Metabolic syndrome, previously known as syndrome X and insulin resistance syndrome, is a combination of conditions occurring concurrently and is characterized by insulin resistance, abdominal obesity, high blood pressure (BP), and dyslipidemia. While there is no consensus definition for metabolic syndrome, several health groups and governing bodies have drafted definitions that vary marginally from one another. These definitions have been listed in the table below.
Table 1. Definition of metabolic syndrome according to international health groups and governing bodies
World Health Organization 19981
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Defined by the presence of IR or its surrogates, impaired glucose tolerance (IGT) or T2DM and two of the following:
- Impaired glucose regulation or diabetes
- Insulin resistance
- BP ≥160/90 mmHg
- Triglycerides ≥150 mg/dL and/or high-density lipoprotein (HDL)-cholesterol <35 mg/dL for men or <39 mg/dL for women
- Waist to hip ratio >0.90 for men, >0.85 (women) and/or body mass index (BMI) >30 kg/m2
- Urinary albumin excretion rate ≥20 μgm-2
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European Group for the Study of Insulin Resistance 19992
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Insulin resistance or fasting glucose >75% of non-diabetic patients and two of the following:
- Fasting plasma glucose ≥ 6.1 mmol/l
- BP ≥140/90 mmHg or treatment for hypertension
- Triglycerides >180 mg/dL, HDL-cholesterol <40 mg/dL, or treatment for dyslipidemia
- Waist circumference ≥94 cm for men or ≥80 cm for women
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National Cholesterol Education Program Adult Treatment Panel III (APT-III) 20013
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Three or more of the following:
- Waist circumference >102 cm for men or >88 cm for women
- Triglycerides ≥150 mg/dL
- HDL-cholesterol <40 mg/dL for men or <50 mg/dL for women
- BP ≥130/≥85 mmHg
- Fasting glucose ≥110 mg/dL
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American Association of Clinical Endocrinology 20034
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Two or more of the following:
- Fasting plasma glucose 110-125 mg/dL
- 120 minute post-glucose challenge (75 g) 140-200 mg/dL
- Triglycerides 150 mg/dL
- HDL-cholesterol <40 mg/dL for men or <50 mg/dL for women
- BP 130/85 mmHg
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International Diabetes Federation (IDF) 20055
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Abdominal obesity based on waist circumference (population-specific measures ranging from ≥85-94 for men or ≥80-90 cm for women) plus any two of the following:
- Triglycerides >150 mg/dL, HDL-cholesterol <40 mg/dL for men or <50 mg/dL for women, or treatment for dyslipidemia
- BP ≥130/≥85 mmHg or treatment for hypertension
- Fasting glucose ≥100 mg/dL or T2DM diagnosis
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American Heart Association/National Heart, Lung, and Blood Institute (AHA/NHLBI) 20046
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- Waist circumference >102 cm for men or >88 cm for women
- Triglycerides ≥150 mg/dL
- HDL-cholesterol <40 mg/dL for men or <50 mg/dL for women
- BP ≥130/85 mmHg
- Fasting glucose ≥110 mg/dL
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IDF, NHLBI, AHA, World Heart Federation, International Atherosclerosis Society, and International Association for the Study of Obesity7
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Three of the following:
- Elevated waist circumference (population-specific measures ranging from ≥85-102 cm for men or ≥80-90 cm for women)
- Triglycerides ≥150 mg/dL
- HDL-cholesterol <40 mg/dL for men or <50 mg/dL for women
- BP ≥130/≥85 mmHg
- Fasting glucose ≥100 mg/dL
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The slight variations in definition result in inconsistent diagnosis of metabolic syndrome. In United States, the National Cholesterol Education Program’s (NCEP) Adult Treatment Panel III (ATP-III) criteria for metabolic syndrome is used most frequently.8 A 2010 study (n=22,719) investigated how the definition used may impact cardiovascular disease (CVD) risk and examined both the IDF and ATP-III definitions. Of the participants with metabolic syndrome, 79% met both the IDF and ATP-III criteria, 14% met only the IDF criteria, and 6% met only the ATP-III criteria. Regardless of criteria met, those with metabolic syndrome had increased self-reported incidence of CVD (27% of participants meeting both criteria, 32% of those meeting only ATP-III criteria, and 25% of those meeting only IDF criteria) when compared to participants without metabolic syndrome (17%). This study draws attention to the importance of using combined definitions when diagnosing metabolic syndrome and acknowledging that no one definition will fit all cases.
