Curr Atheroscler Rep (2014) 16:436 DOI 10.1007/s11883-014-0436-y
NUTRITION (JP FOREYT, SECTION EDITOR)
Childhood Obesity and the Metabolic Syndrome Scott Owens & Riley Galloway
Published online: 20 July 2014 # Springer Science+Business Media New York 2014
Abstract Although research published during the past year suggests the prevalence of childhood obesity in the USA may have plateaued, it remains unacceptably high and places large numbers of youths at elevated risk of chronic diseases. The concept of the metabolic syndrome (MetS) is frequently used to help capture this increased risk. Use of the MetS concept with children remains controversial, however. Addressing issues related to the definition of the MetS and its utility in clinical and research settings has generated a variety of recent investigative efforts. At the same time, the past year revealed a number of promising prevention and treatment interventions for childhood obesity and the MetS. Still unknown, however, is the optimal combination of diet, exercise, and other behavioral changes for improving the obesity and MetS status of children. These issues are the subject of this review. Keywords Children . Diet . Exercise . Risk factors . Genetics . Review
Introduction Gaining a better understanding of childhood obesity and its many complexities has engaged researchers and clinicians for many years. One of the complexities involves the nature of the relationship between childhood obesity and the risk of chronic diseases. A concept frequently used in characterizing this
This article is part of the Topical Collection on Nutrition S. Owens (*) : R. Galloway University of Mississippi, 215 Turner Center, University, MS 38677-1848, USA e-mail: [email protected] R. Galloway e-mail: [email protected]
relationship is that of the metabolic syndrome (MetS). Conceptually, the MetS is the clustering in an individual of a set of cardiometabolic risk factors thought to place the individual at increased risk of the development of cardiovascular diseases and type 2 diabetes [1]. The health consequences of childhood obesity and the MetS are wide-ranging as obesity appears to be on the causal pathway of every major chronic disease [2]. This review will focus on research published during 2013– 2014 related to childhood obesity and the MetS, emphasizing new information regarding prevalence rates, prevention and treatment strategies, and unresolved issues related to the MetS.
Prevalence of Childhood Obesity and the Metabolic Syndrome A pair of studies published in early 2014 based on the most recent National Health and Nutrition Examination Survey (NHANES) data provide tentative support for the notion that the US childhood obesity epidemic may be slowing, plateauing, or, in some age groups, reversing [3•, 4•]. The first study [3•] reported an obesity prevalence of 16.9 % in the 2– 19-year-old age group, which, although unacceptably high, indicated no significant change between the 2003–2004 and 2011–2012 measurement periods. Among 2–5-year-old children, obesity prevalence showed a decline from 13.9 % to 8.4 %. The second study [4•] analyzed an NHANES database of 26,690 children aged 2–19 years, and showed an obesity prevalence of 17.3 %. No significant increase in obesity prevalence was observed compared with data from the 2009–2010 measurement period. These US data are consistent with a recent international report noting a stabilization or decline in childhood obesity prevalence in several westernized countries [5]. Although these recent data may be viewed as encouraging, the relatively high prevalence rates remain
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disconcerting. In addition, the NHANES data indicate a worrisome upward trend in the prevalence of children with the severest forms of obesity as the prevalence of class 3 obesity exceeded 2 % for the first time [4•]. Estimating the prevalence of childhood MetS continues to be challenging and controversial. To begin with, no set of standardized criteria for identifying the MetS in children has gained universal acceptance [6]. More than 40 definitions for childhood MetS have been proposed, most based on adaptations of adult criteria [7]. Differences among the definitions relate mainly to the specific components included and their threshold values. Despite their differences, the various definitions tend to share some common features, including an obesity estimate (typically BMI or waist circumference), blood pressure measures, blood lipid measures [typically triglycerides, LDL cholesterol (LDL-C), or HDL cholesterol (HDL-C)], and a diabetes-related risk factor (fasting glucose, glucose tolerance, or insulin) [8]. Table 1 displays components and threshold values for two commonly used childhood MetS definitions. Despite the prevalence differences across various studies [9, 10], the pattern of MetS prevalence relative to factors such as sex, age/pubertal status, ethnicity, and obesity status tends to be relatively consistent. Relative to sex, MetS prevalence is typically higher in boys than in girls, regardless of the MetS definition used. In their most recent study of US adolescents, Laurson et al. [11] reported a MetS prevalence of 7.9 % in a sample of 1,785 boys compared with 6.9 % in 1,600 girls. Relative to age/pubertal status, MetS prevalence tends to be higher in pubertal children than in the prepubertal population [12]. Regarding ethnicity, NHANES data suggest substantial prevalence differences. For example, in a group of 2,456 adolescents, MetS prevalence in Hispanics was 11.2 % compared with 8.9 % in whites and 4.0 % in African Americans [13]. Lastly, prevalence data relative to obesity status show a
clear and consistent pattern, with the MetS substantially more prevalent in obese as compared with normal-weight children. The 2014 NHANES report on the MetS in adolescents [11], which used the Centers for Disease Control and Prevention weight standards, revealed that MetS prevalence was less than 1 % in normal-weight boys, 6.8 % in overweight boys, and 34.5 % in obese boys. In girls, the MetS prevalence rates were 1.7 % in those of normal weight, 9.2 % in the overweight, and 24.6 % in the obese.
Prevention and Treatment of Childhood Obesity and the Metabolic Syndrome Prevention A number of studies published in the past year support the notion that a healthy diet and ample physical activity can be powerful weapons for preventing childhood obesity and associated metabolic consequences. Data from the Amsterdam Growth and Health Longitudinal Study showed that greater adherence to a Mediterranean dietary pattern beginning in adolescence was associated with lower blood pressure, lower total cholesterol levels, and lower BMI during adolescence and into young adulthood [14•]. Data from Stabelini-Neto et al. [15] indicate that achieving approximately 90 min per day of moderate-to-vigorous physical activity will likely prevent development of the MetS in adolescents. Mendoza and Liu [16] examined a nationally representative sample of US kindergarten students and found that children who engaged in active transport to school (walking or biking) in kindergarten had lower BMI zscores in fifth grade than their peers who were passive commuters to school. Lazorick et al. [17••] reported the results of a longitudinal obesity prevention intervention targeting a single-site cohort of 106 students
Table 1 Criteria for diagnosis of the metabolic syndrome (MetS) in children Source
Ages
Obesity
10 years to less Waist circumference than 16 years greater than or equal to the 90th percentile (or adult cutoff if lower) 12–19 years Waist circumference National Cholesterol greater than or equal Education Program/ to the 90th percentile Adult Trial Panel III (age- and genderas modified for specific from adolescentsb [51] NHANES III) International Diabetes Foundationa [50]
Lipids
Blood pressure
Level of triglycerides above 1.7 mmol/L, HDL-C level below 1.03 mmol/L
Systolic above Glucose level above 130 mmHg or diastolic 5.6 mmol/L or known above 85 mmHg type 2 diabetes
Level of triglycerides above 1.24 mmol/L, HDL-C level below 1.03 mmol/L
Systolic or diastolic above Glucose level 6.1 mmol/L the 90th percentile or above (age-, gender-, and height-specific)
HDL-C HDL cholesterol, NHANES III Third National Health and Nutrition Examination Survey a
Diagnosis of the MetS requires the presence of obesity and two or more of the other criteria.
b
Diagnosis of the MetS requires the presence of three or more of the criteria.
