http://informahealthcare.com/ahb ISSN: 0301-4460 (print), 1464-5033 (electronic) Ann Hum Biol, 2014; 41(5): 383–388 ! 2014 Informa UK Ltd. DOI: 10.3109/03014460.2013.815273
RESEARCH PAPER
Percentiles of waist–hip ratio and the relationship with blood pressure among children and adolescents in Shandong, China Ying-xiu Zhang1, Shu-rong Wang2, Jing-yang Zhou1, Jin-shan Zhao1, and Zun-hua Chu1 Shandong Center for Disease Control and Prevention, Shandong, PR China and 2Shandong Blood Center, Shandong, PR China
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1
Abstract
Keywords
Background: Anthropometric indices such as waist circumference (WC), waist-to-height ratio (WHtR) and waist–hip ratio (WHR) have been recognized as useful alternatives to visceral fat measurement in epidemiological studies. WHR has been used extensively in adults. However, there are very few published data for WHR among children and adolescents. Aim: The present study examined the distribution of WHR and the relationship with blood pressure (BP) among children and adolescents in Shandong, PR China. Subjects and methods: Data for this study were obtained from a large cross-sectional survey of schoolchildren carried out in 2010. A total of 38 822 students (19 456 boys and 19 366 girls) aged 7–17 years participated in this study. WC, Hip circumference (HC), systolic blood pressure (SBP) and diastolic blood pressure (DBP) of all subjects were measured; WHR was calculated as WC divided by HC. Abdominal obesity was defined by previously published WHR references based on Chinese children and adolescents living in Beijing. All subjects were divided into two groups (group 1 with WHR 585th; group 2 with WHR 85th) according to the percentiles of WHR and comparisons of the SBP and DBP between the two groups were made. Results: The WHR levels in Shandong boys and girls were lower than those from German and Pakistani. The overall prevalence of abdominal obesity was 9.53% (95% CI ¼ 9.12–9.95%) for boys and 9.82% (95% CI ¼ 9.40–10.24%) for girls, no statistical differences between the two genders were observed (p40.05). In both boys and girls, the Z-scores of SBP and DBP were all significantly lower in group 1 than in group 2 (p50.01), indicating that children and adolescents with high WHR tended to have higher BP values. Conclusion: WHR is useful in identifying children and adolescents at risk of developing high BP. These findings, together with the known tracking of BP from adolescence into adulthood, highlight the importance of preventing overweight and obesity among children and adolescents in order to prevent the development of hypertension in adults.
Adolescent, blood pressure, child, distribution, waist–hip ratio
Introduction Obesity, especially abdominal obesity, is closely related to the risk for metabolic syndrome. Excessive intra-abdominal fat accumulation increases the risk for cardiovascular disease (CVD) and type 2 diabetes in children and adults (Boyko et al., 2000; Kuk et al., 2006). Anthropometric indices such as waist circumference (WC), waist-to-height ratio (WHtR) and waist–hip ratio (WHR) have been recognized as useful alternatives to visceral fat measurement in epidemiological studies (Hirschler et al., 2005; Taylor et al., 2000). Many studies from different countries have reported the distribution of WC among children and adolescents in recent years (Galcheva et al., 2009; Hatipoglu et al., 2008; Poh et al., 2011; Sung et al., 2008). WHR is a measure of relative overall
Correspondence: Ying-xiu Zhang, Shandong Center for Disease Control and Prevention, 16992 Jingshi Road, Jinan 250014, PR China. Tel: 860531-82679413. Fax: 86-0531-82679413. E-mail: [email protected]
History Received 12 March 2013 Revised 9 May 2013 Accepted 3 June 2013 Published online 11 March 2014
body fat distribution and has been recognized as a useful indicator in epidemiological studies of adults (Megnien et al., 1999). In particular, abdominal obesity, indicated by a high WHR, has been shown to correlate with CVD factors (Megnien et al., 1999). However, little is known about the distribution of WHR among children and adolescents. Shandong Province, located in the lower reaches of the Yellow River, is an important littoral province in East China (a population of 95.79 million in 2010). The distributions of body mass index (BMI), WC and WHtR and the prevalence of overweight and obesity among adolescents in Shandong have been reported in our previous studies (Zhang & Wang, 2012a,b; Zhang et al., 2013). We also reported the relationship of BMI and WC to blood pressure (BP) among children and adolescents in Shandong, China (Zhang & Wang, 2013, 2014). However, no available data on WHR exist for Shandong children and adolescents that can be used for the study of their abdominal obesity. The aim of the present study was to examine the distribution of WHR and the relationship with BP among children and adolescents in Shandong, PR China.
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Subjects and methods The study was approved by the Ethical Committee of the Shandong Center for Disease Control and Prevention, Shandong, PR China.
