The Athlete With Diabetes

General Principles

  • Diabetes mellitus (DM) is a chronic group of metabolic diseases characterized by hyperglycemia resulting from defects in insulin secretion leading to an absolute insulin deficiency due to beta-cell destruction (Type 1), by defects in insulin action due to progressive insulin secretory loss along with increasing insulin resistance (Type 2), or by other causes such as pregnancy, neonatal diabetes, maturity-onset diabetes (monogenic diabetes), or diseases of the exocrine pancreas or because of drug- or chemical-induced causes.

  • A majority of patients with DM have Type 2 (90%). Athletes with DM range in sports participation from youth to competitive Olympic and professional.

  • Each sport and the type of exercise have their own effects on DM management. Numerous factors affect glucose levels, including stress, level of hydration, rate of glycogenolysis and gluconeogenesis, and secretion of counter-regulatory hormones.

  • Management includes excellent clinical care, continuous patient self-management, patient education, and longitudinal support to prevent long-term complications (renal failure, blindness, peripheral vascular disease, and peripheral neuropathy).

Anatomy and Pathophysiology

  • Type 1 DM (T1DM ) has two subtypes: Type 1A and Type 1B. Each type can occur at any age, but typical onset is before the age of 30 years, with peak incidence during adolescence.

  • Type 1A is an autoimmune disease characterized by cellular antibodies that may form against islet cells (ICA), insulin (IAA), and glutamic acid decarboxylase (GAD65). Type 1B is an idiopathic, nonautoimmune disease state with loss of beta-cell function. Both types are caused by loss of insulin secretion due to progressive loss of insulin production.

  • These physiologic changes lead to increased hyperglycemia, weight loss, possible ketoacidosis, and possible death if insulin is not administered.

  • Type 2 DM (T2DM) occurs in most patients older than 40 years and is characterized by defects in both insulin secretion and resistance to insulin action.

  • Impaired insulin secretion, increased hepatic glucose production, and decreased muscle glucose uptake lead to increased levels of insulin production and eventual insulin resistance.

  • Both genetic (family history or familial hyperlipidemia) and environmental (sedentary lifestyle or inappropriate diet with increased caloric intake) factors are involved in the development of insulin resistance. Insulin resistance is associated with obesity, hypertension, and hyperlipidemia and may precede the onset of diagnosed DM by 10–20 years.

  • T2DM occurs in athletes with an increased body mass for their particular sport (football lineman or rugby players) or those who do not remain fit (e.g., certain baseball players).

  • Patients with T1DM and T2DM benefit from regular exercise:

    • Exercise decreases the insulin resistance of peripheral tissues and alleviates the defect of insulin-stimulated glycogen metabolism in skeletal muscles;

    • It improves postprandial hyperglycemia and possibly postprandial insulin secretion.

  • For patients with T2DM, both aerobic and resistance exercises can benefit glycemic control.


  • The incidence of DM is increasing worldwide. It is estimated to affect 439 million individuals worldwide by the year 2030, and it is predicted that prediabetes and DM will affect 52% of the United States (US) population by 2020. Currently, approximately 24 million patients have DM, and 90%–95% of them have T2DM.

General Medical Concerns

  • In comparison with inactive individuals, the additional demands of training and competition affect glucose homeostasis in athletes with DM, thus creating additional challenges.

  • Challenges include the athlete’s safety during athletic participation, adequate glucose monitoring, and diet and insulin adjustments for safe and effective athletic performance.

  • Most competitive athletes learn to manage their DM during training and competition by trial and error while sharing personal experiences with other athletes.

  • Medical concerns include unsafe dietary patterns, using nutritional supplements with no benefit or even detrimental effects, and using illegal drugs.

  • Other concerns include the female athlete triad (amenorrhea, osteoporosis, and eating disorder), rapid weight loss to “make weight” in the respective wrestling or gymnastic competition, and excessive consumption of a single macronutrient (carbohydrate, protein, or fat) in certain athletes such as football players.

  • In sports with weight categories (wrestling, boxing, and weightlifting), insulin is often omitted so that athletes can lose weight before weigh-ins; the consequence is poor glucose control and the risk of ketoacidosis.

Athletes With Type 1 Diabetes Mellitus

  • Appropriate hydration and maintenance of glucose levels can maximize performance. The excitement of competition can increase catecholamine release, resulting in hyperglycemia, but adjustment of insulin dosing is usually unnecessary.

