Exercise is an important part of controlling blood sugar levels with any form of diabetes. Lack of exercise and physical activity, along with overweight and obesity, are the primary triggers for the development of type 2 diabetes. People with diabetes, especially those with type 1 diabetes, must carefully monitor their blood sugar levels and adjust insulin dosages during exercise.
Exercise is important for everyone, but especially for people with diabetes, and even more so for those with type 2 diabetes, prediabetes, or otherwise at risk for developing diabetes. Regular exercise, even moderate amounts, is one of the best ways to lower blood sugar levels and prevent hyperglycemia—abnormally high blood sugar. Exercise moves glucose from the blood into muscles to be burned for energy and increases the body's sensitivity to insulin, so that insulin is effective. Exercise can enable people with diabetes to decrease their daily dosages of insulin or other diabetes medications. Many people are able to manage type 2 diabetes with exercise and diet alone.
Exercise can promote weight loss and help maintain a healthy weight, which is particularly important for people with diabetes. Maintaining a healthy weight and exercising regularly can cut the risk of developing type 2 diabetes in most people.
In addition to lowering blood sugar levels, exercise helps counteract diabetes complications, especially negative effects on the cardiovascular system. Over time, regular exercise can lower resting heart rate and blood pressure to help counter the increased risks for heart attack and stroke that accompany diabetes. Lowering blood pressure also helps prevent eye and kidney problems that are frequent complications of diabetes. Diabetes is often accompanied by high levels of fats—cholesterol and triglycerides—in the blood, which can cause blood vessels to age prematurely. Exercise decreases total cholesterol and triglycerides in the blood and increases high-density lipoprotein (HDL) or good cholesterol. Exercise also increases blood flow to the feet, which can help prevent foot problems that commonly arise with diabetes.
Other general health benefits of exercise can be particularly significant for people with diabetes or at risk for developing this chronic disorder. Exercise strengthens bones and muscles, tones muscles, and improves flexibility and balance. In addition to reducing the risk of obesity, high blood pressure, heart disease, and stroke, exercise can reduce the risk of arthritis and help treat osteoarthritis. Exercise has been shown to help prevent cancer and Alzheimer's disease.
By inducing the release of endorphins in the brain, exercise makes people feel better, reduces stress and fatigue, and improves self-esteem. Stress and depression can contribute to the development of diabetes, and relieving them with exercise is an important part of diabetes management. Although a person who is inactive must start slowly and carefully, a 2016 study found that any amount of exercise helps reduce risk of diabetes but that those who exercise the recommended 150 minutes a week or more lowered their risk more.
Diabetes is a chronic condition in which insulin production or the body's responses to insulin are inadequate, causing high blood sugar (glucose) levels. Type 1, juvenile, or insulin-dependent diabetes, which usually develops in young people, is an autoimmune disease in which the pancreas produces little or no insulin. Type 2 diabetes, which accounts for 90–95% of all diabetes cases, is usually caused by the development of insulin resistance, in which the cells of the body stop responding adequately to insulin. Although type 2 diabetes links strongly to family history and likely involves changes in genes, it also is associated with obesity and lack of physical exercise. Over time, high blood sugar levels from diabetes can cause serious health complications, including high blood pressure, heart disease, stroke, kidney disease, nerve damage (neuropathy), and blindness.
For competitive athletes with diabetes, managing blood glucose levels is a major concern. Training and competition lower blood sugar levels, often requiring insulin dosages to be lowered to prevent hypoglycemia (dangerously low blood sugar). Long-duration exercise can cause blood glucose levels to drop during exercise and up to 30 hours afterward. However, high-intensity exercise, as well as the stress and excitement of competition, induces surges of epinephrine (adrenaline), which causes blood sugar levels to rise.
By regularly monitoring their blood sugar levels during training and competition, most athletes develop detailed knowledge of how exercise of various intensities and duration affects their glucose levels. They learn exactly how to adjust their insulin dosages and intake of carbohydrates to compensate for exercise-induced effects. Some athletes check their blood sugar 30–60 minutes before training, to determine whether to ingest protein and fat, such as peanut butter, to slow digestion and encourage a slow, steady rise in blood sugar to match the exercise-induced decline. Other athletes sip sports drinks throughout training. Although athletes who train daily might not need to adjust their insulin, many athletes check their blood sugar levels numerous times during daily training and competition. The balance of insulin and carbohydrate intake must be recalculated whenever a new training routine or activity is initiated.
Many athletes with diabetes use an insulin pump or a pump combined with long-acting insulin, with a special pack to keep the pump in place. They learn exactly how much to drop the pump rate to compensate for exercise of specific intensities. However, some types of competition do not permit insulin pumps. Most endurance athletes carry glucose to head off hypoglycemia. Cold-weather sports, such as skiing and mountaineering, require glucometers and insulin to be kept close to the body for heat, since insulin can freeze and glucometers are not accurate in the cold.
