- Email: [email protected]
Physical activity, cardiorespiratory fitness, and obesity among Chinese children
Preventive Medicine 52 (2011) 109–113
Contents lists available at ScienceDirect
Preventive Medicine j o u r n a l h o m e p a g e : w w w. e l s e v i e r. c o m / l o c a t e / y p m e d
Physical activity, cardiorespiratory fitness, and obesity among Chinese children Qi-qiang He a,b, Tze-wai Wong b,⁎, Lin Du c, Zhuo-qin Jiang d, Tak-sun Ignatius Yu b, Hong Qiu b, Yang Gao b, Wei-jia Liu c, Jia-gang Wu c a
School of Public Health, Wuhan University, Wuhan, PR China School of Public Health and Primary Care, The Chinese University of Hong Kong, Hong Kong Special Administrative Region, PR China Guangzhou Center for Disease Control and Prevention, 23 Zhongshan Road 3, Guangzhou 510080, Guangdong, PR China d School of Public Health, Sun Yat-sen University, Guangzhou, PR China b c
a r t i c l e
i n f o
Available online 23 November 2010 Keywords: Cardiorespiratory fitness Children Cohort study Obesity Physical activity
a b s t r a c t Objective. To investigate the relationships of cardiorespiratory fitness (CRF) and physical activity (PA) with the risk of overweight/obesity in Chinese schoolchildren. Methods. A total of 1795 children aged 8–13 years at baseline were followed-up for 18 months from 2006 to 2008 in Guangzhou, China. Children were categorized as “normal weight”, “overweight”, and “obese” using Chinese obesity cut-off points. Data on self-reported PA were obtained. CRF was determined by the 20-meter multistage fitness test, and the sex-specific median values were set as the cut-off points for the classification of high and low CRF. Results. Significantly higher CRF was found in children with normal weight (from 6.55 to 8.65 ml/kg/min) or physically active children (from 0.42 to 1.22 ml/kg/min) compared with the reference group. CRF was inversely associated with the kg/m2 change in BMI during the follow-up period (β = −0.63 kg/m2 and −0.64 kg/m2 for boys and girls, respectively, both p b 0.001). Significant association of baseline CRF with overweight/obesity was found in boys (odds ratio (OR) 8.71; 95% confidence interval (CI) 2.59–29.26, p b 0.001), whereas the association was marginally insignificant in girls (OR 6.87; 95% CI 0.96–49.09, p = 0.055). Conclusions. The results showed a strong negative association between CRF levels and children's BMI and weight gain. © 2010 Elsevier Inc. All rights reserved.
Introduction A rising prevalence of childhood obesity has been seen worldwide (Haslam et al., 2006). Childhood obesity can result in adverse health consequences, including cardiovascular disease (CVD) and type 2 diabetes (Perez Gomez and Huffman, 2008). It may persist into adulthood, which is associated with increased morbidity and mortality (McMillan et al., 2006). It is therefore vital to understand the risk factors for childhood obesity. Among numerous factors which may contribute to childhood obesity, physical activity (PA) and cardiorespiratory fitness (CRF) are of particular interest. Several studies have suggested that high CRF might attenuate the health risks attributed to obesity in children (Rizzo et al., 2007), and adolescents (Flouris et al., 2007). Also, there is evidence that decreased PA is associated with obesity, whereas physically active children may have lower risks of chronic diseases than physically inactive children (Dugan, 2008). However, activityrelated energy expenditure at baseline has not been found to predict ⁎ Corresponding author. Department of Community and Family Medicine, The Chinese University of Hong Kong, 4/F, Shatin, New territories, Hong Kong, PR China. Fax: +852 26063500. E-mail address: [email protected] (T. Wong). 0091-7435/$ – see front matter © 2010 Elsevier Inc. All rights reserved. doi:10.1016/j.ypmed.2010.11.005
increasing adiposity (Johnson et al., 2000), and other researchers failed to show associations between adolescent CRF and adult cholesterol, blood pressure, and glucose levels (Eisenmann et al., 2005). Furthermore, it remains controversial as to whether a gender difference exists since some researchers reported a significant relationship between CRF and/or PA and body composition only in girls (Mota et al., 2006; Kim et al., 2005). A better understanding of the association between PA, CRF and childhood obesity is important in assessing the benefits of intervention programs aimed at preventing obesity. However, most previous investigations have been cross-sectional in design (Mota et al., 2006; Ara et al., 2007; Hussey et al., 2007; Stratton et al., 2007), while the limited longitudinal studies were predominately limited to Caucasian populations, and did not account for the influence of PA on body weight (Kim et al., 2005; McGavock et al., 2009; Mota et al., 2009). No studies that address this issue among Chinese children have been reported. China has undergone enormous socioeconomic changes in the past three decades. One consequence is that the prevalence of overweight/obesity is approaching that of the developed countries. A recent Chinese national survey has revealed that the overall prevalence of obesity and overweight in children aged under 7-year old was 7.2% and 19.8%, with an annual rate of increase of 156% and 52% for obesity and overweight, respectively (Ding, 2008). In this
110
Q. He et al. / Preventive Medicine 52 (2011) 109–113
study, we aimed to examine the relationships between PA, CRF and obesity in Chinese children, and determine whether PA and CRF affected the changes in body composition over time in a cohort of school children. Methods Subjects and data collection We analyzed data from a prospective cohort study on air pollution and cardiorespiratory health in Guangzhou, China. The study design and methods have been previously described (He et al., 2008). Briefly, children from one to four primary schools in three districts were recruited. Schools were chosen based on their proximity to the local air monitoring stations and the required sample size in the main study. The baseline study (T1) was conducted from September to November 2006. After 18 months, the children were followedup (T2), from March to May 2008. Written informed consents were obtained from parents of the children. The study protocol has been approved by the Medical Research Ethics Committee of Sun Yat-sen University.
