High-level sport and the challenge of hyperglycemia

Are you doing muscle training in preparation of a fitness championship? Are you training for a marathon or a long-distance cycling event? Does your teen play in a high calibre hockey or soccer team? As a person with T1D or parent of a child with T1D, you probably know that blood sugar management in sports is no easy task.  

A number of scientific studies have shown that fear of hypoglycemia during and after physical activity is the number 1 barrier to doing physical activity for people with T1D. Insulin production should drop rapidly during physical activity, but this response doesn’t occur in people treated with insulin, which can lead to hypoglycemia.

Conversely, the risk of hyperglycemia is also present and can even become crippling for top athletes, especially in competitive events. Some athletes even develop hyperglycemia-related anxiety, which is not as well documented as fear of hypoglycemia.

High-level competitive sport and rising blood sugar levels

All physical activity has an impact on blood sugar levels. The extent of this impact will vary according to the type of exercise, intensity and insulin on board, or IOB, among other factors. Playing high-intensity, competitive sport poses a particular risk for raised blood sugar levels, due in part to the secretion of stress hormones, which release glucose stored in the liver. Hyperglycemia usually causes symptoms such as thirst, the need to urinate, blurred vision, nausea, fatigue and shortness of breath. 

It also appears that some athletes will deliberately make their blood sugar rise before a competition to avoid hypoglycemia, which is not only a safety risk, but also an obstacle to their performance. To avoid this situation, athletes will decrease their insulin doses and/or ingest more carbohydrates in the hours leading up to a sporting event. The high-carb pre-competition diet, which also ensures that the athlete doesn’t run out of energy, can contribute to hyperglycemia if not properly supervised.

European researchers followed a men’s team of 12 professional cyclists living with T1D over the course of a racing season. They analyzed and compared blood sugar data from training sessions, competition days, recovery periods and nights.

Competition days were characterized by significantly more time in hyperglycemia than training days, due in part to stress hormones and strategies to raise blood sugar before the competition. The post-exercise recovery period was also characterized by elevated blood sugar levels, particularly during the hour post-competition. Without a doubt, this is the result of two factors: additional carb intake after the race (to replenish the glucose stores in muscles) and decreased insulin levels (to compensate for the increased sensitivity).

Hyperglycemia-related anxiety: A reality to consider for athletes

Hyperglycemia is thought to affect both athletes’ performance and mental preparation, as was shown in a recently published BETTER project study, which examined the case of an 18-year-old goalie in the Junior A Hockey League who developed hypoglycemia-related anxiety. Researchers have observed that above 13 mmol/L, young athletes experience several physical and cognitive symptoms that impair their ability to follow the puck or anticipate other players’ movements and decisions. The goalie also reports experiencing stomachaches, irritability, dizziness and blurred vision. According to him, the artificial pancreas he’s been using for the past two years helps prevent hypoglycemia, but isn’t as effective at managing hyperglycemic episodes associated with his sport.

For fear of experiencing hyperglycemia, which he describes as a serious problem, the athlete takes more insulin, and eats lighter meals and fewer snacks in the day leading up to a match. This strategy may seem effective. Indeed, the goalie’s glycemic variability data reveals lower glucose levels during the game when he follows this plan. However, this strategy opens the door to post-exercise hypoglycemia, especially if the goalie doesn’t eat sufficiently after a game.

There needs to be better support for all athletes, and particularly those with T1D.

Whether they’re caused deliberately or not, hyperglycemic episodes associated with top-level sport don’t protect athletes from the risk of hypoglycemia. For instance, blood sugar levels data from professional cyclists showed that, despite repeated hyperglycemic episodes on race days or during certain training sessions, athletes spent a high percentage of time (up to 10% of the time) in hypoglycemia during the night that followed. However, nighttime hypoglycemia is more common after training days than after competitions, and particularly following endurance exercises. After physical activity, the body replenishes its energy stores in the muscles and liver in the form of glycogen (a complex carbohydrate) overnight. The body then becomes highly sensitive to insulin to allow the passage of glucose from the bloodstream to the muscles and liver, which can lead to a drop in blood sugar levels. 

A good night’s sleep is extremely important for athletes so that the body can recover and regenerate, so identifying effective strategies to reduce extreme variations in their blood sugar levels and limit the number of times they need to wake up for a snack or insulin is crucial.

These findings, along with the observations of several other studies on the subject, highlight how essential it is to develop customized protocols to help athletes living with T1D avoid, as much as possible, hyperglycemia and hypoglycemia not only during training and competitions, but also during recovery periods and at night.

In particular, healthcare professionals will need to discuss hyperglycemia-related anxiety with their patients who are high-level athletes and factor it into their treatment plan, so that they don’t adopt blood sugar management strategies that could ultimately lead to hypoglycemia, or even severe hypoglycemia (i.e. which they’re unable to treat themselves) several hours after training.


References :

Katz, A. et al. (2023). Hyperglycemia-related anxiety during competition in an elite athlete with type 1 diabetes: a case report. Diabetes & Metabolism 49, 101476. https://www.sciencedirect.com/science/article/pii/S1262363623000587?via%3Dihub

van Weenen, E. et al. (2023). Glycemic patterns of male professional athletes with type 1 diabetes during exercise, recovery and sleep: Retrospective, observational study over an entire competitive season. Diabetes, Obesity and Metabolism 25(9), 2616-2625.https://doi.org/10.1111/dom.15147

Yurkewicz M., et al. (2017). Diabetes and Sports: Managing Your Athlete With Type 1 Diabetes. American Journal of Lifestyle Medicine. 2017;11(1):58-63. doi:10.1177/1559827615583648

Written by: Nathalie Kinnard, scientific writer and research assistant

Reviewed by:

  • Alexandra Katz, Master’s student in nutrition
  • Sarah Haag, RN. BSc.
  • Rémi Rabasa-Lhoret, MD, PhD
  • Anne-Sophie Brazeau, P. Dt., PhD
  • Sonia Fontaine, Claude Laforest, Michel Dostie, Domitille Dervaux, patient partners of the BETTER project

Linguistic revision by: Marie-Christine Payette

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