Original Paper Ann Nutr Metab 2014;64:137–143 DOI: 10.1159/000365013
Received: April 23, 2014 Accepted after revision: June 1, 2014 Published online: July 26, 2014
Prevalence and Regional Disparities in Abdominal Obesity among Children and Adolescents in Shandong, China, Surveyed in 2010 Ying-xiu Zhang Jin-shan Zhao Zun-hua Chu Hai-lian Tan Shandong Center for Disease Control and Prevention, Shandong University Institute of Preventive Medicine, Jinan, China
Key Words Abdominal obesity · Regional disparity · Prevalence · Socioeconomic status · Child · Adolescent
Abstract Background/Aims: A rising prevalence of childhood obesity (assessed by body mass index) has been observed in China. However, there are very few published data on abdominal obesity among children and adolescents. The present study examined the prevalence and regional disparities in abdominal obesity among children and adolescents in Shandong, China. Methods: Data for this study were obtained from a large cross-sectional survey. A total of 42,296 students (21,218 boys and 21,078 girls) aged 7–18 years from 16 districts participated in this study. Height and waist circumference (WC) of all subjects were measured; waist-to-height ratio (WHtR) was calculated from their height and WC. Abdominal obesity was defined as WHtR ≥0.5. All subjects were stratified by gender, age and the area of residence, and abdominal obesity frequencies were compared among different groups. Results: Substantial regional, socioeconomic and urban/rural disparities exist in child and adolescent abdominal obesity. The overall prevalences of abdominal obesity among different groups of children and adolescents
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aged 7–18 years were 19.92% (urban boys), 11.94% (rural boys), 8.43% (urban girls) and 5.85% (rural girls). The prevalence of abdominal obesity varied from 24.98% in high-socioeconomic status (SES) urban boys to 4.58% in low-SES rural girls. Subjects living in coastal and high-urbanization districts had a higher prevalence of abdominal obesity than those living in inland and low-urbanization districts. Conclusions: Abdominal obesity among children and adolescents in China is associated with affluence and urban residence. Interventions and strategies to combat obesity should be based on this specific context, targeting high-SES urban areas. © 2014 S. Karger AG, Basel
Introduction
The prevalence of childhood obesity is increasing rapidly worldwide [1, 2]. Obesity in children and adolescents is known to progress easily to adult obesity and to increase the risks of hypertension, type II diabetes and cardiovascular diseases, making this a serious social and health problem [3, 4]. In 2009–2010, 18.2% of US children and adolescents aged 6–19 years (19.8% of boys and 16.5% of girls) were obese [assessed as body mass index Ying-xiu Zhang Shandong Center for Disease Control and Prevention Shandong University Institute of Preventive Medicine 16992 Jingshi Road, Jinan 250014 (China) E-Mail SDCDCZYX @ 163.com
(BMI) ≥95th percentile] [5]. China is the largest developing country in the world and has now joined the world epidemic of obesity with its rapid economic growth and urbanization [6, 7]. In 2010, it was estimated that 9.9 and 5.1% of Chinese schoolaged children and adolescents were overweight and obese (assessed by BMI), respectively, representing an estimated 30.43 million individuals [8]. Abdominal fat distribution is associated with greater health risks than total body fat [9]. Recent evidence suggests that compared with overall obesity, abdominal obesity appears to be more strongly associated with cardiovascular disease risk factors [10]. In 2003, 17.9% of Greek adolescents aged 13–19 years (13.5% of boys and 21.7% of girls) were abdominally obese [11]. From 1981 to 2007–2009, there was a sevenfold increase in the prevalence of abdominal obesity in Canadian adolescents aged 12–19 years (from 1.8 to 12.8%) [12]. A similar rising trend is also being observed in American White, Black and Hispanic youths [13]. Waist-to-height ratio (WHtR) has been suggested as an alternative measure to identify abdominal adiposity with a simple message: ‘keep your waist circumference to less than half your height’ [14]. An increasing number of studies have documented that it is suitable for population and epidemiologic studies and can be used on a large scale in screening for metabolic risk in both adults and children [15, 16]. Shandong Province, located in the lower reaches of the Yellow River, is an important littoral province in east China. It has a total area of 156,700 km2 (about 60,500 square miles) and had a total population of 95.79 million in 2010. The distribution of BMI and the prevalence of general obesity among children and adolescents in Shandong have been reported in our previous studies [17, 18]. However, little is known about the prevalence of childhood abdominal obesity in this region. In this study, based on provincial data from 2010, we report the prevalence and regional disparities in abdominal obesity among children and adolescents in Shandong, China.