Because competitions differ from training routines, and the break in regular training can itself cause glucose levels to rise, athletes with diabetes may practice competition routines to predict their blood glucose levels better. Some endurance athletes and triathlon competitors are accompanied by medical teams. Others maintain a cell phone link with a diabetes educator during races or have friends along the course to provide carbohydrates and fluids. Some athletes use a continuous glucose monitoring (CGM) system. This is a tiny sensor that can be inserted under the skin for up to a week to measure the glucose level in tissue fluid every few minutes and signal significant changes or readings that exceed preset limits.
Athletes with diabetes, such as professional baseball player Sam Fuld, are important role models for young people with diabetes. Fuld was diagnosed with type 1 diabetes while in Little League and has credited his childhood of insulin scheduling and logging food intake with instilling the discipline required for achievement in sports. Monique Hanley, a distance cyclist and track competitor, helped found HypoActive to promote sports for people with diabetes. Chris Dudley, who played in the NBA for 16 years, founded a basketball camp for children with type 1 diabetes.
People with diabetes must learn how exercise of varying intensity and duration affects their blood glucose levels and how to adjust their insulin or other medication dosages and food intake before, during, and after exercise to avoid hypoglycemia or hyperglycemia. It is important to know how to respond to potentially dangerous changes in blood sugar levels. Exercise should be avoided when insulin is at its peak level. Insulin should never be injected into a part of the body that is being exercised. Fast-acting carbohydrates such as glucose tablets, hard candies, sugar, soda, or fruit juice should always be on hand when people with diabetes are exercising. Larger or more frequent snacks such as nuts, peanut butter, or cheese and crackers are required if these individuals are exercising more than usual. People with diabetes must drink sufficient water before, during, and after exercise.
People with type 1 diabetes should avoid vigorous exercise if their urine or blood tests are positive for ketones, since exercise can further increase moderate or high ketone levels. Urine should be checked for ketones before exercising if individuals are feeling ill or if their blood sugar remains above 240 milligrams per deciliter (mg/dL) or about 13 millimoles per liter (mmol/L). Exercise should probably be avoided in very hot or very cold weather.
Parents, teachers, and coaches must ensure that children and those newly diagnosed with diabetes check their glucose levels frequently. They should watch for signs of sudden highs or lows when the children are playing sports. Signs may include flushing or paleness, shakiness or lethargy, failing to pay attention, or uncharacteristic behaviors.
People with diabetes can participate in most sports and types of exercise. An eye exam is necessary before beginning an exercise program, since some types of exercise can worsen diabetic eye diseases. Weightlifting and jogging can increase pressure in the eyes of those with severe eye problems, and boxing is usually inappropriate because of the risk of eye injury. Exercise can also worsen kidney and nerve problems. High-impact exercise, such as marathon running, can be hard on the cartilage of the joints.
People with diabetes must plan ahead for exercise. Generally, exercise should be delayed until at least 30 minutes after a meal. Often one to three hours after a meal is best, although a high-protein snack may be appropriate before exercise. Blood sugar should be checked before exercising. In most cases, the insulin dose is reduced. If blood sugar is below 100 mg/dL (5.6 mmol/L), a snack of at least 15 g of carbohydrates might be necessary before exercising, and it may be necessary to delay exercise until blood sugar has risen. Some athletes test their blood sugar twice before training to determine which direction their levels are headed and plan accordingly. Warm-ups, 5–10 minutes of slowly increasing the heart rate by walking, for example, should always immediately precede an exercise routine. Blood sugar should be checked after the warm-up. The blood sugar level should be checked again during exercise lasting more than 45 minutes.
Exercise should be concluded with a 5- to 10-minute gradual cool-down and stretching, followed by a blood glucose check. Levels should be checked later on as well, since an exercise-induced glucose drop might not occur for some hours. If blood glucose levels are low, a small carbohydrate snack and/or juice should be consumed after exercising.
With careful monitoring and control, people with diabetes can usually participate in even the most intense exercise without complications. However, poor blood glucose control can render patients too fatigued to exercise. Foot problems are a common complication of exercising with diabetes and can become serious if untreated.
The health benefits of exercise might not become apparent for several months. However, research indicates that one hour of exercise in the afternoon can maintain a lower blood sugar level until the next morning. People with diabetes who are well-versed in their body's responses can sometimes use exercise as a primary method of controlling blood glucose levels. For individuals with diabetes trying to increase their physical activity, strategies such as breaking exercise up into a few time periods or types of activities can help them stick with their plan to exercise.
Research results indicate that increasing muscle mass can lower the risk of developing type 2 diabetes. One study found that for each 10% increase in skeletal muscle index (the ratio of muscle mass to total body weight) there was an 11% reduction in insulin resistance and a 12% reduction in the incidence of prediabetes.
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Margaret Alic, PhD
Revised by Teresa G. Odle, BA, ELS