For many years, scientists and clinicians have recognized the association between several relatively common conditions such as hypertension, abnormal glucose metabolism (diabetes and other milder forms of glucose intolerance), and obesity. The observed association has also included other factors such as abnormal lipids (cholesterol and triglycerides), elevated uric acid, and microscopic amounts of protein in the urine. This association has received many names, including insulin resistance syndrome, syndrome X, and the deadly quartet, and is now widely known as metabolic syndrome (MetSx).
The relevance of MetSx relies on its high prevalence in both developed and less developed countries and on its association with a high risk for developing cardiovascular disease and type 2 diabetes mellitus. This review will summarize the current data regarding the diagnosis and prevalence of MetSx worldwide, its risk factors, clinical relevance, and treatment. This review will also discuss some of the ongoing controversies related to MetSx that major medical organizations and recognized authorities have spurred, and how the lack of a global agreement can distract attention from an epidemic that affects all ages.
Although there is full agreement that several factors such as hypertension, abnormal glucose metabolism, abnormal lipids, and obesity are strongly associated and may indeed share one or more physiopathological pathways, there is significant variability in the way in which MetSx is defined. To illustrate this lack of consensus, Table 1 displays the three most commonly used definitions of MetSx, revealing major differences in the diagnostic criteria. For example, the World Health Organization (WHO) requires a measure of insulin resistance to make the diagnosis of MetSx and includes microalbuminuria as a possible criterion, while the International Diabetes Federation (IDF) requires the presence of central obesity but does not require the documentation of glucose intolerance or insulin resistance to determine the presence of MetSx. A more clinically oriented definition is provided by the National Cholesterol Education Program Adult Treatment Panel III (NCEP ATP III) by using measurements that are commonly used in clinical practice.