The metabolic syndrome : its validity, causes, consequences and uses

Obesity, hypertension, high blood glucose and triglycerides, and low HDL cholesterol are more likely to occur together. A clustering of these risk factors is defined clinically as the metabolic syndrome and indicates high risk of type 2 diabetes and cardiovascular disease. Using data from the nation-wide Australian Diabetes, Obesity and Lifestyle (AusDiab) study, and a comparable study in Mauritius, this thesis examined i) the prevalence of the metabolic syndrome in Australia, ii) whether obesity is the precursor to the development of the multiple abnormalities of the metabolic syndrome, iii) the health consequences of obesity, iv) whether waist cut-points for Europid and South Asian populations used in clinical definitions of the metabolic syndrome adequately reflect risk for type 2 diabetes and v) whether the metabolic syndrome is a valid and useful tool for the prediction of future type 2 diabetes. The AusDiab and Mauritius studies are both national, prospective cohort studies of adults. The AusDiab study involved 11,247 participants in 1999 with 6,537 of these followed-up five years later in 2004. The Mauritius study involved both five year (n=3,771) and eleven year (n=2,802) follow-up of a 1987 baseline cohort. The research reported here confirms i) a prevalence of the metabolic syndrome greater than 25% among Australian adults, regardless of the definition used, ii) that central obesity precedes the development of the other components of the metabolic syndrome, iii) that obesity confers a heightened five year risk for each of type 2 diabetes, the metabolic syndrome, hypertension, dyslipidaemia and cardiovascular disease, iv) that at waist circumference cut-points used in definitions of the metabolic syndrome, a considerably greater five-year risk of diabetes exists in South Asians compared to Europids and v) that the metabolic syndrome is a strong predictor of incident diabetes over five years, but is no better than measurement of fasting glucose alone or published diabetes risk prediction scores. These findings suggest that the metabolic syndrome is a highly prevalent condition that confers a considerably increased risk of type 2 diabetes. The metabolic syndrome is shown here to be no better than other available tools or fasting glucose for estimation of diabetes risk, although clinical definitions were not designed solely for this purpose. The status of obesity in the metabolic syndrome should be as a pre-cursor to the development of the other abnormalities, not simply as one of several type 2 diabetes and cardiovascular disease risk factors. Finally, the results here indicate that waist circumference cut-points in current metabolic syndrome definitions require revision, at least for those of South Asian ancestry. Published papers have been omitted from the eThesis.