Glucose
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beginning in seventh grade and followed across 5 years. The intervention integrated a lifestyle behavior change curriculum within academic subjects. Longitudinal changes in the intervention cohort were compared with those in a nationally representative sample of similarly aged children not receiving the intervention. At follow-up, 13 % of the comparison-group students who had been a healthy weight at the beginning moved to the overweight or obese categories, whereas only 2 % of the intervention cohort moved from healthy weight to overweight or obese. Although these studies highlight the importance of good dietary habits and adequate amounts of physical activity, researchers are also advising that prevention efforts must address the high levels of sedentariness engaged in by children and adolescents [18, 19]. Treatment Successful treatment of childhood obesity and the MetS has important implications. As noted by Magnussen et al. [20], data from longitudinal cohort studies indicate that resolving an individual’s at-risk metabolic status between youth and adulthood largely returns the risk of the individual to a level that is not statistically different from the risk of those who did not have the risk in youth or adulthood. On the other hand, those that retain the risk status into adulthood have a significantly increased risk burden. Some, but not all, recent treatment programs have shown promise in resolving childhood obesity and metabolic risk. In a randomized, crossover clinical trial Saneei et al. [21•] compared the effects on the MetS and its features in 49 adolescent girls who were advised to follow the Dietary Approaches to Stop Hypertension (DASH) eating plan for 6 weeks versus usual dietary advice. Compared with usual dietary advice, the DASH group experienced a significant reduction in the prevalence of the MetS, reduced prevalence of high blood pressure, and improved dietary quality. Saneei et al. concluded that the DASH eating plan can be considered a useful treatment modality for adolescent girls diagnosed with the MetS. Mirza et al. [22] investigated the effects of a low-fat diet versus a low-glycemic-load diet in a group of 113 obese Hispanic children aged 7–15 years randomized to one of the two diets for 3 months and then followed for 2 years. Both groups showed a reduction in BMI zscore at 2 years and improved waist circumference and systolic blood pressure. There were no significant differences by dietary group for changes in BMI, insulin resistance, or components of the MetS. The study showed it was feasible and practical to induce short-term dietary changes in Hispanic youths with either type of diet but with no apparent advantage of one diet over the other. Several multicomponent interventions that combined diet and physical activity have been published within the past year.
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Davis et al. [23••] reported 1-year follow-up results of a 12week, family-based behavioral group treatment program for pediatric obesity. The treatment program consisted of 12 consecutive weekly 2-h sessions that included nutrition-, exercise-, and behavior-related topics. Each meeting also included a group exercise activity. A total of 211 children (mean age 10 years) enrolled in the program and 71 % attended at least 50 % of the 12 weekly meetings. Among the 63 children who provided both baseline and 1-year follow-up data, BMI z score remained significantly lower at 1 year than at the baseline. Rieder et al. [24] reported on the results of a 9-month, multicomponent community-based program for severely obese, inner-city adolescents. Significant improvements were observed at the completion of the 9-month intervention for rates of gain in BMI and BMI zscore. Loss of improvements were observed 9 months after completion of the program however, prompting the researchers to comment that extending the length of the program may be necessary to prevent long-term weight regain. Carraway et al. [25] reported on the long-term efficacy of a 19-day, camp-based immersion treatment program for obese, low-economic status adolescents. The program included a nutrition curriculum, group therapy, cognitive behavioral therapy, and daily physical activity. Long-term (10 months) follow-up (before camp versus end of follow-up) was associated with significant overall improvements in percent overweight. Roberts et al. [26•] demonstrated that a short-term, intensive lifestyle modification program was effective in ameliorating several metabolic risk factors in both normal-weight and overweight/obese children. The participants were 19 overweight/obese and 14 normal-weight children. The 2-week intervention included an ad libitum highfiber, low-fat diet and 2–2.5 h of exercise daily. Only the obese group lost weight (3.9 %), but remained obese. Both groups exhibited significant decreases in the levels of insulin, IL-6, and TNFα. As no associations between changes in weight indices and changes in other biomarkers were observed, the researchers suggested that obesity per se was not the primary driver of the risk factors. Rather, dietary intake and lack of physical activity may be the underlying causes of the observed metabolic abnormalities. They added that the results reinforce the need to encourage healthy diet and exercise habits even in normal-weight children. Although lifestyle changes are the first line of defense against childhood obesity and the MetS, pharmacological interventions are another possible option. Bitkin et al. [27] retrospectively examined the effects of ACE inhibitors on MetS components in 53 children with obesity-associated MetS, consisting of a group of 23 children who were using an ACE inhibitor and a group of 30 children who were not. Group comparisons made across 3–12 months after the ACE inhibitor group began use revealed significantly lower values in the ACE inhibitor group for LDL-C, glucose, insulin, and triglycerides. HDL-C values were significantly higher in the
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ACE inhibitor group. The researchers noted the need for randomized controlled trials of the long-term effectiveness of this drug in children. In a recent review, Marcovecchio and Chiarelli [1] noted that some limited success in children relative to obesity and MetS risk factors has been seen with administration of metformin, sibutramine, and orlistat, although side effects can be an issue. In another review, Garver et al. [28] note that it is too soon tell whether newer antiobesity drugs such as lorcaserin or phenteramine/topiramate might have application in children.
