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Metabolic syndrome (syndrome X, insulin resistance syndrome) is characterized by a clustering of risk factors for cardiovascular disease and type 2 diabetes mellitus. They commonly include excess intra-abdominal fat, insulin resistance, and ≥ 1 of the following: elevated serum triglyceride levels, decreased high-density lipoprotein (HDL) cholesterol level, and hypertension. Causes, complications, diagnosis, and treatment are similar to those of obesity.
In developed countries, metabolic syndrome is a serious problem. It is very common; in the US, > 40% of people > 50 yr may have it. Children and adolescents can develop metabolic syndrome, but in these age groups, no definition is established.
Development of metabolic syndrome depends on distribution as well as amount of fat. Excess fat in the abdomen (called apple shape), particularly when it results in a high waist-to-hip ratio (reflecting a relatively low muscle-to-fat mass ratio), increases risk. The syndrome is less common among people who have excess subcutaneous fat around the hips (called pear shape) and a low waist-to-hip ratio (reflecting a higher muscle-to-fat mass ratio).
Excess abdominal fat leads to excess free fatty acids in the portal vein, increasing fat accumulation in the liver. Fat also accumulates in muscle cells. Insulin resistance develops, with hyperinsulinemia. Glucose metabolism is impaired, and dyslipidemias and hypertension develop. Serum uric acid levels are typically elevated, and a prothrombotic state (with increased levels of fibrinogen and plasminogen activator inhibitor I) and an inflammatory state develop. Patients have an increased risk of obstructive sleep apnea. Other risks include nonalcoholic steatohepatitis, chronic kidney disease, polycystic ovary syndrome (for women), and low plasma testosterone, erectile dysfunction, or both (for men).
Diagnosis
Screening is important. A family history plus measurement of waist circumference and BP are part of routine care. If patients with a family history of type 2 diabetes mellitus, particularly those ≥ 40 yr, have a waist circumference greater than that recommended for race and sex, fasting plasma glucose and a lipid profile must be determined.
Metabolic syndrome has many different definitions, but it is most often diagnosed when ≥ 3 of the following are present: excess abdominal fat, a high fasting plasma glucose level, hypertension, a high triglyceride level, and a low HDL cholesterol level (see Table 3: Obesity and the Metabolic Syndrome: Criteria Often Used for Diagnosis of Metabolic Syndrome* ).
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Table 3
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| Criteria Often Used for Diagnosis of Metabolic Syndrome* |
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Criteria
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Value
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Waist circumference (cm [in])
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≥ 102 (≥ 40) for men
≥ 88 (≥ 35) for women
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Fasting glucose (mg/dL [mmol/L])
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≥ 100 (≥ 5.6)
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BP (mm Hg)
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≥ 130/85
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Triglycerides, fasting (mg/dL [mmol/L])
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≥ 150 (≥ 1.7)
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High-density lipoprotein (HDL) cholesterol (mg/dL [mmol/L])
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< 40 (< 1.04) for men
< 50 (< 1.29) for women
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*At least 3 of the criteria must be present for the diagnosis.
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Treatment
Optimally, the management approach results in weight loss based on a healthy diet and regular physical activity, which includes a combination of aerobic activity and resistance training, reinforced with behavioral therapy. Metformin, an insulin sensitizer, may be useful. Weight loss of ≈ 7% may be sufficient to reverse the syndrome, but if not, each feature of the syndrome should be managed to achieve recommended targets; available drug treatment is very effective.
Other cardiovascular risk factors (eg, smoking cessation) also need to be managed. Increased physical activity has cardiovascular benefits even if weight is not lost.
Last full review/revision October 2008 by Gary Wittert, MB, Bch, MD; Ashish C. Sinha, MD, PhD
Content last modified October 2008
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