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Study population Data for this study were obtained from a large cross-sectional survey of schoolchildren. A total of 38 822 students (19 456 boys and 19 366 girls) from 16 districts in Shandong Province, students of Han nationality, aged 7–17 years, participated in the National Surveys on Chinese Students’ Constitution and Health, which were carried out in September–October 2010. (The first author is the leader of the investigation team in Shandong.) The sampling method was stratified multi-stage sampling based on selected primary and secondary schools. Six public schools (two primary schools, two junior high schools and two senior high schools) from each of the 16 districts in Shandong were randomly selected and invited to participate in the study. From the selected schools, two classes in each grade were selected and all students of the selected classes were invited to join the study. All subjects were primary and secondary students, ranging from 7–17 years of age and all were of Han ancestry that accounts for 99.32% of the total population in Shandong. Age groups were divided following criteria of ‘‘exact age’’, so that, for example, cohort 7.5- (represented by ‘‘7.5’’ in the plots) designates students aged 7.0–7.9 years. Measurements and definitions All measurements were conducted by a team of trained technicians in each of the 16 districts. Each technician is required to pass a training course for anthropometric measurement organized by the investigation team in Shandong. All measurements were taken using the same type of apparatus and followed the same procedures. WC was measured midway between the lowest rib and the superior border of the iliac crest with an inelastic measuring tape at the end of normal expiration. Hip circumference (HC) was measured at the level of widest portion of buttocks (trochanters). Circumferences were measured over the naked skin and noted to the nearest 0.1 cm. WHR was calculated as WC divided by HC. Systolic blood pressure (SBP) and diastolic blood pressure (DBP) were measured using a mercury sphygmomanometer after each subject had rested for at least 15 minutes in a sitting position (Research Section of the Constitution and Health of Chinese Students, 2007). BP was measured twice on the right arm with an appropriately sized cuff and the average value was recorded on the study form. DBP was defined via Korotkoff Sound 5. Abdominal obesity was defined by previously published WHR references based on Chinese
children and adolescents living in Beijing (see Appendix) (Lv et al., 2012) Statistical analyses WHR levels of children and adolescents were presented as percentiles by age-group and gender. The ratio of abdominal obesity was determined and comparisons of abdominal obesity frequencies between boys and girls were made by 2 test. Z-scores of SBP and DBP were calculated from the national reference values (Research Section of the Constitution and Health of Chinese Students, 2007). All subjects were divided into two groups (group 1 with WHR 585th; group 2 with WHR 85th) according to the percentiles of WHR and comparisons of the Z-scores of SBP and DBP between the two groups were made by t-test. All analyses were performed with the statistical package SPSS/ PC+ version 11.5. Significance was defined at the 0.05 level. Data for WHR from German (Haas et al., 2011) and Pakistani (Mushtaq et al., 2011) published in recent years were collected (Table 1), their measuring sites and methods were the same as our study, the 50th percentile of WHR were compared between the present study and the collected data.
Results Distribution of WHR The percentile values of WHR in the sample are shown in Table 2. The 50th percentiles of WHR were slightly larger in boys than girls (by 0.03–0.06 over the age range 7–17 years) and in both genders decreased with age but only up to 14 years old and changed little further. Figures 1 and 2 show the comparisons of the age- and sex-specific 50th WHR percentiles between Chinese children and those from European (German) and South Asian (Pakistani). The WHR levels in Chinese boys and girls were lower than those from German and Pakistani. Table 3 shows the prevalence of abdominal obesity among children and adolescents aged 7–17 years in Shandong, PR China. The overall prevalence of abdominal obesity was 9.53% (95% CI ¼ 9.12–9.95%) for boys and 9.82% (95% CI ¼ 9.40–10.24%) for girls, no statistical differences between the two genders were observed (p40.05). Relationship between WHR and BP Figures 3 and 4 show the 50th percentiles of SBP and DBP in the two groups (group 1 with WHR 585th; group 2 with WHR 85th). For boys, the 50th percentiles of SBP and DBP in group 1 are lower than in group 2 by 3.6–5.0 mmHg and 3.3–4.7 mmHg; and for girls, the 50th percentiles of SBP and DBP in group 1 are lower than in group 2 by 3.1–4.2 mmHg
Table 1. A summary of population studies on children’s WHR. Countries Germany Pakistan Present study
Sample size
Age range
Years of data
Reference
F 1391, M 1633 F 883, M 977 F 19 366, M 19 456
12–18 5–12 7–17
2000–2007 2009–2010 2010
Haas et al. (2011) Mushtaq et al. (2011)
WC measured at midway between the lowest rib and the superior border of iliac crest, HC measured at the level of widest portion of buttocks (trochanters), WHR calculated as WC divided by HC.
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Table 2. Percentile values for WHR of Shandong Chinese children by gender and age.
