learn the effect of exercise on your child’s blood sugar. You will know how insulin and snacks need to be adjusted to avoid low blood sugar. In the records include:

  • The date and the time your child started exercising
  • Blood sugar levels:
    • Just before exercise
    • After 15 minutes of exercise
    • After 30 minutes of exercise, whether your child is still exercising or finished
    • Right after exercise
  • What the last dose of insulin or medicine was before exercise
  • The time your child took the insulin or pills
  • The time your child stopped exercising

If your child is starting an exercise program or if your child has had a change in medicines, it’s important to track the blood sugar response to exercise. Check blood sugar every few hours until bedtime. It’s also important to do this if your child has changed the type of exercise or how long he or she exercises. The blood sugar may stay lower than usual for several hours.

These records can be very helpful to your child’s provider as she or he works with you and your child to control your child’s blood sugar.

Eat before heavy exercise.

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

If your child’s blood sugar is less than 100 milligrams per deciliter (mg/dL), he or she should eat a carbohydrate snack (that is, at least 15 grams of carb) before exercise. Test the blood sugar 15 to 30 minutes later. Your child should wait to exercise until the blood sugar is higher than 100 mg/dL.

Have extra snacks handy during exercise.

Your child must always have a source of sugar handy.

  • Keep sugar packets, sugar cubes, or glucose tablets in a pocket or fanny pack for an emergency. Joggers' wallets for athletic shoes are another way these safety snacks can be carried.
  • Also keep a sandwich or similar snack, like peanuts, a granola bar, or cheese, nearby. The effects of a sugar packet on the blood sugar may last only a few minutes. Combining sugar and protein will help keep the blood sugar up for a longer time.

It’s often hard to guess the amount of a snack your child will need for a particular activity. If your child exercises within an hour after a meal, an extra snack may not be needed. If your child is not physically fit, the blood sugar may drop more quickly than if your child were fitter. It’s very useful to check the blood sugar to figure out what snack works best for your child. If the blood sugar is low (for example, below 100 mg/dL), your child needs a larger snack than when the blood sugar is high.

The type of snack may depend on the length of the activity.

  • Snacks such as milk or juice are used for short-term activities of 30 to 60-minutes because they contain carbohydrates that are quickly absorbed. Milk is better than juice because it has protein. Add more food, such as crackers or bread, if the activity is going to last longer.
  • Snacks that include protein and fat along with carbohydrate are good for long-term activities. A good snack might be a cheese or meat sandwich with a glass of juice.

Extra water is also important, especially in hot weather. A general rule is to drink 8 ounces of fluid for every 30 minutes of vigorous activity. Liquids such as milk, sports drinks, and fruit juices help replace water, salts, and carbs.

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.

You may need to change the insulin dose.

Before your child tries a new activity, talk with your healthcare provider about any changes that might need to be made in your child’s insulin doses. Your child should avoid exercising when insulin is working at peak level because that is when it is keeping the blood sugar at its lowest level. Your provider can tell you when your child’s insulin is at its peak. Talk to your child’s provider about adjusting the insulin dose to fit your child’s exercise needs and schedule.

The injection site may need to change.

Your child’s activity and where the insulin is injected can affect how quickly your child absorbs the insulin. Exercise increases blood flow in the part of the body that is moving. The increased blood flow causes a faster absorption of insulin.

  • If insulin is injected into an arm or leg that your child will be using a lot during exercise, your child’s body may absorb the insulin too fast. For example, 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 belly is usually a good injection site before strenuous exercise.

Temperature can make a difference.

  • High temperature tends to spread insulin more rapidly through the body. If sports activities are done outdoors on a hot day, there may be a higher risk of low blood sugar.
  • Low temperature tends to decrease insulin absorption. Keep this in mind if your child exercises outdoors on a cold day.
  • Results of blood glucose meters may not be accurate in extreme temperatures.

Make sure others know.

Your child should wear a medical alert bracelet or necklace. If your child is on a team, it’s important for teammates and the coach to know about the diabetes. Make sure the coach and teammates know where sugar snacks are kept. Remember that when your child has a low blood sugar level during a sporting event, he or she needs to rest at least 10 minutes after eating some sugar to let the blood sugar go up.

What is delayed hypoglycemia?

Delayed hypoglycemia means that your child has low blood sugar several hours after the exercise is over. It may happen as much as 3 to 12 hours after exercise. It may cause an insulin reaction in the middle of the night. If your child is having delayed hypoglycemia after exercise, discuss it with your healthcare provider. You may need to change the medicine dosage or schedule.

Developed by RelayHealth.
Pediatric Advisor 2013.2 published by RelayHealth.
Last modified: 2013-02-11
Last reviewed: 2013-02-09
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.
© 2013 RelayHealth and/or its affiliates. All rights reserved.
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