Abstract
Objective. Little is known about whether eliminating overweight and obesity could effectively reduce the prevalence of high blood pressure (HBP) in Chinese children. This study aimed to estimate the magnitude of contribution of overweight and obesity associated with HBP in Chinese children, and assess the theoretical HBP prevalence if overweight and obesity were eliminated. Methods. Data on 197,191 participants aged 7–17 years with complete records from the Chinese National Survey on Students’ Constitution and Health conducted in 2010 were included. The population attributable risk of overweight and obesity for HBP was calculated. Results. The prevalence of HBP was 6.8% and 5.8% for boys and girls, respectively. HBP in about 22.9% (95% CI 21.5, 24.2%) of boys and 14.7% (95% CI 13.5, 15.8%) of girls could be attributable to overweight and obesity. If both overweight and obesity were eliminated, the prevalence of HBP theoretically could be reduced to 5.2% in boys and 5.0% in girls. Similar results were found in different age and urban/rural area groups. Conclusion. Eliminating overweight and obesity could theoretically lead to a moderate reduction in the prevalence of HBP in Chinese children.
Key Words::
Introduction
Hypertension is a well-recognized cardiovascular risk factor in adults, contributing to 7.1 million deaths (13% of the global total) every year (Citation1). Although hypertension is rarely diagnosed in children and adolescents, studies reveal that blood pressure (BP) levels in childhood track to BP levels in adulthood, and children with high blood pressure (HBP) have a higher probability of developing hypertension as adults than children with low BP (Citation2). Therefore, the prevention of HBP in early life can lead to a life-long reduction of hypertension (Citation3).
There is growing evidence to support the theory that obesity may be a causal factor for HBP. Potential mechanisms include increased insulin/leptin-mediated sympathetic nervous system stimulation, elevated renin-angiotensin-aldosterone system activation and high salt sensitivity in the obese population (Citation4). In adults, it has been estimated that at least 75% of the incidence of hypertension is related directly to obesity (Citation4). In children, the increased prevalence of overweight and obesity is also associated with a greater prevalence of HBP (Citation5,Citation6). Based on this evidence, eliminating overweight and obesity has become an essential component of the management of HBP in both children and adults (Citation7–9).
Chinese children and adolescents are currently facing a very real obesity epidemic. The prevalence of obesity in children increased from 0.2% in 1985 to 7.3% in 2010 for boys, and from 0.1% in 1985 to 3.8% in 2010 for girls (Citation10). Mirroring the increasing trend in overweight and obesity, the BP levels increased as well (Citation11). However, little is known about whether eliminating childhood overweight and obesity could effectively reduce the prevalence of HBP in the whole population. Chiolero et al. estimated that the proportion of HBP that could be attributable to overweight and obesity ranged from 18% to 26% in African children aged 5–16 years (Citation12). But the magnitude of the contribution of overweight and obesity associated with HBP in Chinese children remains unclear. In addition, since only gender and age, rather than gender, age and height simultaneously, were considered when researchers identified Chinese children with HBP in previous studies (Citation13), the reported HBP prevalences in Chinese children could not be compared to those reported in other countries. A better understanding of the prevalence of HBP and the potential benefits of eliminating overweight and obesity for HBP in Chinese children will be likely to improve the development of related interventions, counselling guidelines and public health policies.
Using data from the Chinese National Survey on Students’ Constitution and Health (CNSSCH), conducted in 2010, we assessed the prevalence of HBP using well-established gender-age-height- specific HBP criteria, estimated the population attributable risk (PAR) of overweight and obesity for HBP, and evaluated the theoretical prevalence of HBP if overweight and obesity were eliminated, in Chinese children aged 7–17 years.
