bs_bs_banner
doi: 10.1111/ppe.12178
1
Distribution of Subcutaneous Fat and the Relationship with Blood Pressure in Obese Children and Adolescents in Shandong, China Ying-xiu Zhang,a Shu-rong Wangb a
Shandong Center for Disease Control and Prevention, Shandong University Institute of Preventive Medicine b
Shandong Blood Center, Jinan, Shandong, China
Abstract Background: The association between elevated blood pressure (BP) and childhood obesity has been documented in several studies. However, the association between BP and body fat distribution in obese children remains poorly understood. We examined the distribution of subcutaneous fat and its association with BP in obese children and adolescents. Methods: Data for this study were obtained from a large cross-sectional survey of school children. A total of 38 873 students (19 485 boys and 19 388 girls) aged 7–17 years participated in this study. Height, weight, BP, subscapular and triceps skinfold thicknesses (SFT) of all subjects were measured. Obesity was defined by using body mass index (BMI) criteria recommended by the Working Group on Obesity in China. A total of 3 579 obese children and adolescents (2 367 boys and 1 212 girls) were examined. Results: Most of the obese children and adolescents had high subcutaneous fat. However, a small number of the obese individuals had a lower SFT levels. Obese children and adolescents with high SFT and central distribution had higher BP levels than those with low SFT and peripheral distribution. Conclusion: Obese children and adolescents assessed by BMI might not necessarily have a high SFT level. The BP level of obese individuals is associated with the level and distribution pattern of SFT. Additional measurement of SFT is better than BMI alone to help identify high BP risks. Keywords: skinfold thickness, blood pressure, distribution, obese child and adolescent.
The prevalence of overweight and obesity in children and youth, with its attendant health risks, has become an important public health concern facing the world today.1 Especially, recent reports indicated that the increase in childhood overweight and obesity is much more rapid in developing countries than in developed countries.2 China is the largest developing country in the world, and has now joined the world epidemic of obesity with its rapid economic growth and urbanisation.3,4 Body mass index (BMI) is a commonly used surrogate measure of adiposity in children. The International Obesity Task Force,5 the US Centers for Disease Control and Prevention,6 and the World Health Organization7 have formulated population-based age Correspondence: Ying-xiu Zhang, Shandong Center for Disease Control and Prevention, Shandong University Institute of Preventive Medicine, 16992 Jingshi Road, Jinan 250014, Shandong, China. E-mail: [email protected]
© 2015 John Wiley & Sons Ltd Paediatric and Perinatal Epidemiology, 2015, ••, ••–••
and sex-specific normal distributions for BMI. The Working Group on Obesity in China (WGOC) has also established a national BMI reference for screening overweight and obesity in Chinese school-aged children and adolescents.8 However, BMI is a measure of excess weight relative to height, rather than excess body fat. It does not distinguish between fat mass and fat-free mass, and its limitations are widely known.9,10 A number of different tools and methodologies have been developed to measure body composition, and skinfold thicknesses (SFT) have been shown to be closely correlated with total body fatness.11,12 The association between elevated blood pressure (BP) and childhood overweight and obesity has been documented in several studies. However, the linkage of BP with body fat distribution in children is not well established. The goals of the present study, therefore, were to (i) examine the distribution of subcutaneous fat in obese children and adolescents and determine
2
Y. Zhang and S. Wang
whether obese individuals assessed by BMI necessarily had a high levels of subcutaneous fat, and (ii) examine the association between BP levels and the distributional pattern of subcutaneous fat in obese children and adolescents.
Methods The 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 crosssectional survey of schoolchildren. A total of 38 873 students (19 485 boys and 19 388 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 to October 2010. All subjects voluntarily joined this study with informed consents. 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. The age, gender-specific BMI cut-off points recommended by the WGOC were used to define obesity (see Appendix S1).8 A total of 3 579 obese children and adolescents (2 367 boys and 1 212 girls) were examined.
