A comprehensive search of various electronic databases for relevant English-language, published, peer-reviewed studies was performed by chapter authors and independently by a librarian using validated search strategies. Full details of the search are included in the Canadian Diabetes Association guidelines.1 Each citation referenced in a new or modified recommendation was assigned a level of evidence by use of standardized checklists. Health benefits, risks and adverse outcomes of interventions were considered in the formulation of the recommendations. Recommendations were assigned a grade from A through D based on the relative strengths of the studies from a methodologic perspective and the studies' findings (Box 1, Table 1).

Certain medications have an independent effect on the risk of cardiovascular morbidity and mortality in addition to their effect on risk factors. The Heart Outcomes Prevention Evaluation (HOPE) study15 demonstrated the benefit of angiotensin-converting-enzyme (ACE) inhibition in people with diabetes who are at high risk for cardiovascular disease. A more recent study16 suggested that the effect of angiotensin-receptor blockers is comparable to that of ACE inhibitors in high-risk groups with diabetes. As a consequence, the updated guidelines recommend the use of ACE inhibitors or angiotensin-receptor blockers at doses shown to be cardioprotective for people at high risk of cardiovascular events, even in the absence of hypertension (grade A, level 1A for those with cardiovascular disease; grade B, level 1A for those in other high-risk groups) (Box 3).

Strict control of blood pressure has a large impact on morbidity and mortality in patients with diabetes.19–21 An observational study found that blood pressure control had a greater impact on quality-adjusted life-years than strict control of cholesterol or glycemia.22 The 2008 guidelines recommend that blood pressure be measured at every patient visit (grade D, consensus) and that hypertension be diagnosed according to the national hypertension guidelines (Box 4).23 The treatment targets remain a systolic blood pressure of less than 130 mm Hg (grade C, level 3) and a diastolic pressure of less than 80 mm Hg (grade B, level 2), irrespective of kidney function. First-line treatments include ACE inhibitors, angiotensin-receptor blockers, thiazides (grade A, level 1A for each) and dihydropyridine calcium-channel blockers (grade B, level 2). An ACE inhibitor or angiotensin-receptor blocker is recommended as initial treatment in the presence of microalbuminuria (grade A, level 1A). They are favoured because of demonstrated cardioprotective benefits (grade A, level 1A).

Large cohort studies have found that regular physical activity is associated with 39%–70% reductions in cardiovascular and all-cause mortality over 15–20 years of follow-up.43–46 The effect of simply recommending that patients exercise more (which is what most clinicians do) is less certain.47 Structured physical activity counselling by physicians or health care providers has been effective in increasing physical activity and producing modest, sustained weight loss.48–51 The recommendation of 150 minutes of moderate to vigorous aerobic exercise spread over 3 days a week (grade B, level 2) is unchanged from the 2003 guidelines (Box 5). The guidelines also recommend resistance exercise 3 times a week in addition to aerobic exercise (grade B, level 2); resistance exercise can be helpful for people with limited mobility. Finally, a cardiac stress test should be considered for previously sedentary people at high risk of cardiovascular disease who wish to undertake exercise more vigorous than brisk walking (grade D, consensus).

The degree of benefit from a medical intervention is based on the absolute risk of vascular events, with patients at higher risk deriving greater benefit.7 The 2008 guidelines state that men aged 45 or more years with diabetes and women aged 50 or more years with diabetes should be considered to be at high risk of cardiovascular disease (grade B, level 2 evidence). This represents a 20% risk of vascular events over a 10-year period, including nonfatal myocardial infarction or cardiac death.14 These age cutoff points are easy to ascertain and capture most patients at high risk who are most likely to benefit from intervention. Patients below these cutoff points who have 1 or more risk factors for cardiovascular disease are also considered to be at high risk (Box 2). This recommendation is more precise than that in the 2003 guideline, and it reflects a compromise between effectiveness (saving as many lives as possible) and efficiency (minimizing treatment given to people who will derive little or no benefit). Patients aged 40 or more years or with a more than 15-year history of diabetes should have baseline resting electrocardiography performed, and it should be repeated every 2 years for those at high risk (both grade D, consensus). Patients with an abnormal electrocardiography result or chest pain should be referred for stress testing, and those with ischemia at low exercise capacity (< 5 metabolic equivalents) should be referred to a cardiologist (grade D, consensus). The guidelines do not provide other explicit criteria for referral to a specialist.