Exercise-induced hypoglycemia (EIH) is the medical term for low blood sugar during or after exercise. The condition can cause a range of symptoms, including weakness, shakiness, and intense fatigue.

Glucose is the body’s primary source of energy. During exercise, the body needs more energy and therefore uses more glucose. It is this increased demand for glucose that can trigger EIH. Other factors may also play a role.

This article describes what EIH is, including its symptoms, causes, treatment, and prevention. It also discusses whether EIH is a sign of diabetes and provides information on when to seek help for EIH.

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Hypoglycemia is a condition in which there is not enough glucose in the blood to meet the body’s energy needs. Doctors generally define hypoglycemia as blood glucose lower than 70 milligrams per deciliter (mg/dl). However, most people do not experience symptoms of hypoglycemia until their blood glucose levels drop below 55 mg/dl.

The body metabolizes carbohydrates into glucose. The glucose then enters the bloodstream, and the pancreas responds by producing insulin. The insulin helps the glucose enter the body’s cells to use it for fuel.

Exercise increases glucose demand, because active muscles require extra fuel. Exercise may also make a person more sensitive to insulin, meaning the insulin works more effectively and reduces blood glucose more rapidly. Together, these factors can cause EIH.

An individual is more likely to experience EIH if they:

  • do an intense workout that demands more energy
  • already have low blood glucose, such as from hunger or from diabetes medication
  • have insulin sensitivity or take insulin

Glucose helps fuel most major body functions. As such, the symptoms of EIH can vary. Some possible signs and symptoms include:

Prolonged or severe hypoglycemia can be life threatening. It may lead to the following:

Exercise places additional energy demands on the body, so the body needs to respond by burning more glucose. Hypoglycemia can occur in people who already have low glucose levels, or those whose bodies metabolize glucose quickly.

Certain factors can contribute to EIH, including:

In some people, exercise triggers a considerable spike in insulin, which removes glucose from the blood. This spike can cause sudden hypoglycemia, even when a person is well nourished and does not take medications to lower their blood glucose.

If a person experiences chronic EIH, a doctor may recommend medication to reverse the condition. However, making appropriate lifestyle changes can address the problem for most people.

EIH is not necessarily a sign of diabetes. Exercise alone can substantially lower blood glucose. However, people with diabetes have additional risk factors for hypoglycemia.

Untreated diabetes causes hyperglycemia, which is high blood glucose. Individuals who take medications to manage their diabetes are at increased risk of hypoglycemia if they take more than they need. Not eating enough food to match activity levels can also be a cause.

Also, people with diabetes may become hypoglycemic if they take medication for diabetes when fasting or starting a restrictive diet.

Mild EIH does not usually require treatment. In many cases, the condition occurs because a person did not eat enough food before working out. To avoid EIH, individuals should try eating a carbohydrate-rich meal 1–2 hours before a workout.

Chronic EIH can sometimes signal an underlying issue with insulin production. If a person experiences chronic EIH, a doctor may prescribe diazoxide to treat low blood sugar.

In rare cases, a doctor may recommend removing a part of the pancreas to slow insulin production.

Below are some strategies for preventing EIH in individuals with diabetes and those without the condition.

Prevention in people with diabetes

The American Diabetes Association (ADA) recommends that people who take diabetes medications to control their blood glucose check their blood glucose levels before exercising. If the reading is below 100 mg/dl, they should have 15–20 grams (g) of carbohydrates to increase their blood glucose.

Some options include:

  • 4 glucose tablets
  • 1 glucose gel tube
  • 1 tablespoon of honey or sugar
  • 4 ounces (oz) of soda or juice

According to the ADA, a person should recheck their blood glucose after 15 minutes. If the reading remains below 100 mg/dl, they should have another 15 g serving of carbohydrates. They should repeat these steps every 15 minutes until their blood glucose is at least 100 mg/dl.

A 2019 review notes that anaerobic exercise, such as high intensity interval training (HIIT), may reduce the risk of hypoglycemia in people with diabetes. HIIT involves brief bursts of intense activity, followed by a rest and then another brief burst of intense activity.

Prevention in people without diabetes

People without diabetes can usually prevent EIH by:

  • gradually building up to new exercise routines to give the body time to adapt
  • eating regular meals throughout the day
  • avoiding drinking alcohol before a workout

Individuals who feel shaky or dizzy during a workout should stop and take a break. They should try drinking 4 oz (113 g) of juice or eating a piece of toast, then resuming their workout later.

Hypoglycemia can be life threatening if blood glucose levels drop too low. A person who experiences one or more of the following symptoms requires emergency medical attention:

  • confusion
  • seizure
  • loss of consciousness
  • symptoms that persist despite resting or consuming more food

People should consult a doctor if they frequently experience EIH or hypoglycemia at other times. If the person has diabetes, this could be a sign that their diabetes medication dosage is incorrect or that they are taking too much insulin.

Hypoglycemia is when blood glucose levels drop too low to support the energy demands of a person’s body. EIH is hypoglycemia that occurs during or following exercise. The condition can affect people with and without diabetes.

Individuals with diabetes are at increased risk of developing EIH, especially if they take insulin or other medications to manage their blood glucose. In such cases, a person should speak with a doctor about the possibility of adjusting their medication dosages.

In people without diabetes, EIH is usually due to not eating enough before exercising, or not giving the body sufficient time to adapt to a new exercise routine. If a person continues to experience frequent EIH despite taking appropriate preventive measures, they should seek guidance from a doctor to determine the underlying cause.