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Columns: Medical Report

Care of the Athlete with Diabetes

Curtis, Vanessa A. M.D., FAAP; Peterson, Andrew R. M.D., M.S.P.H., FAAP

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ACSM's Health & Fitness Journal: July/August 2016 - Volume 20 - Issue 4 - p 39-40
doi: 10.1249/FIT.0000000000000215
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Patients with type 1 diabetes mellitus (T1DM) should be encouraged to live full and healthy lives. For many patients with T1DM, this includes sports participation. This review provides an overview of T1DM and its treatment with emphasis on challenges that are encountered frequently by the athlete and his or her health care providers.

Glucose homeostasis requires a dynamic balance that includes mechanisms to raise and lower blood glucose. Normally, beta cells in the pancreas respond to dietary carbohydrate intake and release insulin to maintain blood glucose within a narrow target for optimal health. Insulin allows blood glucose to be used for energy or stored for future use. Later, when the blood glucose begins to fall, the pancreas quickly halts insulin release. In an exercising or fasted state, when cells need more energy than is available, the body releases counterregulatory hormones (glucagon, epinephrine, norepinephrine, cortisol, and growth hormone) to help mobilize glucose that has been stored and promote energy release from fat stores. In addition, working skeletal muscle expresses transporters that allow it to take in glucose from the blood without the help of insulin. This is very important for glucose homeostasis in athletes.

T1DM is caused by the autoimmune destruction of the pancreatic beta cells. The condition has a prevalence of approximately 1 in 500 Americans less than 20 years of age, with the highest prevalence in non-Hispanic whites (1). This results in an insulin deficiency that prevents the blood glucose from entering cells and providing energy, which, in turn, leads to increases in blood glucose (hyperglycemia) while depriving the cell of its main energy source. The body responds to the lack of available energy by mobilizing energy stored as fat. The unchecked breakdown of the body's fat stores (fatty acid oxidation) results in weight loss and the production of ketones as a byproduct. Ketones do provide an energy substrate but also are strongly anionic and can lead to dangerous acidosis (ketoacidosis).

Patients with T1DM are dependent on injections or infusions of exogenous insulin. For many years, the two available forms of insulin were short-acting regular insulin and intermediate-acting neutral protamine Hagedorn (NPH) insulin. These insulins are given at set doses and times, typically in three daily injections. With this plan, the patient must eat a constant amount of carbohydrates at prescribed times to maintain euglycemia. Although effective and relatively inexpensive, the regular/NPH regimen requires adherence to a rigid lifestyle. With the advent of both longer and more rapid-acting insulins, most athletes prefer a basal-bolus insulin regimen, which allows the matching of an insulin regimen to the patient's lifestyle. These newer insulin regimens make use of long-acting insulin (glargine or detemir) that is given nightly and combined with ultrafast-acting insulins (aspart, lispro, or glulisine) given three to four times per day immediately before eating based on the current blood sugar and the carbohydrate content of the meal. This allows for flexibility in meal timing, size, and content as well as adjustments for blood sugar and activity level.

Insulin pumps have made it possible to provide a continuous infusion of insulin and to give additional boluses of insulin when needed. For some patients, these pumps allow a more convenient and dynamic method of ensuring good glycemic control.

Patients must check their blood sugar four to six times per day by lancing their finger and applying a small drop of blood to a test strip. In addition, some patients take advantage of continuous glucose monitors (CGM), which are wearable devices that monitor blood glucose of the interstitial fluid several times per hour. CGMs allow patients to detect glucose trends and often uncover hidden areas of hyperglycemia. In the near future, the combination of CGM and insulin pump could yield an artificial pancreas, which would respond to circulating blood glucose with appropriate doses of insulin, much like the native pancreas does.

For the long term, it is important for patients with T1DM to maintain good blood sugar control. Patients who maintain good glycemic control can expect to live long, healthy lives and have low risk for diabetic complications. However, patients with prolonged periods of poor glycemic control are at risk for developing microvascular complications that can affect the eyes, kidneys, and nervous system. In addition to the risk of complications from diabetes, patients with T1DM are at risk for other autoimmune diseases, such as thyroiditis and celiac disease, and should be monitored for the development of these conditions.

