Prediabetes and type 2 diabetes mellitus

The incidence of type 2 diabetes mellitus is high, primarily as a consequence of adverse health behaviour (eg, sedentarism, increased consumption of energy-dense foods), and unfortunately the incidence is expected to increase further in all age groups over the next few decades, possibly affecting 2.5 million Canadians by the year 2016.¹ Statistics Canada currently estimates that some 6% of male and 5% of female Canadians older than 12 years of age have been diagnosed with diabetes,² and this is likely a conservative estimate of disease prevalence, given the large number of undiagnosed cases that long remain undetected owing to a lack of overt symptoms. The prevention, diagnosis, and management of type 2 diabetes, and its associated metabolic disorders, are likely to make ever greater demands upon health care professionals, with an increase in the case load of metabolic dysregulation driven by an aging population, a diversifying ethnic milieu, and a growing prevalence of the condition in young people.

There is compelling evidence that prediabetes (characterized by impaired fasting glucose or impaired glucose tolerance), metabolic syndrome, and type 2 diabetes can all be both prevented and treated^3–5 by an increase in patients’ habitual physical activity (PA). Nevertheless, preliminary “safety” screening issues and the subsequent supervision of exercise programs for patients with type 2 diabetes remain concerns in general practice.⁶ Some health care providers and patients believe that exercise itself can pose certain risks for individuals with type 2 diabetes. This article provides an executive summary of findings from a systematic review of the risks of PA in prediabetes and diabetes⁷; it is one in a comprehensive series of reviews examining the risks of PA in patients with various chronic diseases. The evidence obtained from this review provides the foundation for new tools that will simplify the task of exercise clearance: the revised Physical Activity Readiness Questionnaire (PAR-Q+)⁸ and the electronic Physical Activity Readiness Medical Examination (ePARmed-X+) procedure.⁹ Here we will briefly discuss the available published data on the risks of PA in prediabetes and type 2 diabetes, as well as present decision trees that help family physicians provide appropriate prescription of PA and that offer guidance for appropriate ongoing monitoring of patients.

Diabetes is frequently associated with both microvascular and macrovascular disease; depending on their extent, such pathologies can challenge the function of many organs and body systems, particularly the heart. The risks of cardiovascular disease (CVD) and secondary organ damage (eg, kidney, nerve, retina) have long been thought to place those with diabetes at a greatly increased risk of PA-related adverse events. Evidence suggests that glucose control (as indicated by hemoglobin A_1c concentrations) is directly linked to the chances of experiencing a cardiovascular event, with the risk increasing progressively with each 1% increase of hemoglobin A_1c above normal values.¹⁰ Moreover, if a cardiac event does occur, the subsequent prognosis of patients with diabetes is typically worse than that in patients who do not have metabolic dysregulation.¹¹ Large-scale retrospective and epidemiologic studies present conflicting results on the safety of PA in diabetes: acute exercise (> 6 metabolic equivalent task units) has been linked temporally to the occurrence of myocardial infarction¹²; but on the other hand, diabetes apparently had no effect on the presentation of adverse events during cardiac rehabilitation in almost 700 000 participants.¹³

Discussion

Thorough systematic review of the published literature on exercise testing and training in patients with prediabetes and type 2 diabetes revealed no evidence of any PA-related deaths and a very low incidence of non–life-threatening adverse events. This seems to suggest that nonvigorous (mild to moderate) PA is relatively safe in these individuals, despite their increased baseline risk of microvascular and macrovascular conditions, including CVD, nephropathy, and retinopathy. However, probably because of the perceived risks of exercise in this population, most published randomized control research studies carefully screened out their “high-risk” participants and included only those patients with few comorbidities (and specifically excluded individuals with advanced CVD). Moreover, exercise was generally limited to either mild or moderate intensity, with close clinical supervision. These caveats must be considered when assessing the evidence on the risks of PA for this class of patients.

Given available evidence on the incidence of PA-related adverse events in patients with impaired metabolic control, we conclude that the acute adverse event risk increases during and immediately following each bout of PA, but that in the long term, risk progressively decreases as the patient persists with regular PA, as in healthy individuals. Although, the overall risk from PA appears to be low, it is important to consider individual patient characteristics such as age, diabetes-related complications and comorbidities, current and past metabolic control, and current lifestyle (eg, activity levels, smoking status), which can modify the risk of an adverse cardiovascular event. Specific recommendations for PA in patients with either prediabetes or diabetes (Tables 1 and 2,^14,15 respectively) must take into account these potential modifications of risk and are now provided in a new evidence-informed decision tree. These decision trees assist with risk assessment when initiating or increasing PA in patients with prediabetes and diabetes, and take into account the varying levels of information about individual patients that might be available to the family physician (Figures 1 and 2). We also reference the UKPDS (United Kingdom Prospective Diabetes Study) risk engine, an online tool (www.dtu.ox.ac.uk) to assist health care providers in determining the risk of future CVD events¹⁴ in type 2 diabetes. Previous guidelines (from the American College of Sports Medicine and American Heart Association¹⁶) have called for screening to include noninvasive exercise stress testing in all asymptomatic individuals with 2 or more coronary risk factors (including hyperglycemia), and in all patients older than 40 years of age with only 1 CVD risk factor. We regard this recommendation as too conservative, and perhaps financially and logistically questionable; moreover, this sort of stress testing will likely present a considerable barrier to increased PA in those who would benefit the most from such a change of lifestyle (see the article by Riddell and Burr⁷ for a full discussion). In our decision trees, we propose a modified screening approach, using an evidence-based approach and the UKPDS risk engine to predict the risk of a cardiovascular event in any given patient.

• Download figure
• Open in new tab

Figure 1

Clinical decision tree for assessing the risk of adverse events during PA in patients with prediabetes: This decision tree can be used to categorize a patient as high, moderate, or low risk, informing both the requirements of PA prescription and the monitoring of exercise programs.

PA—physical activity.

• Download figure
• Open in new tab

Figure 2

Clinical decision tree for assessing the risk of adverse events during PA in patients with type 2 diabetes mellitus: This decision tree can be used to categorize a patient as high, moderate, or low risk, informing both the requirements of PA prescription and the monitoring of exercise programs.

HDL-C—high-density lipoprotein cholesterol, PA—physical activity, UKPDS—United Kingdom Prospective Diabetes Study.

View this table:

• View inline
• View popup

Table 1

PA and exercise recommendations for prescreening in individuals with prediabetes

View this table:

• View inline
• View popup

Table 2

PA and exercise recommendations for prescreening in individuals with type 2 diabetes

• Copyright© the College of Family Physicians of Canada