Statistical analysis The age, anthropometric data, and PA were compared between overweight/obese children and those with normal weight using t-test and Chi-square test, where appropriate. Their CRF were compared by analysis of covariance (ANCOVA). Pearson's correlation coefficient between CRF and BMI was calculated. Mixed linear regression models were used to determine the independent effects of CRF and PA on the changes in BMI. Inter-district and school variations were taken into account by including the random district and school effects in the models. For bivariate analysis, baseline CRF was classified into two fitness levels. As no standard definition for low CRF exists in Chinese children, genderspecific median values were set as the cut-off points for the classification of high and low CRF. Cut-off points for boys and girls were 46.94 ml/kg/min and 44.82 ml/kg/min, respectively. Mixed-effects logistic regression was used to assess associations of CRF with the odds of overweight/obesity while accounting for the potential within-district and school effects. Statistical analyses were performed using SAS, version 9.1.3 (SAS Institute, Cary, NC).
Results Anthropometric measures In each survey, the same group of technicians measured the children's height (standing erect without shoes) and weight (in light clothes) in standard methods. Body mass index (BMI) was calculated by dividing weight (kg) by height squared (m2). Children were categorized as ‘normal weight’, ‘overweight’, and ‘obese’, using standard age- and gender-specific BMI values (Ji, 2005). Table 1 shows the cut-off points (kg/m2) for overweight and obese children in this study. For bivariate analysis, overweight and obese children were combined as one group. Physical activity Self-reported habitual PA (frequency and duration of indoor/outdoor sports, including ball games (soccer, basketball, volleyball, and table tennis, etc.) and other sports (running/jogging, track-and-field sports, swimming, dancing, and free play, etc.)) among the schoolchildren were obtained using a self-administered standardized questionnaire (Ferris, 1978) completed in the classroom with the instruction of trained investigators. Their PA status was dichotomized into physically active (Pa) and physically inactive (Pi). Pa children were defined as those who participated in sports and/or vigorous free play at least three times per week for at least 30 min each time. Cardiorespiratory fitness CRF was assessed by the 20-meter multistage fitness test (MFT) (Brewer et al., 1988). This test is a useful measure of cardiorespiratory capacity and has been found to be a validated and reliable field test in children and adolescents (Mahoney, 1992). Subjects were asked to run back and forth on a 20-meter course at a pre-determined speed guided by audio signals from a CD player. The running speed was set to increase at 0.5 km/h each minute, from a start speed of 8.5 km/h. Groups of six children were instructed to run at speeds following the audio signal and to complete as many laps as possible, until they could not cope. The children were stopped when they could not follow the signal any more. Predicted maximum oxygen uptake (VO2max) derived from the level (maximal speed) and number of laps in the test was used as a measure of CRF (Yuko Takahashi et al., 2004). Table 1 Cut-off points of body mass index for overweight and obese Chinese children (Guangzhou, China, 2006 to 2008). Age (years)
Boys Overweight
Obesity
Girls Overweight
Obesity
8 9 10 11 12 13 14
18.1 18.9 19.6 20.3 21.0 21.9 22.6
20.3 21.4 22.5 23.6 24.7 25.7 26.4
18.1 19.0 20.0 21.1 21.9 22.6 23.0
19.9 21.0 22.1 23.3 24.5 25.6 26.3
Of 2179 children who participated in the baseline study, 352 were lost to follow-up, 32 did not complete the CRF test in the second survey. The remaining 1795 (82.4%) children (901 boys and 894 girls; mean age: 10.2, SD: 0.8) provided CRF data in both surveys. They had similar age, height, and PA status with those lost to follow up, but there were more girls, and the children were significantly heavier, with higher BMI and lower CRF. There were only 4.5% and 2.1% missing values for PA in T1 and T2, respectively; therefore, the results may have not been significantly affected by the incomplete data. The children's characteristics stratified by BMI are presented in Table 2. CRF was significantly and inversely correlated with BMI in both surveys (r = −0.73, and −0.74 in T1 and T2, respectively; p b 0.001). Subsequent analyses showed similar trends in boys and girls. CRF in normal weight or Pa children were significantly higher than their peers (Table 3). CRF was also inversely associated with the changes in BMI over the study period (Table 4). Compared with those who had a high CRF at the baseline survey, boys with a low CRF had significantly