Methods
Study population
Data were obtained from the CNSSCH in 2010, the largest national representative sample of school-aged children. This data set has been used to estimate the prevalence of a variety of health indicators among children and adolescents in mainland China. The sampling procedures of 2010 CNSSCH have been published previously in detail (Citation10). In brief, this survey used a stratified multistage sampling method to collect participants. Subjects in each province were classified into two area groups (urban or rural area), which were further classified into gender-age-specific subgroups. In each subgroup, equal numbers of participants were selected from primary and secondary schools. In this study, participants of Han nationality (approximately 91.5% of the population nationwide) were selected from 30 of 31 mainland provinces, with a high participation rate of 99.58%. Tibet was surveyed but not included in this study because only Tibetans were selected in Tibet, where the Han nationality was the minority (Citation10). Because of missing data or extreme height, weight or BP values (> 6 standard deviations from the mean), 239 participants were excluded. Thus, the total sample included herein was 197,191.
This survey was conducted according to the guidelines laid down in the Declaration of Helsinki and approved by six ministries of China, including the Ministry of Education, General Administration of Sport, Ministry of Health, State Ethnic Affairs Commission, Ministry of Science and Technology, and Ministry of Finance. Consent was obtained from both parents and students. The project analysing the survey data was approved by the Medical Research Ethics Committee of the University of Queensland (#2011001199).
Measures
Anthropometric measurements were performed according to the same protocol at all survey sites (Citation10). Students were asked to wear light clothes only, and to stand straight without shoes. Height was measured using a wall-mounted stadiometer to the nearest 0.1 cm, and weight was measured with a scale to the nearest 0.1 kg. Both height and weight were measured twice, and the mean value was recorded. Body mass index (BMI) was calculated as the weight divided by the height squared (kg/m2). Since other studies have suggested that ethnic-specific BMI references should be used for different populations (Citation14,Citation15), normal weight was defined as BMI was less than the 85th percentile according to the references for Chinese children, overweight as BMI equal to or higher than the 85th and obesity as BMI equal to or higher than the 95th gender-age-specific percentile (Citation16).
BP was measured according to the recommendation of the National High Blood Pressure Education Program (NHBPEP) Working Group in Children and Adolescents (Citation17), using an auscultation mercury sphygmomanometer with an appropriate cuff size for children. BP measurements were taken after at least 5 min of rest. Systolic blood pressure (SBP) was defined as the onset of “tapping” Korotkoff sounds, and diastolic blood pressure (DBP) as the fifth Korotkoff sounds. An average of three BP measurements at a single visit was calculated for each child. In addition, HBP was defined as SBP or DBP of at least the 95th gender-age-height-specific percentile according to the reference of NHBPEP Working Group, and the height percentile was defined by US Centers for Disease Control and Prevention (Citation17).
All measurement instruments, including the stadiometer, scale and sphygmomanometer, were calibrated before use. All technicians were required to pass a standard training course for measurements, and all measurements were conducted by the same team of field technicians in each administrative region.
Statistical analysis
Descriptive results are expressed as mean and standard deviation for continuous variables and percentage for categorical variables by gender, separately. Prevalences of HBP, overweight and obesity were calculated among different groups by gender. The PAR (%) and its 95% confidence intervals (CI) were estimated based on asymptotic approximations from a logistic regression model using the aflogit module for Stata, which derives PAR using the formulae provided in Greenland and Drescher (Citation18). Calculation of PAR implies a causal relationship between overweight, as well as obesity, and HBP and further assumes that there exists an intervention to prevent overweight and obesity in children (Citation19). Age, province and urban/rural area were adjusted for, and the results are presented by age and area groups. The theoretical prevalence rates of HBP if overweight and/or obesity were eliminated were assessed using the actual prevalence of HBP multiplied by (1-PAR%). We also performed the above analyses after further adjusting for time for physical activity, screen time and homework time. As the results were markedly similar, we presented the results from the most parsimonious models based on the largest sample size. All analyses were performed with Stata 13 software (College Station, TX, USA).
Results
This study included 98,606 boys and 98,585 girls. The characteristics of the participants are shown in , and 6.8% of the boys and 5.8% of the girls were categorized as having HBP.
Table I. Descriptive characteristics of Chinese children aged 7–17 years in 2010.