Current Issues Associated with Childhood Metabolic Syndrome Despite the continued use of the MetS concept, a number of ongoing issues surround the MetS concept and its application to children. For one thing, children, unlike the adults for whom the MetS concept was originally developed, reside in vastly different stages of growth, development, and pubertal status. This calls into question whether such variability can be accommodated by a single MetS definition [1]. Another difficulty is the fact that reference values for some MetS components, such as waist circumference, exist for only some populations and that there remains disagreement over how to measure waist circumference in children [1]. Lack of reference values in some populations for blood pressure or HDL-C level render cross-cultural comparisons problematic [29]. It is also argued that ethnic differences in components of the MetS make a single definition questionable [30]. In this regard, Fitzpatrick et al. [31•] recently developed a model of the MetS specific to African American adolescents. They applied confirmatory factor analysis to a sample of 822 African American adolescents aged 12–17 years in the NHANES database and determined the best fitting model consisting of waist circumference, systolic blood pressure, HDL-C level and fasting insulin level. The model indicated that 19 % of African American boys and 16 % of African American girls were at high risk of the MetS. That HDL-C level, but not the level of triglycerides, was retained in the model for African American adolescents supports the notion that racial/ethnicspecific MetS definitions are probably needed. The clinical utility of the MetS in children continues to be debated. Fitzpatrick et al. [31•] note that, on the one hand, the MetS concept has not generally been viewed as especially helpful in clinical practice given that patients are still treated for the individual risk factors. At the same time, they recognize that modeling the MetS allows clinicians to see how the risk factors cluster together differently in different populations of children, thus shedding light on the pathophysiologic processes in cardiovascular disease in different populations. Bays [32] argues that the term “metabolic syndrome” (MetS) does
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not reflect a unified, pathophysiologic process that accounts for the clustering of metabolic disorders and that the MetS is not a “disease” in the traditional sense and thus is not especially conducive to cause-and-effect logistical discussions with patients. On the other hand, Agudelo et al. [30] note that, despite the diversity in MetS definitions and challenges associated with their application, the MetS has value for early detection and initiation of treatment in at-risk youths. Another contentious issue related to childhood MetS is the use of dichotomous “normal–abnormal” variable categories. Strict cutpoints are difficult to apply in the pediatric population given the well-known fluctuations associated with growth and puberty [1]. This has led to the suggestion that using a continuous metabolic risk score, rather than a dichotomous MetS designation, could improve the value and clinical utility of the MetS concept [33]. In the continuous method, a zscore is calculated (individual value − sample mean/standard deviation of the sample) for each MetS risk factor. A child’s metabolic risk score is calculated by summing the zscores of the individual MetS variables, with a higher total risk score indicating a less favorable metabolic profile. For example, Eloranta et al. [34•] calculated a continuous metabolic risk score in 408 children aged 6–8 years by summing the individual zscores for waist circumference, systolic and diastolic blood pressure, fasting insulin level, glucose level, the level of triglycerides, and HDL-C level in order to determine associations between the MetS and dietary behaviors. The results indicated that skipping main meals, consuming higher amounts of nonroot vegetables, higher consumption of sugar-sweetened beverages, higher consumption of low-fat vegetable-oil-based margarine, and lower consumption of vegetable oils were associated with a higher metabolic risk score. Perhaps the most active area of research during the past year relative to Childhood MetS has been the investigation of alternative risk factors for assessing childhood MetS.
New Candidate Variables for Childhood Metabolic Syndrome Protein Markers The potential value of various cytokines and other protein types for characterizing metabolic risk in children was examined by several researchers in the past year. Rendo-Urteaga et al. [35] suggest cardiotrophin 1 (CT-1) may be one such protein. CT-1 is a 201 amino acid protein member of the IL-6 superfamily of cytokines that plays a role in energy metabolism and has potential links to obesity and type 2 diabetes [36]. CT-1 levels were measured before and after a 10-week weight loss intervention in a group of 44 obese children aged 7–15 years. A significant decrease in CT-1 level was observed following the
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weight loss program, with the decreases in CT-1 level strongly associated with a lower risk of the MetS. Rendo-Urteaga et al. note that CT-1 has a prolonged stability in whole blood, permitting its development for routine clinical use. Ariggo et al. [37] suggest high mobility group box protein B1 (HMGB1) may have use as a new diagnostic marker for the MetS in children. HMGB1 is a 30-kDa ubiquitous nuclear and cytosolic protein secreted by innate immune cells that may be associated with childhood obesity through its relationship with inflammatory cytokines [37]. In this study, 100 children (60 obese children, 40 nonobese children, mean age 11.1 years) were compared with regard to HMGB1 and a variety of other metabolic risk factors. Receiver operating characteristic analysis showed HMGB1 to have higher sensitivity and specificity than other predictors for identifying the MetS in obese children. Ariggo et al. concluded that HMGB1 may be an important diagnostic marker for obesity-related complications such as the MetS. Saki et al. [38] investigated the potential role of retinolbinding protein 4 (RBP4) as a useful marker for the MetS in obese children. RBP4 is a transfer protein for retinol (vitamin A), and has received attention as a potential predictor for insulin resistance and the MetS [39, 40]. The study involved 100 obese children aged 5–17 years from whom measurements of the MetS and insulin resistance were obtained. Significant positive correlations were observed between RBP4 and insulin resistance and between RBP4 and some components of the MetS, including waist circumference, systolic blood pressure, and fasting blood glucose level but not with diastolic blood pressure, HDL-C level, or the level of triglycerides. In addition, as the level of RBP4 increased, the number of components of the MetS increased. Whether assessment of any of these biomarkers will become a routine part of MetS determination in children is yet to be determined. Comparative studies will be needed to determine the extent to which any new variable adds to the knowledge content and utility of MetS assessment. As discussed next, study of genetic associations with childhood MetS was another area of active research in 2013–2014.