higher odds of becoming or remaining overweight/obese in the follow-up study (Table 5). We have performed sensitivity tests by grouping the children into low, moderate, and high PA. No significant association was found between PA and the changes in BMI. Discussion In this paper we examined prospectively the relationship of CRF and PA with childhood obesity in 1795 Chinese schoolchildren. The main finding was that, regardless of gender, CRF was significantly inversely associated with subsequent body weight gain over an 18-month period. In addition, boys with low CRF had significantly increased risks of becoming or remaining overweight or obese. Although PA had no direct effects on BMI, active children showed significantly higher CRF than inactive children. As shown in previous studies (Ara et al., 2007; Dencker et al., 2007), our boys had significantly higher CRF than girls. Nevertheless, there is no consensus on the gender-specific effects of CRF on childhood obesity. We observed significant associations between CRF and BMI in boys, whereas the associations in girls were marginally significant. These concur with results by Byrd-Williams et al. (2008), who found that a high initial CRF in boys was inversely associated with changes in adiposity in a 4-year follow-up study. In contrast, others reported that increased BMI was significantly associated with lower CRF only in girls (Mota et al., 2006), or the effects of low CRF on the risk of becoming overweight were seen only among girls (Kim et al., 2005). The reason for the conflicting findings remains unclear. In the European Youth Heart Study, Moller et al. (2007) noticed a
Q. He et al. / Preventive Medicine 52 (2011) 109–113
111
Table 2 Subjects' characteristics of the follow-up study (Guangzhou, China, 2006 to 2008). T1
T2
Normal weight (n = 1538) Age, years ≤10 years, n (%) N10 years, n (%) Boys, n (%) Height, cm Weight, kg BMI, kg/m2 CRF, ml/kg/min Physically activea, n (%)
10.2(0.8) 1113(72.4) 425(27.6) 724(47.1) 137.8(7.0) 30.7(5.2) 16.1(1.7) 46.7(0.1) 551/1467(37.6)
Overweight/obese (n = 257)
Normal weight (n = 1508)
10.1(0.8) 183(71.2) 74(28.8) 177(68.9)⁎⁎⁎ 141.6(7.0)⁎⁎⁎ 45.4(7.6)⁎⁎⁎ 22.5(2.4)⁎⁎⁎ 39.6(0.2)⁎⁎⁎
Overweight/obese (n = 287)
11.7 (0.7) 93(6.2) 1415(93.8) 712(47.2) 148.4(8.1) 38.2(6.5) 17.2(1.9) 46.9(0.1) 596/1475(40.4)
93/248(37.5)
11.7(0.7) 19(6.6) 268(93.4) 189(65.9)⁎⁎⁎ 152.1(7.0)⁎⁎⁎ 55.6(8.6)⁎⁎⁎ 23.9(2.6)⁎⁎⁎ 38.7(0.2)⁎⁎⁎ 117/283(41.3)
Abbreviation: T1, baseline survey; T2, follow-up survey; BMI, body mass index; CRF, cardiorespiratory fitness. Data are present as mean (SD), mean (SE), or n (percentage) when appropriate. CRF were adjusted for district, school, sex, age, and physical activity. a There were some missing values. ⁎⁎⁎ p b 0.001 for comparisons between “normal weight” and “overweight/obese”.
significant secular decline in CRF in girls. Several differences have been found in CVD risk factors, including blood pressure, triglycerides, fasting total cholesterol, etc. between boys and girls in a study on CRF and body fatness (Eisenmann et al., 2007). In addition, the differences in physiological characteristics, and the physical developmental factors during the adolescence period may be related to the observed gender-difference. Furthermore, the difference in the onset of puberty, behavioral characteristics and environmental risk factors between boys and girls might also have an influence on the association between CRF and childhood obesity. Our results showing a significantly lower level of CRF in overweight/obese children compared with those with normal weight are in agreement with several population-based investigations (Kim et al., 2005; Hussey et al., 2007; McGavock et al., 2009). In addition, we found that initial CRF level was a significant predictor of body weight gain. Within the 18-month follow-up period, children with a low baseline CRF were 6.9–8.7 times (for boys, OR = 8.71, p b 0.001; and for girls, OR = 6.87; p = 0.055) more likely to remain or become overweight or obese than those who have a high CRF at baseline. These risk estimates were much higher than in several longitudinal studies conducted in Caucasian children, that ranged from 3 to 4 times (Kim et al., 2005; McGavock et al., 2009; Mota et al., 2009). However, the lack of a common definition for CRF makes comparison across these studies difficult. Our findings in Chinese children added more data to the limited list of longitudinal studies on the relationship of CRF and childhood obesity. A secular trend with declining CRF and increasing body fatness has been observed in children (Stratton et al., 2007; Moller et al., 2007). Moreover, childhood obesity has been suggested to be associated with increased risks of high blood pressure, dyslipidaemia, insulin resistance, and metabolic syndrome, etc.
