Exercise Can Improve Glycemic Control: How to Get Patients Started

The prevalence of diabetes is increasing in epidemic proportions. Nearly 26 million people in the United States currently have diabetes.¹ Of those, the disease has been diagnosed in approximately 18.8 million—and about 7 million have undiagnosed disease. Moreover, more than 1.9 million new cases occur annually. An additional 79 million people have prediabetes (defined as either impaired fasting glucose, indicated by a glucose level of 100 to 126 mg/dL after an overnight fast, or as impaired glucose tolerance, indicated by a glucose level of 140 to 199 mg/dL after a 2-hour oral glucose tolerance test). The overwhelming majority of persons with diabetes—nearly 90%—have type 2 diabetes.

THE BURDEN OF DIABETES

The healthcare cost of diabetes is significant; according to the Centers for Disease Control and Prevention, approximately $116 billion is spent on direct medical costs, and another $58 billion is spent on other costs associated with the disease, such as missed days of work and a subsequent loss in productivity.

Diabetes is associated with significant morbidity and mortality. Adults with diabetes are 2 to 4 times more likely to have heart disease or stroke. Diabetes is now considered a cardiac risk factor equivalent—the excess risk of fatal coronary heart disease for patients with diabetes is nearly equivalent to those without diabetes who have had a previous coronary event.²

OBESITY AND TYPE 2 DIABETES

The dramatic increase in type 2 diabetes is partly due to the increased prevalence of obesity. Most patients with diabetes are overweight.³ Moreover, adults with diabetes are more than 3 times more likely to be morbidly obese (body mass index of more than 40) than adults without diabetes and more than 1.5 times more likely to be obese (body mass index of 30.0 to 39.9).

Since obesity is a function of energy intake and output, it is important that patients maintain a healthy diet and be physically active. Obesity is partly related to physical inactivity. As a result, increasing activity or exercise may decrease the rising incidence of type 2 diabetes.

Until recently, many medical professionals believed that patients with diabetes should not engage in exercise programs, in view of the increased risk of hypoglycemia that is associated with exercise, especially in persons with type 1 diabetes. When patients with diabetes have inadequate insulin, there is an excessive release of counter-regulatory insulin hormones. Physical activity may increase already high levels of glucose and ketone bodies and thereby precipitate ketoacidosis. However, although there is a risk of hypoglycemia, the benefits of physical activity exceed that risk.

BENEFITS OF EXERCISE

In people with type 2 diabetes, exercise can improve peripheral insulin sensitivity as well as enhance insulin binding. Exercise also decreases abdominal fat, reduces free fatty acids, and increases insulin-sensitive skeletal muscle, which may result in improved glycemic control. Of note, it has been shown that these improvements disappear a few days after exercise is discontinued. Therefore, it is imperative that patients realize that exercise is an activity they must incorporate into their lives.

It has been demonstrated that patients with type 2 diabetes who did not exercise were more likely to die during a 12-year period than their more active, physically fit counterparts.⁴ Exercise is associated with improved control of blood pressure and of glycosylated hemoglobin (HbA_1c) and cholesterol levels. Clearly, people with diabetes can benefit from exercise.

GUIDELINES FOR EXERCISE

Most patients with diabetes can exercise safely. However, it is important for patients to undergo detailed medical screening before beginning any exercise regimen. The American Diabetes Association along with the American College of Sports Medicine recently published a joint position statement on exercise and diabetes, including guidelines about pre-exercise evaluation.⁵

For patients who wish to participate in low-intensity physical activity, such as walking, health care providers should use clinical judgment in deciding whether to recommend pre-exercise testing. For exercise more vigorous than brisk walking or exceeding the demands of everyday living, sedentary and older patients with diabetes will likely benefit from being assessed for conditions that might be associated with risk of cardiovascular disease (CVD), contraindicate certain activities, or predispose to injuries, including severe peripheral neuropathy, severe autonomic neuropathy, and preproliferative or proliferative retinopathy. Before undertaking new higher-intensity physical activity, they are advised to undergo a detailed medical evaluation and screening for blood glucose control, physical limitations, medications, and macrovascular and microvascular complications.

In general, the American Diabetes Association recognizes that most persons with type 1 and type 2 diabetes can and should participate in regular physical
activity.

It is important for patients to work closely with their physicians when starting any exercise regimen; exercise may necessitate a reduction in insulin requirements for those with type 1 diabetes, because exercise has an insulin-like effect. Therefore, exercise-induced hypoglycemia can occur in patients with diabetes who take exogenous insulin. Subsequently, patients should monitor their blood glucose level more closely when initiating an exercise program, as the level will be affected by the duration and intensity of activity.

