Metabolic Syndrome—A Common and Dangerous Health Problem
Francisco Lopez-Jimenez Division of Cardiovascular Diseases, Department of Medicine, Mayo Clinic College of Medicine
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.
Diagnosis
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. This lack
of a standard way to define the diagnosis of MetSx has caused some
skepticism in the scientific community and even some quarrels among
major medical organizations, as documented in the position statement of
the American Diabetes Association (ADA), which minimizes the
importance of diagnosing patients with this ‘new’ nomenclature. This
lack of a unified diagnostic method also makes it difficult to compare or
combine results of studies assessing the incidence and prevalence of
MetSx and the effect of therapeutic interventions on MetSx.
Prevalence
The prevalence of MetSx has been estimated in multiple studies, showing
that about one-quarter of the US population meet diagnostic criteria for
MetSx. National surveys performed with similar methodology prove that the
prevalence of MetSx has increased by 25% in only 10 years, parallel to the
increase in the prevalence of obesity and diabetes.
The prevalence of MetSx is higher in Native Americans and Mexican-
Americans than in Non-Hispanic Whites or African-Americans. Gender
appears to affect the prevalence of MetSx depending on the country or
ethnic group. For example, in France and the US, the prevalence of MetSx
is lower in women than in men, while the opposite occurs among Native
Americans and in Turkey, India, and other parts of the world. It is not clear
why these country- or race-related differences exist, but they may be related
to some genetic traits and to different levels of physical activity between
men and women depending on the country of origin. The prevalence of
MetSx also increases with age, as suggested by prevalence studies showing
that MetSx is six times more common in people older than 50 years
compared with young adults aged between 20 and 29 years. This increased
prevalence with older age may reflect a more sedentary lifestyle in elderly
groups, which is a major risk factor for MetSx, but also reflects the higher
prevalence of several of the MetSx criteria—such as hypertension, diabetes,
and obesity—compared with younger people.
