Also Known As
Syndrome X
Dysmetabolic Syndrome
Insulin Resistance Syndrome
Obesity Syndrome
Reaven Syndrome
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This article waslast modified on November 11, 2019.
What is metabolic syndrome?

Metabolic syndrome is a set of risk factors that increases a person's chance of developing serious conditions such as cardiovascular disease (CVD), type 2 diabetes, and stroke. These risk factors include:

Metabolic syndrome is a common condition that goes by many names (dysmetabolic syndrome, syndrome X, insulin resistance syndrome, obesity syndrome, and Reaven syndrome). Most people identified as having this syndrome have been educated about the importance of watching for signs of diabetes, having their blood pressure monitored and lipid levels checked, and exercising – but there has been little to tie all of these factors together except pursuit of a "healthier lifestyle."

The National Heart, Lung and Blood Institute (NHLBI) estimates that about 34% of Americans have metabolic syndrome. It can affect anyone at any age, but it is most frequently seen in people who are inactive and significantly overweight, with most of their excess fat in the abdominal area.

While several national and international organizations use certain criteria to define metabolic syndrome, others, including the American Diabetes Association (ADA), question the value of the specific diagnosis of metabolic syndrome. They point out that the criteria, taken together, are no more useful at predicting the risk of cardiovascular disease or diabetes than the individual criteria considered separately. The science needs to be clearer, suggests the ADA, before metabolic syndrome be considered a definable syndrome.

The World Health Organization (WHO) was the first to publish an internationally accepted definition for metabolic syndrome in 1998, but the criteria that have received the most widespread acceptance and use in the United States are those established in 2002 as guidelines in the third report of the National Cholesterol Education Program expert panel on Detection, Evaluation, and Treatment of High Blood Cholesterol in Adults (ATP III).

In 2005, the American Heart Association (AHA) in conjunction with the NHLBI also released a scientific statement regarding metabolic syndrome that includes a set of criteria that defines the condition. In order to provide more consistency in both patient care and research, the International Diabetes Federation, NHLBI, AHA, World Heart Federation, and the International Association for the Study of Obesity published a joint statement in 2009 that describes a "harmonized" definition of metabolic syndrome. Waist circumference, with population and country-specific criteria, replaced obesity as a measure of body status.

The table below summarizes the four sets of criteria:

Criteria for Clinical Diagnosis of Metabolic Syndrome

Clinical Measure WHO (1998) AHA/NHLBI (2005) Harmonization Definition (2005)
Criteria for diagnosis Insulin resistance plus two of the other criteria below Three of the criteria listed below Obesity as defined by waist circumference plus two of the other criteria below
Waist circumference (as the definition of obesity)   ≥40 inches (102 centimeters, cm) in men,
≥35 inches (88 cm) in women
≥37 inches (95 centimeters, cm) in men,
≥31 inches (80 cm) in women
Body mass index (BMI) BMI >30 kilograms/meter2    
Triglycerides ≥150 milligrams/deciliter (mg/dL) ≥150 milligrams/deciliter (mg/dL) ≥150 milligrams/deciliter (mg/dL)
HDL-C <35 mg/dL in men,
<39 mg/dL in women
<40 mg/dL in men,
<50 mg/dL in women or taking medication such as statins
<40 mg/dL in men,
<50 mg/dL in women or taking medication such as statins
Blood pressure ≥140/90 mm Hg Systolic ≥130 or diastolic 85 mm Hg or taking medication for high blood pressure Systolic ≥130 or diastolic ≥85 mm Hg or taking medication for high blood pressure
Glucose Impaired glucose tolerance, impaired fasting glucose or type 2 diabetes Fasting >100 mg/dL or taking medication for diabetes Fasting ≥100 mg/dL
Insulin resistance YES NO NO
Urine albumin (microalbuminuria) YES NO NO

Also frequently seen with metabolic syndrome are tendencies for excessive blood clotting and inflammation. While obvious symptoms may be absent, these features are a warning of an increased likelihood of clogged arteries, heart disease, stroke, diabetes, kidney disease, and even premature death. If left untreated, complications from diseases associated with untreated metabolic syndrome can develop in as few as 15 years. Those who have metabolic syndrome and also smoke tend to have an even poorer prognosis.

The root cause of most cases of metabolic syndrome can be traced back to poor eating habits and a sedentary lifestyle. In some cases, a diagnosis of metabolic syndrome has also been assigned to those already diagnosed with hypertension or with poorly controlled diabetes. There also seems to be an association with non-alcoholic fatty liver disease, polycystic ovarian disease, and some cancers. A few cases are thought to be linked to genetic factors.

All of the factors associated with metabolic syndrome are interrelated. Obesity and lack of exercise tend to lead to insulin resistance. Insulin resistance has a negative effect on lipid production, increasing VLDL (very low-density lipoprotein), LDL (low-density lipoprotein – the "bad" cholesterol), and triglyceride levels in the blood and decreasing HDL (high-density lipoprotein – the "good" cholesterol). This can lead to fatty plaque deposits in the arteries which, over time, can lead to cardiovascular disease and strokes. Insulin resistance also leads to increased insulin and glucose levels in the blood. Excess insulin increases sodium retention by the kidneys, which increases blood pressure and can lead to hypertension. Chronically elevated glucose levels in turn damage blood vessels and organs, such as the kidneys. 