Subjects and Methods This study was approved by the Ethical Committee of the Shandong Center for Disease Control and Prevention, Shandong, China. Study Population Data for this study were obtained from a large cross-sectional survey of schoolchildren. A total of 42,296 students of Han nationality (21,218 boys and 21,078 girls) from 16 districts in Shandong
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Ann Nutr Metab 2014;64:137–143 DOI: 10.1159/000365013
Province, aged 7–18 years, participated in the National Surveys on Chinese Students’ Constitution and Health, which were carried out in September and October 2010. To date, it is the largest representative sample of school-aged children and adolescents in Shandong, China. All subjects voluntarily joined this study with informed consent. The sampling method was stratified multistage sampling based on selected primary and secondary schools. Six public schools (2 primary schools, 2 junior high schools and 2 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 to 18 years of age, and all were of Han ancestry, which accounts for approximately 99.32% of the total population in Shandong. All subjects were stratified by gender, age and the area of residence (urban or rural). Classification of Subgroups According to geographic location, the 16 districts were classified into 2 categories, i.e. coastal and inland; coastal regions included Qingdao, Yantai, Weihai, Rizhao and Dongying, and the other 11 districts were inland regions. The information about gross domestic product (GDP) per capita of the 16 districts in 2010 was collected from the Shandong Statistical Yearbook [19]. The 16 districts were divided into 3 groups [high socioeconomic status (SES), moderate SES and low SES] according to their GDP per capita in 2010. High SES was defined as GDP per capita above USD 8,000 (Jinan, Qingdao, Yantai, Weihai, Dongying and Zibo); moderate SES was defined as GDP per capita above USD 5,000 but below USD 8,000 (Weifang, Taian, Laiwu, Binzhou and Rizhao), and low SES was defined as GDP per capita below USD 5,000 (Jining, Dezhou, Liaocheng, Linyi and Heze). To show the distribution of obesity prevalence between districts, all subpopulations were redivided into 6 regions, as follows: (1) high-SES urban areas; (2) moderate-SES urban areas; (3) low-SES urban areas; (4) high-SES rural areas; (5) moderate-SES rural areas, and (6) low-SES rural areas. Measurements All measurements were conducted by a team of trained technicians in each of the 16 districts. Each technician was 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. Height without shoes was measured using metal column height-measuring stands to the nearest 0.1 cm. Waist circumference (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 to the nearest 0.1 cm. WHtR was calculated as WC divided by height, and abdominal obesity was defined as WHtR ≥0.5 [14]. Statistical Analyses The prevalence of abdominal obesity in each group was determined, and comparisons of abdominal obesity frequencies among different groups were made by χ2 test. All analyses were performed with the statistical package SPSS/PC+ version 11.5. Significance was defined at the 0.05 level.
Zhang/Zhao/Chu/Tan
Table 1. Prevalence of abdominal obesity among children and adolescents aged 7 – 18 years in urban and rural areas in Shandong, China
Age, years
Urban boys
7.0 – 7.9 8.0 – 8.9 9.0 – 9.9 10.0 – 10.9 11.0 – 11.9 12.0 – 12.9 13.0 – 13.9 14.0 – 14.9 15.0 – 15.9 16.0 – 16.9 17.0 – 17.9 18.0 – 18.9
Rural boys
Urban girls
Rural girls
n
%
n
%
n
%
n
%
860 956 872 917 915 919 865 842 892 896 884 889
21.63 20.19 26.61 30.75 27.76 22.96 19.88 14.73 14.91 11.16 14.03 13.72
893 945 868 891 879 859 896 827 915 818 847 873
11.76 15.34 13.82 15.49 15.13 13.27 15.18 9.55 10.71 7.70 6.73 7.67
905 908 908 926 908 843 852 868 929 866 869 843
10.61 10.35 11.01 12.20 8.26 9.25 7.51 6.91 7.10 6.70 5.18 5.58
885 910 911 897 847 867 909 838 850 814 856 869
6.89 8.68 6.70 7.25 6.02 4.96 5.61 4.30 5.18 4.91 4.56 4.72
19.92
15
20
11.94
10
8.43 5.85
Prevalence (%)
20 Prevalence (%)
p
93.37 64.03 157.81 204.33 208.21 142.54 110.81 62.08 56.56 25.24 70.86 59.32
0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000
25
25
17.71 14.97
15 10
7.91
6.72
5
5 0
χ2
Urban boys
Rural boys
Urban girls
Rural girls
Fig. 1. The total prevalence of abdominal obesity classified by ur-
ban and rural areas.
Results
Prevalence of Abdominal Obesity The prevalence of abdominal obesity among children and adolescents in the sample by age, gender and urban/ rural categories is shown in table 1. The prevalence of abdominal obesity in urban boys was significantly higher than in the other 3 groups (rural boys, urban girls and rural girls) in all age categories (p < 0.05). The overall prevalences of abdominal obesity among the different groups of children and adolescents aged 7–18 years were 19.92% (urban boys), 11.94% (rural boys), 8.43% (urban girls) and 5.85% (rural girls); statistically significant difAbdominal Obesity among Children and Adolescents in Shandong, China
0
Coastal boys
Inland boys
Coastal girls
Inland girls
Fig. 2. The total prevalence of abdominal obesity classified by coastal and inland areas.