As shown in , in general, the prevalence of HBP, overweight and obesity decreased with age. The prevalence of HBP ranged from 2.8% to 8.8%, while the prevalences of overweight and obesity ranged from 6.7% to 16.0% and 1.2% to 10.4%, respectively. Rural children displayed a higher prevalence of HBP, and a lower overweight and obesity prevalence than their urban peers. In addition, a higher prevalence of HBP was observed in overweight and obese children, which was two to four times greater than that in their normal weight counterparts.
Table II. Prevalence of high blood pressure (HBP), overweight and obesity in Chinese children aged 7–17 years among different groups in 2010.
presents the PAR% of HBP due to overweight and obesity among different age and area groups. Overall, the PAR% of HBP due to overweight and obesity was 22.9% (95% CI 21.5, 24.2%) in boys and 14.7% (95% CI 13.5, 15.8%) in girls. Among different ages, PAR% ranged from 16.3% (95% CI 12.2, 20.3%) to 31.6% (95% CI 27.0, 36.0%) in boys and 10.5% (95% CI 7.7, 13.2%) to 22.4% (95% CI 17.3, 27.2%) in girls.
Table III. Population attributable risk and 95% confidence interval of high blood pressure due to overweight and obesity in Chinese children aged 7–17 years among different groups in 2010.
As shown in , if both overweight and obesity were eliminated, the theoretical prevalence rates of HBP were 5.2% (95% CI 5.1, 5.3%) for boys and 5.0% (95% CI 4.9, 5.0%) for girls. Among different ages, the variations between the actual and theoretical prevalence of HBP in boys, ranging from 1.2% (95% CI 0.9, 1.4%) to 2.1% (95% CI 1.8, 2.3%), were larger than those in girls, ranging from 0.4% (95% CI 0.3, 0.6%) to 1.3% (95% CI 1.1, 1.6%). In addition, the theoretical prevalence of HBP were 4.7% (95% CI 4.6, 4.8%) in urban boys and 4.6% (95% CI 4.5, 4.7%) in urban girls. Rural boys and girls were expected to have a theoretical HBP prevalence of 5.7% (95% CI 5.6, 5.9%) and 5.4% (95% CI 5.3, 5.5%), respectively.
Table IV. Theoretical high blood pressure (HBP) prevalence and 95% confidence interval if overweight or/and obesity were eliminated in Chinese children aged 7–17 years in 2010.
Discussion
This study employed an analytical approach to provide the theoretical efficacy of eliminating overweight and obesity for HBP prevalence in Chinese children. Our study data showed that the actual prevalence of HBP was 6.8% and 5.8% for boys and girls aged 7–17 years in 2010, respectively. Theoretically, HBP in 22.9% of boys and 14.7% of girls was attributable to overweight and obesity. If both overweight and obesity were eliminated, the theoretical HBP prevalence could be reduced to 5.2% in boys and 5.0% in girls.
Since gender and the ever-changing biometric factors intrinsic to growth (age and height) are associated with the development of childhood BP, the identification of HBP should be based on gender-age-height-specific HBP criteria (Citation17). However, most studies have reported the prevalence of HBP in Chinese children using gender-age-specific references, which may not be comparable to the results of other countries (Citation13). In this study, we used the HBP criteria of the NHBPEP Working Group, which is widely used in different countries (Citation20–22). Compared with studies in other countries using the same HBP criteria, Chinese children in this study displayed a lower prevalence of HBP than their peers in Africa and Greece (Citation12,Citation22,Citation23), but higher than their counterparts in the USA and South Korea (Citation20,Citation21).