(Jolliffe and Janssen, 2006). Our findings suggest that improving CRF in children might prevent overweight and obesity. Regular assessments of CRF would identify unfit children whose risks of developing several cardiovascular and lipid diseases could be reduced. Low levels of PA have been suggested to be associated with an increased risk of obesity. A meta-analysis of 50 studies by Rowlands et al. (2000) revealed a small to moderate relationship between body fatness and activity in children. The 2002 China national nutrition and health survey also showed that overweight children spent 0.5 h less on moderate/vigorous activities per week compared to those with normal weight (Li et al., 2007). The absence of any significant association between PA and the changes in BMI in our study might be due to inaccuracies in the estimation of the children's PA, or a weak association between PA and BMI changes. However, previous studies have also reported inconsistent findings (Harro, 1997). Gender differences have also been reported (Hussey et al., 2007). The intensity, frequency, and duration of PA should be taken into account when determining the effects of PA on children's body composition. Some authors have postulated that there may be a threshold of intensity of PA that is influential on body fatness (Abbott and Davies, 2004). Fulton et al. in their review summarized that several developed recommendations advocated 60 or more minutes of daily moderateto vigorous-intensity PA to promote health among youth. This is much higher than the cut-off points for the definition of ‘physically active’ in our study (Fulton et al., 2004). However, although PA was not associated with children's BMI and weight gain, we have demonstrated significantly higher CRF in physically active children than inactive children. CRF has been considered a better index of the activity level than direct and short-term measures of PA (Grund et al., 2000). Our findings of a significant inverse relationship of CRF with
Table 3 Comparisons of CRF in different BMI categories and physical activity groups (Guangzhou, China, 2006 to 2008). Physical activitya
BMI category Normal weight
Overweight/obese
Physically active
Physically inactive
n
Mean(SE)
n
Mean(SE)
n
Mean(SE)
n
Mean(SE)
T1 Boys Girls
724 814
48.17(0.11) 45.15(0.09)
177 80
40.75(0.23)⁎⁎⁎ 38.61(0.27)⁎⁎⁎
365 279
47.05(0.12) 44.85(0.11)
498 573
46.42(0.10)††† 44.43(0.08)††
T2 Boys Girls
712 796
49.06(0.13) 44.67(0.10)
189 98
40.41(0.25)⁎⁎⁎ 37.40(0.27)⁎⁎⁎
405 308
47.88(0.13) 44.22(0.10)
476 569
46.66(0.12)††† 43.69(0.08)†††
Abbreviation: T1, baseline survey; T2, follow-up survey; CRF, cardiorespiratory fitness; BMI, body mass index. BMI categories were adjusted for district, school, age, and physical activity. Compared with normal weight, ***: p b 0.001. “Physical activity” group was adjusted for district, school, age, and BMI. Compared with “physically active”, ††: p b 0.01; †††: p b 0.001. a There were some missing values.
112
Q. He et al. / Preventive Medicine 52 (2011) 109–113
Table 4 Mixed linear regression analysis of CRF and PA (in separate models) with the changes in BMI⁎ among children (Guangzhou, China, 2006 to 2008). Predictors
CRF, ml/kg/min PA
Boys
Girls
β
SE
p-value
β
SE
p-value
− 0.63 0.01
0.07 0.07
b0.001 0.989
− 0.64 − 0.07
0.09 0.09
b 0.001 0.355
Abbreviation: CRF, cardiorespiratory fitness. PA, physical activity. BMI, body mass index. ⁎ Adjusted for district, school, and age. District and school were taken as a random effect.