ferences were observed between any two groups (p < 0.01). Urban boys (19.92%) had the highest and rural girls (5.85%) the lowest prevalence of abdominal obesity (fig. 1). Geographic Distribution of Abdominal Obesity Figure 2 shows the prevalence of abdominal obesity classified by coastal and inland areas. The overall prevalences of abdominal obesity among children and adolescents aged 7–18 years from the 5 coastal districts were 17.71% in boys and 7.91% in girls; by contrast, these figures were 14.97% in boys and 6.72% in girls from the 11 inland districts. The prevalence of abdominal obesity was Ann Nutr Metab 2014;64:137–143 DOI: 10.1159/000365013
139
Table 2. Prevalence of abdominal obesity among children and adolescents aged 7 – 18 years in different SES districts
Gender
Age, years
Boys
Total
7.0 – 7.9 8.0 – 8.9 9.0 – 9.9 10.0 – 10.9 11.0 – 11.9 12.0 – 12.9 13.0 – 13.9 14.0 – 14.9 15.0 – 15.9 16.0 – 16.9 17.0 – 17.9 18.0 – 18.9 7.0 – 7.9 8.0 – 8.9 9.0 – 9.9 10.0 – 10.9 11.0 – 11.9 12.0 – 12.9 13.0 – 13.9 14.0 – 14.9 15.0 – 15.9 16.0 – 16.9 17.0 – 17.9 18.0 – 18.9
Girls
Prevalence (%)
Moderate SES
Low SES
n
%
n
%
n
%
n
%
1,753 1,901 1,740 1,808 1,794 1,778 1,761 1,669 1,807 1,714 1,731 1,762 1,790 1,818 1,819 1,823 1,755 1,710 1,761 1,706 1,779 1,680 1,725 1,712
16.60 17.78 20.23 23.23 21.57 18.28 17.49 12.16 12.78 9.51 10.46 10.73 8.77 9.52 8.85 9.76 7.18 7.08 6.53 5.63 6.18 5.83 4.87 5.14
743 788 747 770 763 737 753 751 773 743 759 749 756 773 767 770 774 696 749 748 754 724 728 715
19.52 21.07 24.90 27.53 26.21 22.25 21.38 15.05 16.56 11.57 12.65 13.48 11.64 12.42 11.47 12.73 9.04 9.34 8.28 7.09 7.96 7.46 6.87 7.13
489 534 506 502 496 488 469 468 473 491 483 497 505 503 501 499 457 464 479 489 487 488 486 495
16.16 17.79 18.97 23.11 20.56 18.03 17.48 11.11 12.68 8.96 10.35 10.66 7.92 8.95 8.38 9.02 6.56 6.47 6.05 5.11 5.75 5.33 4.12 4.44
521 579 487 536 535 553 539 450 561 480 489 516 529 542 551 554 524 550 533 469 538 468 511 502
12.86 13.30 14.37 17.16 15.89 13.20 12.06 8.44 7.66 6.88 7.16 6.78 5.48 5.9 5.63 6.32 4.96 4.73 4.5 3.84 4.09 3.85 2.74 2.99
25 20
High SES
Boys Girls
19.37 15.55
15 10
11.42 9.33 6.53
4.62
5 0
High SES
Moderate SES
Low SES
Fig. 3. The total prevalence of abdominal obesity in different SES
districts.
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Ann Nutr Metab 2014;64:137–143 DOI: 10.1159/000365013
χ2
p
9.90 13.77 20.94 19.06 20.23 17.36 18.92 12.15 23.07 7.73 9.58 14.33 15.39 15.97 13.78 15.46 8.16 10.30 7.51 6.07 8.32 7.07 11.88 11.08
0.0071 0.0010 0.0000 0.0001 0.0000 0.0002 0.0001 0.0023 0.0000 0.0210 0.0083 0.0008 0.0005 0.0003 0.0010 0.0004 0.0169 0.0058 0.0234 0.0481 0.0156 0.0291 0.0026 0.0039
significantly higher in coastal districts than in inland districts (boys: χ2 = 27.36, p < 0.01; girls: χ 2 = 10.41, p < 0.01). SES and Abdominal Obesity The prevalence of abdominal obesity among children and adolescents by age and regional SES is shown in table 2. An increasing trend was observed from the low-SES group to the moderate- and high-SES groups in all age groups (7–18 years). The overall prevalences of abdominal obesity in the 3 SES groups were 11.42, 15.55 and 19.37% in boys and 4.62, 6.53 and 9.33% in girls, respectively (fig. 3). For both boys and girls, statistically significant differences were observed between any two groups (p < 0.01). The prevalence of abdominal obesity among children and adolescents by regional SES and urban/rural category is shown in table 3. The prevalence of abdominal obesity in high-SES urban areas was 24.98% in boys and 11.90% in girls and thereby much higher compared to the other groups. For both boys and girls, the highest and lowest prevalences of abdominal obesity were observed in highZhang/Zhao/Chu/Tan
Table 3. Prevalence of abdominal obesity among children and adolescents aged 7 – 18 years in different populations
Boys n
High-SES urban areas Moderate-SES urban areas High-SES rural areas Low-SES urban areas Moderate-SES rural areas Low-SES rural areas χ2 p value
Girls %
4,596 24.98 2,953 19.74 4,480 13.62 3,158 12.73 2,943 11.35 3,088 10.07 505.91 0.0000
n
20
%
4,530 11.90 2,943 7.14 4,424 6.69 3,152 4.66 2,910 5.91 3,119 4.58 222.27 0.0000
Prevalence (%)
Population
25
Boys Girls 15.09
15
18.33
16.88
11.06 10 6.46 5 0
7.82
8.68
4.17
Approx. 20
Approx. 30
Approx. 40
Approx. 50
Percentage of urban population
SES urban areas and low-SES rural areas (10.07% in boys and 4.58% in girls), respectively. Urbanization Level and Abdominal Obesity The 16 districts were also divided into 4 groups according to the percentage of urban population (approx. 20, 30, 40 and 50%). Figure 4 shows that the prevalence of abdominal obesity increased with the degree of urbanization (boys: χ2 = 80.07, p < 0.01; girls: χ 2 = 65.71, p < 0.01). The prevalence of abdominal obesity increased from 11.06% in boys and 4.17% in girls in the low-urbanization districts (percentage of urban population above 20% but below 30%) to 18.33% in boys and 8.68% in girls in the high-urbanization districts (percentage of urban population above 50%).
Fig. 4. The total prevalence of abdominal obesity in different urbanization districts.
Obesity, especially abdominal obesity, has become a worldwide public health concern. To the best of our knowledge, this is the first study examining the prevalence and regional disparities in abdominal obesity among children and adolescents in Shandong, China. Using an international standard (WHtR ≥0.5) and based on data from a large province-wide survey, we found that substantial regional, socioeconomic and urban/rural disparities exist in child and adolescent abdominal obesity. The prevalence of abdominal obesity varied from 24.98% (high-SES urban boys) to 4.58% (low-SES rural girls) in different areas of Shandong. Our study provides novel information on the prevalence of abdominal obesity in Shandong children and adolescents, and the results of this study will provide valuable evidence for the control of abdominal obesity.
