Metabolic syndrome: definition and prevalence in children

EDITORIALS

Metabolic syndrome: definition and prevalence in children

Wei Chen^I; Gerald S. Berenson^II

^IMD, PhD. Tulane Center for Cardiovascular Health, Department of Epidemiology, Tulane University Health Sciences Center, New Orleans, LA, USA

^IIMD. Tulane Center for Cardiovascular Health, Department of Epidemiology, Tulane University Health Sciences Center, New Orleans, LA, USA

Metabolic syndrome, a concurrence of disorders including obesity, insulin resistance, dyslipidemia and hypertension, has gained importance because of its association with subsequent development of cardiovascular disease and type 2 diabetes. The extent of coronary atherosclerosis in children and young adults increases markedly with the increasing number of multiple risk factors.¹ The metabolic syndrome is highly prevalent in adults, and the coexistence of these multiple cardiovascular risk variables also occurs commonly in children.^2,3 Importantly, multiple risk factors reinforce each other and persist (track) from childhood into adulthood.³ Recent studies suggest that metabolic syndrome may even originate in the embryonic and fetal stages.

In this month's issue of Jornal de Pediatria, Ferreira et al.⁴ reported the results of their study on the prevalence of the metabolic syndrome and the relationships between its components and insulin resistance in 52 obese children aged 7-10 years, defined by body mass index (BMI) > 95th percentile. In these children, they found a prevalence of metabolic syndrome (17.3%) defined by a clustering of central obesity, hypertriglyceridemia, low HDL cholesterol, hyperglycemia and elevated blood pressure. They also recognized that the clustering of these risk factors is strongly associated with insulin resistance measured as the homeostasis model assessment (HOMA) of insulin resistance. The important issue addressed by the authors is the role of obesity and insulin resistance in the development of metabolic syndrome in children. We and others have shown that obesity is more important than hyperinsulinemia as the primary etiologic process.⁵ Distressingly, overweight and obesity prevalence among both adults and children is rising throughout the world. Overweight prevalence tripled in U.S. children and adolescents in the past two decades. According to recent estimates, 17.1% of 2-19 year-old children are overweight.⁶ Consequently, the metabolic syndrome in children becomes a global public health problem. The research focus of the metabolic syndrome has shifted to its prevention in early life.

Significant clustering of the metabolic syndrome components has been consistently demonstrated in various ethnic groups and populations; however, there are still some concerns and debates regarding the definition of metabolic syndrome.⁷ Several organizations (World Health Organization, National Cholesterol Education Program, International Diabetes Federation, American College of Endocrinology, and European Group for the Study of Insulin Resistance) have proposed definitions of the metabolic syndrome for adults using different components and cutoff points. One consequence of the nonuniform definition is that currently available data on the frequency of the syndrome in various populations vary widely. A detailed review on the prevalence of metabolic syndrome using different criteria has been published recently.⁸ In spite of attempts in recent years to reach agreement on the definition of the syndrome, comparisons of published prevalence rates for different populations worldwide are difficult.

Although the prevalence of the metabolic syndrome is rising in children, there have been no consistent criteria available to diagnose the metabolic syndrome in pediatric populations in terms of the components and cutoff points. Percentiles and adjusted values have been commonly used as cutoff points for the metabolic syndrome components in children and adolescents.^4,9 As in adults, the comparison of the prevalence among pediatric populations is problematic. An alternative method is to analyze the clustering of the components as continuous variables. We applied intraclass correlation² and path analysis in our studies on the metabolic syndrome in children, adolescents and adults from the Bogalusa Heart Study. Although the degree of clustering of the risk variables can be determined by using this approach, it does not provide prevalence data. In Ferreira's study, the authors used both percentiles and age- and sex-specific cutoff values of the components to define the metabolic syndrome in children. A recent report by Weiss et al. showed alarming high rates of metabolic syndrome among obese youths: 38.7% in moderately obese children and 49.7% in severely obese children.¹⁰ The definition used in Weiss' study is BMI > 97th percentile, triglyceride > 95th percentile, HDL cholesterol < 5th percentile and glucose between 140-200 mg/dL. Obviously, the huge variations in the prevalence rates are in large part because of the different components and cutoff points used in the two studies. In fact, according to Weiss' criteria, the prevalence of the metabolic syndrome would be much higher in Ferreira's study sample of obese children if the two-factor clustering is taken into account. Cook et al. analyzed a sample of adolescents aged 12-19 years from the Third National Health and Nutrition Examination Survey (NHANES III) (1988-1994) using the same components as Ferreira's study, but different cutoff points. They found that the prevalence of the metabolic syndrome is 6.8% among overweight adolescents and 28.7% among obese adolescents.⁹

