Impaired post-ischaemic microvascular hyperaemia in Indian Asians is unexplained by diabetes or other cardiovascular risk factors

Associations Between Prediabetes, by Three Different Diagnostic Criteria, and Incident CVD Differ in South Asians and Europeans

OBJECTIVE

We examined longitudinal associations between prediabetes and cardiovascular disease (CVD) (coronary heart disease [CHD] and stroke) in Europeans and South Asians.

RESEARCH DESIGN AND METHODS

This was a U.K. cohort study of 1,336 Europeans and 1,139 South Asians, aged 40-69 years at baseline (1988-1991). Assessment included blood pressure, blood tests, anthropometry, and questionnaires. Prediabetes was determined by OGTT or HbA1c, using either International Expert Committee (IEC) (HbA1c 6.0-6.5% [42-48 mmol/mol]) or American Diabetes Association (ADA) (HbA1c 5.7-6.5% [39-48 mmol/mol]) cut points. Incident CHD and stroke were established at 20 years from death certification, hospital admission, primary care record review, and participant report.

RESULTS

Compared with normoglycemic individuals, IEC-defined prediabetes was related to both CHD and CVD risk in Europeans but not South Asians (subhazard ratio for CHD 1.68 [95% CI 1.19, 2.38] vs. 1.00 [0.75, 1.33], ethnicity interaction P = 0.008, and for CVD 1.49 [1.08, 2.07] vs. 1.03 [0.78, 1.36], ethnicity interaction P = 0.04). Conversely, IEC-defined prediabetes was associated with stroke risk in South Asians but not Europeans (1.73 [1.03, 2.90] vs. 0.85 [0.44, 1.64], ethnicity interaction P = 0.11). Risks were adjusted for age, sex, smoking, total-to-HDL cholesterol ratio, waist-to-hip ratio, systolic blood pressure, and antihypertensive use. Associations were weaker for OGTT or ADA-defined prediabetes. Conversion from prediabetes to diabetes was greater in South Asians, but accounting for time to conversion did not account for these ethnic differences.

CONCLUSIONS

Associations between prediabetes and CVD differed by prediabetes diagnostic criterion, type of CVD, and ethnicity, with associations being present for overall CVD in Europeans but not South Asians. Substantiation of these findings and investigation of potential explanations are required.

Ethnic Differences in Associations Between Blood Pressure and Stroke in South Asian and European Men

It is unknown whether associations between blood pressure (BP) and stroke vary between Europeans and South Asians, despite higher stroke rates in the latter. We report findings from a UK cohort study of 1375 European and 1074 South Asian men, not receiving antihypertensive medication, aged 40 to 69 years at baseline (1988-1991). Assessment included BP, blood tests, anthropometry, and questionnaires. Incident stroke was established at 20 years from death certification, hospital and primary care records, and participant report. South Asians had higher systolic BP, diastolic BP, and mean arterial pressure than Europeans, and similar pulse pressure. Associations between systolic BP or diastolic BP and stroke were stronger in South Asians than Europeans, after adjustment for age, smoking status, waist/hip ratio, total/high-density lipoprotein-cholesterol ratio, diabetes mellitus, fasting glucose, physical activity, and heart rate (systolic BP: Europeans [odds ratio, 1.22; 95% confidence interval, 0.98-1.51], South Asians [1.56; 1.24-1.95]; ethnic difference P=0.04; diastolic BP: Europeans [0.90; 0.71-1.13], South Asians [1.68; 1.32-2.15]; P<0.001). Hemodynamic correlates of stroke risk differed by ethnicity: in combined models, mean arterial pressure but not pulse pressure was detrimentally associated with stroke in South Asians, whereas the converse was true for Europeans. The combination of hyperglycemia and hypertension appeared particularly detrimental for South Asians. There are marked ethnic differences in associations between BP parameters and stroke. Undue focus on systolic BP for risk prediction, and current age and treatment thresholds may be inappropriate for individuals of South Asian ancestry.

Microcirculatory rarefaction in South Asians - a potential mechanism for increased cardiovascular risk and diabetes

People of South Asian descent have an increased risk of cardiovascular disease (CVD) and diabetes, but little is known about the microcirculation in South Asian people despite evidence that this plays an important role in the aetiology of CVD. We compared the retinal microcirculation in a population-based sample of 287 middle-aged adults (144 European 143 South Asian) matched for age and sex. Retinal photographs were taken and analysed using a validated semi-automated program and microvascular measures were compared. Blood pressure, anthropometry and fasting bloods were also measured. South Asians had significantly fewer arteriolar and venular vessels and bifurcations. Arterioles and venules were longer and venules were also more tortuous in South Asians. These differences were not explained by adjustment for traditional risk factors including blood pressure, body mass index, diabetes or measures of insulin resistance. People of South Asian descent have rarefaction of the retinal microcirculation compared to age-sex matched individuals of European descent. Reduced microvascular density could contribute to the elevated risk of CVD and impaired glucose tolerance in South Asian people.