Exercise and Diabetes. Sheri R. Colberg

lower than those classified as diabetes. About 25% of individuals with prediabetes will develop type 2 diabetes (T2D) within 3 to 5 years (U.S. Department of Health and Human Services 2011). Moreover, it is now estimated that one in three Americans born in the year 2000 or later will develop diabetes during their lifetimes, with rates closer to 50% in high-risk, ethnic populations (Narayan 2003, 2006).

      In spite of the salutary effects of achieving optimal blood glucose control, only slightly more than half of individuals with diabetes currently are reaching recognized treatment goals (Cheung 2009). Although physical activity has long been considered a cornerstone of diabetes management and a critical factor in optimizing treatment, prescribing specific exercise for individuals with various types of diabetes (or even prediabetes) can be a daunting task for the time-pressured health-care provider or the diabetes-naïve fitness professional. A fundamental need in facilitating such exercise prescription is an enhanced understanding of the types of diabetes and how physical activity requirements and abilities may differ among them.

      Case in Point: Weight, Blood Pressure, and T2D

      MJ, a 48-year-old woman diagnosed with T2D 4 years ago, is having trouble controlling her weight and blood pressure. She wants to discuss safe and appropriate ways to be more physically active to address these issues and improve her overall health and diabetes management. From her physician, she already has received medical clearance to start increasing her activity level with no specific restrictions. Her medications include a sulfonylurea (glipizide) and an antihypertensive agent. MJ reports testing her blood glucose usually just once a day in the morning before breakfast. She currently is not doing any planned exercise and has not been active for the past 10 years or so, although she claims to be motivated to start being more physically active now to increase her energy levels.

       Resting Measurements

      Height: 64 inches

      Weight: 190 lb

      BMI: 32.6 kg/m² (obese)

      Heart rate: 85 beats per minute (bpm)

      Blood pressure: 138/86 mmHg (on medication)

       Fasting Labs

      Plasma glucose: 148 mg/dl A1C: 7.4%

      Total cholesterol: 190 mg/dl

      Triglycerides: 200 mg/dl

      High-density lipoprotein cholesterol: 38 mg/dl

      Low-density lipoprotein cholesterol: 112 mg/dl

       Questions to Consider

      1. How should MJ go about increasing her physical activity level?

      2. Does MJ need to take any precautions related to exercise participation?

      3. What strategies will help motivate MJ and support her efforts to establish regular physical activity as a lifelong habit?

      (Continued)

      BASICS OF DIABETES SELF-MANAGEMENT

      Effective management of any type of diabetes involves use of self-monitoring of blood glucose (SMBG), administration of appropriate medications to regulate blood glucose levels, regular participation in physical activity and exercise, and body weight management, as well as dietary and other lifestyle improvements, for example, stress management (St John 2010, American Diabetes Association 2013b). Regular physical activity facilitates improved blood glucose control in T2D and may offer a similar benefit in gestational diabetes mellitus (GDM) (Dyck 1998, Davenport 2008, Colberg 2010). Although regular exercise does not uniformly improve glycemic management in those with type 1 diabetes (T1D) unless appropriate regimen changes are made, exercise is still considered a safe and effective adjunct therapy for diabetes management and complication prevention (American Diabetes Association 2013b). Exercise interventions for individuals with diabetes ideally should involve a multidisciplinary team of specialists that includes the diabetes (or other qualified) physician, certified diabetes educator, registered dietician, and exercise professional to facilitate individual education and lifestyle changes to manage this disease. Self-management skills are essential to success, and diabetes education is an important tool to improve glycemic control, regardless of the type of diabetes that an individual has (American Diabetes Association 2013b).

      CLASSIFICATION AND ETIOLOGY OF DIABETES

      Four classifications of diabetes are categorized based on etiology: T1D, T2D, GDM (diagnosed during pregnancy), and diabetes resulting from other specific origins (e.g., genetic defects, drugs and chemicals, pancreatic disease, surgery, and infections). The major types are T1D and T2D, with the latter type describing 90–95% of all cases, whereas T1D accounts for only 5–10% of the population with diabetes (American Diabetes Association 2013a). The major characteristics of these classifications are given in Table 1.1.

      Table 1.1 Characteristics of T1D, T2D, and Gestational Diabetes

       T1D

      T1D is caused by autoimmune destruction of pancreatic β-cells usually leading to an absolute deficiency of insulin secretion and likely triggered by environmental factors that remain poorly defined or predicted (American Diabetes Association 2013a). Formerly called juvenile-onset or insulin-dependent diabetes, T1D is commonly diagnosed in children and adolescents, but this immune-mediated type of diabetes can occur in individuals of any age. About half of the cases of T1D currently are being diagnosed in adults and frequently are diagnosed and classified as latent autoimmune diabetes of the adult (LADA). Rates of β-cell destruction involved in the onset of T1D generally are slower in older-onset cases than in youth—thus giving rise to the LADA category, which is still not clearly defined or universally used. In addition, many older individuals with this type of diabetes initially may be misdiagnosed with T2D instead.

       T2D

      Insulin resistance is the hallmark of T2D, and the risk of developing it increases with age, obesity, and physical inactivity. Genetic and environmental factors are strongly implicated in the development of T2D, but they are complex and not clearly defined. Some β-cell dysfunction or β-cell loss is evident at onset, leading to relative rather than absolute defects in insulin secretion (American Diabetes Association 2013a). This type of diabetes disproportionately affects ethnic minorities: its prevalence rates are about twofold greater in Hispanic and Latino, African American, Native American, Asian, and Pacific Islander populations than in non-Hispanic whites (U.S. Department of Health and Human Services 2011). It is also more common in individuals with hypertension or dyslipidemias and in women with a prior history of GDM (American Diabetes Association 2013a). Formerly called adult-onset or non–insulin-dependent diabetes and associated with older age, this type of diabetes leads many individuals to become insulin-requiring over the course of the disease. Moreover, its diagnosis in youth has risen dramatically over the past two decades. The initial diagnosis of T1D in children and adolescents can be complicated by the presence of insulin resistance and obesity, although recognition of T2D in youth may be delayed by the misconception that only adults can develop it.

       Gestational Diabetes

      GDM is also on the rise and is associated with a 40–60% chance of the mother developing T2D in the next 5 to 10 years (U.S. Department of Health and Human Services 2011, American Diabetes Association 2013a). Moreover, it is known to be potentially harmful to both mother and fetus if not controlled (Hapo Study Cooperative Research Group 2008, Metzger 2010). For example, larger or fatter infants have been shown to be more likely to develop both hypoglycemia and hyperinsulinemia in the few hours following birth, suggesting a strong relationship between maternal glycemia and fetal insulin production (Metzger 2010). It is generally diagnosed with a 75 g oral glucose tolerance test (OGTT) that is given to all women not known to have prior diabetes at 24–28 weeks of gestation. Given the rise in prevalence of undiagnosed T2D among women of childbearing age, however, it is now reasonable to screen women with diabetes risk factors at their initial prenatal visit. Women