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Gender
Age/years
n
P3
P5
P10
P15
P25
P50
P75
P85
P90
P95
P97
Boys
7.5 8.5 9.5 10.5 11.5 12.5 13.5 14.5 15.5 16.5 17.5
1753 1901 1740 1808 1794 1778 1761 1669 1807 1714 1731
0.72 0.76 0.75 0.75 0.72 0.72 0.73 0.71 0.72 0.72 0.73
0.75 0.77 0.76 0.77 0.75 0.74 0.74 0.72 0.73 0.73 0.74
0.78 0.79 0.78 0.78 0.77 0.75 0.76 0.74 0.75 0.75 0.75
0.80 0.80 0.79 0.79 0.78 0.77 0.77 0.75 0.76 0.76 0.76
0.82 0.82 0.81 0.81 0.80 0.79 0.78 0.77 0.77 0.77 0.78
0.86 0.86 0.85 0.85 0.84 0.83 0.81 0.80 0.80 0.80 0.81
0.90 0.91 0.90 0.90 0.89 0.88 0.87 0.85 0.85 0.84 0.85
0.93 0.93 0.93 0.93 0.92 0.92 0.90 0.88 0.88 0.86 0.88
0.95 0.95 0.95 0.94 0.94 0.95 0.92 0.90 0.90 0.89 0.90
1.00 0.97 0.97 0.96 0.97 0.99 0.95 0.94 0.94 0.92 0.94
1.06 0.99 0.99 0.98 0.99 1.00 0.99 0.96 0.98 0.94 1.00
Girls
7.5 8.5 9.5 10.5 11.5 12.5 13.5 14.5 15.5 16.5 17.5
1790 1818 1819 1823 1755 1710 1761 1706 1779 1680 1725
0.71 0.74 0.72 0.71 0.69 0.69 0.69 0.68 0.69 0.68 0.68
0.74 0.75 0.74 0.73 0.71 0.70 0.70 0.69 0.70 0.69 0.69
0.76 0.77 0.76 0.74 0.73 0.72 0.71 0.70 0.71 0.71 0.71
0.78 0.78 0.77 0.76 0.74 0.73 0.72 0.71 0.72 0.72 0.72
0.79 0.80 0.78 0.77 0.76 0.74 0.74 0.73 0.74 0.73 0.73
0.83 0.83 0.82 0.81 0.79 0.77 0.77 0.76 0.76 0.77 0.77
0.86 0.87 0.86 0.85 0.84 0.82 0.81 0.80 0.81 0.80 0.80
0.89 0.90 0.89 0.88 0.87 0.85 0.85 0.83 0.83 0.83 0.83
0.91 0.93 0.92 0.90 0.89 0.88 0.87 0.85 0.85 0.85 0.85
0.96 0.96 0.94 0.93 0.93 0.94 0.93 0.89 0.89 0.87 0.89
1.02 0.97 0.95 0.94 0.95 1.00 0.96 0.91 0.93 0.90 0.92
0.90
0.88
0.88
0.86 0.84
0.86
0.82 0.84
0.80 0.82
0.78
German 0.80
Pakistani
German Pakistani
0.76
Shandong 0.78
Shandong
0.74
0.76
0.72
0.74
0.70 5
6
7
8
9
10
11
12
13
14
15
16
17
18
Age/years
5
6
7
8
9
10
11
12
13
14
15
16
17
18
Age/years
Figure 1. Comparison of the WHR P50 for boys from German, Pakistani and Shandong.
Figure 2. Comparison of the WHR P50 for girls from German, Pakistani and Shandong.
and 3.2–4.0 mmHg, respectively. Table 4 shows the comparison of Z-scores of SBP and DBP for children and adolescents in the two groups. In both boys and girls, the Z-scores of SBP and DBP were all significantly lower in group 1 than in group 2 (p50.01), indicating that children and adolescents with high WHR tended to have higher BP values.
distribution of WHR for children and adolescents in Shandong, PR China, and the results of this article will provide valuable evidence for the control of central obesity. Worldwide, the prevalence of overweight and obesity is increasing among children and adolescents (Popkin & Doak, 1998; Wang & Lobstein, 2006). China, which used to be known for her slender people, has now joined the world epidemic of obesity with its rapid economic growth and urbanization (Chan, 2008; Chen, 2008; Ji & Cheng, 2009; Liou et al., 2009). The national data confirmed that Shandong province is one of the areas of China with higher prevalence of overweight and obesity among children and adolescents (Ji & Cheng, 2008). We have reported that the prevalence of combined overweight and obesity (BMI P85) among Shandong children and adolescents aged 7–18 years increased from 2.18% for boys and 2.25% for girls in 1985 to 33.17% for boys and 19.09% for girls in 2010, respectively (Zhang & Wang, 2012a). In this study, we found that the prevalence of
Discussion Abdominal obesity, which is also called central obesity, is associated with a higher risk of the development of chronic diseases such as CVD and diabetes and anthropometric indices predictive of abdominal obesity include WC, WHtR and WHR (Hirschler et al., 2005; Taylor et al., 2000). WHR has been recognized as a useful indicator in epidemiological studies of adults. However, measurement of WHR is not yet a common practice in children and adolescents. To the best of our knowledge, this is the first study examining the
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Table 3. Prevalence (95% CI) of abdominal obesity in boys and girls in Shandong, PR China.
120 110
Age, years
n
Girls %
n
7.5 1753 8.61 (7.30–9.93) 1790 8.5 1901 7.73 (6.53–8.93) 1818 9.5 1740 8.16 (6.87–9.45) 1819 10.5 1808 8.46 (7.18–9.75) 1823 11.5 1794 10.20 (8.80–11.60) 1755 12.5 1778 12.37 (10.84–13.90) 1710 13.5 1761 12.44 (10.89–13.98) 1761 14.5 1669 9.35 (7.95–10.74) 1706 15.5 1807 9.96 (8.58–11.34) 1779 16.5 1714 8.46 (7.14–9.78) 1680 17.5 1731 9.19 (7.82–10.55) 1725 Total 19 456 9.53 (9.12–9.95) 19 366
% 7.77 8.75 9.73 9.76 10.94 11.87 11.81 8.56 9.39 8.81 10.14 9.82
(6.53–9.01) (7.45–10.04) (8.37–11.09) (8.92–11.71) (9.48–12.40) (10.34–13.40) (10.30–13.32) (7.23–9.89) (8.03–10.74) (7.45–10.16) (8.72–11.57) (9.40–10.24)
0.357 0.261 0.101 0.056 0.474 0.650 0.570 0.422 0.561 0.717 0.340 0.339
SBP1 SBP2
90
DBP1 DBP2
80 70 60 50 7
8
9
10
11
12
13
14
15
16
17
Age/years
Figure 4. Comparison of the P50 values of SBP and DBP for girls with different WHR levels. 1. WHR5P85; 2. WHR P85.
