Diabetes | May 9, 2014 | Author: The Super Pharmacist
Blood glucose and insulin dosing in type I diabetes can be complicated, even when people stick to routine diets with routine amounts of physical activity. The complexity increases dramatically in diabetic athletes who expend great deals of energy. While hyperglycaemia is possible after vigorous exercise, the greatest threat to diabetic athletes is hypoglycaemia. Despite these risks, there have been several gold-medal winning Olympians and other high-level professional athletes who have successfully managed their type I diabetes during sports.1 There are ways to safely and effectively manage diabetes therapy as an athlete, but it does require some forethought and planning.
Exercise has two seemingly opposite effects on blood glucose. When the body is performing a sport, cells throughout the body require additional nutrition in the form of glucose. In order for glucose to move from the bloodstream into cells, insulin is required. In order to achieve optimum performance, athletes with type I diabetes must have sufficient amounts of insulin available so that their cells can receive adequate nourishment. They must also have sufficient amounts of glucose. Therefore, a diabetic athlete’s insulin and glucose requirements increase during exercise. Exercise increases the cells’ demand for glucose. As blood glucose decreases, it stimulates the release of several hormones in an attempt to normalize glucose levels in the blood. In people without diabetes, hypoglycaemia during exercise is rare because of these hormones. In people with type I diabetes, however, the pancreas does not produce insulin or glucagon and other hormonal responses may be blunted or amplified. Consequently, hypoglycaemia during exercise is a real concern in people with type I diabetes. On the other hand, regular exercise increases insulin sensitivity and decreases insulin requirements.2 This is true of both type I and type II diabetes. So people who are in excellent physical shape actually require less insulin overall, because their cells are more sensitive to its effects. This means that diabetic athletes must determine their energy requirements during acute exercise and reassess those needs during training as they proceed through different levels of physical fitness. [table id=1 /]
Since some of the key hormonal players are absent in people with type I diabetes, the body's normal response to exercise cannot occur. As a result, the diabetic athlete has too much circulating insulin during exercise. In other words, whatever insulin they needed to achieve good glycaemic control while at rest is now too much insulin during exercise. Insulin levels may be 2 to 3 times higher than needed during exercise.3 This is a potentially dangerous effect because it can cause rapid drops in blood glucose levels. The total amount of glucose in the blood is only about 3 to 4 grams, but glucose requirements can increase 5- to 6-fold above resting levels.4In fact, hypoglycaemia can occur within minutes if the diabetic athlete does not properly adjust his insulin dose before exercise or if they do not consume a sufficient amount of carbohydrates during exercise.5
The blood glucose level (e.g., finger stick testing) should always be done immediately prior to exercise. The target range for blood glucose immediately prior to exercise should be between 90 and 250 mg/dL (5 to 13.9 mmol/L). If blood glucose is outside of this range, exercise should be avoided until levels can be brought within this range. Blood glucose should also be checked every 30 to 45 min. during exercise and adjustments should be made based on the result. Specific diabetes management is based on the pre-exercise blood glucose concentration. While all diabetic athletes should speak to their primary care physician, paediatrician, or endocrinologist to develop a specific regimen, the approach listed in Table 2 is reasonable for most diabetic athletes. [table id=2 /]
It may seem counterintuitive or paradoxical that blood glucose levels may increase during extreme exertion. This occurs because high-intensity exercise can stimulate the release of catecholamines such as adrenaline. Circulating adrenaline can cause the liver to increase its production of glucose. This temporary hyperglycaemia may also occur in sports that require bursts of energy (e.g., periodic sprinting during football among periods of jogging or standing).6
The primary goal of diabetes management during exercise is to make sure that there is enough circulating carbohydrate in the blood. That means that diabetic athletes can reduce the amount of insulin that they would normally take when they know that they will be participating in sports. Alternatively, they can eat extra carbohydrates prior to exercise. If they do not want to change insulin dosing, diabetic athletes may need anywhere between 15 to 40 g of additional carbohydrates for every 30 min. of physical activity. Some or all of this added carbohydrate should be eaten between 15 and 30 min. before beginning exercise.7 This carbohydrate snack is ideally some combination of rapid-acting and slow-acting carbohydrate (i.e., a high glycaemic index and low glycaemic index snack, respectively). This combination will help prevent hypoglycaemia both during exercise and after exercise. It is also advisable to eat a snack after exercise that has a mix of protein and carbohydrates, possibly with an additional bolus of short acting insulin.8 Even under the best of circumstances it is impossible to exactly predict insulin requirements using injected insulin. However, it is possible to come close. One reasonable approach is to adjust the pre-exercise insulin dose for aerobic exercise or sport that would be considered moderate or intense. Any exercise that will last for more than 60 min. may require insulin adjustment. Insulin adjustments may not be necessary for mild exercise or for short duration intense exercise.
In diabetic athletes who wish to perform elite level or highly competitive sports, insulin pumps may help with insulin dosing and glucose management. This allows for more timely alterations in basal levels of insulin infusion. In fact, devices that combine insulin infusion with continuous blood glucose monitoring may provide even tighter glucose control. Continuous blood glucose monitoring provides an excellent assessment of insulin requirements. These measurements can be used to plan insulin dosing and nutritional requirements for future sports outings.