Waist Circumference in Children and Adolescents from Different Ethnicities

In their Bulletin 2001; 79 the World Health Organisation (WHO) had published: “The last two decades have witnessed the emergence and consolidation of an economic paradigm which emphasizes domestic deregulation and the removal of barriers to international trade and finance. If properly managed, such an approach can lead to perceptible gains in health status.” Globalization in the last two decades influenced lifestyle and especially food patterns all over the world (Bauchner H, 2008 and Hu FB, 2008). In a “Nutrition transition” the consumption of dietary fat and/ or high -caloric meals and sweetened drinks has been increased, in developed countries as well as in developing ones (Hawkes C, 2006). At the same time overweight and obesity just as increased and dietrelated chronic diseases like diabetes mellitus II, hypertension or lipid disorders or cardiovascular diseases known from elder adults are observed in children and adolescents. Waist circumference (WC) is a generally accepted measure of central obesity that is a traditional risk factor for cardiovascular disease (CVD). A worldwide standardization of WC is warranted because of considerable differences between different ethnicities. For adults pragmatic ethnic-specific cut-off values for WC were defined between >85 cm and >94 cm for men and between >80 cm and >90 cm for women (Alberti et al., 2005). For children and adolescents from different ethnicities no uniform definition of WC cut-offs exists because of physiological growth and development. The aim of this study is to develop ageand gender-specific reference curves of WC for German children and adolescents, to define cut-off values, to collect percentile curves from other ethnicities, and to compare global findings. Calculation of our cut-off values is based on conventional anthropometric and non-anthropometric cardiovascular risk factors. WC is obligate for the definition of the metabolic syndrome already in youths. Early detection and intervention by lifestyle change are mandatory to prevent adult adiposity and its multiple complications. Thus, precise diagnosis is prerogative for the estimation of the worldwide prevalence of the metabolic syndrome and global intervention.


Introduction
In their Bulletin 2001; 79 the World Health Organisation (WHO) had published: "The last two decades have witnessed the emergence and consolidation of an economic paradigm which emphasizes domestic deregulation and the removal of barriers to international trade and finance. If properly managed, such an approach can lead to perceptible gains in health status." Globalization in the last two decades influenced lifestyle and especially food patterns all over the world (Bauchner H, 2008 andHu FB, 2008). In a "Nutrition transition" the consumption of dietary fat and/ or high -caloric meals and sweetened drinks has been increased, in developed countries as well as in developing ones (Hawkes C, 2006). At the same time overweight and obesity just as increased and diet-related chronic diseases like diabetes mellitus II, hypertension or lipid disorders or cardiovascular diseases known from elder adults are observed in children and adolescents. Waist circumference (WC) is a generally accepted measure of central obesity that is a traditional risk factor for cardiovascular disease (CVD). A worldwide standardization of WC is warranted because of considerable differences between different ethnicities. For adults pragmatic ethnic-specific cut-off values for WC were defined between >85 cm and >94 cm for men and between >80 cm and >90 cm for women (Alberti et al., 2005). For children and adolescents from different ethnicities no uniform definition of WC cut-offs exists because of physiological growth and development. The aim of this study is to develop age-and gender-specific reference curves of WC for German children and adolescents, to define cut-off values, to collect percentile curves from other ethnicities, and to compare global findings. Calculation of our cut-off values is based on conventional anthropometric and non-anthropometric cardiovascular risk factors. WC is obligate for the definition of the metabolic syndrome already in youths. Early detection and intervention by lifestyle change are mandatory to prevent adult adiposity and its multiple complications. Thus, precise diagnosis is prerogative for the estimation of the worldwide prevalence of the metabolic syndrome and global intervention.  Haas et al., 2011). The CASPIAN Study was performed in 2003-2004 and contributes representative samples of 1616 Iranian children (757 boys and 859 girls) and of 2608 Iranian adolescents (1216 males and 1392 females) in these age groups. The Belo Horizonte Heart Study contributes 464 Brazilian children (241 boys and 223 girls) and 545 Brazilian adolescents (255 males and 290 females) to this large data set of the BIG study consisting of 11,788 youths from three continents. All the three studies followed the Declaration of Helsinki and the same methodology. The ethical committee of the medical faculty of the Ludwig-Maximilians-University Munich, the Bavarian Ministry of Science and Education, and the local school authorities approved the Prevention Education Program (PEP). Written informed consent together with oral consent from children and adolescents was obtained from all parents, assessment of the pubertal status was not accepted. Exclusion criteria of the PEP Family Heart Study were non-German ethnicity (2.6% of children from 17 non-German ethnicities to avoid ethnic bias), incomplete data sets, apparent cardiovascular, metabolic, endocrine and malignant diseases, extreme physical activities, special nutrition habits and taking any medication. Continuously trained research assistants performed all measurements along the study manual as previously described (Schwandt et al., 1999(Schwandt et al., , 2009. Physical examination included measurements of weight, height, body mass index (BMI), waist circumference (WC), waist-to-height ratio (WHtR), skin fold thickness (SFT), percent body fat (%BF) and blood pressure (BP). Lipids, lipoproteins and glucose were measured in fasting venous blood samples, processed and stored at -20°C every year during November and December. Definition of risk factors is shown in