Genetic Markers of the Metabolic Syndrome Development of the MetS involves an important genetic component, and research over the past year has added to our understanding of this relationship [29]. Olza et al. [10] examined the association of single-nucleotide polymorphisms in the neuropeptide Y gene (NPY) and features of the MetS in a group of 292 obese and 242 nonobese children. Neuropeptide Y is a peptide that acts as a neurotransmitter or neuromodulator that has been implicated in several human diseases, including obesity [10]. The study demonstrated for the first time the association of NPY gene variant rs16131 with
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obesity and its possible impact on the early onset of features of the MetS in children. Zaki and Amr [41] compared the presence of the apolipoprotein A5 gene variant T-1131C in 150 obese adolescent boys and girls with the MetS and 204 age- and sexmatched normal healthy controls. The T-1131C polymorphism may predispose an individual to cardiovascular diseases and insulin resistance [41]. Multiple regression analysis showed that carriers of the T-1131C gene variant had an increased risk of the MetS. The allele frequency of T-1131C was significantly greater (31.3 %) in the MetS group than in the control group (11.7 %). Zaki and Amr concluded that the T-1131C polymorphism is a risk factor for the development of the MetS in obese adolescents. The search for genetic markers of childhood MetS will certainly continue. As with the cytokines mentioned earlier, the role of genetic markers in evaluating childhood MetS remains to be determined. Anthropometric Markers of the Metabolic Syndrome Some researchers over the past year suggested a second look should be taken at anthropometric measurements for identifying the MetS in children. Santoro et al. [42] examined whether three simple anthropometric measures easily obtained in a clinical setting could identify the MetS in obese children. The three measures were waist-to-height ratio, family history of type 2 diabetes, and the presence or absence of acanthosis nigricans. These three measures were obtained from each of 1,808 obese boys and girls along with a separate assessment of the MetS. Logistic regression indicated that the odds ratio for the MetS in children who had the combination of a high waistto-height ratio, a family history of type 2 diabetes, and the presence of acanthosis nigricans was 3.60 [95 % confidence interval (CI) 1.6–8.12, p=0.002]. Santoro et al. concluded that assessment of these three measures is a powerful tool in the hands of clinicians for identifying children at risk of obesity complications. Nambiar et al. [43•] investigated the extent to which a single anthropometric measure, the waist-to-height ratio, could identify the MetS in a group of 109 obese boys and girls aged 10.0– 16.5 years. Logistic regression indicated waist-to-height ratio to be the best predictor of the MetS, followed by BMI zscore and homeostatic model assessment for insulin resistance. Weight z score and waist circumference zscore were not significant predictors. Nambiar et al.concluded that waist-to-height ratio is the simplest index to calculate and interpret, making it an ideal, noninvasive screening tool in clinical practice. Behavioral Markers of the Metabolic Syndrome Several researchers have noted that although genetics is an important contributor to the development of childhood MetS,
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childhood behaviors are the main contributing factors [6, 15, 44]. Recent studies addressing the diet and physical activity behaviors of children are discussed next. Diet Wennberg et al. [45] analyzed whether poor breakfast habits at age 16 years predicted the MetS syndrome at age 43 years. Poor breakfast habits were defined as either skipping breakfast or only eating or drinking something sweet. Logistic regression showed the odds ratio for the MetS at age 43 years was 1.68 (95 % CI 1.01–2.78) for those with poor breakfast habits at age 16 years compared with breakfast eaters. Wang et al. [46] examined longitudinal changes in components of the MetS associated with added sugar consumption in a group of 8–10-year-old children followed for 2 years. Multiple linear regression models found that although added sugar intake was not associated with adiposity measures, higher consumption of added sugar of 10 g per day from liquid sources was associated with higher fasting glucose and higher fasting insulin levels. No associations were observed with higher consumption of added sugar from solid sources. Wang et al. suggested the need for increased focus on reducing consumption of liquid sugars in children. Physical Activity Wennberg et al. [47] examined whether TV viewing and low levels of leisure-time physical activity during adolescence predicted the MetS in mid-adulthood. TV viewing and physical activity levels at age 16 years were estimated from selfadministered questionnaires. The presence of the MetS at age 43 years was determined in 82 % of the original cohort (888 participants). The odds ratio for the presence of the MetS at age 43 years was 2.14 (95 % CI 1.24–3.71) in those who reported watching several TV shows per day at age 16 years as compared with those who reported watching one show per week or less at age 16 years. The odds ratio for the presence of the MetS at age 43 years in those who reported doing leisuretime physical activity several times per month or less at age 16 years was 2.31 (95 % CI 1.134.69) compared with those reporting doing daily leisure-time physical activity at age 16 years. Wennberg et al. concluded that reduced TV viewing in adolescence, in addition to regular physical activity, may contribute to cardiometabolic health later in life. Owens and Gutin [48] have argued that vigorous physical activity appears to have an especially beneficial influence on components of the MetS in children. They suggest that the higher mechanic loads of vigorous physical activity, as compared with moderate or light activity, increase the probability that stem cells will differentiate into lean tissue types (muscle or bone) rather than fat cells. In support, Racil et al. [49••] randomized 34 obese female adolescents to 12 weeks of
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moderate-intensity exercise, 12 weeks of high-intensity exercise, or a nonexercise control group. Following training, decreases in percent body fat, LDL-C level, and insulin level were significantly greater in the high-intensity exercise group compared with the other two groups. Racil et al. note that the greater improvements in risk factors in the high-intensity group versus the moderate-intensity group occurred despite equal training volumes in the two exercise groups.
Conclusions Although recent data suggest childhood obesity prevalence in the USA may have plateaued, the high prevalence suggests associated health risks for obese children will be a major public health concern for the foreseeable future. The MetS concept is one attempt to capture this risk. The definition of childhood MetS, and its clinical utility, remains a subject of debate. Whether refinements to current definitions of childhood MetS using newly considered biomarkers will enhance acceptability for clinicians and researchers is unclear. In the meantime, the search for more effective childhood obesity prevention and treatment interventions continues apace. Both diet and physical activity play key roles, but the optimal “dose” of each requires further investigation. Compliance with Ethics Guidelines Conflict of Interest Scott Owens and Riley Galloway declare they have no conflict of interest. Human and Animal Rights and Informed Consent This article does not contain any studies with human or animal subjects performed by any of the authors.