130 120 110 SBP1 100 mmHg
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100
p mmHg
Boys
SBP2 DBP1
90
DBP2
80 70 60 50 7
8
9
10
11
12
13
14
15
16
17
Age/years
Figure 3. Comparison of the P50 values of SBP and DBP for boys with different WHR levels. 1. WHR5P85; 2. WHR P85.
abdominal obesity among Shandong children and adolescents has reached 9.53% for boys and 9.82% for girls, indicating that obesity, especially abdominal obesity, has become an increasingly important public health problem among children and adolescents in Shandong, China, which would arouse special attention. Comprehensive strategies of intervention should include periodical monitoring, education on pattern of nutrition, healthy dietary behaviour and oxygen-consuming physical exercises. Hypertension in adults remains a major public health problem and has its onset in childhood (Lurbe & Redon, 2000; Rosner et al., 1993). Children with elevated BP are more likely to become hypertensive adults (Chen & Wang, 2008; Sun et al., 2007; Vos et al., 2003). Shandong province is also one of the areas of China with higher prevalence of hypertension; data of the China Health and Nutrition Survey conducted in 2002 show that the prevalence of hypertension among adults in Shandong had reached 29.22% (Zhou & Zhang, 2008). In this study, we found that children and adolescents with high WHR tended to have higher BP values. These findings underline the importance of preventing
overweight and obesity among children and adolescents in order to prevent the development of hypertension in adults. WHR has been used extensively in adults. However, findings from studies on the validity of WHR as an indicator of CVD risk factors was inconsistent, some studies reported WHR to be a better predictor of CVD risk factors than WC and BMI (Dobbelsteyn et al., 2001; Esmaillzadeh et al., 2004; Lakka et al., 2002); whereas most studies introduced WC as a better predictor of CVD risk factors than either BMI or WHR (Foucan et al., 2002; Taylor et al., 1998; Wang & Hoy, 2004; Zhu et al., 2002). There are very few published data for WHR among children and adolescents. Although the present study indicated that higher WHR is associated with an increased risk for elevated BP among children and adolescents, further study should be done to confirm its validity as an indicator of CVD risk factors compared with other anthropometric indices. Comparisons of WHR data between different studies need to be undertaken with caution since WC and HC may be measured at different sites that makes comparisons difficult (Wang et al., 2003). In the study, according to the principle of comparability, we compared Chinese children’s WHR with data from European (German) and South Asian (Pakistani) where the method and site of measuring WC and HC was the same as our study. The WHR levels in Chinese boys and girls were lower than those from German and Pakistani. This may be related to ethnic differences in body fat patterning and the difference in the prevalence of obesity, cultural background, socio-economical levels, living environments, nutritional habits and lifestyle. The major strength of this study is that, based on the data from a large sample, it examines the distribution of WHR and the relationship with BP among children and adolescents. However, this study has several limitations. First, there is a lack of national reference data for WHR among Chinese adolescents, so the data for Beijing were used as the reference; the definition of abdominal obesity (assessed by WHR) is neither an international criterion nor a national standard. Therefore, caution should be exercised when the prevalence rates in this study are compared with other findings. Second,
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Table 4. Comparisons of Z-score of SBP and DBP for children and adolescents with different WHR. Group 2 (WHR P85)
Group 1 (WHR 5P85) n
ZSBP
ZDBP
n
ZSBP
ZDBP
16 547 16 495
0.46 (0.45–0.47) 0.43 (0.42–0.44)
0.37 (0.36–0.38) 0.32 (0.31–0.33)
2909 2871
0.87 (0.83–0.91)* 0.75 (0.71–0.79)*
0.85 (0.82–0.88)* 0.71 (0.68–0.74)*
Gender Boys Girls
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Data were presented as mean (95% CI). *Significant difference between the WHR 5P85 group and WHR P85 group (p50.01).
the absence of detailed information concerning living environments, nutritional status, dietary pattern and physical activity at the individual level also limited our study. Third, because of various restraints, sexual maturation and other biochemical indicators (e.g. blood lipids and blood glucose) were not measured and further studies are required to further investigate the use of WHR in predicting cardiovascular risk in Han Chinese children. In summary, based on the data from a large sample, the distribution of WHR and the relationship with BP among children and adolescents were examined for the first time in Shandong, China. The reference values obtained from the present study can provide baseline data for analysis of time trends, as well as for international comparisons. Children and adolescents with high WHR tended to have higher BP values. These findings, together with the known tracking of BP from adolescence into adulthood, highlight the importance of preventing overweight and obesity among children and adolescents in order to prevent the development of hypertension in adults.
Acknowledgements Surveys on students’ constitution and health are conducted under the auspices of the department of education in Shandong Province, PR China. We thank all the team members and all participants. Special thanks to Mr B. Yu for providing access to the survey data.
Declaration of interest The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper. This study was supported by the medical and health program of Shandong, China (2009-HZ049).
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Zhang YX, Wang SR. 2012b. Differences in development and the prevalence of obesity among children and adolescents in different socioeconomic status districts in Shandong, China. Ann Hum Biol 39: 290–296. Zhang YX, Li YL, Zhao JS, Chu ZH, Zhou JY. 2013. Distributions of waist circumference and waist-to-height ratio for children and adolescents in Shandong, China. Eur J Pediatr 172:185–191. Zhang YX, Wang SR. 2013. The relationship of waist circumference distribution to blood pressure levels among children and adolescents in Shandong, China. Int J Cardiol 168:1516–1520. Zhang YX, Wang SR. 2014. Comparison of blood pressure levels among children and adolescents with different body mass index and waist circumference: study in a large sample in Shandong, China. Eur J Nutr 53:627–634. Zhou JY, Zhang JL. 2008. Dietary nutrition and health status of Shandong population. Jinan, Shandong, China: Shandong Electronic Audio & Video Publishing House. p 17 [in Chinese]. Zhu S, Wang Z, Heshka S, Heo M, Faith MS, Heymsfield SB. 2002. Waist circumference and obesity-associated risk factors among whites in the NHANES III: clinical action thresholds. Am J Clin Nutr 76: 743–749.