Accordion Title
About Metabolic Syndrome
  • Tests

    A healthcare practitioner may suspect that a person has metabolic syndrome if the person has excess weight around the waist and a sedentary lifestyle, but both laboratory and non-laboratory tests are important in establishing the diagnosis. Recommended tests include:

    Laboratory Tests

    • Glucose. Usually a fasting glucose test is performed but, in some cases, a healthcare practitioner may also order a post prandial glucose (after a meal) or a GTT (glucose tolerance test – several glucose tests that are taken before and at timed intervals after a glucose challenge). The goal of glucose testing is to determine whether a person has diabetes or a decreased ability to process glucose (impaired glucose tolerance), which can eventually result in diabetes.
    • Hemoglobin A1c (HbA1c). This is a measure of glucose control and can be used for the diagnosis of diabetes.
    • Lipid profile. This measures HDL, LDL, triglycerides, and VLDL. If the triglycerides are significantly elevated, a direct measurement of the LDL may need to be done.

    There are other laboratory tests that are not recommended for diagnosing metabolic syndrome but that may ordered by some healthcare practitioners to provide additional information. They include:

    • C-peptide. This is a reliable indicator of endogenous (a person's own) insulin production.
    • Urine albumin. An early indicator of kidney disease, this test is used to help monitor diabetics and is recommended under the WHO criteria.
    • hs-CRP. This is a measure of low levels of inflammation that may be tested as part of an evaluation of cardiac risk.
    • sdLDL. This is a measurement of the number of small dense low-density lipoprotein molecules a person has. LDL varies in size, and the smaller denser molecules, which tend to form when elevated triglycerides and VLDL are present in the blood, are thought to be more aggressive in causing atherosclerosis. This test is now commercially available, but is not performed by many laboratories and is not ordered frequently. Its ultimate clinical utility has yet to be determined. It may be evaluated in a LDL particle testing.

    Non-Laboratory Tests

    • Blood pressure, to check for hypertension
    • Weight and waist circumference, to document abdominal obesity
    • BMI (body mass index), an alternate measure of obesity that is used by many healthcare practitioners; it is calculated by taking: (Weight in pounds X 705) / (height in inches squared); for example: (150 pounds X 705) / (67 inches X 67 inches) = a BMI of 23.5. An adult with a BMI greater than 30 is considered obese. This calculation does not, however, describe where the excess weight is on the body.
  • Treatment

    The primary "treatment" for metabolic syndrome is "lifestyle modification" to correct obesity. Those affected should lose excess weight and exercise regularly. It is also advisable to stop smoking cigarettes.

    Weight loss and exercise can:

    Drug treatment may be necessary to address other aspects of metabolic syndrome. Hypertension should be treated. Statins may be prescribed to treat unhealthy lipid levels. Some healthcare practitioners also recommend aspirin to decrease the risk of inappropriate blood clots. Some may prescribe medications to increase insulin sensitivity (although there is not widespread agreement on this).

    People with metabolic syndrome should work with their healthcare provider and other medical professionals, such as a nutritionist, to develop an individualized treatment plan and to monitor its effectiveness.

  • Metabolic Syndrome: Additional Details

    Insulin is a hormone that allows glucose to move into tissue cells, where is it is used for energy production. Insulin then prompts the liver to either store the remaining excess blood glucose as glycogen (for short-term energy storage) and/or to use it to produce fatty acids (which then become triglycerides). In people with insulin resistance, additional insulin must be released by the pancreas to overcome the tissue cells' resistance and allow glucose to enter the cells. This resistance and response to resistance can lead to increased insulin and glucose concentrations in the blood. Over time, increased glucose levels can harm blood vessels and organs such as the kidneys. Increased insulin levels can increase sodium retention by the kidneys, resulting in increases in blood pressure (which can lead to hypertension).

    The liver uses triglycerides, cholesterol, and protein to make triglyceride-rich very low-density lipoproteins (VLDL). In the blood, an enzyme removes triglycerides from VLDL to first produce intermediate density lipoproteins (IDL) and then low-density lipoproteins (LDL - the "bad" cholesterol). LDL is not all bad; it is an essential part of lipid metabolism and is necessary for the integrity of cell walls and for sex hormone and steroid production. However, in excess, LDL can oxidize and accumulate, eventually leading to fatty deposits in artery walls and to hardening and scarring of the blood vessels (and to cardiovascular disease and blood clots).

    LDL molecules are produced in a variety of sizes. Small dense LDL (sdLDL) are thought to be more prone to have their cholesterol deposited in artery walls than their larger counterparts. In obese and/or insulin-resistant people, excessive amounts of VLDL and triglycerides remain in the blood and lead to increases in the number of sdLDL produced.

    High-density lipoprotein (HDL – the "good" cholesterol) ordinarily transports excess cholesterol from the tissues back to the liver. In the liver, the cholesterol is either recycled for future use or excreted into bile. HDL's reverse transport is the only way that cells can get rid of excess cholesterol. It helps protect the arteries and, if there is enough HDL present, it can even reverse the build up of fatty plaques in the arteries. When there are excessive amounts of VLDL and triglyceride present, however, HDL concentrations in the blood decrease.

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