Epidemiology of the metabolic syndrome

Abstract

Insulin resistance-an essential component of the metabolic syndrome-has been known for nearly 70 years. During the last 25 years numerous studies have shown that insulin resistance tend to occur concomitantly with a cluster of cardiovascular risk factors including increased blood pressure, lipid levels, obesity and a wide range of other factors associated with increased risk of developing CVD. This clustering of risk factors have been given many names, but during the last 10-15 years the label Metabolic Syndrome has been used as the common name for the condition. The definition has changed over time, and consequently it is difficult to compare epidemiological studies over time or between regions, as they have often used different definitions. Independent of ethnicity, the prevalence of the metabolic syndrome increases by age. There are distinct effects of ethnicity, where the age-adjusted prevalence of the metabolic syndrome is highest in East-Asia and in the Middle East region. Within countries there are also marked differences with higher prevalence in Afro-American and Mexican-Hispanic groups than in white Caucasian groups in USA. Based on a number of epidemiological studies, the clinical value of the Metabolic Syndrome has been questioned. The clinical relevance here refers to the issue-whether the presence of the metabolic syndrome predicts adverse outcome like diabetes and CVD, and whether it does so over and above the effect of the individual risk factors. Most studies indicate that it is the presence of the individual risk factors, not the syndrome that carries the clinically relevant information. Consequently, the syndrome may be a convenient term for a clustering of risk factors, but it seems to have limited clinical impact as an entity in itself.