The metabolic syndrome is a complex of risk factors for cardiovascular disease and diabetes mellitus which are inter-related and cluster together more often than by chance. The five main risk factors include glucose abnormalities, dyslipidemia with low levels of high density lipoprotein (HDL) cholesterol or raised triglycerides, central obesity, and raised blood pressure. Insulin resistance is thought to be a pivotal factor linking these various disturbances together. Thus, names such as ‘syndrome X’ (metabolic as opposed to cardiac) and the ‘insulin resistance syndrome’ had previously been applied to this clustering of metabolic risk factors. The importance of the metabolic syndrome is that individuals with it have double the risk for developing cardiovascular disease and a five-fold increased risk for developing diabetes . A formal definition of the metabolic syndrome was first published in 1998 by a WHO Consultation group . This required evidence of insulin resistance, albeit indirect, together with two other risk factors to make the diagnosis. This was followed in 2001 by a definition from the US National Cholesterol Education Program Adult Treatment Panel III (ATP III) , which required the presence of any three risk factors without necessarily including insulin resistance. In 2005, the International Diabetes Federation (IDF) refined the WHO diagnostic criteria by dropping the necessity of insulin resistance but instead made abdominal obesity a requirement together with two other risk factors . This insistence on increased waist circumference, together with a stricter upper limit for this, was the major difference from the ATP III definition, whereas the other risk factor thresholds were the same. Most recently, an attempt has been made to harmonize the criteria, involving the IDF, the National Heart, Lung, and Blood Institute (NHLBI), the American Heart Association, the World Heart Federation, the International Atherosclerosis Society and the International Association for the Study of Obesity . The result is that the necessity for increased waist circumference has been dropped, and the presence of any three risk factors from the five is sufficient to make the diagnosis of metabolic syndrome. The limits for waist circumference are, for the present, determined by national or regional thresholds.
National Heart & Lung Institute, Imperial College London, Royal Brompton Hospital, London, UK
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