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Mirza NM, Palmer MG, Sinclair KB, McCarter R, He J, Ebbeling CB, et al. Effects of a low glycemic load or a low-fat dietary intervention on body weight in obese Hispanic American children and adolescents: a randomized controlled trial. Am J Clin Nutr. 2013;97:276–85. 23.•• Davis AM, Daldalian MC, Mayfield CA, Dean K, Black WR, Sampilo ML, et al. Outcomes from an urban pediatric obesity program targeting minority youth: the Healthy Hawks program. Child Obes. 2013;9:492–500. A recent family-based group obesity treatment program showed improved BMI z score in children at 1-year follow-up. 24. Rieder J, Khan UI, Heo M, Mossavar-Rahmani Y, Blank AE, Strauss T, et al. Evaluation of a community-based weight management program for predominantly severely obese, difficult-to-reach, inner-city minority adolescents. Child Obes. 2013;9:292–304. 25. Carraway ME, Lutes LD, Crawford Y, Pratt KJ, McMillan AG, Scripture LG, et al. Camp-based immersion treatment for obese, low socioeconomic status, multi-ethnic adolescents. Child Obes. 2014;10:122–31. 26.• Roberts CK, Izadpanah A, Angadi SS, Barnard RJ. Effects of an intensive short-term diet and exercise intervention: comparison between normal-weight and obese children. Am J Physiol Regul Integr Comp Physiol. 2013;305:R552–7. This reports a recent study showing that lifestyle variables of diet and physical activity have a direct impact on cardiometabolic risk factors independently of changes in body composition. 27. Bitkin EC, Boyraz M, Taskin N, Akcay A, Ulucan K, Akyol MB, et al. Effects of ACE inhibitors on insulin resistance and lipid profile in children with metabolic syndrome. J Clin Res Pediatr Endocrinol. 2013;5:164–9. 28. Garver WS, Newman SB, Gonzales-Pacheco DM, Castillo JJ, Jelinek D, Heidenreich RA, et al. The genetics of childhood obesity and interaction with dietary macronutrients. Genes Nutr. 2013;8: 271–87. 29. D'Adamo E, Santoro N, Caprio S. Metabolic syndrome in pediatrics: old concepts revised, new concepts discussed. Curr Probl Pediatr Adolesc Health Care. 2013;43:114–23. 30. Agudelo GM, Bedoya G, Estrada A, Patino FA, Munoz AM, Velasquez CM. Variations in the prevalence of metabolic syndrome in adolescents according to different criteria used for diagnosis: which definition should be chosen for this age group? Metab Syndr Relat Disord. 2014;12:202–9. 31.• Fitzpatrick SL, Lai BS, Brancati FL, Golden SH, Hill-Briggs F. Metabolic syndrome risk profiles among African American adolescents: National Health and Nutrition Examination Survey, 20032010. Diabetes Care. 2013;36:436–42. This reports a recent crosssectional study showing that an ethnicity-specific MetS definition is needed for African American adolescents. 32. Bays H. Adiposopathy, “sick fat,” Ockham's razor, and resolution of the obesity paradox. Curr Atheroscler Rep. 2014;16:409. 33. Eisenmann JC. On the use of a continuous metabolic syndrome score in pediatric research. Cardiovasc Diabetol. 2008;7:17. 34.• Eloranta AM, Lindi V, Schwab U, Kiiskinen S, Venalainen T, Lakka HM, et al. Dietary factors associated with metabolic risk score in Finnish children aged 6-8 years: the PANIC study. Eur J Nutr. 2013. doi:10.1007/s00394-013-0646-z. This reports a recent crosssectional study showing association between poor diet and MetS risk. 35. Rendo-Urteaga T, Garcia-Calzon S, Martinez-Anso E, Chueca M, Oyarzabal M, Azcona-Sanjulian MC, et al. Decreased cardiotrophin-1 levels are associated with a lower risk of developing the metabolic syndrome in overweight/obese children after a weight loss program. Metabolism. 2013;62:1429–36. 36. Moreno-Aliaga MJ, Perez-Echarri N, Marcos-Gomez B, Larequi E, Gil-Bea FJ, Viollet B, et al. Cardiotrophin-1 is a key regulator of glucose and lipid metabolism. Cell Metab. 2011;14:242–53.
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NUTRITION (JP FOREYT, SECTION EDITOR)
Childhood Obesity and the Metabolic Syndrome Scott Owens & Riley Galloway
Published online: 20 July 2014 # Springer Science+Business Media New York 2014
Abstract Although research published during the past year suggests the prevalence of childhood obesity in the USA may have plateaued, it remains unacceptably high and places large numbers of youths at elevated risk of chronic diseases. The concept of the metabolic syndrome (MetS) is frequently used to help capture this increased risk. Use of the MetS concept with children remains controversial, however. Addressing issues related to the definition of the MetS and its utility in clinical and research settings has generated a variety of recent investigative efforts. At the same time, the past year revealed a number of promising prevention and treatment interventions for childhood obesity and the MetS. Still unknown, however, is the optimal combination of diet, exercise, and other behavioral changes for improving the obesity and MetS status of children. These issues are the subject of this review. Keywords Children . Diet . Exercise . Risk factors . Genetics . Review
Introduction Gaining a better understanding of childhood obesity and its many complexities has engaged researchers and clinicians for many years. One of the complexities involves the nature of the relationship between childhood obesity and the risk of chronic diseases. A concept frequently used in characterizing this
This article is part of the Topical Collection on Nutrition S. Owens (*) : R. Galloway University of Mississippi, 215 Turner Center, University, MS 38677-1848, USA e-mail: [email protected] R. Galloway e-mail: [email protected]
relationship is that of the metabolic syndrome (MetS). Conceptually, the MetS is the clustering in an individual of a set of cardiometabolic risk factors thought to place the individual at increased risk of the development of cardiovascular diseases and type 2 diabetes [1]. The health consequences of childhood obesity and the MetS are wide-ranging as obesity appears to be on the causal pathway of every major chronic disease [2]. This review will focus on research published during 2013– 2014 related to childhood obesity and the MetS, emphasizing new information regarding prevalence rates, prevention and treatment strategies, and unresolved issues related to the MetS.
Prevalence of Childhood Obesity and the Metabolic Syndrome A pair of studies published in early 2014 based on the most recent National Health and Nutrition Examination Survey (NHANES) data provide tentative support for the notion that the US childhood obesity epidemic may be slowing, plateauing, or, in some age groups, reversing [3•, 4•]. The first study [3•] reported an obesity prevalence of 16.9 % in the 2– 19-year-old age group, which, although unacceptably high, indicated no significant change between the 2003–2004 and 2011–2012 measurement periods. Among 2–5-year-old children, obesity prevalence showed a decline from 13.9 % to 8.4 %. The second study [4•] analyzed an NHANES database of 26,690 children aged 2–19 years, and showed an obesity prevalence of 17.3 %. No significant increase in obesity prevalence was observed compared with data from the 2009–2010 measurement period. These US data are consistent with a recent international report noting a stabilization or decline in childhood obesity prevalence in several westernized countries [5]. Although these recent data may be viewed as encouraging, the relatively high prevalence rates remain
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disconcerting. In addition, the NHANES data indicate a worrisome upward trend in the prevalence of children with the severest forms of obesity as the prevalence of class 3 obesity exceeded 2 % for the first time [4•]. Estimating the prevalence of childhood MetS continues to be challenging and controversial. To begin with, no set of standardized criteria for identifying the MetS in children has gained universal acceptance [6]. More than 40 definitions for childhood MetS have been proposed, most based on adaptations of adult criteria [7]. Differences among the definitions relate mainly to the specific components included and their threshold values. Despite their differences, the various definitions tend to share some common features, including an obesity estimate (typically BMI or waist circumference), blood pressure measures, blood lipid measures [typically triglycerides, LDL cholesterol (LDL-C), or HDL cholesterol (HDL-C)], and a diabetes-related risk factor (fasting glucose, glucose tolerance, or insulin) [8]. Table 1 displays components and threshold values for two commonly used childhood MetS definitions. Despite the prevalence differences across various studies [9, 10], the pattern of MetS prevalence relative to factors such as sex, age/pubertal status, ethnicity, and obesity status tends to be relatively consistent. Relative to sex, MetS prevalence is typically higher in boys than in girls, regardless of the MetS definition used. In their most recent study of US adolescents, Laurson et al. [11] reported a MetS prevalence of 7.9 % in a sample of 1,785 boys compared with 6.9 % in 1,600 girls. Relative to age/pubertal status, MetS prevalence tends to be higher in pubertal children than in the prepubertal population [12]. Regarding ethnicity, NHANES data suggest substantial prevalence differences. For example, in a group of 2,456 adolescents, MetS prevalence in Hispanics was 11.2 % compared with 8.9 % in whites and 4.0 % in African Americans [13]. Lastly, prevalence data relative to obesity status show a
clear and consistent pattern, with the MetS substantially more prevalent in obese as compared with normal-weight children. The 2014 NHANES report on the MetS in adolescents [11], which used the Centers for Disease Control and Prevention weight standards, revealed that MetS prevalence was less than 1 % in normal-weight boys, 6.8 % in overweight boys, and 34.5 % in obese boys. In girls, the MetS prevalence rates were 1.7 % in those of normal weight, 9.2 % in the overweight, and 24.6 % in the obese.