Socioeconomic factors may play an important role in the development of obesity. Many previous studies have confirmed that the population distribution of childhood obesity is associated with SES and that the patterns vary from country to country, depending on the degree of economic development of a country [20, 21]. Studies from developed countries showed that high-SES youths are less likely to be obese than their lower-SES counterparts [22– 25]. In contrast, in developing countries such as Indonesia, Brazil and China, high-SES youths are more likely to be obese than their lower-SES counterparts [26–28]. This may be related to cultural differences and economic development. Similarly, most developed countries report that children resident in rural areas have a higher risk of obesity compared with children resident in urban areas [29, 30], while developing countries report a reverse association [31, 32]. This study indicated that boys and girls from urban areas were more likely to be obese than their peers from rural areas, which may be related to the urban/ rural difference in SES, living conditions and lifestyle. In China, urban residents have higher SES than those living in rural areas. Children and adolescents with high SES have better access to energy-dense foods. In addition, a Chinese national study reported that urban youths spend 0.8 more hours every day on sedentary activity than their rural counterparts [33]. China is a developing country with highly unbalanced regional development. Based on national data in 2010, a large disparity in the prevalence of overweight/obesity was found among different regions in China. The preva-
Abdominal Obesity among Children and Adolescents in Shandong, China
Ann Nutr Metab 2014;64:137–143 DOI: 10.1159/000365013
Discussion
141
lence rate of combined overweight and obesity (assessed by BMI) in children and adolescents aged 7–18 years had reached 32.6% in boys and 19.1% in girls in the large coastal cities; by contrast, these figures were 8.2% in boys and 5.3% in girls in the western rural regions [8]. In this study, we found that the prevalence of abdominal obesity in children and adolescents was higher in coastal districts than in inland districts. Socioeconomic discrepancies might help explain the findings between the two regions. For example, the GDP per capita in coastal and inland districts in this study was USD 10,463 versus USD 5,505 in 2010. In most developing countries, urbanization has been shown to be a major factor associated with a high prevalence of obesity. A study from Tunisia showed that the prevalence of general obesity (assessed by BMI) and abdominal obesity (assessed by WC) increased with the degree of urbanization in adult women; the prevalences of general and abdominal obesity, respectively, were 9.5 and 16.5% in rural dispersed areas, 19.4 and 24.8% in rural clustered areas, 25.9 and 32.4% in other cities and 30.2 and 36.6% in big cities [34]. In the present study, we also found that the prevalence of abdominal obesity increased with the degree of urbanization in children and adolescents. One of the possible explanations for this finding may be that urbanization is associated with a variety of lifestyle and behavioral changes, including physical inactivity and high-fat, energy-rich diets. People who live in urbanized areas of a developing country may be the first to have access to energy-dense foods, to have a decline in work-related physical activity and to have access to motorized transportation [35, 36]. Due to the use of the WHtR cutoff of 0.5, prevalence rates for abdominal obesity are internationally comparable. Data from the German Health Interview and Examination Survey for Children and Adolescents (KiGGS) show that 10.7% of the boys and 8.0% of the girls aged 11–17 years had abdominal obesity (WHtR ≥0.5) in 2003– 2006 [37]. Based on three national data sets, Garnett et al. [38] reported that the prevalence of abdominal obesity (WHtR ≥0.5) increased from 8.6% in 1985 to 13.6% in 1995 and 18.3% in 2007 in Australian schoolchildren aged 7–15 years. Our results show that the prevalences of abdominal obesity in children and adolescents aged 7–18 years were 15.97% in boys and 7.15% in girls; in particular, these figures have reached 24.98% in boys and 11.90% in girls in high-SES urban areas. It is clear that obvious changes in diet and activity have occurred in China; these changes include increased intake of edible oils, fried foods and animal-source foods and snacking, as well as declin142
Ann Nutr Metab 2014;64:137–143 DOI: 10.1159/000365013
ing occupational, domestic and travel activity and increasing time watching TV [39–42]. Environmental risk factors may be the main reason for the high prevalence of abdominal obesity in Chinese children and adolescents. The major strength of this study is that, based on the data from a large population, it examines the prevalence and regional disparities in abdominal obesity among children and adolescents. However, this study has several limitations. Firstly, one district (Zaozhuang) did not participate in the national survey on students’ constitution and health, and thus the sample did not cover all districts of Shandong province. Secondly, this study is a macroanalysis based on regional SES data; the absence of individual SES information probably underestimated the true effects of SES on obesity. Thirdly, the absence of detailed information concerning living environments, nutritional status, dietary patterns and physical activity at the individual level also limited our study. In summary, this study demonstrated that the prevalence of childhood abdominal obesity is high in Shandong Province, one of the most populous provinces in China. Abdominal obesity among children and adolescents is associated with affluence and urban residence. Interventions and strategies to combat obesity should be based on this specific context, targeting high-SES urban areas.
Acknowledgments Surveys on students’ constitution and health are conducted under the auspices of the Department of Education in Shandong Province, China. We thank all the team members and participants. Special thanks to Mr. B. Yu for providing access to the survey data.
Disclosure Statement There are no conflicts of interest for any of the authors.
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Copyright: S. Karger AG, Basel 2014. Reproduced with the permission of S. Karger AG, Basel. Further reproduction or distribution (electronic or otherwise) is prohibited without permission from the copyright holder.