Appendix Cut-points for screening abdominal obesity using WHR in Chinese children and adolescents living in Beijing (Lv et al., 2012). Age/years
Boys
Girls
7 8 9 10 11 12 13 14 15 16 17 18
0.96 0.96 0.96 0.95 0.94 0.93 0.91 0.90 0.90 0.90 0.90 0.91
0.93 0.93 0.92 0.90 0.88 0.87 0.86 0.86 0.86 0.85 0.85 0.85
RESEARCH PAPER
Percentiles of waist–hip ratio and the relationship with blood pressure among children and adolescents in Shandong, China Ying-xiu Zhang1, Shu-rong Wang2, Jing-yang Zhou1, Jin-shan Zhao1, and Zun-hua Chu1 Shandong Center for Disease Control and Prevention, Shandong, PR China and 2Shandong Blood Center, Shandong, PR China
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1
Abstract
Keywords
Background: Anthropometric indices such as waist circumference (WC), waist-to-height ratio (WHtR) and waist–hip ratio (WHR) have been recognized as useful alternatives to visceral fat measurement in epidemiological studies. WHR has been used extensively in adults. However, there are very few published data for WHR among children and adolescents. Aim: The present study examined the distribution of WHR and the relationship with blood pressure (BP) among children and adolescents in Shandong, PR China. Subjects and methods: Data for this study were obtained from a large cross-sectional survey of schoolchildren carried out in 2010. A total of 38 822 students (19 456 boys and 19 366 girls) aged 7–17 years participated in this study. WC, Hip circumference (HC), systolic blood pressure (SBP) and diastolic blood pressure (DBP) of all subjects were measured; WHR was calculated as WC divided by HC. Abdominal obesity was defined by previously published WHR references based on Chinese children and adolescents living in Beijing. All subjects were divided into two groups (group 1 with WHR 585th; group 2 with WHR 85th) according to the percentiles of WHR and comparisons of the SBP and DBP between the two groups were made. Results: The WHR levels in Shandong boys and girls were lower than those from German and Pakistani. The overall prevalence of abdominal obesity was 9.53% (95% CI ¼ 9.12–9.95%) for boys and 9.82% (95% CI ¼ 9.40–10.24%) for girls, no statistical differences between the two genders were observed (p40.05). In both boys and girls, the Z-scores of SBP and DBP were all significantly lower in group 1 than in group 2 (p50.01), indicating that children and adolescents with high WHR tended to have higher BP values. Conclusion: WHR is useful in identifying children and adolescents at risk of developing high BP. These findings, together with the known tracking of BP from adolescence into adulthood, highlight the importance of preventing overweight and obesity among children and adolescents in order to prevent the development of hypertension in adults.
Adolescent, blood pressure, child, distribution, waist–hip ratio
Introduction Obesity, especially abdominal obesity, is closely related to the risk for metabolic syndrome. Excessive intra-abdominal fat accumulation increases the risk for cardiovascular disease (CVD) and type 2 diabetes in children and adults (Boyko et al., 2000; Kuk et al., 2006). Anthropometric indices such as waist circumference (WC), waist-to-height ratio (WHtR) and waist–hip ratio (WHR) have been recognized as useful alternatives to visceral fat measurement in epidemiological studies (Hirschler et al., 2005; Taylor et al., 2000). Many studies from different countries have reported the distribution of WC among children and adolescents in recent years (Galcheva et al., 2009; Hatipoglu et al., 2008; Poh et al., 2011; Sung et al., 2008). WHR is a measure of relative overall
Correspondence: Ying-xiu Zhang, Shandong Center for Disease Control and Prevention, 16992 Jingshi Road, Jinan 250014, PR China. Tel: 860531-82679413. Fax: 86-0531-82679413. E-mail: [email protected]
History Received 12 March 2013 Revised 9 May 2013 Accepted 3 June 2013 Published online 11 March 2014
body fat distribution and has been recognized as a useful indicator in epidemiological studies of adults (Megnien et al., 1999). In particular, abdominal obesity, indicated by a high WHR, has been shown to correlate with CVD factors (Megnien et al., 1999). However, little is known about the distribution of WHR among children and adolescents. Shandong Province, located in the lower reaches of the Yellow River, is an important littoral province in East China (a population of 95.79 million in 2010). The distributions of body mass index (BMI), WC and WHtR and the prevalence of overweight and obesity among adolescents in Shandong have been reported in our previous studies (Zhang & Wang, 2012a,b; Zhang et al., 2013). We also reported the relationship of BMI and WC to blood pressure (BP) among children and adolescents in Shandong, China (Zhang & Wang, 2013, 2014). However, no available data on WHR exist for Shandong children and adolescents that can be used for the study of their abdominal obesity. The aim of the present study was to examine the distribution of WHR and the relationship with BP among children and adolescents in Shandong, PR China.
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Subjects and methods The study was approved by the Ethical Committee of the Shandong Center for Disease Control and Prevention, Shandong, PR China.