  • Athletes with T1DM learn their personal requirements from training and recognize that they always require certain amount of insulin supplementation.

  • When an athlete with T1DM is insulin deficient, hyperglycemia occurs with a risk of further elevation in glucose levels, which may exacerbate or precipitate ketoacidosis. Moreover, osmotic diuresis with relative dehydration occurs as well.

  • Morning endurance sports are less likely to cause hypoglycemia owing to physiologically elevated diurnal cortisol and growth hormone levels. Events that occur later in the day require adjustments in food and insulin.

  • Certain athletes with T1DM intentionally avoid achieving good blood glucose control before their competitive event to have increased lipid utilization, which prevents exercise-induced hypoglycemia.

Athletes With Type 2 Diabetes Mellitus

  • The duration the athlete has been diagnosed with T2DM and specific sport will determine management. Endogenous insulin production or secretion early in the disease requires little, if any, exogenous insulin. These athletes maintain the ability to physiologically decrease or increase endogenous insulin secretion and are generally able to achieve optimal glucose levels remain in the desired range.

  • With progression of the disease, endogenous insulin secretion diminishes and exogenous insulin administration becomes necessary and must be adjusted to prevent hypoglycemia.

  • It is not uncommon for such athletes to decrease exogenous insulin requirement by ≥50% with competition.

  • Because athletes with T2DM also frequently use medications (e.g., insulin secretagogues and sensitizers), such medications are often decreased as training and insulin sensitivity increases and body fat decreases, resulting in an overall increase in lean body mass.

Sport-Specific Issues

Endurance Athletes (Distance Cyclists and Runners)

  • Appropriate glucose management before, during, and after exercise is crucial to care of an athlete with DM.

  • Endurance runners often strive for optimal prerun blood glucose levels of 120–180 mg/dL, use minimal insulin, and estimate a glucose reduction of 10–15 mg/dL/mile.

  • When running for 30–60 minutes, self-monitoring of blood glucose or continuous glucose monitoring (CGM) during the training period will delineate the athlete’s predicted response.

  • Distance cyclists and runners may choose to set the basal rate of insulin infusion via continuous subcutaneous insulin infusion (CSII) or insulin pump at a lower rate or may select a decreased long-acting basal insulin dosage (not uncommon to have to decrease by 50%). Carbohydrates are then gradually ingested to match energy utilization with exercise. By creating a steady-state balance between exercise requirements, basal insulin infusion, and ingestion of energy (carbohydrates), glucose levels are held constant (e.g., 130–150 mg/dL) over several hours.

  • When a cyclist or runner with T1DM encounters a demanding section of a course, they will either adjust the basal rate of insulin downward or ingest additional carbohydrates to maintain optimal glucose levels.

  • For runners and cyclists who are prone to hypoglycemia, performing a series of anaerobic sprints or resistance exercise before the aerobic endurance event may help prevent subsequent hypoglycemia.

  • Running sports pose special problems for athletes with DM and include skin breakdown or other lesions due to vascular compromise or neuropathy.

  • Athletes should travel with at least two pairs of well-fitting shoes that (i) are well broken-in, (ii) have no areas of material weakness or breakdown, and (iii) cause no discomfort with exercise. In addition, (iv) athletes should have their feet examined by the ATC/healthcare provider on a weekly basis, (5) avoid switching to a new pair of shoes on competition day, and (6) avoid using any alcohol-based lotion on the feet that may cause skin drying.

Altitude Sports

  • Glycemic control decreases in athletes with T1DM and may affect certain patients with T2DM at high altitudes. Hyperglycemia is due to (i) increased sympathetic tone with subsequent increased hepatic glucose production, (ii) increased insulin resistance, and (iii) loss of appetite at high altitude.

  • Other problems encountered include variation in reliability of glucose monitors and adequate insulin protection from temperature extremes. As insulin temperature approaches freezing temperatures, it becomes less active.

  • High-altitude athletes should maintain insulin close to their body to maintain optimal insulin temperature.

Water Sports, Swimming, or Scuba

  • Water sports limit the use of insulin pumps and continuous glucose monitors depending on the specific device and company model. While insulin pumps are water resistant and one model is waterproof to 12 feet for up to 24 hours, other models do not withstand pressure.

  • Insulin pumps usually are removed before showering or bathing, whereas implanted glucose monitor skin sensors can remain in place; however, separate external glucose monitor devices are not waterproof.