BMI changes in both genders suggest that promoting PA in children could reduce the development of obesity by improving their CRF levels. Several limitations should be noted when interpreting our results. Firstly, CRF and PA were both assessed indirectly. Although performance in the MFT may be affected by motivation, previous studies have shown that this test was reliable, and the predicted CRF was highly correlated with the measured values in the laboratory (Mahoney, 1992). Despite the problems of recall bias, self-reported PA is the most commonly used method in epidemiological studies. Reliable estimates of PA by self-reporting are generally found in children aged 11 years or more (Sallis et al., 1993). Estimated PA levels have been shown to be consistently higher than those measured by other instruments (Welk et al., 2000). However, direct determinations of CRF and PA level are impractical in populationbased studies. In our study, PA levels were dichotomized, but our results were broadly consistent with previous studies (Ara et al., 2007; Dencker et al., 2006). Secondly, BMI has been widely used to define overweight and obesity among children. However, it does not necessarily reflect body compositions that are related to fitness. Nevertheless, precise measures of body fat are not feasible for population surveys. Furthermore, overweight/obesity during childhood determined by BMI has been showed to be a strong predictor of obesity and coronary heart disease risk factors in young adulthood (Janssen et al., 2005). Thirdly, while several epidemiological studies have suggested that dietary energy intake was related to BMI (Obarzanek et al., 1994; Zaimin et al., 2003), we did not obtain these data. Finally, pubertal level was also not assessed. These potential confounders might have affected our results. In conclusion, this study documents significant negative relationships of CRF with the changes in BMI in Chinese children. The observed difference in CRF between physically active and inactive children may be clinically unimportant for the individual. However, given the high prevalence of childhood obesity, improving the CRF of children could result in substantial public health benefit. Future studies with a better documentation of PA and the inclusion of data on dietary intake, puberty and socioeconomic factors should elucidate the complex relationships.
Conflict of interest statement The authors declare that there are no conflicts of interest.
Table 5 Logistical regression analysis of becoming or remaining overweight/obese in the follow-up study (Guangzhou, China, 2006 to 2008).
Boys Girls
CRF at T1
n
Overweight/obese at T2
ORa (95% CI)
p-value
High Low High Low
451 450 447 447
72 117 33 65
1.0 8.71(2.59–29.26) 1.0 6.87(0.96–49.09)
b 0.001 0.055
Abbreviation: T1, baseline survey; T2, follow-up survey; CRF, cardiorespiratory fitness; OR, odds ratio; CI, confidence interval. a Adjusted for district, school, age, BMI at T1, and CRF difference between T1 and T2. District and school were taken as a random effect.
Acknowledgments We thank Prof. Wilson Tam and Dr. Xin Gao for their excellent technical assistance. We are also very grateful to the students, their parents, the schools' principals and their teachers who participated in this study, and all of the field investigators. References Abbott, R.A., Davies, P.S., 2004. Habitual physical activity and physical activity intensity: their relation to body composition in 5.0–10.5-y-old children. Eur. J. Clin. Nutr. 58, 285–291. Ara, I., Moreno, L.A., Leiva, M.T., Gutin, B., Casajus, J.A., 2007. Adiposity, physical activity, and physical fitness among children from Aragon, Spain. Obesity 15, 1918–1924 (Silver Spring). Brewer, J., Ramsbottom, R., Williams, C., 1988. Multistage Fitness Test. National Coaching Foundation, Leeds. Byrd-Williams, C.E., Shaibi, G.Q., Sun, P., et al., 2008. Cardiorespiratory fitness predicts changes in adiposity in overweight Hispanic boys. Obesity 16, 1072–1077 (Silver Spring). Dencker, M., Thorsson, O., Karlsson, M.K., et al., 2006. Daily physical activity and its relation to aerobic fitness in children aged 8–11 years. Eur. J. Appl. Physiol. 96, 587–592. Dencker, M., Thorsson, O., Karlsson, M.K., et al., 2007. Gender differences and determinants of aerobic fitness in children aged 8–11 years. Eur. J. Appl. Physiol. 99, 19–26. Ding, Z.Y., 2008. National epidemiological survey on childhood obesity, 2006. Zhonghua Er Ke Za Zhi 46, 179–184. Dugan, S.A., 2008. Exercise for preventing childhood obesity. Phys. Med. Rehabil. Clin. N. Am. 19, 205–216. Eisenmann, J.C., Wickel, E.E., Welk, G.J., Blair, S.N., 2005. Relationship between adolescent fitness and fatness and cardiovascular disease risk factors in adulthood: the Aerobics Center Longitudinal Study (ACLS). Am. Heart J. 149, 46–53. Eisenmann, J.C., Welk, G.J., Ihmels, M., Dollman, J., 2007. Fatness, fitness, and cardiovascular disease risk factors in children and adolescents. Med. Sci. Sports Exerc. 