Age-and gender-specific percentiles of waist circumference in German children and adolescents
The anthropometric characteristics of healthy German children are demonstrated in Table 2   Table 2. Weight, height, waist circumference (WC), hip circumference (HC), body mass index (BM), waist to hip ratio (WHR) and waist to height ratio (WHtR) by age and sex in 3531 German boys and girls (mean± SD)  Among boys and girls, WC increased continuously from 3 years to 11 years at all percentiles, steepest at the 97 th percentile in both genders (Figure 1). At the 50 th percentile, this corresponds to an increase of WC by 14 cm in boys and by 13 cm in girls from age 3 years to age 11 years (Table 2). However, in adolescents WC increased less, by 11 cm in males and only by 5 cm in females with even slight decreases between 15 years and 18 years (Table 3). Smoothed reference curves for the 3 rd , 10 th , 25 th , 50 th , 75 th and 97 th percentiles for waist and body mass index in 3 years to 11-years old German boys and girls  www.intechopen.com

Waist Circumference in
Please use Adobe Acrobat Reader to read this book chapter for free. Just open this same document with Adobe Reader. If you do not have it, you can download it here. You can freely access the chapter at the Web Viewer here. Table 3. Age-and sex-specific WC percentile values (cm) for German children 3-11 years of age in the PEP Family Heart Study  The prevalence of severe obesity (WC>97 th percentile) was significantly (p<0.05) higher in boys than in girls (4.1% vs. 2.8%) corresponding to similar gender differences for BMI >97 th percentile (6.3% vs. 4.9%) in this cohort children. Females were significantly taller and heavier than males at age 12 y, whereas from age 14 to 18 years males were significantly taller and heavier than females. Female adolescents reached their maximal weight and height at age 17 years one year earlier than males. As demonstrated in Table 5 the increase of WC in males was twice of that in females (11.4 cm respectively 6.0 cm)  Table 5. Percentile values of waist circumference in 3026 German adolescents aged 12-18 years

Cut-off points of waist circumference in adolescents
Since the International Diabetes Federation (IDF) proposed that the metabolic syndrome should not be diagnosed in children younger than age 10 years (Zimmet et al. 2007) we calculated cut-off points only for the group of adolescents.

Cut-off points in terms of seven anthropometric variables
Receiver operating characteristic (ROC) curves were calculated from <90 th percentiles of skin fold thickness (SFT) from biceps, triceps and sub-scapular areas, SFT sum, percent body fat, waist-to-height ratio and waist-to-hip ratio. In both genders WHtR at the >90th percentile was closest to 1 in terms of an area under the curve (AUC) of 0.974 in males and 0.986 in females, followed by BF% (0.937) in males respectively by WHR (0.935) in females. (Figure 2).

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Cut-off points in terms of eight non-anthropometric CVD risk factors
The WC cut-off points in children were 93.5 cm for hypertension, increased LDL-Cholesterol, low HDL-Cholesterol, increased triglycerides (TG), non-HDL-Cholesterol and TG/ HDL-Cholesterol ratio and not different for boys and girls except for fasting hyperglycaemia and an increased LDL-Cholesterol/HDL-Cholesterol ratio (Table 6). However, in adolescents the age-adjusted cut-off values were much more different between males and females than among children..

Comparison with other ethnicities 3.3.1 Iranian and German children
The study population comprised 2076 (991 boys) Iranian and 1721 (851 boys) German children aged 6-11 years . Except height, the Iranian children had higher anthropometric measures than German children did (Table 7). The age-specific reference curves of WC demonstrate a continuous increase in Iranian children from 6 years to 11 years whereas at 9 years the increase levelled off in German children ( Figure 3).