Prevention and Treatment of Childhood Obesity and the Metabolic Syndrome Prevention A number of studies published in the past year support the notion that a healthy diet and ample physical activity can be powerful weapons for preventing childhood obesity and associated metabolic consequences. Data from the Amsterdam Growth and Health Longitudinal Study showed that greater adherence to a Mediterranean dietary pattern beginning in adolescence was associated with lower blood pressure, lower total cholesterol levels, and lower BMI during adolescence and into young adulthood [14•]. Data from Stabelini-Neto et al. [15] indicate that achieving approximately 90 min per day of moderate-to-vigorous physical activity will likely prevent development of the MetS in adolescents. Mendoza and Liu [16] examined a nationally representative sample of US kindergarten students and found that children who engaged in active transport to school (walking or biking) in kindergarten had lower BMI zscores in fifth grade than their peers who were passive commuters to school. Lazorick et al. [17••] reported the results of a longitudinal obesity prevention intervention targeting a single-site cohort of 106 students
Table 1 Criteria for diagnosis of the metabolic syndrome (MetS) in children Source
Ages
Obesity
10 years to less Waist circumference than 16 years greater than or equal to the 90th percentile (or adult cutoff if lower) 12–19 years Waist circumference National Cholesterol greater than or equal Education Program/ to the 90th percentile Adult Trial Panel III (age- and genderas modified for specific from adolescentsb [51] NHANES III) International Diabetes Foundationa [50]
Lipids
Blood pressure
Level of triglycerides above 1.7 mmol/L, HDL-C level below 1.03 mmol/L
Systolic above Glucose level above 130 mmHg or diastolic 5.6 mmol/L or known above 85 mmHg type 2 diabetes
Level of triglycerides above 1.24 mmol/L, HDL-C level below 1.03 mmol/L
Systolic or diastolic above Glucose level 6.1 mmol/L the 90th percentile or above (age-, gender-, and height-specific)
HDL-C HDL cholesterol, NHANES III Third National Health and Nutrition Examination Survey a
Diagnosis of the MetS requires the presence of obesity and two or more of the other criteria.
b
Diagnosis of the MetS requires the presence of three or more of the criteria.
Glucose
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beginning in seventh grade and followed across 5 years. The intervention integrated a lifestyle behavior change curriculum within academic subjects. Longitudinal changes in the intervention cohort were compared with those in a nationally representative sample of similarly aged children not receiving the intervention. At follow-up, 13 % of the comparison-group students who had been a healthy weight at the beginning moved to the overweight or obese categories, whereas only 2 % of the intervention cohort moved from healthy weight to overweight or obese. Although these studies highlight the importance of good dietary habits and adequate amounts of physical activity, researchers are also advising that prevention efforts must address the high levels of sedentariness engaged in by children and adolescents [18, 19]. Treatment Successful treatment of childhood obesity and the MetS has important implications. As noted by Magnussen et al. [20], data from longitudinal cohort studies indicate that resolving an individual’s at-risk metabolic status between youth and adulthood largely returns the risk of the individual to a level that is not statistically different from the risk of those who did not have the risk in youth or adulthood. On the other hand, those that retain the risk status into adulthood have a significantly increased risk burden. Some, but not all, recent treatment programs have shown promise in resolving childhood obesity and metabolic risk. In a randomized, crossover clinical trial Saneei et al. [21•] compared the effects on the MetS and its features in 49 adolescent girls who were advised to follow the Dietary Approaches to Stop Hypertension (DASH) eating plan for 6 weeks versus usual dietary advice. Compared with usual dietary advice, the DASH group experienced a significant reduction in the prevalence of the MetS, reduced prevalence of high blood pressure, and improved dietary quality. Saneei et al. concluded that the DASH eating plan can be considered a useful treatment modality for adolescent girls diagnosed with the MetS. Mirza et al. [22] investigated the effects of a low-fat diet versus a low-glycemic-load diet in a group of 113 obese Hispanic children aged 7–15 years randomized to one of the two diets for 3 months and then followed for 2 years. Both groups showed a reduction in BMI zscore at 2 years and improved waist circumference and systolic blood pressure. There were no significant differences by dietary group for changes in BMI, insulin resistance, or components of the MetS. The study showed it was feasible and practical to induce short-term dietary changes in Hispanic youths with either type of diet but with no apparent advantage of one diet over the other. Several multicomponent interventions that combined diet and physical activity have been published within the past year.
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Davis et al. [23••] reported 1-year follow-up results of a 12week, family-based behavioral group treatment program for pediatric obesity. The treatment program consisted of 12 consecutive weekly 2-h sessions that included nutrition-, exercise-, and behavior-related topics. Each meeting also included a group exercise activity. A total of 211 children (mean age 10 years) enrolled in the program and 71 % attended at least 50 % of the 12 weekly meetings. Among the 63 children who provided both baseline and 1-year follow-up data, BMI z score remained significantly lower at 1 year than at the baseline. Rieder et al. [24] reported on the results of a 9-month, multicomponent community-based program for severely obese, inner-city adolescents. Significant improvements were observed at the completion of the 9-month intervention for rates of gain in BMI and BMI zscore. Loss of improvements were observed 9 months after completion of the program however, prompting the researchers to comment that extending the length of the program may be necessary to prevent long-term weight regain. Carraway et al. [25] reported on the long-term efficacy of a 19-day, camp-based immersion treatment program for obese, low-economic status adolescents. The program included a nutrition curriculum, group therapy, cognitive behavioral therapy, and daily physical activity. Long-term (10 months) follow-up (before camp versus end of follow-up) was associated with significant overall improvements in percent overweight. Roberts et al. [26•] demonstrated that a short-term, intensive lifestyle modification program was effective in ameliorating several metabolic risk factors in both normal-weight and overweight/obese children. The participants were 19 overweight/obese and 14 normal-weight children. The 2-week intervention included an ad libitum highfiber, low-fat diet and 2–2.5 h of exercise daily. Only the obese group lost weight (3.9 %), but remained obese. Both groups exhibited significant decreases in the levels of insulin, IL-6, and TNFα. As no associations between changes in weight indices and changes in other biomarkers were observed, the researchers suggested that obesity per se was not the primary driver of the risk factors. Rather, dietary intake and lack of physical activity may be the underlying causes of the observed metabolic abnormalities. They added that the results reinforce the need to encourage healthy diet and exercise habits even in normal-weight children. Although lifestyle changes are the first line of defense against childhood obesity and the MetS, pharmacological interventions are another possible option. Bitkin et al. [27] retrospectively examined the effects of ACE inhibitors on MetS components in 53 children with obesity-associated MetS, consisting of a group of 23 children who were using an ACE inhibitor and a group of 30 children who were not. Group comparisons made across 3–12 months after the ACE inhibitor group began use revealed significantly lower values in the ACE inhibitor group for LDL-C, glucose, insulin, and triglycerides. HDL-C values were significantly higher in the
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ACE inhibitor group. The researchers noted the need for randomized controlled trials of the long-term effectiveness of this drug in children. In a recent review, Marcovecchio and Chiarelli [1] noted that some limited success in children relative to obesity and MetS risk factors has been seen with administration of metformin, sibutramine, and orlistat, although side effects can be an issue. In another review, Garver et al. [28] note that it is too soon tell whether newer antiobesity drugs such as lorcaserin or phenteramine/topiramate might have application in children.