In these previous studies, another problem resulted from the inconsistent criteria used in children is that BMI is used as both a stratifying indicator and a component of the syndrome.^10,11 Although obesity is an important determinant of the metabolic syndrome, it is far from being a necessary and sufficient etiologic factor of the syndrome. Therefore, the observations such as "No nonobese subjects met the criteria for the metabolic syndrome",¹⁰ "the metabolic syndrome was found almost exclusively among obese teens"¹¹ or "The syndrome was present in 0.1% of adolescents with a BMI below the 85th percentile"⁹ are in large part due to the definition of obese and nonobese children. In these studies, very few or no nonobese children had the obesity component by the authors' definition. In Ferreira's and Cook's studies, they used the BMI percentile to define obesity and used a central obesity measure as a component of the metabolic syndrome. The concern is that the prevalence may be overestimated because central obesity measured by waist circumference is expected to be strongly correlated with overall obesity measured by BMI. The high prevalence is, to some extent, due to the sample selection of obese children. Another concern is that fasting glucose was repeatedly included in both clustering analysis as a component and the calculation of HOMA index, which in part accounted for a strong correlation between insulin resistance and the metabolic syndrome.^4,10

Such discrepancies in the prevalence and inconsistent definition criteria highlight a need of universal definition of the metabolic syndrome for children. While a global definition of the metabolic syndrome for adults is being attempted, it is suggested that the metabolic syndrome should be considered a "loose" concept instead of a strict definition.¹² This argument is especially true for children.

References

1. Berenson GS, Srinivasan SR, Bao W, Newman WP 3rd, Tracy RE, Wattigney WA. Association between multiple cardiovascular risk factors and atherosclerosis in children and young adults. The Bogalusa Heart Study. N Engl J Med. 1998;338:1650-6.

2. Chen W, Bao W, Begum S, Elkasabany A, Srinivasan SR, Berenson GS. Age-related patterns of the clustering of cardiovascular risk variables of syndrome X from childhood to young adulthood in a population made up of black and white subjects: the Bogalusa Heart Study. Diabetes. 2000;49:1042-8.

3. Bao W, Srinivasan SR, Wattigney WA, Berenson GS. Persistence of multiple cardiovascular risk clustering related to syndrome X from childhood to young adulthood. The Bogalusa Heart Study. Arch Intern Med. 1994;154:1842-7.

4. Ferreira AP, Oliveira CE, França NM. Metabolic syndrome and risk factors for cardiovascular disease in obese children: the relationship with insulin resistance (HOMA-IR). J Pediatr (Rio J). 2007;83:21-6.

5. Srinivasan SR, Myers L, Berenson GS. Predictability of childhood adiposity and insulin for developing insulin resistance syndrome (syndrome X) in young adulthood: the Bogalusa Heart Study. Diabetes. 2002;51:204-9.

6. Ogden CL, Carroll MD, Curtin LR, McDowell MA, Tabak CJ, Flegal KM. Prevalence of overweight and obesity in the United States, 1999-2004. JAMA. 2006;295:1549-55.

7. Kahn R, Buse J, Ferrannini E, Stern M. The metabolic syndrome: time for a critical appraisal. Joint statement from the American Diabetes Association and the European Association for the Study of Diabetes. Diabetologia. 2005;48:1684-99.

8. Cameron AJ, Shaw JE, Zimmet PZ. The metabolic syndrome: prevalence in worldwide populations. Endocrinol Metab Clin North Am. 2004;33:351-75.

9. Cook S, Weitzman M, Auinger P, Nguyen M, Dietz WH. Prevalence of a metabolic syndrome phenotype in adolescents: findings from the third National Health and Nutrition Examination Survey, 1988-1994. Arch Pediatr Adolesc Med. 2003;157:821-7.

10. Weiss R, Dziura J, Burgert TS, Tamborlane WV, Taksali SE, Yeckel CW, et al. Obesity and the metabolic syndrome in children and adolescents. N Engl J Med. 2004;350:2362-74.

11. Goodman E, Daniels SR, Morrison JA, Huang B, Dolan LM. Contrasting prevalence of and demographic disparities in the World Health Organization and National Cholesterol Education Program Adult Treatment Panel III definitions of metabolic syndrome among adolescents. J Pediatr. 2004;145:445-51.

12. Ko GT. Metabolic syndrome or "central obesity syndrome"? Diabetes Care. 2006;29:752.

5. Srinivasan SR, Myers L, Berenson GS. Predictability of childhood adiposity and insulin for developing insulin resistance syndrome (syndrome X) in young adulthood: the Bogalusa Heart Study. Diabetes. 2002;51:204-9.

Publication Dates

• Publication in this collection
  19 Mar 2007
• Date of issue
  Feb 2007