Received: April 23, 2014 Accepted after revision: June 1, 2014 Published online: July 26, 2014
Prevalence and Regional Disparities in Abdominal Obesity among Children and Adolescents in Shandong, China, Surveyed in 2010 Ying-xiu Zhang Jin-shan Zhao Zun-hua Chu Hai-lian Tan Shandong Center for Disease Control and Prevention, Shandong University Institute of Preventive Medicine, Jinan, China
Key Words Abdominal obesity · Regional disparity · Prevalence · Socioeconomic status · Child · Adolescent
Abstract Background/Aims: A rising prevalence of childhood obesity (assessed by body mass index) has been observed in China. However, there are very few published data on abdominal obesity among children and adolescents. The present study examined the prevalence and regional disparities in abdominal obesity among children and adolescents in Shandong, China. Methods: Data for this study were obtained from a large cross-sectional survey. A total of 42,296 students (21,218 boys and 21,078 girls) aged 7–18 years from 16 districts participated in this study. Height and waist circumference (WC) of all subjects were measured; waist-to-height ratio (WHtR) was calculated from their height and WC. Abdominal obesity was defined as WHtR ≥0.5. All subjects were stratified by gender, age and the area of residence, and abdominal obesity frequencies were compared among different groups. Results: Substantial regional, socioeconomic and urban/rural disparities exist in child and adolescent abdominal obesity. The overall prevalences of abdominal obesity among different groups of children and adolescents
© 2014 S. Karger AG, Basel 0250–6807/14/0642–0137$39.50/0 E-Mail [email protected] www.karger.com/anm
aged 7–18 years were 19.92% (urban boys), 11.94% (rural boys), 8.43% (urban girls) and 5.85% (rural girls). The prevalence of abdominal obesity varied from 24.98% in high-socioeconomic status (SES) urban boys to 4.58% in low-SES rural girls. Subjects living in coastal and high-urbanization districts had a higher prevalence of abdominal obesity than those living in inland and low-urbanization districts. Conclusions: Abdominal obesity among children and adolescents in China is associated with affluence and urban residence. Interventions and strategies to combat obesity should be based on this specific context, targeting high-SES urban areas. © 2014 S. Karger AG, Basel
Introduction
The prevalence of childhood obesity is increasing rapidly worldwide [1, 2]. Obesity in children and adolescents is known to progress easily to adult obesity and to increase the risks of hypertension, type II diabetes and cardiovascular diseases, making this a serious social and health problem [3, 4]. In 2009–2010, 18.2% of US children and adolescents aged 6–19 years (19.8% of boys and 16.5% of girls) were obese [assessed as body mass index Ying-xiu Zhang Shandong Center for Disease Control and Prevention Shandong University Institute of Preventive Medicine 16992 Jingshi Road, Jinan 250014 (China) E-Mail SDCDCZYX @ 163.com
(BMI) ≥95th percentile] [5]. China is the largest developing country in the world and has now joined the world epidemic of obesity with its rapid economic growth and urbanization [6, 7]. In 2010, it was estimated that 9.9 and 5.1% of Chinese schoolaged children and adolescents were overweight and obese (assessed by BMI), respectively, representing an estimated 30.43 million individuals [8]. Abdominal fat distribution is associated with greater health risks than total body fat [9]. Recent evidence suggests that compared with overall obesity, abdominal obesity appears to be more strongly associated with cardiovascular disease risk factors [10]. In 2003, 17.9% of Greek adolescents aged 13–19 years (13.5% of boys and 21.7% of girls) were abdominally obese [11]. From 1981 to 2007–2009, there was a sevenfold increase in the prevalence of abdominal obesity in Canadian adolescents aged 12–19 years (from 1.8 to 12.8%) [12]. A similar rising trend is also being observed in American White, Black and Hispanic youths [13]. Waist-to-height ratio (WHtR) has been suggested as an alternative measure to identify abdominal adiposity with a simple message: ‘keep your waist circumference to less than half your height’ [14]. An increasing number of studies have documented that it is suitable for population and epidemiologic studies and can be used on a large scale in screening for metabolic risk in both adults and children [15, 16]. Shandong Province, located in the lower reaches of the Yellow River, is an important littoral province in east China. It has a total area of 156,700 km2 (about 60,500 square miles) and had a total population of 95.79 million in 2010. The distribution of BMI and the prevalence of general obesity among children and adolescents in Shandong have been reported in our previous studies [17, 18]. However, little is known about the prevalence of childhood abdominal obesity in this region. In this study, based on provincial data from 2010, we report the prevalence and regional disparities in abdominal obesity among children and adolescents in Shandong, China.