Although the prevalence of both HBP and obesity in Chinese children has kept increasing during the past two decades (Citation10,Citation11), it remains unclear whether eliminating overweight and obesity could reduce the HBP burden efficiently. A recent study summarized the effect of childhood obesity prevention programmes on BP, including interventions for improving dietary intake, increasing physical activity, reducing sedentary behaviour, or a combination of these (Citation9). That study found pooled intervention effects of −1.64 mmHg for SBP and −1.44 mmHg for DBP. However, different methods may lead to different potential outcomes (Citation24), and a more pronounced improvement in BP was observed in interventions which combined diet and physical activity (Citation9). Assuming the causal effect of obesity on HBP and the existence of interventions to prevent obesity in children (Citation4–9), we estimated the beneficial effect of eliminating overweight and obesity for HBP in this study. In the present study, after eliminating overweight and obesity, theoretical reductions of HBP prevalence of 22.9% and 14.7% in boys and girls, respectively, were estimated. The magnitudes of the estimated PAR% were similar to those in previous studies conducted in children (Citation12,Citation25). Although the theoretical HBP reduction we estimated was moderate, a better BP profile in children may result in a lower risk of hypertension and cardiovascular disease in the future (Citation1,Citation2).
However, although overweight and obese children were more likely to be classified as having HBP, the HBP prevalence in children with normal weight was still more than 5% in this study, which has been observed in other studies as well (Citation20,Citation23,Citation26). In addition, our study evaluated that even if all of the overweight and obesity cases were eliminated, a reduction in HBP prevalence of less than 20% was theoretically predicted to be observed in the whole population. This moderate decrease in HBP was also observed among different age, gender and urban/rural area groups. In particular, although a lower rate of overweight and obesity was found in rural areas, the prevalence of HBP is equal to or even higher than that in urban areas, even after eliminating overweight and obesity. These findings were in favour of the hypothesis that other factors besides overweight and obesity, such as sodium intake, preterm birth and family history, are important in determining the presence of HBP (Citation27–29). Our results implied that considering weight loss alone is moderately effective, and an efficient intervention aimed at reducing HBP should include a wide range of approaches, particularly in rural areas of China.
In addition, since most of the children with HBP were neither overweight nor obese, programmes aiming to reduce HBP need to be conducted in the general paediatric population, regardless of weight status. In agreement with our findings, Wang et al. compared different approaches to managing HBP in children, and found that population-based intervention was less costly and more effective than other strategies, including treating HBP only in overweight and obese children (Citation30).
This study has several strengths. The data were derived from a national survey with a large sample size (n = 197,191) and HBP was identified by gender-age-height-specific BP reference, which facilitates comparability to other studies. However, there may be limitations to identifying children with HBP using the HBP criteria developed based on US children and adolescents (Citation31). Other limitations include the fact that the BP levels were obtained at a single visit. According to the guidelines, HBP should be confirmed on repeated visits and our results are likely to overestimate the prevalence of HBP (Citation17). Furthermore, some potential factors not considered in this survey, including preterm birth, sodium intake and family history, could modify the association between obesity and overweight and HBP (Citation19). However, The PARs of overweight and obesity for HBP prevalence after adjusting for physical activity and sedentary behaviour were similar to the results before adjustment.
In conclusion, 6.8% of boys and 5.8% of girls aged 7–17 years were categorized as having HBP in 2010. We found that the elimination of overweight and obesity could theoretically lead to a moderate reduction in HBP. This study suggests that interventions aiming to reduce HBP should be conducted in the general population, regardless of weight status. In addition, multiple approaches should be employed to improve the BP profile in Chinese children, in addition to weight loss management.
Acknowledgements
The authors would like to thank W. K. Liao, W. H. Xing, X. Zhang and the members of CNSSCH for providing access to the survey data. We also appreciate the cooperation of all the students who participated in the survey.
Funding
This work was supported by a grant from the National Health and Medical Research Council of Australia [no. APP1045000] awarded to ZW, Research Special Fund for Public Welfare Industry of Health of China [no. 201202010] awarded to JM and Specialized Research Fund for the Doctoral Program of Higher Education of China [no. 20120001110016] awarded to JM.
Declaration of interest: The authors declare no conflicts of interest. The authors alone are responsible for the content and writing of the paper.
Related Research Data
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