39, 1251–1256. Ferris, B.G., 1978. Epidemiology Standardization Project (American Thoracic Society). Am. Rev. Respir. Dis. 118, 1–120. Flouris, A.D., Canham, C.H., Faught, B.E., Klentrou, P., 2007. Prevalence of cardiovascular disease risk in Ontario adolescents. Arch. Dis. Child. 92, 521–523. Fulton, J.E., Garg, M., Galuska, D.A., Rattay, K.T., Caspersen, C.J., 2004. Public health and clinical recommendations for physical activity and physical fitness: special focus on overweight youth. Sports Med. 34, 581–599. Grund, A., Dilba, B., Forberger, K., et al., 2000. Relationships between physical activity, physical fitness, muscle strength and nutritional state in 5- to 11-year-old children. Eur. J. Appl. Physiol. 82, 425–438. Harro, M., 1997. Validation of a questionnaire to assess physical activity of children ages 4–8 years. Res. Q. Exerc. Sport 68, 259–268. Haslam, D., Sattar, N., Lean, M., 2006. ABC of obesity. Obesity—time to wake up. BMJ 333, 640–642. He, Q.Q., Wong, T.W., Du, L., et al., 2008. Nutrition and children's respiratory health in Guangzhou, China. Public Health 122, 1425–1432. Hussey, J., Bell, C., Bennett, K., O'Dwyer, J., Gormley, J., 2007. Relationship between the intensity of physical activity, inactivity, cardiorespiratory fitness and body composition in 7–10-year-old Dublin children. Br. J. Sports Med. 41, 311–316. Janssen, I., Katzmarzyk, P.T., Srinivasan, S.R., et al., 2005. Utility of childhood BMI in the prediction of adulthood disease: comparison of national and international references. Obes. Res. 13, 1106–1115. Ji, C.Y., 2005. Report on childhood obesity in China (1)—body mass index reference for screening overweight and obesity in Chinese school-age children. Biomed. Environ. Sci. 18, 390–400. Johnson, M.S., Figueroa-Colon, R., Herd, S.L., et al., 2000. Aerobic fitness, not energy expenditure, influences subsequent increase in adiposity in black and white children. Pediatrics 106, E50. Jolliffe, C.J., Janssen, I., 2006. Vascular risks and management of obesity in children and adolescents. Vasc. Health Risk Manag. 2, 171–187. Kim, J., Must, A., Fitzmaurice, G.M., et al., 2005. Relationship of physical fitness to prevalence and incidence of overweight among schoolchildren. Obes. Res. 13, 1246–1254. Li, Y., Zhai, F., Yang, X., et al., 2007. Determinants of childhood overweight and obesity in China. Br. J. Nutr. 97, 210–215. Mahoney, C., 1992. 20-MST and PWC170 validity in non-Caucasian children in the UK. Br. J. Sports Med. 26, 45–47. McGavock, J.M., Torrance, B.D., McGuire, K.A., Wozny, P.D., Lewanczuk, R.Z., 2009. Cardiorespiratory fitness and the risk of overweight in youth: the Healthy Hearts Longitudinal Study of Cardiometabolic Health. Obesity 17, 1802–1807 (Silver Spring). McMillan, C., Sattar, N., McArdle, C.S., 2006. ABC of obesity. Obesity and cancer. BMJ 333, 1109–1111. Moller, N.C., Wedderkopp, N., Kristensen, P.L., Andersen, L.B., Froberg, K., 2007. Secular trends in cardiorespiratory fitness and body mass index in Danish children: the European Youth Heart Study. Scand. J. Med. Sci. Sports 17, 331–339. Mota, J., Flores, L., Flores, L., Ribeiro, J.C., Santos, M.P., 2006. Relationship of single measures of cardiorespiratory fitness and obesity in young schoolchildren. Am. J. Hum. Biol. 18, 335–341.
Q. He et al. / Preventive Medicine 52 (2011) 109–113 Mota, J., Ribeiro, J.C., Carvalho, J., Santos, M.P., Martins, J., 2009. Cardiorespiratory fitness status and body mass index change over time: a 2-year longitudinal study in elementary school children. Int. J. Pediatr. Obes. 26, 1–5. Obarzanek, E., Schreiber, G.B., Crawford, P.B., et al., 1994. Energy intake and physical activity in relation to indexes of body fat: the National Heart, Lung, and Blood Institute Growth and Health Study. Am. J. Clin. Nutr. 60, 15–22. Perez Gomez, G., Huffman, F.G., 2008. Risk factors for type 2 diabetes and cardiovascular diseases in Hispanic adolescents. J. Adolesc. Health 43, 444–450. Rizzo, N.S., Ruiz, J.R., Hurtig-Wennlof, A., Ortega, F.B., Sjostrom, M., 2007. Relationship of physical activity, fitness, and fatness with clustered metabolic risk in children and adolescents: the European youth heart study. J. Pediatr. 150, 388–394. Rowlands, A.V., Ingledew, D.K., Eston, R.G., 2000. The effect of type of physical activity measure on the relationship between body fatness and habitual physical activity in children: a meta-analysis. Ann. Hum. Biol. 27, 479–497.