Subjects and Methods This study was approved by the Ethical Committee of the Shandong Center for Disease Control and Prevention, Shandong, China. Study Population Data for this study were obtained from a large cross-sectional survey of schoolchildren. A total of 42,296 students of Han nationality (21,218 boys and 21,078 girls) from 16 districts in Shandong
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Province, aged 7–18 years, participated in the National Surveys on Chinese Students’ Constitution and Health, which were carried out in September and October 2010. To date, it is the largest representative sample of school-aged children and adolescents in Shandong, China. All subjects voluntarily joined this study with informed consent. The sampling method was stratified multistage sampling based on selected primary and secondary schools. Six public schools (2 primary schools, 2 junior high schools and 2 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 to 18 years of age, and all were of Han ancestry, which accounts for approximately 99.32% of the total population in Shandong. All subjects were stratified by gender, age and the area of residence (urban or rural). Classification of Subgroups According to geographic location, the 16 districts were classified into 2 categories, i.e. coastal and inland; coastal regions included Qingdao, Yantai, Weihai, Rizhao and Dongying, and the other 11 districts were inland regions. The information about gross domestic product (GDP) per capita of the 16 districts in 2010 was collected from the Shandong Statistical Yearbook [19]. The 16 districts were divided into 3 groups [high socioeconomic status (SES), moderate SES and low SES] according to their GDP per capita in 2010. High SES was defined as GDP per capita above USD 8,000 (Jinan, Qingdao, Yantai, Weihai, Dongying and Zibo); moderate SES was defined as GDP per capita above USD 5,000 but below USD 8,000 (Weifang, Taian, Laiwu, Binzhou and Rizhao), and low SES was defined as GDP per capita below USD 5,000 (Jining, Dezhou, Liaocheng, Linyi and Heze). To show the distribution of obesity prevalence between districts, all subpopulations were redivided into 6 regions, as follows: (1) high-SES urban areas; (2) moderate-SES urban areas; (3) low-SES urban areas; (4) high-SES rural areas; (5) moderate-SES rural areas, and (6) low-SES rural areas. Measurements All measurements were conducted by a team of trained technicians in each of the 16 districts. Each technician was 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. Height without shoes was measured using metal column height-measuring stands to the nearest 0.1 cm. Waist circumference (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 to the nearest 0.1 cm. WHtR was calculated as WC divided by height, and abdominal obesity was defined as WHtR ≥0.5 [14]. Statistical Analyses The prevalence of abdominal obesity in each group was determined, and comparisons of abdominal obesity frequencies among different groups were made by χ2 test. All analyses were performed with the statistical package SPSS/PC+ version 11.5. Significance was defined at the 0.05 level.
Zhang/Zhao/Chu/Tan
Table 1. Prevalence of abdominal obesity among children and adolescents aged 7 – 18 years in urban and rural areas in Shandong, China
Age, years
Urban boys
7.0 – 7.9 8.0 – 8.9 9.0 – 9.9 10.0 – 10.9 11.0 – 11.9 12.0 – 12.9 13.0 – 13.9 14.0 – 14.9 15.0 – 15.9 16.0 – 16.9 17.0 – 17.9 18.0 – 18.9
Rural boys
Urban girls
Rural girls
n
%
n
%
n
%
n
%
860 956 872 917 915 919 865 842 892 896 884 889
21.63 20.19 26.61 30.75 27.76 22.96 19.88 14.73 14.91 11.16 14.03 13.72
893 945 868 891 879 859 896 827 915 818 847 873
11.76 15.34 13.82 15.49 15.13 13.27 15.18 9.55 10.71 7.70 6.73 7.67
905 908 908 926 908 843 852 868 929 866 869 843
10.61 10.35 11.01 12.20 8.26 9.25 7.51 6.91 7.10 6.70 5.18 5.58
885 910 911 897 847 867 909 838 850 814 856 869
6.89 8.68 6.70 7.25 6.02 4.96 5.61 4.30 5.18 4.91 4.56 4.72
19.92
15
20
11.94
10
8.43 5.85
Prevalence (%)
20 Prevalence (%)
p
93.37 64.03 157.81 204.33 208.21 142.54 110.81 62.08 56.56 25.24 70.86 59.32
0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000
25
25
17.71 14.97
15 10
7.91
6.72
5
5 0
χ2
Urban boys
Rural boys
Urban girls
Rural girls
Fig. 1. The total prevalence of abdominal obesity classified by ur-
ban and rural areas.
Results
Prevalence of Abdominal Obesity The prevalence of abdominal obesity among children and adolescents in the sample by age, gender and urban/ rural categories is shown in table 1. The prevalence of abdominal obesity in urban boys was significantly higher than in the other 3 groups (rural boys, urban girls and rural girls) in all age categories (p < 0.05). The overall prevalences of abdominal obesity among the different groups of children and adolescents aged 7–18 years were 19.92% (urban boys), 11.94% (rural boys), 8.43% (urban girls) and 5.85% (rural girls); statistically significant difAbdominal Obesity among Children and Adolescents in Shandong, China
0
Coastal boys
Inland boys
Coastal girls
Inland girls
Fig. 2. The total prevalence of abdominal obesity classified by coastal and inland areas.
