BACKGROUND: The close association of type 2 diabetes and atherosclerotic 
cardiovascular disease (CVD) suggests that they share a common physiologic 
antecedent, postulated to be tissue resistance to insulin. Insulin resistance is 
associated with a cluster of risk factors recognized as the metabolic syndrome.
OBJECTIVE: To describe the epidemiology of the insulin resistance syndrome, also 
known as the metabolic syndrome.
METHODS: Overall obesity, central obesity, dyslipidemia characterized by 
elevated levels of triglycerides and low levels of high-density lipoprotein 
cholesterol, hyperglycemia, and hypertension are common traits that, when they 
occur together, constitute the metabolic syndrome. The World Health Organization 
and the National Cholesterol Education Program Adult Treatment Panel III have 
proposed working definitions for the syndrome based on these traits. 
Cross-sectional and longitudinal epidemiologic studies provide an emerging 
picture of the prevalence and outcomes of the syndrome.
RESULTS: National survey data suggest the metabolic syndrome is very common, 
affecting about 24% of US adults who are 20 to 70 years of age and older. The 
syndrome is more common in older people and in Mexican Americans. People with 
the syndrome are about twice as likely to develop CVD and over 4 times as likely 
to develop type 2 diabetes compared with subjects who do not have metabolic 
syndrome. While this syndrome may have a genetic basis, environmental factors 
are important modifiable risk factors for the condition.
CONCLUSIONS: The metabolic syndrome is very common and will become even more 
common as populations age and become more obese. Treatment for component traits 
is known to reduce the risk for type 2 diabetes and CVD; whether risk is reduced 
by treatment of the syndrome, specifically, remains uncertain. Primary care 
physicians must recognize that the co-occurrence of risk factors for type 2 
diabetes and CVD represents an extremely adverse metabolic state warranting 
aggressive risk factor intervention.