Jan. 17, 2024 -- If you have type 1 diabetes and vowed to exercise more this year, there are doctor-approved ways that could help you meet your goal and stay safe. 

Many with type 1 diabetes don't get enough exercise, and aside from the usual grumblings that keep people from physical activity,  research suggests that a fear of hypoglycemia – when your blood sugar gets too low -- could be a particular issue for patients with type 1 diabetes.

Exercise, food, insulin, and blood glucose can become a crazy balancing act in a matter of minutes, especially if you are new to physical activity. Complicating matters: A workout can mask the signs of hypoglycemia, making it harder to spot.

"Exercise gives you false symptoms, like sweating, increased heart rate, and tiredness," said  Michael Riddell , PhD, a professor of kinesiology and health science at York University in Toronto, and cochair of the Type 1 Diabetes Exercise Initiative, the largest observational exercise study in adults with type 1 diabetes.

Riddell also lives with type 1 diabetes and exercises regularly and is a vocal advocate for helping patients move more.

"Physicians [who have patients with type 1 diabetes] really should encourage exercise because it has so many health benefits," said Riddell.

Among them are better glycemic control and reduced insulin requirements, Riddell said. In a  review Riddell led, patients with type 1 diabetes who exercised at least twice a week had lower body mass index, better A1c concentrations, and fewer complications like retinopathy and microalbuminuria, which means you have an increase in protein in your urine. They also were less likely to experience issues with cholesterol and high blood pressure.

If you’re still struggling to exercise, keep in mind doing so will help lessen all those risks, Riddell said.

All About Timing

For many people, the best time to exercise is simple: Whenever they can fit it in. Still, timing may help blood glucose control.

Consider mealtimes, for example. "Don't exercise when you've taken a (dose) of insulin for a meal," Riddell said. "Your insulin is already working, and your blood sugar will start trending down. If you add exercise, it may go down too quickly."

While exercise before a meal is best, post-meal exercise is okay too — just be sure to reduce your mealtime insulin dose, as the exercise will intensify its effect, Riddell said.

Some  research suggested that exercise in the morning before eating may reduce the risk for hypoglycemia. One  randomized trial found that people with type 1 diabetes who exercised before breakfast were 50% less likely to experience dangerous drops in blood sugar over the next 24 hours, compared with those who exercised after lunch. What's more, on days following morning exercise, these people saw more normal-range blood glucose readings than on days after.

Hormones may play a role. "Cortisol is produced in higher quantities in the morning, and it causes higher blood sugars," said  Sarah Kim , MD, an endocrinologist at UCLA Health. So, "you may not have as much of a drop in blood sugar."

Then there's the  dawn phenomenon , when hormones (like cortisol) signal the liver to produce extra glucose to wake you up. It happens in about half of patients with type 1 diabetes, and a morning workout may help counter its effects.

But regardless of when you choose to exercise, staying consistent is key.

"Routine is really important," said  Jason Baker , MD, an assistant professor of medicine and endocrinologist at Weill Cornell Medicine in New York City. Always exercising at the same times, and for the same durations and intensities, can help you learn how your body responds, so you know what to expect and how to prepare, Baker said.

Start Tracking at T-Minus 30

Patients should keep an eye on their glucose numbers starting about a half hour before the workout. Continuous glucose monitors (CGMs) are great tools for this, but keep in mind that there can be a 10- to 15-minute delay between the sensor and changes in blood sugar. 

"I always recommend patients still follow up with a finger stick," said Baker, "to make sure they have good data and are making the right treatment decision."

If the numbers are trending down, patients can have a snack without insulin immediately before starting the workout, Kim said. "If blood sugar is 150-200 mg/dL, they may still want to eat without any insulin because we expect the exercise itself to drop the blood sugar into a normal range." If blood sugar is higher than that, you may skip the snack.

Stay Aware, Be Prepared

Exercise intensity matters, so it's good to be aware of how hard you’re working out. However, a lot can affect one's exertion.

For example, a small  randomized trial published last year suggested that immersive fitness video games can impair your ability to tell how hard you’re working. The game's visuals, music, and interaction may distract you from your body is feeling, the researchers explained.

Instead of relying on feel alone, peek at your blood sugar readings periodically during the workout, Riddell said.

If you have an  insulin pump , you may be able to connect the pump to the glucose monitor, so it can adjust insulin based on CGM data.

If that's not an option, the pump may still have an activity or exercise mode. "That will reduce the amount of basal insulin the pump is providing," Kim said. "The patient can turn it on for the duration of the exercise" — and keep it on, even after the workout, until blood glucose returns to a stable range.

Just in case, patients should always keep a sugar source in their pocket, Baker said. "Don't plan to run to the store across the street or back to your gym locker for some sugar," Baker said. "When blood sugar drops, you may feel out of it and won't be thinking clearly."

A source with  15 g of carbohydrate, like three to four glucose tablets or six Lifesaver[ZM1]  candies, can raise blood sugar quickly.

How to Choose the Best Type of Exercise

In general, aerobic exercise (steady state, moderate intensity) lowers blood glucose, while anaerobic exercise (shorter bursts, higher intensity) raises it.

Riddell's suggestion: Do interval-style workouts with a mix of both. The combo may help blood glucose stay in range.

Try 30 minutes of aerobic exercise with anaerobic activities mixed in, like sprints, push-ups, sit-ups, burpees, or squats.

For beginners, "don't exercise for more than 30 minutes," Riddell added. Going longer than that may reduce blood sugar too much.

Change Your Habits, Change Your Insulin

"As physicians, we need to remind [patients] that when they change their behavior, they also need to change their insulin," Riddell said. The more physically active a patient is, the less insulin they'll probably need.

"You can take 20% less basal insulin throughout the day, and up to 50% less mealtime insulin if you're physically active after the meal," said Riddell. "Then you'll have weight loss, you won't have to treat with as much carbohydrate, and you won't have as much hypoglycemia."


Medscape Medical News



Michael Riddell, PhD, professor of kinesiology and health science, York University, Toronto.

Sarah Kim, MD, endocrinologist, UCLA Health.

Jason Baker, MD, assistant professor of medicine, endocrinologist, Weill Cornell Medicine, New York City. 

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