Aerobic exercise. Although all types of exercise should be discussed with patients with diabetes, keep in mind that most research has focused on aerobic exercise. Numerous studies have documented the benefit of such exercise for this population. Gregg and colleagues⁶ demonstrated that patients with diabetes who walked at least 2 h/wk, compared with inactive individuals, had a 30% lower all-cause mortality rate and a 34% lower CVD mortality rate. The lowest mortality rates were for persons who walked 3 to 4 h/wk and for those whose walking regimen involved moderate increases in their heart and breathing rates. Therefore, at a minimum, physicians should emphasize aerobic exercises, such as walking, when counseling patients with diabetes.

One simple suggestion for patients is that they should use a pedometer, which is an inexpensive tool that has been shown to be effective. Patients are recommended to walk 10,000 steps daily, which translates to approximately 5 miles. This number is based on studies that show 10,000 steps daily improves cardiovascular fitness. On average, most people take less than 5000 steps daily; therefore, 10,000 steps will represent a significant increase in activity.

Recommending that patients walk 10,000 steps daily provides them with a simple goal—if, near the end of the day, they have not walked 10,000 steps, they should walk, go up and down the stairs, or march or jog in place until they reach the goal. Pedometers are also beneficial because they provide patients instant feedback on a daily basis that allows them to continually revise their program.

Researchers estimate that 1 death per year may be preventable for every 61 people who could be persuaded to walk at least 2 h/wk, which is around 25 min/d, 5 d/wk. Moreover, the Diabetes Prevention Program has suggested that overweight persons who exercise for 30 min/d, 5 d/wk and make moderate dietary changes cut their risk of diabetes to half of that for overweight individuals with high blood glucose.⁷ These findings are on par with the current physical activity recommendations from the US Surgeon General for general health.

Exercise counseling is best when it is specific. A walking program can help condition patients by gradually increasing the frequency, time, and the distance they walk (Box).

In a meta-analysis of 12 aerobic training studies and 2 resistance-training studies, Boule and colleagues⁸ showed that exercise training reduced glycosylated hemoglobin by an amount that should decrease the risk of diabetic complications. Hu and colleagues⁹ examined the relationship of total physical activity and incidence of type 2 diabetes in women as part of the Nurses’ Health Study. The study subjects were surveyed about their level of aerobic activity, and data from women whose primary exercise was walking were compared with data from those who engaged in more vigorous activities such as jogging, bicycling, or swimming. At the end of the study, aerobic exercise decreased the risk of type 2 diabetes, and greater physical activity was associated with a substantial reduction in diabetes risk.

Strength training. Some data indicate that strength training may aid people with type 2 diabetes. Because some patients who have poor endurance and are overweight find it difficult to engage in aerobic activity, strength training may be helpful in improving their functional capacity and their physical strength for increasing aerobic activity. Holten and colleagues¹⁰ studied 10 patients with type 2 diabetes and 7 healthy men to determine the effects of a 6-week strength-training program on diabetes. The researchers found that study participants who performed strength training for 30 minutes three times per week demonstrated increased insulin action in skeletal muscle.

Castaneda and colleagues¹¹ studied 43 Hispanic patients with type 2 diabetes during a 16-week resistance-training program. At the end of the study, patients who completed the program, compared with a nonexercising control group, demonstrated a significant reduction in HbA_1c as well as a decrease in fasting insulin levels and waist circumference.

The American College of Sports Medicine recommends that persons with type 2 diabetes should undergo resistance training at least 2 d/wk as part of a well-rounded exercise program. A minimum of 8 to 10 exercises involving the major muscle groups should be performed, with each exercise including a minimum of one set of 10 to 15 repetitions maintained to near fatigue.¹² The American Diabetes Association recommends for nearly all patients with diabetes a moderate weight training program that involves light weights and many repetitions for maintaining or enhancing upper-body strength.¹³

Gestational diabetes. Exercise may also be beneficial for patients with gestational diabetes. Aerobic exercise has been shown to decrease the need for insulin in patients with gestational diabetes. Some data suggest that resistance exercise can improve insulin sensitivity, glucose disposal rate, and glycemic control. Brankston and colleagues¹⁴ evaluated the effects of circuit-type resistance training on the need for insulin in 32 women with gestational diabetes who were randomly assigned to either diet or diet plus resistance exercise. The exercise program consisted of 8 exercises performed in a circuit, typically 2 to 3 sets of 15 repetitions performed 3 times per week. At the end of the study, the amount of insulin prescribed was significantly lower in the diet-plus-exercise group, and their initiation of insulin therapy was longer.

CONCLUSION

In addition to a healthy diet, patients with diabetes need to adopt a healthy exercise regimen. Walking is a simple activity that does not require any special equipment or training, and it has been shown to reduce morbidity and mortality. Strength training is also an important component of a well-rounded exercise program and has independently been shown to produce benefits in those with diabetes, such as reduced HbA_1c levels, increased insulin sensitivity, and improved fasting blood glucose levels. Regular physical activity is crucial for maintaining optimal health and vitality, especially in patients with diabetes. It is therefore imperative to discuss the benefits of exercise with patients who have diabetes.