Exercise-induced low blood sugar, or hypoglycemia, occurs when the body's stores of blood sugar are used up too quickly. Typically, this only affects people with diabetes, Samar Hafida, MD, an endocrinologist at Harvard's Joslin Diabetes Center, tells LIVESTRONG.com
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If you have diabetes, there are some important things you need to know about low blood sugar after exercise. If left untreated, hypoglycemia can have serious health consequences.
How Exercise Lowers Blood Sugar
Blood sugar, also called glucose, is the body's main source of energy; it mainly comes from the carbohydrates in food, according to Kaiser Permanente. The body regulates blood sugar levels with the help of the hormone insulin, which moves glucose out of the bloodstream and into the cells.
Exercise lowers blood sugar levels by increasing the body's insulin sensitivity, aka its ability to use insulin, according to the American Diabetes Association (ADA). This helps the muscles get more glucose. Additionally, physical activity allows the cells to take in more glucose, whether insulin is available or not. This further reduces blood sugar.
Exercise also depletes the body's glycogen stores, according to the Joslin Diabetes Center. When you eat, your liver stores some glucose in the form of glycogen for later use. During exercise, this glycogen is converted back into glucose for fuel. After exercise, it can take the body anywhere from four to 24 hours to replenish its glycogen stores, depending on the intensity of the activity. That means even if exercise doesn't cause low blood sugar in the moment, it can increase the risk of hypoglycemia for people with diabetes for up to 24 hours after a workout.
Dr. Hafida says that exercise doesn't pose a risk of hypoglycemia for people without diabetes. Even though a person without diabetes may sometimes feel the symptoms of low blood sugar, their blood glucose levels will usually still be within the normal range.
Recognizing Hypoglycemia After Exercise
Because exercise can make it more difficult to recognize hypoglycemia, familiarize yourself with a broad range of symptoms of low blood sugar. They can vary from person to person, but in general, here's what to look out for, according to the Cleveland Clinic:
- Sudden, intense hunger
- Fast heartbeat
- Weakness or shaking
- Pale skin
- Irritability or mood changes
- Blurred vision
If left untreated, severe cases of hypoglycemia can cause seizures, loss of consciousness and, in rare cases, death. If you are taking blood sugar-lowering medications, be sure to keep glucose tablets (or other foods that can raise blood sugar quickly) close at hand.
It's important to raise low blood sugar levels right away to avoid complications. The ADA recommends treating low blood sugar by following the 15-15 rule:
- Consume 15 grams of simple carbs (i.e., glucose tablets, candy or fruit juice).
- Wait 15 minutes. (It takes about that long for the body to metabolize carbs into glucose.)
- If your symptoms have not improved after 15 minutes, recheck your blood sugar. If your blood sugar levels are still too low, eat another 15 grams of carbs, then wait another 15 minutes. Call your doctor if your symptoms don't improve after repeating the process.
Exercising With Diabetes
People with diabetes have systems that either don't make enough insulin or can't use insulin correctly, leading to high blood sugar, according to Harvard Health Publishing. As a result, people with diabetes often need to take medications to manage their blood sugar. Some of these medications can lead to low blood sugar during or after exercise.
Exercise-related low blood sugar is less likely to be an issue for people with diabetes who are taking blood sugar stabilizers. "Medications like SGLT2 inhibitors [such as Jardiance, Invokana and Farxiga] do not lower blood sugars below normal levels," says Dr. Hafida. "So people taking [these medications] don't need to worry about adjusting their medications for exercise."
Hypoglycemia only poses a serious risk for people with diabetes who are taking blood sugar-lowering medications such as insulin or sulfonylureas, according to Dr. Hafida. If a person with diabetes takes too much insulin or doesn't consume enough carbs, physical activity can remove too much glucose from the blood, leading to hypoglycemia. That's why it's a good idea to check your blood glucose both before and after exercising, to make sure your levels aren't too low before you start, and to also make sure they don't dip too low after you finish.
Per the Joslin Diabetes Center, if your blood sugar level is less than 100 mg/dL, you should have a small snack or some fruit juice before starting to exercise.
While it's important to watch out for hypoglycemia, you shouldn't let the chance of low blood sugar stop you from exercising. Exercise lowers blood sugar, so it should be a key part of any healthy diabetes treatment plan, according to Harvard Health Publishing.
- Kaiser Permanente: "How Our Bodies Turn Food Into Energy"
- Harvard Health Publishing: "Diabetes"
- American Diabetes Association: "Blood Sugar and Exercise"
- Joslin Diabetes Center: "Why Is My Blood Glucose Sometimes Low after Physical Activity?"
- Mayo Clinic: "Dehydration"
- American Diabetes Association: "Hypoglycemia (Low Blood Sugar)"
- Harvard Health Publishing: "The Importance of Exercise When You Have Diabetes"
- Cleveland Clinic: "Hypoglycemia (Low Blood Sugar)"
Is this an emergency? If you are experiencing serious medical symptoms, please see the National Library of Medicine’s list of signs you need emergency medical attention or call 911.