Metabolic syndrome: major impact on coronary risk in a population with low cholesterol levels—a prospective and cross-sectional evaluation
Introduction
Metabolic syndrome (MS) [1], dysmetabolic syndrome or insulin-resistance syndrome [2] (or syndrome X as it was initially designated [3]), which is closely linked to insulin resistance, is a condition which is recognized as raising the risk of cardiovascular disease. It was originally described by Reaven [3] as a quartet of hypertension, glucose intolerance and dyslipidemia (high triglyceride, low high-density lipoprotein-cholesterol (HDL-C)), with insulin resistance or hyperinsulinemia. Central obesity is often associated [4] and other phenotypes, such as impaired fibrinolysis, microalbuminuria, small dense low-density lipoprotein (LDL) particles and markers of acute phase reactants, were later found to be associated [5]. With such an evolving recognition of risk factor clusters, it is not surprising that both the prevalence of MS and its impact on coronary heart disease (CHD) risk in the community were not clearly discernible. The definition used, as well as the population studied, obviously may affect these. The new National Cholesterol Education Program guidelines (Adult Treatment Panel III) [6] recognized MS as a secondary target of risk-reduction therapy and selected to define MS when three or more of certain five risk determinants are present.
It is thus timely to evaluate the prevalence of MS and its significance on CHD risk in populations with high and low levels of LDL-cholesterol (LDL-C). Turkish adults, having essentially low levels of total or LDL-C [7], are a suitable substrate to investigate, particularly in view of a coexisting high prevalence of low HDL-C [8] and anticipatedly of MS [9]. The Turkish population possesses a high prevalence of hypertension (46% of adults aged 30 or over) [10] and a risk factor profile that varies from that of Western populations inasmuch as the relative role of atherogenic lipoprotein phenotype is more pronounced [7]. It is therefore the aim of this study to evaluate prospectively and cross-sectionally (a) the prevalence of MS, (b) the impact (relative and attributable risk) of MS on CHD risk, and (c) the relative roles of the standard MS components and other relevant markers on CHD risk in a population sample representative of middle-aged and elderly Turkish adults.
Section snippets
Study population
Participants in this population-based study form the cohort of the Turkish Adult Risk Factor Study, a prospective survey on the prevalence of cardiac disease and risk factors in adults in Turkey carried out periodically since 1990 in seven geographical regions of the country [11], [12]. Since HDL-C measurements were not performed before the follow-up visit in 1997/98, the latter examination formed the baseline. Further follow-ups were carried out in 2000 and, in half of the cohort, in year
Prospective evaluation
At baseline examination in 1997, 321 men (27% of the sample) and 465 women (38.6%) were identified as having MS. During the follow-up period, 41 deaths from CHD and 85 nonfatal CHD occurred. Coronary deaths developed in 15 individuals with MS (1.9%) as contrasted with 21 in subjects without MS (1.3%). Nonfatal CHD developed in 47 individuals with MS (6.0%) compared to 43 in subjects without MS (2.7%). Overall fatal and nonfatal CHD occurred in 7.9% of participants with MS versus 4.0% without
Discussion
This population-based prospective study sought to assess the predictive value of MS with respect to fatal and nonfatal coronary events in a sample which was representative of the Turkish adult population and had a wide age span, from age 28 years onwards.
Acknowledgments
The financial support of the Turkish Society of Cardiology and of pharmaceutical and nutrition firms in Istanbul (Unilever, Roche, Pfizer, Merck Sharp Dohme, Astra and Bristol Myers-Squibb) is gratefully acknowledged.
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