Current Issues Associated with Childhood Metabolic Syndrome Despite the continued use of the MetS concept, a number of ongoing issues surround the MetS concept and its application to children. For one thing, children, unlike the adults for whom the MetS concept was originally developed, reside in vastly different stages of growth, development, and pubertal status. This calls into question whether such variability can be accommodated by a single MetS definition [1]. Another difficulty is the fact that reference values for some MetS components, such as waist circumference, exist for only some populations and that there remains disagreement over how to measure waist circumference in children [1]. Lack of reference values in some populations for blood pressure or HDL-C level render cross-cultural comparisons problematic [29]. It is also argued that ethnic differences in components of the MetS make a single definition questionable [30]. In this regard, Fitzpatrick et al. [31•] recently developed a model of the MetS specific to African American adolescents. They applied confirmatory factor analysis to a sample of 822 African American adolescents aged 12–17 years in the NHANES database and determined the best fitting model consisting of waist circumference, systolic blood pressure, HDL-C level and fasting insulin level. The model indicated that 19 % of African American boys and 16 % of African American girls were at high risk of the MetS. That HDL-C level, but not the level of triglycerides, was retained in the model for African American adolescents supports the notion that racial/ethnicspecific MetS definitions are probably needed. The clinical utility of the MetS in children continues to be debated. Fitzpatrick et al. [31•] note that, on the one hand, the MetS concept has not generally been viewed as especially helpful in clinical practice given that patients are still treated for the individual risk factors. At the same time, they recognize that modeling the MetS allows clinicians to see how the risk factors cluster together differently in different populations of children, thus shedding light on the pathophysiologic processes in cardiovascular disease in different populations. Bays [32] argues that the term “metabolic syndrome” (MetS) does
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not reflect a unified, pathophysiologic process that accounts for the clustering of metabolic disorders and that the MetS is not a “disease” in the traditional sense and thus is not especially conducive to cause-and-effect logistical discussions with patients. On the other hand, Agudelo et al. [30] note that, despite the diversity in MetS definitions and challenges associated with their application, the MetS has value for early detection and initiation of treatment in at-risk youths. Another contentious issue related to childhood MetS is the use of dichotomous “normal–abnormal” variable categories. Strict cutpoints are difficult to apply in the pediatric population given the well-known fluctuations associated with growth and puberty [1]. This has led to the suggestion that using a continuous metabolic risk score, rather than a dichotomous MetS designation, could improve the value and clinical utility of the MetS concept [33]. In the continuous method, a zscore is calculated (individual value − sample mean/standard deviation of the sample) for each MetS risk factor. A child’s metabolic risk score is calculated by summing the zscores of the individual MetS variables, with a higher total risk score indicating a less favorable metabolic profile. For example, Eloranta et al. [34•] calculated a continuous metabolic risk score in 408 children aged 6–8 years by summing the individual zscores for waist circumference, systolic and diastolic blood pressure, fasting insulin level, glucose level, the level of triglycerides, and HDL-C level in order to determine associations between the MetS and dietary behaviors. The results indicated that skipping main meals, consuming higher amounts of nonroot vegetables, higher consumption of sugar-sweetened beverages, higher consumption of low-fat vegetable-oil-based margarine, and lower consumption of vegetable oils were associated with a higher metabolic risk score. Perhaps the most active area of research during the past year relative to Childhood MetS has been the investigation of alternative risk factors for assessing childhood MetS.
New Candidate Variables for Childhood Metabolic Syndrome Protein Markers The potential value of various cytokines and other protein types for characterizing metabolic risk in children was examined by several researchers in the past year. Rendo-Urteaga et al. [35] suggest cardiotrophin 1 (CT-1) may be one such protein. CT-1 is a 201 amino acid protein member of the IL-6 superfamily of cytokines that plays a role in energy metabolism and has potential links to obesity and type 2 diabetes [36]. CT-1 levels were measured before and after a 10-week weight loss intervention in a group of 44 obese children aged 7–15 years. A significant decrease in CT-1 level was observed following the
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weight loss program, with the decreases in CT-1 level strongly associated with a lower risk of the MetS. Rendo-Urteaga et al. note that CT-1 has a prolonged stability in whole blood, permitting its development for routine clinical use. Ariggo et al. [37] suggest high mobility group box protein B1 (HMGB1) may have use as a new diagnostic marker for the MetS in children. HMGB1 is a 30-kDa ubiquitous nuclear and cytosolic protein secreted by innate immune cells that may be associated with childhood obesity through its relationship with inflammatory cytokines [37]. In this study, 100 children (60 obese children, 40 nonobese children, mean age 11.1 years) were compared with regard to HMGB1 and a variety of other metabolic risk factors. Receiver operating characteristic analysis showed HMGB1 to have higher sensitivity and specificity than other predictors for identifying the MetS in obese children. Ariggo et al. concluded that HMGB1 may be an important diagnostic marker for obesity-related complications such as the MetS. Saki et al. [38] investigated the potential role of retinolbinding protein 4 (RBP4) as a useful marker for the MetS in obese children. RBP4 is a transfer protein for retinol (vitamin A), and has received attention as a potential predictor for insulin resistance and the MetS [39, 40]. The study involved 100 obese children aged 5–17 years from whom measurements of the MetS and insulin resistance were obtained. Significant positive correlations were observed between RBP4 and insulin resistance and between RBP4 and some components of the MetS, including waist circumference, systolic blood pressure, and fasting blood glucose level but not with diastolic blood pressure, HDL-C level, or the level of triglycerides. In addition, as the level of RBP4 increased, the number of components of the MetS increased. Whether assessment of any of these biomarkers will become a routine part of MetS determination in children is yet to be determined. Comparative studies will be needed to determine the extent to which any new variable adds to the knowledge content and utility of MetS assessment. As discussed next, study of genetic associations with childhood MetS was another area of active research in 2013–2014.