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Study population Data for this study were obtained from a large cross-sectional survey of schoolchildren. A total of 38 822 students (19 456 boys and 19 366 girls) from 16 districts in Shandong Province, students of Han nationality, aged 7–17 years, participated in the National Surveys on Chinese Students’ Constitution and Health, which were carried out in September–October 2010. (The first author is the leader of the investigation team in Shandong.) The sampling method was stratified multi-stage sampling based on selected primary and secondary schools. Six public schools (two primary schools, two junior high schools and two senior high schools) from each of the 16 districts in Shandong were randomly selected and invited to participate in the study. From the selected schools, two classes in each grade were selected and all students of the selected classes were invited to join the study. All subjects were primary and secondary students, ranging from 7–17 years of age and all were of Han ancestry that accounts for 99.32% of the total population in Shandong. Age groups were divided following criteria of ‘‘exact age’’, so that, for example, cohort 7.5- (represented by ‘‘7.5’’ in the plots) designates students aged 7.0–7.9 years. Measurements and definitions All measurements were conducted by a team of trained technicians in each of the 16 districts. Each technician is required to pass a training course for anthropometric measurement organized by the investigation team in Shandong. All measurements were taken using the same type of apparatus and followed the same procedures. WC was measured midway between the lowest rib and the superior border of the iliac crest with an inelastic measuring tape at the end of normal expiration. Hip circumference (HC) was measured at the level of widest portion of buttocks (trochanters). Circumferences were measured over the naked skin and noted to the nearest 0.1 cm. WHR was calculated as WC divided by HC. Systolic blood pressure (SBP) and diastolic blood pressure (DBP) were measured using a mercury sphygmomanometer after each subject had rested for at least 15 minutes in a sitting position (Research Section of the Constitution and Health of Chinese Students, 2007). BP was measured twice on the right arm with an appropriately sized cuff and the average value was recorded on the study form. DBP was defined via Korotkoff Sound 5. Abdominal obesity was defined by previously published WHR references based on Chinese
children and adolescents living in Beijing (see Appendix) (Lv et al., 2012) Statistical analyses WHR levels of children and adolescents were presented as percentiles by age-group and gender. The ratio of abdominal obesity was determined and comparisons of abdominal obesity frequencies between boys and girls were made by 2 test. Z-scores of SBP and DBP were calculated from the national reference values (Research Section of the Constitution and Health of Chinese Students, 2007). All subjects were divided into two groups (group 1 with WHR 585th; group 2 with WHR 85th) according to the percentiles of WHR and comparisons of the Z-scores of SBP and DBP between the two groups were made by t-test. All analyses were performed with the statistical package SPSS/ PC+ version 11.5. Significance was defined at the 0.05 level. Data for WHR from German (Haas et al., 2011) and Pakistani (Mushtaq et al., 2011) published in recent years were collected (Table 1), their measuring sites and methods were the same as our study, the 50th percentile of WHR were compared between the present study and the collected data.
Results Distribution of WHR The percentile values of WHR in the sample are shown in Table 2. The 50th percentiles of WHR were slightly larger in boys than girls (by 0.03–0.06 over the age range 7–17 years) and in both genders decreased with age but only up to 14 years old and changed little further. Figures 1 and 2 show the comparisons of the age- and sex-specific 50th WHR percentiles between Chinese children and those from European (German) and South Asian (Pakistani). The WHR levels in Chinese boys and girls were lower than those from German and Pakistani. Table 3 shows the prevalence of abdominal obesity among children and adolescents aged 7–17 years in Shandong, PR China. The overall prevalence of abdominal obesity was 9.53% (95% CI ¼ 9.12–9.95%) for boys and 9.82% (95% CI ¼ 9.40–10.24%) for girls, no statistical differences between the two genders were observed (p40.05). Relationship between WHR and BP Figures 3 and 4 show the 50th percentiles of SBP and DBP in the two groups (group 1 with WHR 585th; group 2 with WHR 85th). For boys, the 50th percentiles of SBP and DBP in group 1 are lower than in group 2 by 3.6–5.0 mmHg and 3.3–4.7 mmHg; and for girls, the 50th percentiles of SBP and DBP in group 1 are lower than in group 2 by 3.1–4.2 mmHg
Table 1. A summary of population studies on children’s WHR. Countries Germany Pakistan Present study
Sample size
Age range
Years of data
Reference
F 1391, M 1633 F 883, M 977 F 19 366, M 19 456
12–18 5–12 7–17
2000–2007 2009–2010 2010
Haas et al. (2011) Mushtaq et al. (2011)
WC measured at midway between the lowest rib and the superior border of iliac crest, HC measured at the level of widest portion of buttocks (trochanters), WHR calculated as WC divided by HC.
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Table 2. Percentile values for WHR of Shandong Chinese children by gender and age.