  • Scuba diving is discouraged for athletes with T1DM, although several accomplished divers dive with partners who are aware of their condition. Since recreational dives usually last 30–45 minutes, glucose monitoring can be accomplished on an interval basis at the surface level.

Ice Hockey, Wrestling, or Football

  • Use of external devices is discouraged in these sports. Wrestling and football competitions can cause damage to insulin pumps or external glucose monitors. Hockey players cannot wear any equipment that would be harmful to another player. A letter from a healthcare provider is required for any special medical equipment.

  • Athletes often resort to intermittent insulin injections and glucose monitoring outside the competition area.

Baseball or Softball

  • These sports are ideal for athletes with DM because they require bursts of anaerobic energy without prolonged exercise periods.

  • In the dugout, during each inning, athletes should test their glucose levels, ingest carbohydrates, and maintain hydration as needed.

  • There has been some success in using insulin pumps with these sports.


  • Most diabetic triathletes have T1DM and, through their training, have learned to satisfactorily manage their insulin and glucose levels, making insulin adjustments on competition days based on training experiences.

  • During the swimming element, either a waterproof pump is worn or the insulin pump and glucose monitor are removed.

  • After exiting the water, athletes may attach an external glucose monitor and insulin pump. The process requires ≤10 seconds.

  • Athletes may suspend, continue, or increase the same infusion based on glucose monitor readings without ceasing activity.

  • With special permission from race officials, along the course route, athletes may be provided with glucose supplements.

Risk of Exercise

  • Hypoglycemia is a major risk in athletes with T1DM, with additional risks of exacerbation of hyperglycemia and ketoacidosis. All diabetics are at an increased risk of coronary artery and peripheral vascular disease.

  • Other associated risks include retinopathy, injury from neuropathy (ankle and foot injuries), and autonomic dysfunction (abnormal sweating mechanisms, affecting heat dissipation or abnormal heart rate response to exercise) ( Fig. 33.1 ).

    Figure 33.1

    Signs of neuropathic joint disease and peripheral vascular disease.

  • Running is prohibited in patients with active proliferative retinopathy, which must be treated, stabilized, and cleared by an ophthalmologist before resuming activity.

Special Equipment

  • CSII is a device that contains a reservoir of rapid-acting insulin within a pump along with a small computer and catheter connected to a quick-release device inserted into the subcutaneous tissue of the athlete (abdomen). Basal insulin is provided in the form of a continuous slow infusion. A bolus of insulin can be administered to cover carbohydrate intake. The device can be interrupted or suspended for short periods of time (<60 minutes) without and adverse effects.

  • In addition, CGM can be used to monitor glucose levels. A small sensor is implanted in the subcutaneous tissue, which analyzes glucose levels in the interstitial fluid. Severe low or high levels are signaled, allowing the athlete to have more control over his/her DM management and exercise programs.


Principles of Glucose Management in Diabetes Mellitus

  • The American Diabetes Association recommends following glycemic goals:

    • Fasting glucose of 90–130 mg/dL

    • 2-hour postprandial glucose <180 mg/dL

    • Limit postprandial glucose versus premeal glucose to ≤50 mg/dL

  • The total daily dose (TDD) of insulin = 0.7 × weight in kg

    • Basal insulin dose per 24 hours = 50% of TDD

    • Bolus insulin dose per 24 hours = 50% of TDD

    • Percentages vary from individual to individual based on glucose measurements and activity, work, and exercise schedule.

    • Prandial insulin can be determined by weight (0.1 units/ kg/meal, see Example 1) or can be determined by pre-meal glucose measurements and calculated grams of carbohydrate in the upcoming meal (1 unit for each 30 g of glucose in the meal, see Example 2).

      • Example 1: 70 kg male × 0.1 units/meal = 7 units with that meal

      • Example 2: Pre-meal glucose = 150 mg% (Target level is 120 mg%)

      • For blood glucose levels above a described target number, i.e., one unit for each 15 g of glucose (150–120 = 30 mg%/15 = 2 units)


        60 g glucose meal (60 g/30 = 2 × 1 unit for each 30 g of glucose in meal = 2 units)

        Total units given pre=meal = 4 units.

  • Patients with T1DM require bolus insulin before meals ( Table 33.1 ) and basal insulin ( Table 33.2 ) throughout the day.

Jul 19, 2019 | Posted by in SPORT MEDICINE | Comments Off on The Athlete With Diabetes

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