Anthropometric measurements All measurements were performed by well-trained health professionals in each of the 16 districts using the same type of apparatus and followed the same procedures; these apparatus were calibrated. Height without shoes was measured using metal column height-measuring stands to the nearest 0.1 cm. Weight was measured using lever scales to the nearest 0.1 kg,
while the subjects wore only their underwear. SFT were measured on the right side of the body using Skinfold Caliper (Minjian, GMCS-PZQ; Beijing Xindong Huateng Sports Instruments Company, Limited) to the nearest 0.5 mm, at the two sites: (i) triceps, halfway between the acromion process and the olecranon process, and (ii) subscapular, 1.0 cm below the tip of the scapula, at an angle of 45° to the lateral side of the body. In each participant, three measurements were taken, and the middle value was recorded for one skinfold site. The sum of subscapular skinfold and triceps thickness (SSFT) was analysed. Subscapular/triceps ratio (STR), an index of subcutaneous adipose tissue distribution (central/peripheral), was also calculated.
Blood pressure measurements Systolic blood pressure (SBP) and diastolic blood pressure (DBP) were measured using a mercury sphygmomanometer after each subject had rested for at least 15 min in a sitting position. 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. Based on the national data, BP reference standards for Chinese children and adolescents has been established in 2010,13 the reference values of SBP and DBP percentiles for Chinese children and adolescents were applied in this study. Relatively high BP status was defined as SBP and/or DBP ≥ 95th percentile for age and gender.
Statistical analyses Z-scores of SBP and DBP were calculated from the national reference values.14 The age and sex-specific quartiles for SSFT and STR of children and adolescents were calculated, and all obese individuals were classified into four groups (Q1–Q4). Obese individuals in the upper fourth (Q4) of SSFT and STR were defined as ‘high subcutaneous body fat’ and ‘central distribution’, and those in the lower fourth (Q1) were defined as ‘low subcutaneous body fat’ and ‘peripheral distribution’, respectively. Comparisons of Z-scores for SBP and DBP among the four groups were made by one-way ANOVA, and comparisons of relatively high BP frequencies among different groups were made by chi-square test. © 2015 John Wiley & Sons Ltd Paediatric and Perinatal Epidemiology, 2015, ••, ••–••
Subcutaneous fat and blood pressure
3
Table 1. Distribution of obese children and adolescents by subcutaneous fat levels (n, %) Gender Boys
Girls
Targets
doi: 10.1111/ppe.12178
1
Distribution of Subcutaneous Fat and the Relationship with Blood Pressure in Obese Children and Adolescents in Shandong, China Ying-xiu Zhang,a Shu-rong Wangb a
Shandong Center for Disease Control and Prevention, Shandong University Institute of Preventive Medicine b
Shandong Blood Center, Jinan, Shandong, China
Abstract Background: The association between elevated blood pressure (BP) and childhood obesity has been documented in several studies. However, the association between BP and body fat distribution in obese children remains poorly understood. We examined the distribution of subcutaneous fat and its association with BP in obese children and adolescents. Methods: Data for this study were obtained from a large cross-sectional survey of school children. A total of 38 873 students (19 485 boys and 19 388 girls) aged 7–17 years participated in this study. Height, weight, BP, subscapular and triceps skinfold thicknesses (SFT) of all subjects were measured. Obesity was defined by using body mass index (BMI) criteria recommended by the Working Group on Obesity in China. A total of 3 579 obese children and adolescents (2 367 boys and 1 212 girls) were examined. Results: Most of the obese children and adolescents had high subcutaneous fat. However, a small number of the obese individuals had a lower SFT levels. Obese children and adolescents with high SFT and central distribution had higher BP levels than those with low SFT and peripheral distribution. Conclusion: Obese children and adolescents assessed by BMI might not necessarily have a high SFT level. The BP level of obese individuals is associated with the level and distribution pattern of SFT. Additional measurement of SFT is better than BMI alone to help identify high BP risks. Keywords: skinfold thickness, blood pressure, distribution, obese child and adolescent.