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Gender
Age/years
n
P3
P5
P10
P15
P25
P50
P75
P85
P90
P95
P97
Boys
7.5 8.5 9.5 10.5 11.5 12.5 13.5 14.5 15.5 16.5 17.5
1753 1901 1740 1808 1794 1778 1761 1669 1807 1714 1731
0.72 0.76 0.75 0.75 0.72 0.72 0.73 0.71 0.72 0.72 0.73
0.75 0.77 0.76 0.77 0.75 0.74 0.74 0.72 0.73 0.73 0.74
0.78 0.79 0.78 0.78 0.77 0.75 0.76 0.74 0.75 0.75 0.75
0.80 0.80 0.79 0.79 0.78 0.77 0.77 0.75 0.76 0.76 0.76
0.82 0.82 0.81 0.81 0.80 0.79 0.78 0.77 0.77 0.77 0.78
0.86 0.86 0.85 0.85 0.84 0.83 0.81 0.80 0.80 0.80 0.81
0.90 0.91 0.90 0.90 0.89 0.88 0.87 0.85 0.85 0.84 0.85
0.93 0.93 0.93 0.93 0.92 0.92 0.90 0.88 0.88 0.86 0.88
0.95 0.95 0.95 0.94 0.94 0.95 0.92 0.90 0.90 0.89 0.90
1.00 0.97 0.97 0.96 0.97 0.99 0.95 0.94 0.94 0.92 0.94
1.06 0.99 0.99 0.98 0.99 1.00 0.99 0.96 0.98 0.94 1.00
Girls
7.5 8.5 9.5 10.5 11.5 12.5 13.5 14.5 15.5 16.5 17.5
1790 1818 1819 1823 1755 1710 1761 1706 1779 1680 1725
0.71 0.74 0.72 0.71 0.69 0.69 0.69 0.68 0.69 0.68 0.68
0.74 0.75 0.74 0.73 0.71 0.70 0.70 0.69 0.70 0.69 0.69
0.76 0.77 0.76 0.74 0.73 0.72 0.71 0.70 0.71 0.71 0.71
0.78 0.78 0.77 0.76 0.74 0.73 0.72 0.71 0.72 0.72 0.72
0.79 0.80 0.78 0.77 0.76 0.74 0.74 0.73 0.74 0.73 0.73
0.83 0.83 0.82 0.81 0.79 0.77 0.77 0.76 0.76 0.77 0.77
0.86 0.87 0.86 0.85 0.84 0.82 0.81 0.80 0.81 0.80 0.80
0.89 0.90 0.89 0.88 0.87 0.85 0.85 0.83 0.83 0.83 0.83
0.91 0.93 0.92 0.90 0.89 0.88 0.87 0.85 0.85 0.85 0.85
0.96 0.96 0.94 0.93 0.93 0.94 0.93 0.89 0.89 0.87 0.89
1.02 0.97 0.95 0.94 0.95 1.00 0.96 0.91 0.93 0.90 0.92
0.90
0.88
0.88
0.86 0.84
0.86
0.82 0.84
0.80 0.82
0.78
German 0.80
Pakistani
German Pakistani
0.76
Shandong 0.78
Shandong
0.74
0.76
0.72
0.74
0.70 5
6
7
8
9
10
11
12
13
14
15
16
17
18
Age/years
5
6
7
8
9
10
11
12
13
14
15
16
17
18
Age/years
Figure 1. Comparison of the WHR P50 for boys from German, Pakistani and Shandong.
Figure 2. Comparison of the WHR P50 for girls from German, Pakistani and Shandong.
and 3.2–4.0 mmHg, respectively. Table 4 shows the comparison of Z-scores of SBP and DBP for children and adolescents in the two groups. In both boys and girls, the Z-scores of SBP and DBP were all significantly lower in group 1 than in group 2 (p50.01), indicating that children and adolescents with high WHR tended to have higher BP values.
distribution of WHR for children and adolescents in Shandong, PR China, and the results of this article will provide valuable evidence for the control of central obesity. Worldwide, the prevalence of overweight and obesity is increasing among children and adolescents (Popkin & Doak, 1998; Wang & Lobstein, 2006). China, which used to be known for her slender people, has now joined the world epidemic of obesity with its rapid economic growth and urbanization (Chan, 2008; Chen, 2008; Ji & Cheng, 2009; Liou et al., 2009). The national data confirmed that Shandong province is one of the areas of China with higher prevalence of overweight and obesity among children and adolescents (Ji & Cheng, 2008). We have reported that the prevalence of combined overweight and obesity (BMI P85) among Shandong children and adolescents aged 7–18 years increased from 2.18% for boys and 2.25% for girls in 1985 to 33.17% for boys and 19.09% for girls in 2010, respectively (Zhang & Wang, 2012a). In this study, we found that the prevalence of
Discussion Abdominal obesity, which is also called central obesity, is associated with a higher risk of the development of chronic diseases such as CVD and diabetes and anthropometric indices predictive of abdominal obesity include WC, WHtR and WHR (Hirschler et al., 2005; Taylor et al., 2000). WHR has been recognized as a useful indicator in epidemiological studies of adults. However, measurement of WHR is not yet a common practice in children and adolescents. To the best of our knowledge, this is the first study examining the
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Table 3. Prevalence (95% CI) of abdominal obesity in boys and girls in Shandong, PR China.
120 110
Age, years
n
Girls %
n
7.5 1753 8.61 (7.30–9.93) 1790 8.5 1901 7.73 (6.53–8.93) 1818 9.5 1740 8.16 (6.87–9.45) 1819 10.5 1808 8.46 (7.18–9.75) 1823 11.5 1794 10.20 (8.80–11.60) 1755 12.5 1778 12.37 (10.84–13.90) 1710 13.5 1761 12.44 (10.89–13.98) 1761 14.5 1669 9.35 (7.95–10.74) 1706 15.5 1807 9.96 (8.58–11.34) 1779 16.5 1714 8.46 (7.14–9.78) 1680 17.5 1731 9.19 (7.82–10.55) 1725 Total 19 456 9.53 (9.12–9.95) 19 366
% 7.77 8.75 9.73 9.76 10.94 11.87 11.81 8.56 9.39 8.81 10.14 9.82
(6.53–9.01) (7.45–10.04) (8.37–11.09) (8.92–11.71) (9.48–12.40) (10.34–13.40) (10.30–13.32) (7.23–9.89) (8.03–10.74) (7.45–10.16) (8.72–11.57) (9.40–10.24)
0.357 0.261 0.101 0.056 0.474 0.650 0.570 0.422 0.561 0.717 0.340 0.339
SBP1 SBP2
90
DBP1 DBP2
80 70 60 50 7
8
9
10
11
12
13
14
15
16
17
Age/years
Figure 4. Comparison of the P50 values of SBP and DBP for girls with different WHR levels. 1. WHR5P85; 2. WHR P85.