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Although it is beneficial for patients with T1DM to participate in sports, vigorous exercise introduces another variable that affects blood sugar and thus poses a challenge to athletes with T1DM. As previously mentioned, exercising muscle can take in glucose even in the absence of insulin. This can have a significant effect on circulating blood glucose during and after exercise. Conversely, stress hormones surrounding competition have the opposite effect and raise blood sugar. The direction, magnitude, and timing of these glycemic changes are individual and dependent on the intensity and duration of exercise. Furthermore, in some sports (especially team sports) it can be very difficult for the athlete to predict how much exercise they are going to be doing during practice or competition, further adding difficulty to insulin dosing and meal planning.

The best way to learn how exercise affects blood glucose in an athlete with T1DM is through frequent blood sugar checks. An athlete may need to check his or her blood sugar as often as hourly, or at times even more frequently, during training sessions. For some sports, this can be made easier by using a CGM.

Insulin pumps can be left on during some sports, but are not practical during others. For example, a cyclist can put the pump in a jersey pocket; however, swimmers or gymnasts typically disconnect their pumps for training and competition. Many contact sport athletes prefer to disconnect their pump; however, it is possible to continue to use the pump by encasing it in special padding. If the athlete needs to disconnect from the pump during long periods of training or competition, it may be necessary to transition to injectable insulin therapy to prevent dangerous and performance-decrementing hyperglycemia.

After strenuous exercise, muscles continue to take up extra blood glucose in the absence of insulin as a normal part of the recovery process. Athletes (whether they have diabetes or not) recover better from training sessions if there is adequate fuel immediately after exercise to help the muscles repair and replenish their glycogen stores. The savvy athlete with T1DM will take advantage of this postexercise window and consume additional carbohydrates matched with insulin to maximize his or her training response. It should be noted that insulin is a banned substance for athletes who do not have diabetes, and it has the potential for abuse in diabetic athletes. Conversely, some athletes with T1DM will intentionally underdose their insulin so that they develop hyperglycemia, glycosuria, and fatty acid oxidation, resulting in weight loss. This practice is remarkably dangerous and can lead to ketoacidosis through the short term and microvascular diabetic complications through the long term.

Medical providers who care for athletes with T1DM on the sideline, locker room, and training room will encounter both hyperglycemia and hypoglycemia. An athlete with hyperglycemia will be dehydrated and may have difficulty concentrating. He or she should delay exercise until he or she can rehydrate and he or she may require extra insulin. If a patient is hyperglycemic and has developed ketones in his or her urine (because of inadequate insulin), he or she should not be allowed to exercise.

An athlete with hypoglycemia will present with an adrenergic response (tremulous, diaphoretic) and may develop neuroglycopenic signs (irritable, confused, seizures). The treatment of hypoglycemia is to provide a source of fast-acting carbohydrate (we recommend 15 g of carbohydrate, which can be achieved with 4 oz of juice, four glucose tabs, 1.5 Shot Blocks, etc.) every 15 minutes until hypoglycemia is resolved. If the athlete has altered mental status such that he or she cannot safely and reliably take an oral source of carbohydrate, he or she can be given an intramuscular injection of glucagon to raise blood sugar. Injectable glucagon is prescribed to all who have insulin-dependent diabetes and should be readily available at the sidelines, and can be life saving.

Athletes with T1DM can participate and be successful in any sport. However, diabetes does present challenges to the athlete in glycemic control and recovery. Medical providers who care for athletes with T1DM should understand the basic concepts of treatment, appreciate the challenges faced by the athlete, and be familiar with signs and acute management of hyper- and hypoglycemia.

1. Pettitt DJ, Talton J, Dabelea D, et al Prevalence of diabetes in U.S. youth in 2009: the SEARCH for Diabetes in Youth Study. Diabetes Care. 2014;37(2):402–8.
© 2016 American College of Sports Medicine.