113
Sallis, J.F., Buono, M.J., Roby, J.J., Micale, F.G., Nelson, J.A., 1993. Seven-day recall and other physical activity self-reports in children and adolescents. Med. Sci. Sports Exerc. 25, 99–108. Stratton, G., Canoy, D., Boddy, L.M., Taylor, S.R., Hackett, A.F., Buchan, I.E., 2007. Cardiorespiratory fitness and body mass index of 9–11-year-old English children: a serial cross-sectional study from 1998 to 2004. Int. J. Obes. Lond. 31, 1172–1178. Welk, G.J., Corbin, C.B., Dale, D., 2000. Measurement issues in the assessment of physical activity in children. Res. Q. Exerc. Sport 71 (2 Suppl), 59–73. Yuko Takahashi, N.K., Matsuzaka, Akira, Yamazoe, Masayuki, Ikeda, Akiko, 2004. Validity of the multistage 20-m shuttle-run test for Japanese children, adolescents, and adults. Pediatr. Exerc. Sci. 16, 113–125. Zaimin, Wang, Patterson, Carla M., Hills, Andrew P., 2003. The relationship between BMI and intake of energy and fat in Australian youth: a secondary analysis of the National Nutrition Survey 1995. Nutr. Dietetics. 60, 23–29.
Contents lists available at ScienceDirect
Preventive Medicine j o u r n a l h o m e p a g e : w w w. e l s e v i e r. c o m / l o c a t e / y p m e d
Physical activity, cardiorespiratory fitness, and obesity among Chinese children Qi-qiang He a,b, Tze-wai Wong b,⁎, Lin Du c, Zhuo-qin Jiang d, Tak-sun Ignatius Yu b, Hong Qiu b, Yang Gao b, Wei-jia Liu c, Jia-gang Wu c a
School of Public Health, Wuhan University, Wuhan, PR China School of Public Health and Primary Care, The Chinese University of Hong Kong, Hong Kong Special Administrative Region, PR China Guangzhou Center for Disease Control and Prevention, 23 Zhongshan Road 3, Guangzhou 510080, Guangdong, PR China d School of Public Health, Sun Yat-sen University, Guangzhou, PR China b c
a r t i c l e
i n f o
Available online 23 November 2010 Keywords: Cardiorespiratory fitness Children Cohort study Obesity Physical activity
a b s t r a c t Objective. To investigate the relationships of cardiorespiratory fitness (CRF) and physical activity (PA) with the risk of overweight/obesity in Chinese schoolchildren. Methods. A total of 1795 children aged 8–13 years at baseline were followed-up for 18 months from 2006 to 2008 in Guangzhou, China. Children were categorized as “normal weight”, “overweight”, and “obese” using Chinese obesity cut-off points. Data on self-reported PA were obtained. CRF was determined by the 20-meter multistage fitness test, and the sex-specific median values were set as the cut-off points for the classification of high and low CRF. Results. Significantly higher CRF was found in children with normal weight (from 6.55 to 8.65 ml/kg/min) or physically active children (from 0.42 to 1.22 ml/kg/min) compared with the reference group. CRF was inversely associated with the kg/m2 change in BMI during the follow-up period (β = −0.63 kg/m2 and −0.64 kg/m2 for boys and girls, respectively, both p b 0.001). Significant association of baseline CRF with overweight/obesity was found in boys (odds ratio (OR) 8.71; 95% confidence interval (CI) 2.59–29.26, p b 0.001), whereas the association was marginally insignificant in girls (OR 6.87; 95% CI 0.96–49.09, p = 0.055). Conclusions. The results showed a strong negative association between CRF levels and children's BMI and weight gain. © 2010 Elsevier Inc. All rights reserved.
Introduction A rising prevalence of childhood obesity has been seen worldwide (Haslam et al., 2006). Childhood obesity can result in adverse health consequences, including cardiovascular disease (CVD) and type 2 diabetes (Perez Gomez and Huffman, 2008). It may persist into adulthood, which is associated with increased morbidity and mortality (McMillan et al., 2006). It is therefore vital to understand the risk factors for childhood obesity. Among numerous factors which may contribute to childhood obesity, physical activity (PA) and cardiorespiratory fitness (CRF) are of particular interest. Several studies have suggested that high CRF might attenuate the health risks attributed to obesity in children (Rizzo et al., 2007), and adolescents (Flouris et al., 2007). Also, there is evidence that decreased PA is associated with obesity, whereas physically active children may have lower risks of chronic diseases than physically inactive children (Dugan, 2008). However, activityrelated energy expenditure at baseline has not been found to predict ⁎ Corresponding author. Department of Community and Family Medicine, The Chinese University of Hong Kong, 4/F, Shatin, New territories, Hong Kong, PR China. Fax: +852 26063500. E-mail address: [email protected] (T. Wong). 0091-7435/$ – see front matter © 2010 Elsevier Inc. All rights reserved. doi:10.1016/j.ypmed.2010.11.005
increasing adiposity (Johnson et al., 2000), and other researchers failed to show associations between adolescent CRF and adult cholesterol, blood pressure, and glucose levels (Eisenmann et al., 2005). Furthermore, it remains controversial as to whether a gender difference exists since some researchers reported a significant relationship between CRF and/or PA and body composition only in girls (Mota et al., 2006; Kim et al., 2005). A better understanding of the association between PA, CRF and childhood obesity is important in assessing the benefits of intervention programs aimed at preventing obesity. However, most previous investigations have been cross-sectional in design (Mota et al., 2006; Ara et al., 2007; Hussey et al., 2007; Stratton et al., 2007), while the limited longitudinal studies were predominately limited to Caucasian populations, and did not account for the influence of PA on body weight (Kim et al., 2005; McGavock et al., 2009; Mota et al., 2009). No studies that address this issue among Chinese children have been reported. China has undergone enormous socioeconomic changes in the past three decades. One consequence is that the prevalence of overweight/obesity is approaching that of the developed countries. A recent Chinese national survey has revealed that the overall prevalence of obesity and overweight in children aged under 7-year old was 7.2% and 19.8%, with an annual rate of increase of 156% and 52% for obesity and overweight, respectively (Ding, 2008). In this