130 120 110 SBP1 100 mmHg
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100
p mmHg
Boys
SBP2 DBP1
90
DBP2
80 70 60 50 7
8
9
10
11
12
13
14
15
16
17
Age/years
Figure 3. Comparison of the P50 values of SBP and DBP for boys with different WHR levels. 1. WHR5P85; 2. WHR P85.
abdominal obesity among Shandong children and adolescents has reached 9.53% for boys and 9.82% for girls, indicating that obesity, especially abdominal obesity, has become an increasingly important public health problem among children and adolescents in Shandong, China, which would arouse special attention. Comprehensive strategies of intervention should include periodical monitoring, education on pattern of nutrition, healthy dietary behaviour and oxygen-consuming physical exercises. Hypertension in adults remains a major public health problem and has its onset in childhood (Lurbe & Redon, 2000; Rosner et al., 1993). Children with elevated BP are more likely to become hypertensive adults (Chen & Wang, 2008; Sun et al., 2007; Vos et al., 2003). Shandong province is also one of the areas of China with higher prevalence of hypertension; data of the China Health and Nutrition Survey conducted in 2002 show that the prevalence of hypertension among adults in Shandong had reached 29.22% (Zhou & Zhang, 2008). In this study, we found that children and adolescents with high WHR tended to have higher BP values. These findings underline the importance of preventing
overweight and obesity among children and adolescents in order to prevent the development of hypertension in adults. WHR has been used extensively in adults. However, findings from studies on the validity of WHR as an indicator of CVD risk factors was inconsistent, some studies reported WHR to be a better predictor of CVD risk factors than WC and BMI (Dobbelsteyn et al., 2001; Esmaillzadeh et al., 2004; Lakka et al., 2002); whereas most studies introduced WC as a better predictor of CVD risk factors than either BMI or WHR (Foucan et al., 2002; Taylor et al., 1998; Wang & Hoy, 2004; Zhu et al., 2002). There are very few published data for WHR among children and adolescents. Although the present study indicated that higher WHR is associated with an increased risk for elevated BP among children and adolescents, further study should be done to confirm its validity as an indicator of CVD risk factors compared with other anthropometric indices. Comparisons of WHR data between different studies need to be undertaken with caution since WC and HC may be measured at different sites that makes comparisons difficult (Wang et al., 2003). In the study, according to the principle of comparability, we compared Chinese children’s WHR with data from European (German) and South Asian (Pakistani) where the method and site of measuring WC and HC was the same as our study. The WHR levels in Chinese boys and girls were lower than those from German and Pakistani. This may be related to ethnic differences in body fat patterning and the difference in the prevalence of obesity, cultural background, socio-economical levels, living environments, nutritional habits and lifestyle. The major strength of this study is that, based on the data from a large sample, it examines the distribution of WHR and the relationship with BP among children and adolescents. However, this study has several limitations. First, there is a lack of national reference data for WHR among Chinese adolescents, so the data for Beijing were used as the reference; the definition of abdominal obesity (assessed by WHR) is neither an international criterion nor a national standard. Therefore, caution should be exercised when the prevalence rates in this study are compared with other findings. Second,
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Table 4. Comparisons of Z-score of SBP and DBP for children and adolescents with different WHR. Group 2 (WHR P85)
Group 1 (WHR 5P85) n
ZSBP
ZDBP
n
ZSBP
ZDBP
16 547 16 495
0.46 (0.45–0.47) 0.43 (0.42–0.44)
0.37 (0.36–0.38) 0.32 (0.31–0.33)
2909 2871
0.87 (0.83–0.91)* 0.75 (0.71–0.79)*
0.85 (0.82–0.88)* 0.71 (0.68–0.74)*
Gender Boys Girls
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Data were presented as mean (95% CI). *Significant difference between the WHR 5P85 group and WHR P85 group (p50.01).
the absence of detailed information concerning living environments, nutritional status, dietary pattern and physical activity at the individual level also limited our study. Third, because of various restraints, sexual maturation and other biochemical indicators (e.g. blood lipids and blood glucose) were not measured and further studies are required to further investigate the use of WHR in predicting cardiovascular risk in Han Chinese children. In summary, based on the data from a large sample, the distribution of WHR and the relationship with BP among children and adolescents were examined for the first time in Shandong, China. The reference values obtained from the present study can provide baseline data for analysis of time trends, as well as for international comparisons. Children and adolescents with high WHR tended to have higher BP values. These findings, together with the known tracking of BP from adolescence into adulthood, highlight the importance of preventing overweight and obesity among children and adolescents in order to prevent the development of hypertension in adults.
Acknowledgements Surveys on students’ constitution and health are conducted under the auspices of the department of education in Shandong Province, PR China. We thank all the team members and all participants. Special thanks to Mr B. Yu for providing access to the survey data.
Declaration of interest The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper. This study was supported by the medical and health program of Shandong, China (2009-HZ049).
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Appendix Cut-points for screening abdominal obesity using WHR in Chinese children and adolescents living in Beijing (Lv et al., 2012). Age/years
Boys
Girls
7 8 9 10 11 12 13 14 15 16 17 18
0.96 0.96 0.96 0.95 0.94 0.93 0.91 0.90 0.90 0.90 0.90 0.91
0.93 0.93 0.92 0.90 0.88 0.87 0.86 0.86 0.86 0.85 0.85 0.85
