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Date of release: 07 December, 2009

Updated definition for metabolic syndrome


The metabolic syndrome is a complex of risk factors for cardiovascular disease and diabetes mellitus which are inter-related and cluster together more often than by chance. The five main risk factors include glucose abnormalities, dyslipidemia with low levels of high density lipoprotein (HDL) cholesterol or raised triglycerides, central obesity, and raised blood pressure. Insulin resistance is thought to be a pivotal factor linking these various disturbances together. Thus, names such as ‘syndrome X’ (metabolic as opposed to cardiac) and the ‘insulin resistance syndrome’ had previously been applied to this clustering of metabolic risk factors. The importance of the metabolic syndrome is that individuals with it have double the risk for developing cardiovascular disease and a five-fold increased risk for developing diabetes [1]. A formal definition of the metabolic syndrome was first published in 1998 by a WHO Consultation group [2]. This required evidence of insulin resistance, albeit indirect, together with two other risk factors to make the diagnosis. This was followed in 2001 by a definition from the US National Cholesterol Education Program Adult Treatment Panel III (ATP III) [3], which required the presence of any three risk factors without necessarily including insulin resistance. In 2005, the International Diabetes Federation (IDF) refined the WHO diagnostic criteria by dropping the necessity of insulin resistance but instead made abdominal obesity a requirement together with two other risk factors [4]. This insistence on increased waist circumference, together with a stricter upper limit for this, was the major difference from the ATP III definition, whereas the other risk factor thresholds were the same. Most recently, an attempt has been made to harmonize the criteria, involving the IDF, the National Heart, Lung, and Blood Institute (NHLBI), the American Heart Association, the World Heart Federation, the International Atherosclerosis Society and the International Association for the Study of Obesity [1]. The result is that the necessity for increased waist circumference has been dropped, and the presence of any three risk factors from the five is sufficient to make the diagnosis of metabolic syndrome. The limits for waist circumference are, for the present, determined by national or regional thresholds.

Comment

With an increasing incidence of obesity and hence type 2 diabetes in most developed countries, the incidence of metabolic syndrome is clearly increasing. Indeed, about one-quarter of US adults now have the syndrome [5] and, had the IDF waist circumference criterion been adopted in the US, this figure would undoubtedly have been much higher. However, its presence has been seldom recognized by clinicians in general, largely because of uncertainty as to how to make the diagnosis. This new statement is a welcome rationalization as it enables the diagnosis of metabolic syndrome to be made using simple and straightforward criteria, without resort to complicated investigations. This should encourage practitioners to make the diagnosis and then treat the condition by tackling its components. Since the majority of patients with metabolic syndrome will have central obesity, dietary measures are an essential part of management. A weight-reducing diet that is low in glycemic index and cholesterol will help to improve insulin resistance, dyslipidemia and hypertension. If there is evidence of insulin resistance, then additional treatment with the insulin sensitizing drug, metformin, can be justified. There is increasing evidence that metformin can slow or halt the progression to type 2 diabetes [6]. The judicious use of lipid-active agents and antihypertensive drugs may also be necessary. For postmenopausal women, hormone replacement therapy (HRT) may well be of benefit. Menopause itself produces a type of metabolic syndrome [7], and HRT regimens can be devised that will improve insulin resistance, raise HDL cholesterol or lower triglycerides, and lower blood pressure [8]. It still remains for the criteria to be determined as to what constitutes an increased waist circumference, and this is being tackled by the WHO and the NHLBI, whose deliberations are awaited.

Comentario

John Stevenson
National Heart & Lung Institute, Imperial College London, Royal Brompton Hospital, London, UK

    References

  1. Alberti KG, Eckel RH, Grundy SM, et al. Harmonizing the metabolic syndrome: a joint interim statement of the International Diabetes Federation Task Force on Epidemiology and Prevention; National Heart, Lung, and Blood Institute; American Heart Association; World Heart Federation; International Atherosclerosis Society; and International Association for the Study of Obesity. Circulation 2009;120:1640-45. Published Oct 20.
    http://www.ncbi.nlm.nih.gov/pubmed/19805654

  2. Alberti KG, Zimmet PZ. Definition, diagnosis, and classification of diabetes mellitus and its complications. Part I. Diagnosis and classification of diabetes mellitus provisional report of a WHO consultation. Diabetes Med 1998;15:539-53.
    http://www.ncbi.nlm.nih.gov/pubmed/9686693

  3. National Cholesterol Education Program (NCEP) Expert Panel on Detection, Evaluation and Treatment of High Blood Cholesterol in Adults (Adult Treatment Panel III) final report. Circulation 2002;106:3143-421.
    http://www.ncbi.nlm.nih.gov/pubmed/12485966

  4. Alberti KG, Zimmet P, Shaw J; IDF Epidemiology Task Force Consensus Group. The metabolic syndrome a new worldwide definition. Lancet 2005;366:1059-62.
    http://www.ncbi.nlm.nih.gov/pubmed/16182882

  5. Bonow RO, Eckel RH. Diet, obesity, and cardiovascular risk. N Engl J Med 2003;348:2057-58.
    http://www.ncbi.nlm.nih.gov/pubmed/12761363

  6. Salpeter SR, Buckley NS, Kahn JA, Salpeter EE. Meta-analysis: metformin treatment in persons at risk for diabetes mellitus. Am J Med 2008;121:149-57.
    http://www.ncbi.nlm.nih.gov/pubmed/18261504

  7. Spencer CP, Godsland IF, Stevenson JC. Is there a menopausal metabolic syndrome? Gynecol Endocrinol 1997;11:341-55.
    http://www.ncbi.nlm.nih.gov/pubmed/9385535

  8. Stevenson JC. HRT and cardiovascular disease. In Lumsden MA, ed, Best Practice and Research Clinical Obstetrics and Gynaecology, Vol 23. New York: Elsevier, 2009:109-20