Development of the multiple metabolic syndrome: an epidemiologic perspective.

It has been observed repeatedly that risk factors for cardiovascular diseases tend to co-occur within individuals (1, 2). Typically, disturbances of glucose metabolism, dyslipidemias, central obesity, and elevated blood pressure are among the metabolic and hemodynamic components considered. These observations have been made both on the individual level and at the population level as associations between these risk factors. Since each of these conditions is highly prevalent in adulthood, it is reasonable to expect clusters due to chance alone. However, it has been speculated for some time that co-occurrence of these conditions is due to a common underlying process. Several terms have been proposed to describe the clustering of metabolic disorders, among them syndrome X, the insulin resistance syndrome, and the multiple metabolic syndrome (table 1) (3-13). For the purposes of this review, the latter terminology, the multiple metabolic syndrome, will be adopted since it does not rely on assumptions about underlying etiologic mechanisms and retains a certain neutrality. The term "multiple metabolic" implies primarily more than one metabolic abnormality, but does not preclude the interpretation that several syndromes may, in fact, be subsumed under this heading. This review will focus on the multiple metabolic syndrome largely from an epidemiologic perspective. There are several excellent review papers that have concentrated on the physiologic or clinical perspectives (3, 12, 14).