What is it?
Metabolic syndrome is a set of cardiovascular risk factors that includes: central abdominal obesity, a decreased ability to process glucose (increased blood glucose and/or insulin resistance), dyslipidaemia, and hypertension. Patients who have this syndrome have been shown to be at an increased risk of developing cardiovascular disease and/or type 2 diabetes. Metabolic syndrome is a common condition that goes by many other names (dysmetabolic syndrome, syndrome X, insulin resistance syndrome, obesity syndrome, and Reaven’s syndrome). Most people identified as having this syndrome have been educated about the importance of checking their lipid levels, watching for symptoms of diabetes, having their blood pressure monitored, and exercising – but there has been little to tie all of these factors together except pursuit of a "healthier lifestyle."
It is estimated that around 25% of adults in the Western World have metabolic syndrome. It can affect anyone at any age, but it is most frequently seen in those who are significantly overweight - with most of their excess fat in the central abdominal area - and physically inactive.
While several national and international organisations 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 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. There is therefore an ongoing debate about the scientific validity of the term ‘metabolic syndrome’. However, most clinicians are agreed that it is a clinically useful term as it alerts the clinic to the increased cardiovascular risk and risk of the patient developing diabetes.
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 as guidelines in the ATP III (the third report of the National Cholesterol Education Program expert panel on Detection, Evaluation, and Treatment of High Blood Cholesterol in Adults).
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. The table below summarizes the three sets of criteria:
Criteria for Clinical Diagnosis of Metabolic Syndrome
|clinical measure||WHO1||ATP III2||AHA/NHLBI3|
|Waist Circumference||≥102 cm in men,
≥88 cm in women
|Same as ATP III|
|BMI||BMI >30 kg/m2|
|Triglycerides||≥1.64mmol/L||Same as WHO||Same as WHO|
|HDL-C||<0.9mmol/L in men,
<1.0mmol/L in women
|<1.0mmol/L in men,
<1.2mmol/L in women
|Same as ATP III|
|Blood Pressure||≥140/90 mm Hg||≥130/85 mm Hg||Same as ATP III|
|Glucose||IGT, IFG, or T2D||Fasting >6.1mmol/L (IFG)||Fasting >5.6mmol/L (IFG)|
1. Alberti KG, Zimmet PZ. Diabet Med 1998;15:539–553.
2. National Cholesterol Education Program (NCEP) Adult Treatment Panel III final report. Circulation 2002;106:3143–3421.
3. Grundy, SM, et al. Circulation 2005;112:2735–2752.
Notes: WHO requires insulin resistance plus two additional risk factors for diagnosis; ATP III requires three of five risk factors for diagnosis. AHA/NHLBI recommends that triglycerides, HDL-C, and blood pressure should be considered abnormal when drug treatment is prescribed.
Abbreviations: BMI=Body mass index; IGT=Impaired Glucose Tolerance; IFG=Impaired Fasting Glucose; T2D=Type 2 Diabetes
Adapted from: Pizzi, R., Agreeing to Disagree: ADA, AHA Publish Opposing Views on Metabolic Syndrome, Clincal Laboratory News, January 2006 Volume 32, No. 1
Also frequently seen with metabolic syndrome but not included in the ATP III criteria are pro-thrombotic (blood clotting) and pro-inflammatory tendencies. While overt disease 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 patients who have metabolic syndrome and also smoke tend to have an even poorer prognosis.
Another feature commonly present in metabolic syndrome but not included in the diagnostic criteria is hyperuricaemia (an increased level of uric acid in the blood). In many patients this does not cause any symptoms but excessive amounts of uric acid can be associated with gout.
The root cause of most cases of metabolic syndrome can be traced back to poor eating habits and a sedentary lifestyle. Some cases occur in those already diagnosed with hypertension and in those with poorly controlled diabetes; a few are thought to be linked to genetic factors that are still being researched.
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 bloodstream 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.