Racial and ethnic minorities in the US are disproportionately afflicted with diabetes (see Figure 1 and Table 1) and type-2 diabetes is considerably more common in African-Americans than in whites.3–5 In the Atherosclerosis Risk in Communities Study, the incidence of diabetes was 2.4 times greater in African- American women and 1.5 times greater in African- American men than in their white counterparts.6
Racial and ethnic minorities in the US are disproportionately afflicted with diabetes (see Figure 1 and Table 1) and type-2 diabetes is considerably more common in African-Americans than in whites.3–5 In the Atherosclerosis Risk in Communities Study, the incidence of diabetes was 2.4 times greater in African- American women and 1.5 times greater in African- American men than in their white counterparts.6
Diabetes also disproportionately affects Hispanics in the US.7 Hispanic/Latino Americans are 1.5 times more likely, with Mexican Americans—the largest Hispanic/Latino subgroup—more than twice as likely to have diabetes as non-Hispanic whites of similar age. Residents of Puerto Rico are also 1.8 times more likely to have diagnosed diabetes than non-Hispanic white Americans. Although studies have determined that overweight and obesity contribute heavily to racial/ethnic disparities in diabetes prevalence, Hispanics still have higher prevalence of diabetes than non-Hispanic whites at each level of body mass index (BMI).8With the presence of obesity, insulin resistance and diabetes in Hispanic Americans, it is expected that rates of CHD will markedly increase over the next several years. Native Hawaiians—and Japanese and Filipino residents of Hawaii—are also at double the risk of having diagnosed diabetes compared with white Hawaiian residents. Even at low levels of BMI, many Asian populations appear to be susceptible to the development of excessive abdominal obesity, which causes them to develop insulin resistance at lower thresholds than those of Caucasians9 and, as a consequence, Asian populations are seeing increasing rates of diabetes.10 Native Americans have the highest rates of diabetes, at 16%, which is more than double (2.2 times) the prevalence in non-Hispanic whites of similar age. Mortality rates due to diabetes, however, are highest in African-Americans, which is most probably due to the presence of concomitant risk factors, most prominently comorbid hypertension.11–13 It is expected, with the persistent growth of minority populations, that the epidemic of diabetes and subsequent cardiovascular disease (CVD) will only continue to rise over the next few decades.
Management of Cardiovascular Risk Factors
Lifestyle Modification
Numerous studies have shown that attention to lifestyle modification can dramatically reduce progression to type-2 diabetes.14–16 However, this can be particularly challenging in racial and ethnic minority groups and the rise in the rate of obesity has been greatest in minorities. Achieving and sustaining weight loss is often very challenging, but remains extremely important in reducing the cardiovascular risk associated with type-2 diabetes17 and it has been suggested in at least one study of overweight patients with type-2 diabetes that intentional weight loss may lead to as much as a 25% reduction in total mortality over 12 years.18 Current guidelines also recommend regular, moderate physical activity and here, too, all cardiometabolic risk factors improve with sustained physical activity.19 In particular, the Diabetes Prevention Program11 showed that walking 30 minutes a day, six days a week—combined with dietary changes, with average weight loss of 5% or 7%—led to a reduction in diabetes of approximately 60%.20 Racial and ethnic minority groups are often culturally bound to diet and physical activity habits, and the clinician needs to be aware of these potential barriers when attempting to identify and manage these factors.
Hypertension
Both the American Diabetes Association and the Seventh Report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure set the target goal of <130/80 millimetres of mercury (mmHg) in patients with diabetes. Most patients with type-2 diabetes and elevated blood pressure will require two or more agents to lower blood pressure to the recommended goal of <130/80mmHg21, which is particularly the case for African-Americans.22 Initial drug therapy should utilize agents that have been demonstrated to reduce CVD and renal risk in patients with diabetes, including angiotensin-converting enzyme (ACE) inhibitors, angiotensin II receptor blockers (ARBs), beta-blockers, diuretics and calcium-channel blockers (CCBs).21 Considering the increased risk of CHD with type-2 diabetes, beta-blockers, and ACE inhibitors should be considered as initial therapy for hypertension, especially in patients >55 years of age or with documented atherosclerosis.23,24 There was concern that thiazide diuretics may cause glucose intolerance and new-onset diabetes. However, in the diabetic cohort of The Antihypertensive and Lipid-Lowering Treatment to Prevent Heart Attack Trial, chlorthalidone—a thiazide-type diuretic—was effective in preventing CVD. Recent evidence has suggested that blockers of the renin-angiotensin system may actually prevent new-onset diabetes, although the recent Diabetes Reduction Assessment with Ramipril and Rosiglitazone Medication has not confirmed this.25 Within African-Americans, the antihypertensive responsiveness to monotherapy with ACE inhibitors, ARBs, and beta-blockers may be less than the response to diuretics and CCBs, but these differences are corrected when diuretics are added to the neurohormonal antagonists. The International Society on Hypertension in Blacks has crafted guidelines and an algorithm to guide ideal management of high blood pressure in African Americans.22 Of note, however, African-American patients with systolic blood pressure >15mmHg or a diastolic blood pressure >10mmHg above goal should be treated with first-line combination therapy. Also currently emerging are data on South Asians and their high rates of CHD, which may be due to their high rates of hypertension, although this is reported mainly from non-American epidemiological studies.26 The World Health Organization has reported that Indian men in the age range of 40 to 55 years have the highest blood pressure among populations from 20 other developing countries, but more information is clearly needed.27
Dyslipidemia
Multiple clinical trials have demonstrated the benefit of statin therapy in patients with type-2 diabetes and elevated low-density lipoprotein cholesterol (LDL-C), particularly in secondary prevention of CVD.28–31 In the Heart Protection Study (HPS), diabetic participants showed a highly significant reduction of 22% (p <0.0001) in major coronary events, strokes, and revascularisation with simvastatin.28,32 With regard to primary prevention, the HPS also demonstrated that the proportion of first major vascular events was reduced by 33% in diabetic patients (p = 0.0003).32 Furthermore, in diabetic, hypertensive patients with normal or average LDL-C levels, the Anglo-Scandinavian Cardiac Outcomes Trial (ASCOT) demonstrated benefit in type-2 diabetics with atorvastatin 10 milligrams (mg) versus placebo in the reduction of the risk for nonfatal MI and fatal CHD by 36% (p = 0.0005).33 Recently, the Collaborative Atorvastatin Diabetes Study (CARDS) of 2,838 adults with type-2 diabetes and, again, no history of CVD or hyperlipidemia demonstrated a 36% reduction in acute CHD events, 48% reduction in stroke, and 27% reduction in death rate (p = 0.059) in patients on atorvastatin 10mg.34 This study confirmed that statin therapy reduces first CVD events in patients with type-2 diabetes without high cholesterol in primary prevention.
