Cardiovascular risk factors in non-insulin-dependent diabetics compared to non-diabetic controls: a population-based survey among Asians in Singapore
Introduction
People with non-insulin-dependent diabetes mellitus (NIDDM) are about three times as likely as non-diabetics to get coronary heart disease (CHD), and furthermore cardiovascular disease occurs early in the course of diabetes [1]. The classical risk factors for CHD are cigarette smoking, hypertension, and dyslipidaemias (high low-density-lipoprotein (LDL) cholesterol, low high-density-lipoprotein (HDL) cholesterol, and high fasting triglyceride). NIDDM seems to be linked with hypertension and dyslipidaemia through insulin resistance, which tends to be associated with centralised adiposity [2], and syndrome X (metabolic syndrome). This is characterised by increased insulin resistance, glucose intolerance, hypertension, and dyslipidaemia with high fasting triglyceride and low HDL-cholesterol [3].
With regard to haemostatic (thrombotic) factors, blood fibrinogen is an established risk factor and factor VIIc and plasminogen activator inhibitor type 1 (PAI-1) are probable risk factors for CHD [4]. Syndrome X could also link NIDDM with haemostatic factors as it is being expanded and called the `athero-thrombogenic syndrome'. It can include increased PAI-1 [5].
Lipoprotein (Lp)(a) has LDL-like properties which could increase atherosclerosis [6]and, being structurally similar to plasminogen, inhibits plasminogen binding to the endothelial cell with reduced plasmin generation and fibrinolysis [7]. However Lp(a) has not been shown to be a cardiovascular risk factor in prospective as opposed to case-control studies and its role is not fully clear [8].
There is evidence that oxidative free-radicals have a role in the development of degenerative diseases including CHD 9, 10. There is further evidence that anti-oxidants (including vitamins A, C and E, and selenium) are protective against CHD, though it is considered inconclusive 11, 12, 13. Iron is a pro-oxidant and high levels of blood ferritin, which measures stored iron, is a possible risk factor for CHD, though this is considered unproven 13, 14. Diabetics are usually put on a special diet and so possibly their dietary intake of anti-oxidants and pro-oxidants are different from non-diabetics.
Singapore has a population of 3.3 million people composed of Chinese 76%, Malays 14%, Indians (South Asians) 7%, and others 3% whose origins have been described [15]. The country has undergone rapid economic development and the commonest causes of death are now cardiovascular diseases and cancers. The Singapore Thyroid and Heart Study found that NIDDM was common and highest in Indians, then Malays, and then Chinese [16]. The National University of Singapore Heart Study is a further population-based survey of cardiovascular risk factors, including the newer ones not studied previously, and this paper compares a range of cardiovascular risk factors between people with NIDDM and non-diabetics (controls).
Section snippets
Sample
The National University of Singapore Heart Study was a cross-sectional survey of a random sample of people aged 30–69 years from the general population of Singapore. Details of the sampling have been described elsewhere [17]. There was disproportionate sampling to obtain an equal number of subjects by gender and the three main ethnic groups (Chinese, Malays and Indians). The response rate was 71.2%. As diabetes in Singapore is uncommon in people under 40 years of age, this study examines the
Results
Out of a total of 656 people, 126 (19.2%) had NIDDM, with 82 (65.1%) being known and on treatment and 44 (34.9%) being newly diagnosed in the survey. The prevalences of NIDDM were males 22.5% (Chinese 14.8%, Malays 22.1%, and Indians 29.9%) and females 16.1% (Chinese 9.6%, Malays 15.2%, and Indians 23.0%).
Table 1 shows the comparisons for obesity indices. For both genders, mean body mass index (which measures general obesity), and mean waist-hip ratio and abdominal diameter (which measure
Discussion
This study has compared a broad range of cardiovascular risk factors between individuals with NIDDM and non-diabetic controls in three Asian ethnic groups (Chinese, Malays, and Indians) in Singapore. Both the cases and controls were from a random sample of the general population and hence there will not have been any selection bias with regard to risk factors, that may be present with diabetic patients and controls from a clinic or hospital. People with NIDDM included those already diagnosed as
Acknowledgements
The National University of Singapore Heart Study was funded by the National University of Singapore and the National Medical Research Council.
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