ferences were observed between any two groups (p < 0.01). Urban boys (19.92%) had the highest and rural girls (5.85%) the lowest prevalence of abdominal obesity (fig. 1). Geographic Distribution of Abdominal Obesity Figure 2 shows the prevalence of abdominal obesity classified by coastal and inland areas. The overall prevalences of abdominal obesity among children and adolescents aged 7–18 years from the 5 coastal districts were 17.71% in boys and 7.91% in girls; by contrast, these figures were 14.97% in boys and 6.72% in girls from the 11 inland districts. The prevalence of abdominal obesity was Ann Nutr Metab 2014;64:137–143 DOI: 10.1159/000365013
139
Table 2. Prevalence of abdominal obesity among children and adolescents aged 7 – 18 years in different SES districts
Gender
Age, years
Boys
Total
7.0 – 7.9 8.0 – 8.9 9.0 – 9.9 10.0 – 10.9 11.0 – 11.9 12.0 – 12.9 13.0 – 13.9 14.0 – 14.9 15.0 – 15.9 16.0 – 16.9 17.0 – 17.9 18.0 – 18.9 7.0 – 7.9 8.0 – 8.9 9.0 – 9.9 10.0 – 10.9 11.0 – 11.9 12.0 – 12.9 13.0 – 13.9 14.0 – 14.9 15.0 – 15.9 16.0 – 16.9 17.0 – 17.9 18.0 – 18.9
Girls
Prevalence (%)
Moderate SES
Low SES
n
%
n
%
n
%
n
%
1,753 1,901 1,740 1,808 1,794 1,778 1,761 1,669 1,807 1,714 1,731 1,762 1,790 1,818 1,819 1,823 1,755 1,710 1,761 1,706 1,779 1,680 1,725 1,712
16.60 17.78 20.23 23.23 21.57 18.28 17.49 12.16 12.78 9.51 10.46 10.73 8.77 9.52 8.85 9.76 7.18 7.08 6.53 5.63 6.18 5.83 4.87 5.14
743 788 747 770 763 737 753 751 773 743 759 749 756 773 767 770 774 696 749 748 754 724 728 715
19.52 21.07 24.90 27.53 26.21 22.25 21.38 15.05 16.56 11.57 12.65 13.48 11.64 12.42 11.47 12.73 9.04 9.34 8.28 7.09 7.96 7.46 6.87 7.13
489 534 506 502 496 488 469 468 473 491 483 497 505 503 501 499 457 464 479 489 487 488 486 495
16.16 17.79 18.97 23.11 20.56 18.03 17.48 11.11 12.68 8.96 10.35 10.66 7.92 8.95 8.38 9.02 6.56 6.47 6.05 5.11 5.75 5.33 4.12 4.44
521 579 487 536 535 553 539 450 561 480 489 516 529 542 551 554 524 550 533 469 538 468 511 502
12.86 13.30 14.37 17.16 15.89 13.20 12.06 8.44 7.66 6.88 7.16 6.78 5.48 5.9 5.63 6.32 4.96 4.73 4.5 3.84 4.09 3.85 2.74 2.99
25 20
High SES
Boys Girls
19.37 15.55
15 10
11.42 9.33 6.53
4.62
5 0
High SES
Moderate SES
Low SES
Fig. 3. The total prevalence of abdominal obesity in different SES
districts.
140
Ann Nutr Metab 2014;64:137–143 DOI: 10.1159/000365013
χ2
p
9.90 13.77 20.94 19.06 20.23 17.36 18.92 12.15 23.07 7.73 9.58 14.33 15.39 15.97 13.78 15.46 8.16 10.30 7.51 6.07 8.32 7.07 11.88 11.08
0.0071 0.0010 0.0000 0.0001 0.0000 0.0002 0.0001 0.0023 0.0000 0.0210 0.0083 0.0008 0.0005 0.0003 0.0010 0.0004 0.0169 0.0058 0.0234 0.0481 0.0156 0.0291 0.0026 0.0039
significantly higher in coastal districts than in inland districts (boys: χ2 = 27.36, p < 0.01; girls: χ 2 = 10.41, p < 0.01). SES and Abdominal Obesity The prevalence of abdominal obesity among children and adolescents by age and regional SES is shown in table 2. An increasing trend was observed from the low-SES group to the moderate- and high-SES groups in all age groups (7–18 years). The overall prevalences of abdominal obesity in the 3 SES groups were 11.42, 15.55 and 19.37% in boys and 4.62, 6.53 and 9.33% in girls, respectively (fig. 3). For both boys and girls, statistically significant differences were observed between any two groups (p < 0.01). The prevalence of abdominal obesity among children and adolescents by regional SES and urban/rural category is shown in table 3. The prevalence of abdominal obesity in high-SES urban areas was 24.98% in boys and 11.90% in girls and thereby much higher compared to the other groups. For both boys and girls, the highest and lowest prevalences of abdominal obesity were observed in highZhang/Zhao/Chu/Tan
Table 3. Prevalence of abdominal obesity among children and adolescents aged 7 – 18 years in different populations
Boys n
High-SES urban areas Moderate-SES urban areas High-SES rural areas Low-SES urban areas Moderate-SES rural areas Low-SES rural areas χ2 p value
Girls %
4,596 24.98 2,953 19.74 4,480 13.62 3,158 12.73 2,943 11.35 3,088 10.07 505.91 0.0000
n
20
%
4,530 11.90 2,943 7.14 4,424 6.69 3,152 4.66 2,910 5.91 3,119 4.58 222.27 0.0000
Prevalence (%)
Population
25
Boys Girls 15.09
15
18.33
16.88
11.06 10 6.46 5 0
7.82
8.68
4.17
Approx. 20
Approx. 30
Approx. 40
Approx. 50
Percentage of urban population
SES urban areas and low-SES rural areas (10.07% in boys and 4.58% in girls), respectively. Urbanization Level and Abdominal Obesity The 16 districts were also divided into 4 groups according to the percentage of urban population (approx. 20, 30, 40 and 50%). Figure 4 shows that the prevalence of abdominal obesity increased with the degree of urbanization (boys: χ2 = 80.07, p < 0.01; girls: χ 2 = 65.71, p < 0.01). The prevalence of abdominal obesity increased from 11.06% in boys and 4.17% in girls in the low-urbanization districts (percentage of urban population above 20% but below 30%) to 18.33% in boys and 8.68% in girls in the high-urbanization districts (percentage of urban population above 50%).
Fig. 4. The total prevalence of abdominal obesity in different urbanization districts.