The prevalence of overweight and obesity in children and youth, with its attendant health risks, has become an important public health concern facing the world today.1 Especially, recent reports indicated that the increase in childhood overweight and obesity is much more rapid in developing countries than in developed countries.2 China is the largest developing country in the world, and has now joined the world epidemic of obesity with its rapid economic growth and urbanisation.3,4 Body mass index (BMI) is a commonly used surrogate measure of adiposity in children. The International Obesity Task Force,5 the US Centers for Disease Control and Prevention,6 and the World Health Organization7 have formulated population-based age Correspondence: Ying-xiu Zhang, Shandong Center for Disease Control and Prevention, Shandong University Institute of Preventive Medicine, 16992 Jingshi Road, Jinan 250014, Shandong, China. E-mail: [email protected]
© 2015 John Wiley & Sons Ltd Paediatric and Perinatal Epidemiology, 2015, ••, ••–••
and sex-specific normal distributions for BMI. The Working Group on Obesity in China (WGOC) has also established a national BMI reference for screening overweight and obesity in Chinese school-aged children and adolescents.8 However, BMI is a measure of excess weight relative to height, rather than excess body fat. It does not distinguish between fat mass and fat-free mass, and its limitations are widely known.9,10 A number of different tools and methodologies have been developed to measure body composition, and skinfold thicknesses (SFT) have been shown to be closely correlated with total body fatness.11,12 The association between elevated blood pressure (BP) and childhood overweight and obesity has been documented in several studies. However, the linkage of BP with body fat distribution in children is not well established. The goals of the present study, therefore, were to (i) examine the distribution of subcutaneous fat in obese children and adolescents and determine
2
Y. Zhang and S. Wang
whether obese individuals assessed by BMI necessarily had a high levels of subcutaneous fat, and (ii) examine the association between BP levels and the distributional pattern of subcutaneous fat in obese children and adolescents.
Methods The 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 crosssectional survey of schoolchildren. A total of 38 873 students (19 485 boys and 19 388 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 to October 2010. All subjects voluntarily joined this study with informed consents. 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. The age, gender-specific BMI cut-off points recommended by the WGOC were used to define obesity (see Appendix S1).8 A total of 3 579 obese children and adolescents (2 367 boys and 1 212 girls) were examined.
Anthropometric measurements All measurements were performed by well-trained health professionals in each of the 16 districts using the same type of apparatus and followed the same procedures; these apparatus were calibrated. Height without shoes was measured using metal column height-measuring stands to the nearest 0.1 cm. Weight was measured using lever scales to the nearest 0.1 kg,
while the subjects wore only their underwear. SFT were measured on the right side of the body using Skinfold Caliper (Minjian, GMCS-PZQ; Beijing Xindong Huateng Sports Instruments Company, Limited) to the nearest 0.5 mm, at the two sites: (i) triceps, halfway between the acromion process and the olecranon process, and (ii) subscapular, 1.0 cm below the tip of the scapula, at an angle of 45° to the lateral side of the body. In each participant, three measurements were taken, and the middle value was recorded for one skinfold site. The sum of subscapular skinfold and triceps thickness (SSFT) was analysed. Subscapular/triceps ratio (STR), an index of subcutaneous adipose tissue distribution (central/peripheral), was also calculated.
Blood pressure measurements Systolic blood pressure (SBP) and diastolic blood pressure (DBP) were measured using a mercury sphygmomanometer after each subject had rested for at least 15 min in a sitting position. 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. Based on the national data, BP reference standards for Chinese children and adolescents has been established in 2010,13 the reference values of SBP and DBP percentiles for Chinese children and adolescents were applied in this study. Relatively high BP status was defined as SBP and/or DBP ≥ 95th percentile for age and gender.
Statistical analyses Z-scores of SBP and DBP were calculated from the national reference values.14 The age and sex-specific quartiles for SSFT and STR of children and adolescents were calculated, and all obese individuals were classified into four groups (Q1–Q4). Obese individuals in the upper fourth (Q4) of SSFT and STR were defined as ‘high subcutaneous body fat’ and ‘central distribution’, and those in the lower fourth (Q1) were defined as ‘low subcutaneous body fat’ and ‘peripheral distribution’, respectively. Comparisons of Z-scores for SBP and DBP among the four groups were made by one-way ANOVA, and comparisons of relatively high BP frequencies among different groups were made by chi-square test. © 2015 John Wiley & Sons Ltd Paediatric and Perinatal Epidemiology, 2015, ••, ••–••
Subcutaneous fat and blood pressure
3
Table 1. Distribution of obese children and adolescents by subcutaneous fat levels (n, %) Gender Boys
Girls
Targets