According to an analysis of the National Health and Nutrition Examination Survey (NHANES), an estimated 34% of adults in the United States (US) over the age of 20 had metabolic syndrome from 2003-2006.9 The prevalence of T2DM for the same time period was 10.2%, meaning that metabolic syndrome is roughly three times more prevalent than T2DM in the US.10 There are no global data available for prevalence of metabolic syndrome.
Metabolic syndrome is linked to diabetes mellitus, with metabolic syndrome commonly found in those with diabetes. A 2010 study found that among 8,571 patients with metabolic syndrome, 40% had diabetes.8 Additionally, many definitions of metabolic syndrome include blood glucose measures that are consistent with both type 1 and type 2 diabetes. Although the two are related, they are distinct in that metabolic syndrome involves a number of metabolic disfunctions not characterized by diabetes.
Metabolic syndrome increases a patient’s chances of CVD. A 2010 meta-analysis found metabolic syndrome increases risk of CVD (10.4% incidence among those with metabolic syndrome vs 3.6% among those without), stroke (6.0% vs 2.4%), myocardial infraction (6.4% vs 2.8%), CVD mortality (4.3% vs 2.3%), and all-cause mortality (13.4% vs 9.0%).11
References
- Alberti KG, Zimmet PZ. Definition, diagnosis and classification of diabetes mellitus and its complications. Part 1: diagnosis and classification of diabetes mellitus provisional report of a WHO consultation. Diabet Med. Jul 1998;15(7):539-53. doi:10.1002/(sici)1096-9136(199807)15:7<539::aid-dia668>3.0.co;2-s
- Balkau B, Charles MA. Comment on the provisional report from the WHO consultation. European Group for the Study of Insulin Resistance (EGIR). Diabet Med. May 1999;16(5):442-3. doi:10.1046/j.1464-5491.1999.00059.x
- Executive Summary of The Third Report of The National Cholesterol Education Program (NCEP) Expert Panel on Detection, Evaluation, And Treatment of High Blood Cholesterol In Adults (Adult Treatment Panel III). Jama. May 16 2001;285(19):2486-97. doi:10.1001/jama.285.19.2486
- Einhorn D, Reaven GM, Cobin RH, et al. American College of Endocrinology position statement on the insulin resistance syndrome. Endocr Pract. May-Jun 2003;9(3):237-52.
- Alberti KG, Zimmet P, Shaw J. The metabolic syndrome--a new worldwide definition. Lancet. Sep 24-30 2005;366(9491):1059-62. doi:10.1016/s0140-6736(05)67402-8
- Grundy SM, Brewer HB, Jr., Cleeman JI, Smith SC, Jr., Lenfant C. Definition of metabolic syndrome: report of the National Heart, Lung, and Blood Institute/American Heart Association conference on scientific issues related to definition. Arterioscler Thromb Vasc Biol. Feb 2004;24(2):e13-8. doi:10.1161/01.atv.0000111245.75752.c6
- 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. Oct 20 2009;120(16):1640-5. doi:10.1161/circulationaha.109.192644
- Brown TM VJ, Bittner V, Safford MM. Variations in prevalent cardiovascular disease and future risk by metabolic syndrome classification in the Reasons for Geographic and Racial Differences in Stroke (REGARDS) study. Am Heart J .2010. p. 385-391.
- Ervin RB. Prevalence of metabolic syndrome among adults 20 years of age and over, by sex, age, race and ethnicity, and body mass index: United States, 2003-2006. Natl Health Stat Report. May 5 2009;(13):1-7.
- National Center for Health S. Health, United States. Health, United States, 2008: With Special Feature on the Health of Young Adults. National Center for Health Statistics (US); 2009.
- Mottillo S, Filion KB, Genest J, et al. The Metabolic Syndrome and Cardiovascular Risk. Journal of the American College of Cardiology. 2010;56(14):1113-1132. doi:doi:10.1016/j.jacc.2010.05.034