Running With Type 1 Diabetes

Regular exercise has health benefits for those with type 1 diabetes, including increased cardiovascular fitness, greater muscle strength, and improved insulin sensitivity.

While physical activity is very important in managing type 1 diabetes, understanding exactly how it impacts blood sugars can be difficult and worrisome, particularly for those who are newly diagnosed.

This article covers the health benefits of running for people with type 1 diabetes. It also explains how to monitor and manage your blood sugar while running, and how to prevent low blood sugar (hypoglycemia) after exercise.

How Running Affects Blood Sugar

Typically, exercise can help to lower blood sugars by increasing insulin sensitivity and burning glucose. For some people, running can cause hypoglycemia (low blood sugar) during, after, or later in the day, or overnight after exercise.

But sometimes, certain people with type 1 diabetes can experience the opposite: Their blood sugar goes up. This shouldn’t discourage you from running, because once you understand how your body responds to running, you’ll be able to manage your blood sugar better.

The type of exercise, duration, frequency, and how trained a person is can also affect your blood sugar.

Aerobic vs. Anaerobic Exercise

Understanding the difference between aerobic and anaerobic exercise is important for people who have type 1 diabetes, since each type has a different impact on glucose levels.

Aerobic exercise is physical activity that increases your heart rate and your body’s use of oxygen. In fact, the term aerobic means “requiring oxygen.” You can think of aerobic exercises as those that require endurance, such as running, cycling, and swimming.

Aerobic exercise increases insulin sensitivity, resulting in decreased glucose levels during your workout and afterwards.

Anaerobic exercise, on the other hand, is physical activity that is shorter in duration but more intense. Sprinting, jumping, and heavy weight lifting are examples of anaerobic exercise, as they require quick bursts of energy.

Your body needs to use more glucose during anaerobic exercise to convert it to energy. But to accomplish this, your body has to make and release more glucose into your blood. As a result, anaerobic exercise can result in increased glucose levels both during and after your workout.

Getting Ready to Run

Your pre-exercise blood sugar level, timing of your last meal, and the amount of insulin you have on board can also affect your blood sugar.

Unfortunately, these factors can affect people in different ways, but once you’ve figured out your own individual trends, you’ll be able to run safely without fearing big glucose excursions (highs and lows).

Here’s what you need to know before starting your run:

Pre-Run Glucose Levels

Before you head out, you’ll need to check your blood sugar and ensure you have enough insulin on board. This information will influence how you fuel up for your workout with food.

According to Amanda Kirpitch MA, RDN, CDE, CDN, a nutrition and diabetes expert in New Jersey, “Target glucose pre-exercise is recommended to be around 126–180 milligrams per deciliter (mg/dL).”

If your blood sugar is below target, Kirpitch recommends consuming 10 to 20 grams of carbohydrates. You may need to consume more if you have active insulin from a previous meal bolus. “If blood glucose is less than 90 mg/dL, then the carbohydrate intake should be higher, around 30-40 grams,” she explains.

If your blood sugar is above 250 mg/dL, you should check your blood or urine for ketones. If ketones are present before your run (or during your run), you will need to avoid vigorous exercise entirely to prevent ketoacidosis.

Pre-Run Snacks and Meals

If your blood sugar is less than 90 mg/dL, it’s probably best to consume a snack rich in carbohydrate and protein. This will help prevent your blood sugar from dropping during your run.

The amount of carbohydrates you need to consume will depend on your blood sugar pre-run, the duration and intensity of your exercise, and how you respond to exercise.

According to Kirpitch, you should consume “about 15 grams of carbohydrate for blood sugar that is less than 126 mg/dL and more carbohydrate for blood sugar that is less than 90 mg/dL.”

Pairing this snack with protein will help to avoid hypoglycemia. For most people, this snack should not be taken with insulin, while other people may need to take a small amount of insulin.

Managing Glucose While You Run

How you manage your blood sugar while running or doing exercise is highly specific to you. It can depend on what type of insulin therapy you are on, how intensely you plan on exercising, your body’s sensitivity to exercise, and much more.

Insulin Adjustments

How you adjust your insulin will really depend on your body’s sensitivity to exercise. It’s best to keep a log, track your blood sugar levels, and work with your medical team to create an individualized insulin plan for diabetes.

Some children are very sensitive to exercise, and if wearing an insulin pump, they need to suspend their basal or long-acting insulin during long bouts of physical activity.

Other people may prevent low blood sugar by eating extra carbohydrates pre-run and keeping their insulin as is. On the other hand, some people need to reduce their basal insulin by a certain percentage during exercise sessions to prevent low blood sugar.

Kirpitch says, “Reductions in bolus insulin throughout the day as well as overnight basal insulin are important considerations given the increased risk for hypoglycemia that is present for several hours following the activity as well as overnight.”

Blood Sugar Monitoring

The more frequently you test your blood sugar, the better you will understand how your body responds to exercise.

Investing in a continuous glucose monitor (CGM) can help you understand how your body responds to exercise so that you can adjust your insulin and carbohydrate intake. Another option is to do frequent blood sugar tests before, during (every 30 to 45 minutes), and after your workout.

While every person with diabetes is different, most people with type 1 diabetes benefit from “maintaining glucose between 100–200 mg/dL during activity,” says Kirpitch.

