OBJECTIVE:To investigate the effect of body mass index (BMI) and body fat distribution as measured by waist-to-hip ratio (WHR) on the cardiovascular risk factor profile of the three major ethnic groups in Singapore (Chinese, Malay and Indian people) and to determine if WHO recommended cut-off values for BMI and WHR are appropriate for the different sub-populations in Singapore. DESIGN: Cross-sectional population study. SUBJECTS: A total of 4723 adult subjects (64% Chinese individuals, 21% Malay individuals and 15% Indian individuals) were selected through a multi-staged sampling technique to take part in the National Health Survey in 1998. MEASUREMENTS: Data on socio-economic status (education level, occupation, housing type) and lifestyle habits (smoking and physical activity), body weight, body height, waist and hip circumferences and blood pressure measured using standardised protocols. Fasting venous blood samples were obtained for determination of serum total cholesterol (TC), high density lipoprotein cholesterol (HDL), low density lipoprotein cholesterol (LDL), triglycerides (TG). Venous blood samples were taken for 2 h oral glucose tolerance test (2 h glu). RESULTS: Absolute and relative risks for at least one cardiovascular risk factor (elevated TC, elevated TC=HDL ratio, elevated TG, hypertension and diabetes mellitus) were determined for various categories of BMI and WHR. At low categories of BMI (BMI between 22 and 24 kg=m 2 ) and WHR (WHR between 0.80 and 0.85 for women, and between 0.90 and 0.95 for men), the absolute risks are high, ranging from 41 to 81%. At these same categories the relative risks are significantly higher compared to the reference category, ranging from odds ratio of 1.97 to 4.38. These categories of BMI and WHR are all below the cut-off values of BMI and WHR recommended by WHO. CONCLUSIONS:The results show that, at relatively low BMI and WHR, Singaporean adults experience elevated levels of risks (absolute and relative) for cardiovascular risk factors. These findings, in addition to earlier reported high percentage body fat among Singaporeans at low levels of BMI, confirm the need to revise the WHO cut-off values for the various indices of obesity and fat distribution, viz BMI and WHR, in Singapore.

Prevalence of diabetes was high across all three ethnic groups. Ethnic differences in prevalence of diabetes, insulin resistance, central obesity, hypertension, smoking, and lipid profile could explain the differential coronary heart disease rates in the three major ethnic groups in Singapore.

The increased susceptibility of Asian Indian males to CHD has been confirmed in a longitudinal study. All of the examined established risk factors for CHD were found to play important but varying roles in the ethnic groups in Singapore.

Indians had the highest prevalence of diabetes among Asian countries. The age at which the peak prevalence of diabetes was reached was approximately 10 years younger in Indian compared with Chinese and Japanese subjects. Diabetes and IGR will be underestimated in Asians based on the fasting glucose testing alone.

Individuals with isolated low HDL cholesterol are at increased risk of coronary artery disease. It has been reported previously that this is an insulin-resistant state. We analyzed data from the 1992 Singapore National Health Survey with the objective of defining the clinical and metabolic parameters associated with isolated low HDL cholesterol. A total of 3,568 individuals were selected by stratified random sampling. Subjects with low HDL cholesterol (<0.9 mmol/l) and "ideal" total cholesterol (<5.2 mmol/l) were identified. Data on anthropometry, blood pressure (BP), insulin resistance, glucose tolerance, sex, smoking habit, and ethnic group were examined. We found that this group was heterogeneous. Those with fasting triglyceride (TG) >1.7 mmol/l (low HDL/high TG) displayed features of the insulin resistance syndrome characterized by obesity, higher diastolic BP, greater insulin resistance, and a greater tendency to have diabetes or impaired glucose tolerance (IGT). If fasting TG was <1.7 mmol/l (isolated low HDL cholesterol), individuals were similar to the general population in terms of insulin resistance and obesity. Both groups were more commonly men and Asian Indian. The ethnic difference in prevalence could not be explained by differences in diet, exercise, alcohol ingestion, or smoking. Our data support the view that Asian Indians are genetically predisposed to isolated low HDL cholesterol as well as the insulin resistance syndrome. The higher prevalence of isolated low HDL cholesterol, the young age at which individuals exhibit this phenotype (mean age 32.5 years), along with the greater propensity for Asian Indians to develop insulin resistance and IGT contribute to the threefold increased incidence of myocardial infarction in those <65 years of age in this ethnic group.