Historical Development of the Concept
After many years of discussion, a consensus was reached in 2005 based on the definition proposed by the International Diabetes Federation (IDF).
In 1920, Kylin was the first to describe the coexistence of hypertension, hyperglycemia, and gout as a metabolic syndrome. In 1947, Vague observed that the male pattern of obesity was frequently associated with diabetes mellitus and cardiovascular diseases. In 1988, Reaven introduced the term “Syndrome X.” One year later, Kaplan referred to the condition as the “Deadly Quartet.” In 1992, the term “Insulin Resistance Syndrome” was introduced. Eventually, the term “Metabolic Syndrome” became widely accepted to describe the clustering of metabolic risk factors associated with cardiovascular disease. However, variations in its definition persisted.
In 1998, the World Health Organization (WHO) became the first organization to provide a formal definition of metabolic syndrome. This definition required the presence of glucose intolerance or diabetes, together with at least two of the following criteria: elevated fasting glucose, elevated blood pressure, elevated triglycerides, reduced high-density lipoprotein (HDL) cholesterol, obesity, or microalbuminuria.
In response, the European Group for the Study of Insulin Resistance (EGIR) modified the WHO definition. In this revised definition, insulin resistance became the essential criterion, accompanied by at least two additional factors: elevated fasting glucose, elevated blood pressure, elevated triglycerides and/or reduced HDL cholesterol, or increased waist circumference.
In 2001, the National Cholesterol Education Program (NCEP) published its own definition. According to this definition, metabolic syndrome is present when three or more of the following five risk factors are met: elevated fasting glucose, elevated blood pressure, reduced HDL cholesterol, elevated triglycerides, and increased waist circumference.
Subsequently, the American Association of Clinical Endocrinologists (AACE) presented its perspective on the definition of metabolic syndrome. Insulin resistance, together with factors such as elevated triglycerides, reduced HDL cholesterol, elevated blood pressure, elevated fasting glucose, and elevated glucose levels after an oral glucose tolerance test (OGTT), were proposed as indicators of metabolic syndrome. Initially, no specific threshold values were established, allowing clinicians to diagnose metabolic syndrome based on clinical judgment.
The large number of competing definitions suggested that a unified definition would be desirable. To achieve this goal, the International Diabetes Federation (IDF) proposed a new definition of metabolic syndrome in April 2005.
Definition of Metabolic Syndrome
Metabolic syndrome is defined as central obesity together with any two of the following four factors: elevated triglycerides, reduced HDL cholesterol, elevated blood pressure, and elevated fasting plasma glucose or diabetes mellitus.
In 2006, the International Diabetes Federation (IDF) proposed a unified worldwide definition of metabolic syndrome. According to the IDF definition, an individual is diagnosed with metabolic syndrome if the following criteria are fulfilled:
Central Obesity
Defined by waist circumference:
with ethnic-specific values for other populations.
Plus Any Two of the Following Four Factors
Elevated Triglycerides
Reduced HDL Cholesterol
Elevated Blood Pressure
Elevated Fasting Plasma Glucose (FPG)
If fasting plasma glucose exceeds 5.6 mmol/L (100 mg/dL), an oral glucose tolerance test (OGTT) is strongly recommended, although it is not required for the diagnosis of metabolic syndrome.
Ethnic Group | Men | Women |
Europeans | ≥ 94 cm | ≥ 80 cm |
South Asians | ≥ 90 cm | ≥ 80 cm |
Chinese | ≥ 90 cm | ≥ 80 cm |
Japanese | ≥ 90 cm | ≥ 80 cm |
South and Central Americans | Use South Asian recommendations until more specific data become available | |
Sub-Saharan Africans | Use European recommendations until more specific data become available | |
Eastern Mediterranean and Middle Eastern populations (Arabs) | Use European recommendations until more specific data become available |
For clinical purposes in the United States, the ATP III criteria continue to be widely used:
These waist circumference thresholds approximately correspond to a body mass index (BMI) of 30 kg/m² in European populations. However, the American guidelines explicitly acknowledge that metabolic syndrome may already be present in individuals with waist circumferences between 94 and 102 cm and should be managed accordingly.
The primary purpose of identifying metabolic syndrome is to recognize individuals at increased cardiovascular risk and to implement interventions aimed at preventing cardiovascular events. Because the American thresholds are largely based on studies involving patients with established cardiovascular disease, whereas the goal is prevention or delay of cardiovascular disease onset, the IDF definition is recommended. Otherwise, a substantial proportion of high-risk individuals may remain untreated.