Should we dump the metabolic syndrome? No

Importance of a name

Recently the American Diabetes Association and the European Association for the Study of Diabetes questioned both the existence and usefulness of the metabolic syndrome.9 It was a comprehensive and thought provoking review which may have heightened interest in the syndrome but missed the point.

The review started by asking whether it was a syndrome at all. At its simplest syndrome means a collection of things. Our definition of metabolic syndrome is stronger: a cluster of inter-related risk factors for cardiovascular disease and diabetes with association greater than by chance alone. This has been shown repeatedly.10 11 Although the aetiology of the syndrome is uncertain, strong hypotheses implicate central adiposity, insulin resistance, and low grade inflammation.10 Aetiology is unknown for many other conditions whose existence is accepted, including type 2 diabetes. The syndrome is not attempting to create a new disease but to identify a risk state, like pre-diabetes (which was created by the American Diabetes Association) or dyslipidaemia.

Identifying risk

Although the syndrome has had several definitions during its evolution, today there are two main closely related definitions, as described above.5 6 Both use specific cut-off points for continuous variables, which allows them to be used in all clinical settings. The use of cut-off points is common throughout medicine where yes or no answers are the norm, including in the diagnosis of hypertension or diabetes. The decision to use different waist cut-off values for different ethnic groups is supported by available data that relate waist circumference to risk of diabetes and cardiovascular disease. For example, the prevalence of type 2 diabetes is consistently higher among Asians than Europids at any level of excess abdominal fat.4 12

The syndrome is not intended to give an absolute risk of cardiovascular disease or diabetes but to highlight people at increased relative risk on whom doctors can then focus. Absolute risk would require information on other factors such as low density lipoprotein cholesterol concentration, family history, age, and smoking. The question also arises whether the risk associated with the syndrome is greater than the sum of the parts. The evidence is equivocal, but again it is irrelevant – risk increases with the number of abnormal components.

We believe the syndrome has clinical value. In the specialised academic world of the syndrome’s critics, every person may automatically have all known risk factors checked routinely but in the “real world” of primary health care, this definition helps identify people at high risk without the need for sophisticated technology. The federation’s recommendations provide a simple approach that will allow the identification of most people who are at risk. Other measurements can then be made and preventive steps taken to reduce the long term burden of disease. Although lifestyle measures are of prime importance, sometimes drug treatment is needed.

Focus on the syndrome has also brought diabetologists and cardiologists together, ensuring much better appreciation of risk of diabetes among cardiologists and cardiovascular disease among diabetologists. This results in better management of people with type 2 diabetes, given that over 70% of them may die from cardiovascular disease. The most important outcome is that clinicians are focused on high risk patients. The increased prevalence of the underlying causes of the metabolic syndrome (obesity and sedentary lifestyle) portends an enormous increase in cardiovascular disease and type 2 diabetes worldwide.4 The diagnosis of the metabolic syndrome provides a focus on the cluster of cardiovascular disease and diabetes risk factors that require attention and emphasises the multifactorial nature of the risk for these diseases. As such, the syndrome continues to have an important role in both public health and individual care.