Obesity, especially abdominal obesity, has become a worldwide public health concern. To the best of our knowledge, this is the first study examining the prevalence and regional disparities in abdominal obesity among children and adolescents in Shandong, China. Using an international standard (WHtR ≥0.5) and based on data from a large province-wide survey, we found that substantial regional, socioeconomic and urban/rural disparities exist in child and adolescent abdominal obesity. The prevalence of abdominal obesity varied from 24.98% (high-SES urban boys) to 4.58% (low-SES rural girls) in different areas of Shandong. Our study provides novel information on the prevalence of abdominal obesity in Shandong children and adolescents, and the results of this study will provide valuable evidence for the control of abdominal obesity.
Socioeconomic factors may play an important role in the development of obesity. Many previous studies have confirmed that the population distribution of childhood obesity is associated with SES and that the patterns vary from country to country, depending on the degree of economic development of a country [20, 21]. Studies from developed countries showed that high-SES youths are less likely to be obese than their lower-SES counterparts [22– 25]. In contrast, in developing countries such as Indonesia, Brazil and China, high-SES youths are more likely to be obese than their lower-SES counterparts [26–28]. This may be related to cultural differences and economic development. Similarly, most developed countries report that children resident in rural areas have a higher risk of obesity compared with children resident in urban areas [29, 30], while developing countries report a reverse association [31, 32]. This study indicated that boys and girls from urban areas were more likely to be obese than their peers from rural areas, which may be related to the urban/ rural difference in SES, living conditions and lifestyle. In China, urban residents have higher SES than those living in rural areas. Children and adolescents with high SES have better access to energy-dense foods. In addition, a Chinese national study reported that urban youths spend 0.8 more hours every day on sedentary activity than their rural counterparts [33]. China is a developing country with highly unbalanced regional development. Based on national data in 2010, a large disparity in the prevalence of overweight/obesity was found among different regions in China. The preva-
Abdominal Obesity among Children and Adolescents in Shandong, China
Ann Nutr Metab 2014;64:137–143 DOI: 10.1159/000365013
Discussion
141
lence rate of combined overweight and obesity (assessed by BMI) in children and adolescents aged 7–18 years had reached 32.6% in boys and 19.1% in girls in the large coastal cities; by contrast, these figures were 8.2% in boys and 5.3% in girls in the western rural regions [8]. In this study, we found that the prevalence of abdominal obesity in children and adolescents was higher in coastal districts than in inland districts. Socioeconomic discrepancies might help explain the findings between the two regions. For example, the GDP per capita in coastal and inland districts in this study was USD 10,463 versus USD 5,505 in 2010. In most developing countries, urbanization has been shown to be a major factor associated with a high prevalence of obesity. A study from Tunisia showed that the prevalence of general obesity (assessed by BMI) and abdominal obesity (assessed by WC) increased with the degree of urbanization in adult women; the prevalences of general and abdominal obesity, respectively, were 9.5 and 16.5% in rural dispersed areas, 19.4 and 24.8% in rural clustered areas, 25.9 and 32.4% in other cities and 30.2 and 36.6% in big cities [34]. In the present study, we also found that the prevalence of abdominal obesity increased with the degree of urbanization in children and adolescents. One of the possible explanations for this finding may be that urbanization is associated with a variety of lifestyle and behavioral changes, including physical inactivity and high-fat, energy-rich diets. People who live in urbanized areas of a developing country may be the first to have access to energy-dense foods, to have a decline in work-related physical activity and to have access to motorized transportation [35, 36]. Due to the use of the WHtR cutoff of 0.5, prevalence rates for abdominal obesity are internationally comparable. Data from the German Health Interview and Examination Survey for Children and Adolescents (KiGGS) show that 10.7% of the boys and 8.0% of the girls aged 11–17 years had abdominal obesity (WHtR ≥0.5) in 2003– 2006 [37]. Based on three national data sets, Garnett et al. [38] reported that the prevalence of abdominal obesity (WHtR ≥0.5) increased from 8.6% in 1985 to 13.6% in 1995 and 18.3% in 2007 in Australian schoolchildren aged 7–15 years. Our results show that the prevalences of abdominal obesity in children and adolescents aged 7–18 years were 15.97% in boys and 7.15% in girls; in particular, these figures have reached 24.98% in boys and 11.90% in girls in high-SES urban areas. It is clear that obvious changes in diet and activity have occurred in China; these changes include increased intake of edible oils, fried foods and animal-source foods and snacking, as well as declin142
Ann Nutr Metab 2014;64:137–143 DOI: 10.1159/000365013
ing occupational, domestic and travel activity and increasing time watching TV [39–42]. Environmental risk factors may be the main reason for the high prevalence of abdominal obesity in Chinese children and adolescents. The major strength of this study is that, based on the data from a large population, it examines the prevalence and regional disparities in abdominal obesity among children and adolescents. However, this study has several limitations. Firstly, one district (Zaozhuang) did not participate in the national survey on students’ constitution and health, and thus the sample did not cover all districts of Shandong province. Secondly, this study is a macroanalysis based on regional SES data; the absence of individual SES information probably underestimated the true effects of SES on obesity. Thirdly, the absence of detailed information concerning living environments, nutritional status, dietary patterns and physical activity at the individual level also limited our study. In summary, this study demonstrated that the prevalence of childhood abdominal obesity is high in Shandong Province, one of the most populous provinces in China. Abdominal obesity among children and adolescents is associated with affluence and urban residence. Interventions and strategies to combat obesity should be based on this specific context, targeting high-SES urban areas.
Acknowledgments Surveys on students’ constitution and health are conducted under the auspices of the Department of Education in Shandong Province, China. We thank all the team members and participants. Special thanks to Mr. B. Yu for providing access to the survey data.
Disclosure Statement There are no conflicts of interest for any of the authors.
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Ann Nutr Metab 2014;64:137–143 DOI: 10.1159/000365013
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