Genetic Markers of the Metabolic Syndrome Development of the MetS involves an important genetic component, and research over the past year has added to our understanding of this relationship [29]. Olza et al. [10] examined the association of single-nucleotide polymorphisms in the neuropeptide Y gene (NPY) and features of the MetS in a group of 292 obese and 242 nonobese children. Neuropeptide Y is a peptide that acts as a neurotransmitter or neuromodulator that has been implicated in several human diseases, including obesity [10]. The study demonstrated for the first time the association of NPY gene variant rs16131 with
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obesity and its possible impact on the early onset of features of the MetS in children. Zaki and Amr [41] compared the presence of the apolipoprotein A5 gene variant T-1131C in 150 obese adolescent boys and girls with the MetS and 204 age- and sexmatched normal healthy controls. The T-1131C polymorphism may predispose an individual to cardiovascular diseases and insulin resistance [41]. Multiple regression analysis showed that carriers of the T-1131C gene variant had an increased risk of the MetS. The allele frequency of T-1131C was significantly greater (31.3 %) in the MetS group than in the control group (11.7 %). Zaki and Amr concluded that the T-1131C polymorphism is a risk factor for the development of the MetS in obese adolescents. The search for genetic markers of childhood MetS will certainly continue. As with the cytokines mentioned earlier, the role of genetic markers in evaluating childhood MetS remains to be determined. Anthropometric Markers of the Metabolic Syndrome Some researchers over the past year suggested a second look should be taken at anthropometric measurements for identifying the MetS in children. Santoro et al. [42] examined whether three simple anthropometric measures easily obtained in a clinical setting could identify the MetS in obese children. The three measures were waist-to-height ratio, family history of type 2 diabetes, and the presence or absence of acanthosis nigricans. These three measures were obtained from each of 1,808 obese boys and girls along with a separate assessment of the MetS. Logistic regression indicated that the odds ratio for the MetS in children who had the combination of a high waistto-height ratio, a family history of type 2 diabetes, and the presence of acanthosis nigricans was 3.60 [95 % confidence interval (CI) 1.6–8.12, p=0.002]. Santoro et al. concluded that assessment of these three measures is a powerful tool in the hands of clinicians for identifying children at risk of obesity complications. Nambiar et al. [43•] investigated the extent to which a single anthropometric measure, the waist-to-height ratio, could identify the MetS in a group of 109 obese boys and girls aged 10.0– 16.5 years. Logistic regression indicated waist-to-height ratio to be the best predictor of the MetS, followed by BMI zscore and homeostatic model assessment for insulin resistance. Weight z score and waist circumference zscore were not significant predictors. Nambiar et al.concluded that waist-to-height ratio is the simplest index to calculate and interpret, making it an ideal, noninvasive screening tool in clinical practice. Behavioral Markers of the Metabolic Syndrome Several researchers have noted that although genetics is an important contributor to the development of childhood MetS,
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childhood behaviors are the main contributing factors [6, 15, 44]. Recent studies addressing the diet and physical activity behaviors of children are discussed next. Diet Wennberg et al. [45] analyzed whether poor breakfast habits at age 16 years predicted the MetS syndrome at age 43 years. Poor breakfast habits were defined as either skipping breakfast or only eating or drinking something sweet. Logistic regression showed the odds ratio for the MetS at age 43 years was 1.68 (95 % CI 1.01–2.78) for those with poor breakfast habits at age 16 years compared with breakfast eaters. Wang et al. [46] examined longitudinal changes in components of the MetS associated with added sugar consumption in a group of 8–10-year-old children followed for 2 years. Multiple linear regression models found that although added sugar intake was not associated with adiposity measures, higher consumption of added sugar of 10 g per day from liquid sources was associated with higher fasting glucose and higher fasting insulin levels. No associations were observed with higher consumption of added sugar from solid sources. Wang et al. suggested the need for increased focus on reducing consumption of liquid sugars in children. Physical Activity Wennberg et al. [47] examined whether TV viewing and low levels of leisure-time physical activity during adolescence predicted the MetS in mid-adulthood. TV viewing and physical activity levels at age 16 years were estimated from selfadministered questionnaires. The presence of the MetS at age 43 years was determined in 82 % of the original cohort (888 participants). The odds ratio for the presence of the MetS at age 43 years was 2.14 (95 % CI 1.24–3.71) in those who reported watching several TV shows per day at age 16 years as compared with those who reported watching one show per week or less at age 16 years. The odds ratio for the presence of the MetS at age 43 years in those who reported doing leisuretime physical activity several times per month or less at age 16 years was 2.31 (95 % CI 1.134.69) compared with those reporting doing daily leisure-time physical activity at age 16 years. Wennberg et al. concluded that reduced TV viewing in adolescence, in addition to regular physical activity, may contribute to cardiometabolic health later in life. Owens and Gutin [48] have argued that vigorous physical activity appears to have an especially beneficial influence on components of the MetS in children. They suggest that the higher mechanic loads of vigorous physical activity, as compared with moderate or light activity, increase the probability that stem cells will differentiate into lean tissue types (muscle or bone) rather than fat cells. In support, Racil et al. [49••] randomized 34 obese female adolescents to 12 weeks of
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moderate-intensity exercise, 12 weeks of high-intensity exercise, or a nonexercise control group. Following training, decreases in percent body fat, LDL-C level, and insulin level were significantly greater in the high-intensity exercise group compared with the other two groups. Racil et al. note that the greater improvements in risk factors in the high-intensity group versus the moderate-intensity group occurred despite equal training volumes in the two exercise groups.
Conclusions Although recent data suggest childhood obesity prevalence in the USA may have plateaued, the high prevalence suggests associated health risks for obese children will be a major public health concern for the foreseeable future. The MetS concept is one attempt to capture this risk. The definition of childhood MetS, and its clinical utility, remains a subject of debate. Whether refinements to current definitions of childhood MetS using newly considered biomarkers will enhance acceptability for clinicians and researchers is unclear. In the meantime, the search for more effective childhood obesity prevention and treatment interventions continues apace. Both diet and physical activity play key roles, but the optimal “dose” of each requires further investigation. Compliance with Ethics Guidelines Conflict of Interest Scott Owens and Riley Galloway declare they have no conflict of interest. Human and Animal Rights and Informed Consent This article does not contain any studies with human or animal subjects performed by any of the authors.
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