Fig. 3. LMS percentile curves of Iranian and German children (age 6-11)
The comparison of increased WC in German and Iranian adolescents mean age 12.2± 1.7 respectively 12.6±1.7 years reveals a significantly (p<0.05) higher prevalence in Iranian subjects than in German adolescents (Table 8). Accordingly, the prevalence of the metabolic syndrome as defined by IDF was higher in Iranian (2.1%) adolescents than in German adolescents (0.5%).

Comparisons of Bazilian Iranian and German (BIG study)
The Brazilian-Iranian-German (BIG) Study compared 4473 children ( 6 to <10 years) and 6800 adolescents (10 to <16 years) participating in the Belo Horizonte Heart Study in Brazil, the CASPIAN Study in Iran and the PEP Family Heart Study in Germany .

Turkish and German children
Comparing 2473 Turkish and German first graders (mean age 6.4 years) participating in the PEP Family Heart Study in Nuremberg Turkish boys (58.5±8.9 vs. 56.9±6.1) and Turkish girls (57.6±9.2 vs. 55.8±5.8) girls had significantly higher values than German children did although living in the same town. These differences might be due to different lifestyle as well as to genetic factors ).

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Waist Circumference in Children and Adolescents from Different Ethnicities 87
Age-and gender-specific percentile values are shown in table 10 and table 11 for 320 Turkish (155 boys and 165 girls) and 3531 German (1788 boys and 1743 girls) children participating in the PEP Family Heart Study. Table 10. Percentiles for waist circumference in 3 -11 y old boys Table 11. Percentiles for waist circumference in 3 -11 y old Girls www.intechopen.com Please use Adobe Acrobat Reader to read this book chapter for free.
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The WC differences between Turkish and German boys decreases from age 3 to age 11 whereas the mean differences in girls increases from age 3 to age 11 years. Figure 4 and Figure 5 demonstrate the importance of choosing the percentile for comparisons. At the 50th percentile the difference of increasing WC between years 3 and 11 in German and Turkish children is only slight whereas the curve in Turkish girls is much more steeper compared with the other three curves.  Table 12 and Table 13 compare the mean WC values from 6 respectively 11 years old children from 11 countries in boys and in girls. The continuous increase of waist circumference in these countries is shown in figure 5 and figure 6    6. Zannolli R, 1996 11. Inokuchi M, 20077. Kelishadi R, 200712. Hatipoglu N, 20078. Fernandez JR, 2004 14. Eisenmann JC: 2005 9. Savva SC, 2001 15. Sung RY, 200710. McCarthy HD, 200116. Gómez-Diaz RA, 2005

Conclusions
In 4473 children and 6829 adolescents from Germany, Iran and Brazil the mean prevalence of increased waist circumference (≥ 90 th percentile) was 7.0% respectively 10.5%. Increased waist circumference (≥ 90 th percentile) is a clinically accessible diagnostic tool and a measure of central obesity that is essential for the global IDF definition of the metabolic syndrome (Zimmet et al. 2007). For adolescents aged 10 years and older increased WC and two or more other features like hypertension, hyperglycaemia, hypertriglyceridemia, and low HDL-Cholesterol are diagnostic.

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The relatively homogeneous WC mean values in adolescents of the three different ethnicities in the BIG Study  are far lower than WC mean values of adolescents from USA describing 79.6±12.5 cm in males and 78.8±11.7 cm in females (Jolliffe and Janssen, 2007). These considerable differences between 2906 male and 3116 female US adolescents and 3409 male and 3328 female BIG adolescents might be explained by different age ranges (12-20 years vs. 10-<16 years), different periods of data collection (1988-2002 vs. 2000-2008) and/or different measure points (iliac crest vs. mid-point between lowest rib and iliac crest). Furthermore, heterogeneity of the study populations might have affected the outcome since The National Health and Nutrition Examination Surveys NHANES are nationally representative cross-sectional including Hispanic, Black and White participants. This comparison of two large cross-sectional studies demonstrates the outstanding importance of comparable design and methodology of the studies. The main strength of the BIG study is that original data of a very large number (11,273) of children and adolescents from Germany, Iran and Brazil of youths from three continents were measured and evaluated by the same methodology. One limitation of the study is that genetic and environmental effects (e.g. physical activity, nutrition and second hand tobacco smoke exposition respectively active smoking) on anthropometric measures are not included.