If you are monitoring your blood sugar or wearing a continuous glucose monitor and your blood sugar drops below 100 mg/dL, Kirpitch says, “It’s important to introduce some carbohydrate to elevate the blood glucose and avoid having to discontinue the run due to hypoglycemia.”

Continuous Glucose Monitor

A continuous glucose monitor (CGM) measures interstitial glucose (which correlates well with plasma glucose).

There are two types of CGM devices. Most CGM devices are real-time CGM, which continuously report glucose levels and include alarms for when blood sugar goes above or below target ranges.

The other type of device is intermittently scanning CGM (isCGM), which is approved for adult use only. This device does not have alarms and does not communicate continuously. It is said to be less expensive than other CGMs.

A CGM can be helpful during exercise sessions because it helps you to understand how your blood sugar is trending during your exercise session and assist you in making insulin and carbohydrate adjustments.

Automated Insulin Delivery Systems

Emerging evidence suggests that automated insulin delivery systems may lower the risk of exercise-related hypoglycemia.

This type of system consists of three components: an insulin pump, a continuous glucose monitor, and an algorithm that determines insulin delivery.

Such a system can be advantageous because insulin delivery can not only be suspended, but also increased or decreased based on glucose levels.

Glucose Tablets and Fast-Acting Carbohydrates

In the event that your blood sugar drops during your run and you experience hypoglycemia, it is extremely important to be able to treat it right away. Symptoms of hypoglycemia may include dizziness, shaking, and sweating.

Carrying fast-acting carbohydrates in the form of sports drinks, gels, glucose tablets, or jellybeans will bring your blood sugar up quickly and safely. Carrying your own fuel can also help to keep your blood sugar stable during a run.

“Ideally, with proper fueling, the risk for hypoglycemia can be mitigated, but carrying options for treatment as well as fueling is essential,” Kirpitch explains.

When you refuel depends on how long you run. If your runs last about one to two hours, plan on refueling with 30 to 60 grams of carbohydrates per hour, starting 30 minutes into your run. If your run lasts longer than two hours, you will need to refuel with about 60 to 90 grams per hour.

If you are going for a shorter run—less than 30 minutes, for example—you are less likely to need to refuel during a run. But carrying fast-acting carbohydrates is always recommended. Having it ensures you are prepared in the instance you have low blood sugar.

Preventing Hypoglycemia After Your Run

Engaging in long-lasting aerobic exercise can result in reduced blood sugars, hours or even days after exercising. The highest risk of hypoglycemia happens overnight following the exercise. But it’s possible to see increased insulin sensitivity for 24 to 48 hours after your aerobic exercise session.

To help prevent post-workout hypoglycemia, you can try reducing your basal or bolus insulin before and/or during your workout. Take note, however, that this method may not be effective enough to reduce hypoglycemia during exercise, and it may result in hyperglycemia after your workout.

“Exercising in the afternoon further increases the risk for nocturnal hypoglycemia,” Kirpitch says. “Reducing bolus insulin for food around activity and utilizing carbohydrate-containing snacks as needed can help to balance out the amount of circulating insulin and risk for hypoglycemia.”

The Best Time to Exercise

Insulin levels are typically lower in the early morning hours (pre-breakfast) and glucose-raising hormones can be higher then. If you are prone to low blood sugar, running in the morning may be a better option.

According to Kirpitch, “Morning runs may be preferred as they contain the least amount of factors impacting glycemic control given there is no active insulin or nutritional intake after a long period of rest.”

There isn’t a universal rule regarding what time is best to exercise. The time that is best for someone else with type 1 diabetes may not be right for you.

Kirpitch explains, “The decreased insulin sensitivity many people experience in the morning may also put them at lower risk for hypoglycemia, but some experience hyperglycemia that is exacerbated by morning activity and find that difficult to manage as well.”

It can take some trial and error to find the best time to exercise for you. Start by finding the time(s) that most reasonably fit your schedule. From there, you can start to figure out what patterns and techniques allow for the best glycemic control within the timeframes available to you.

Contraindications

For some people with type 1 diabetes, certain types of exercise are contraindicated.

If you have retinopathy, peripheral neuropathy, autonomic neuropathy, or diabetic kidney disease, you should discuss exercise with your doctor before beginning a running program.

Summary

Exercise is an essential part of managing type 1 diabetes. Anaerobic exercises like interval training are more likely to cause hyperglycemia, while aerobic exercises like running can lead to hypoglycemia during or after your run.

Knowing when to fuel-up before a run, how much to eat, and what foods to reach for is critical for preventing glucose highs and lows during and after exercise. Be sure to monitor your glucose levels every 30 to 45 minutes while you work out. If your blood sugar rises above 250 mg/dL, you need to stop exercising to prevent ketoacidosis.

A Word From Verywell

Fear of hypoglycemia is normal. Experiencing low blood sugar can be scary and the steps to prevent it can feel overwhelming.

To prevent this from happening, it’s important to get support. Work through your fear with your endocrinologist or medical team and come up with a individualized plan to prevent hypoglycemia.

The more education you have, the better equipped you’ll be. It’s easier said than done, but you can do it. Remember that type 1 diabetes doesn’t discriminate. In fact, some professional athletes have type 1 diabetes, so if they can do it, you can too.