There do not appear to be significant differences in LDL-C and total cholesterol levels across racial and ethnic-minority groups. Lipid goals, however, are based on individualised risk stratification, which is where minority patients are often at higher risk. African-Americans have a propensity to risk-factor clustering. Current National Cholesterol Education Program Expert Panel on Detection, Evaluation, And Treatment of High Blood Cholesterol In Adults (Adult Treatment Panel III) (NCEP ATP III) guidelines recommend, for a patient with type-2 diabetes who does not have documented CVD, a goal LDL-C of less than 100mg per decilitre (mg/dL).35 The NCEP ATP III issued an interim report in 2004,35 based on the implications of five recent clinical trials, including ASCOT and the HPS,36 making available the optional LDL-C goal of <70mg/dL for patients with established CVD and those at ‘very high risk’ of future CVD events, including those with type-2 diabetes mellitus.35 Furthermore, the results of CARDS, which were subsequently published, provide further rationale for initiation of statin therapy in patients with type-2 diabetes and CVD, regardless of baseline LDL-C level.34 Admittedly, these trials contained an underrepresentation of racial and ethnic minorities. Antiplatelet Therapy
Type-2 diabetes, especially when combined with hypertension and atherogenic dyslipidemia, is associated with a prothrombotic state. Meta-analyses of multiple studies, including large-scale diabetes trials, support the use of low-dose aspirin therapy (75mg–162mg per day), which is routinely recommended for primary prevention of CVD in patients with diabetes older than 40 years of age or with multiple risk factors and is also indicated for secondary prevention in all patients with overt CVD, if no contraindications exist.37 Other antiplatelet agents (e.g. clopidogrel) may be considered as a substitute in the case of aspirin allergy.Aspirin therapy is extremely inexpensive with no cost barrier, which can often disenfranchise economically disadvantaged racial/ethnic minorities, and should be utilised in all patients with type-2 diabetes. However, despite its proven efficacy, aspirin therapy is still currently underutilized in patients with diabetes.38
Intensive Multifaceted Strategy
Ultimately, it is the combination and intensity of therapeutic lifestyle changes and pharmacological risk management that are key to prevention of cardiovascular events in the diabetic population. In a study of combined intense lifestyle and pharmacological lipid treatment, 409 patients with coronary-artery disease were given comprehensive diet plans, monthly followup and extensive cardiovascular medication in addition to lipid-lowering therapy. This led to a 78% risk reduction for cardiovascular events versus those with usual care (no dietary interventions, little or no lipidlowering therapy, continued smoking; p<0.003).39 Similarly, in the European Steno-2 Study of patients with type-2 diabetes and macroalbuminuria, 80 patients were randomly assigned to receive conventional guideline-appropriate treatment and the remaining 80 received multifactorial intensive therapy targeting multiple CHD risk factors.40 The mean follow-up was 7.8 years and the mean patient age was 55.1 years. As expected, the multifactorial treatment group demonstrated a decrease of approximately 50% in cardiovascular and macrovascular events (p=0.008). These studies, although not in racial and ethnic minorities, provide further documentation that the management of global risk is important by the utilization of intensive treatment with multifactorial approaches to cardiovascular risk reduction.
Summary
It is widely known that the incidence of type-2 diabetes is increasing worldwide, especially in industrialised, Westernized populations, and currently affects approximately one in four adults. It is disproportionately affecting patients of ethnic and racial minority populations, putting them at increased risk for the development of CVD, including MI and stroke. Aggressive management and control to optimal levels of blood pressure, lipids and appropriate use of low-dose aspirin therapy could, theoretically, prevent much of the large burden of cardiovascular events in these patient populations. Although typically under-represented in clinical trials, the current recommendations for management of these at-risk populations must include intensive therapeutic lifestyle changes, appropriate antihypertensive medications and lipid-modifying therapy. Risk reduction with statin therapy in patients either with or without dyslipidemia suggests a great opportunity to further reduce risk. Different racial and ethnic groups may be at unique risk, whether due to diet or eating habits, physical activity or smoking. Only with a combined intensive and culturally sensitive multifactorial approach can the cardiovascular morbidity and mortality then begin to decline in these at-risk patients.