110
Q. He et al. / Preventive Medicine 52 (2011) 109–113
study, we aimed to examine the relationships between PA, CRF and obesity in Chinese children, and determine whether PA and CRF affected the changes in body composition over time in a cohort of school children. Methods Subjects and data collection We analyzed data from a prospective cohort study on air pollution and cardiorespiratory health in Guangzhou, China. The study design and methods have been previously described (He et al., 2008). Briefly, children from one to four primary schools in three districts were recruited. Schools were chosen based on their proximity to the local air monitoring stations and the required sample size in the main study. The baseline study (T1) was conducted from September to November 2006. After 18 months, the children were followedup (T2), from March to May 2008. Written informed consents were obtained from parents of the children. The study protocol has been approved by the Medical Research Ethics Committee of Sun Yat-sen University.
Statistical analysis The age, anthropometric data, and PA were compared between overweight/obese children and those with normal weight using t-test and Chi-square test, where appropriate. Their CRF were compared by analysis of covariance (ANCOVA). Pearson's correlation coefficient between CRF and BMI was calculated. Mixed linear regression models were used to determine the independent effects of CRF and PA on the changes in BMI. Inter-district and school variations were taken into account by including the random district and school effects in the models. For bivariate analysis, baseline CRF was classified into two fitness levels. As no standard definition for low CRF exists in Chinese children, genderspecific median values were set as the cut-off points for the classification of high and low CRF. Cut-off points for boys and girls were 46.94 ml/kg/min and 44.82 ml/kg/min, respectively. Mixed-effects logistic regression was used to assess associations of CRF with the odds of overweight/obesity while accounting for the potential within-district and school effects. Statistical analyses were performed using SAS, version 9.1.3 (SAS Institute, Cary, NC).
Results Anthropometric measures In each survey, the same group of technicians measured the children's height (standing erect without shoes) and weight (in light clothes) in standard methods. Body mass index (BMI) was calculated by dividing weight (kg) by height squared (m2). Children were categorized as ‘normal weight’, ‘overweight’, and ‘obese’, using standard age- and gender-specific BMI values (Ji, 2005). Table 1 shows the cut-off points (kg/m2) for overweight and obese children in this study. For bivariate analysis, overweight and obese children were combined as one group. Physical activity Self-reported habitual PA (frequency and duration of indoor/outdoor sports, including ball games (soccer, basketball, volleyball, and table tennis, etc.) and other sports (running/jogging, track-and-field sports, swimming, dancing, and free play, etc.)) among the schoolchildren were obtained using a self-administered standardized questionnaire (Ferris, 1978) completed in the classroom with the instruction of trained investigators. Their PA status was dichotomized into physically active (Pa) and physically inactive (Pi). Pa children were defined as those who participated in sports and/or vigorous free play at least three times per week for at least 30 min each time. Cardiorespiratory fitness CRF was assessed by the 20-meter multistage fitness test (MFT) (Brewer et al., 1988). This test is a useful measure of cardiorespiratory capacity and has been found to be a validated and reliable field test in children and adolescents (Mahoney, 1992). Subjects were asked to run back and forth on a 20-meter course at a pre-determined speed guided by audio signals from a CD player. The running speed was set to increase at 0.5 km/h each minute, from a start speed of 8.5 km/h. Groups of six children were instructed to run at speeds following the audio signal and to complete as many laps as possible, until they could not cope. The children were stopped when they could not follow the signal any more. Predicted maximum oxygen uptake (VO2max) derived from the level (maximal speed) and number of laps in the test was used as a measure of CRF (Yuko Takahashi et al., 2004). Table 1 Cut-off points of body mass index for overweight and obese Chinese children (Guangzhou, China, 2006 to 2008). Age (years)
Boys Overweight
Obesity
Girls Overweight
Obesity
8 9 10 11 12 13 14
18.1 18.9 19.6 20.3 21.0 21.9 22.6
20.3 21.4 22.5 23.6 24.7 25.7 26.4
18.1 19.0 20.0 21.1 21.9 22.6 23.0
19.9 21.0 22.1 23.3 24.5 25.6 26.3
Of 2179 children who participated in the baseline study, 352 were lost to follow-up, 32 did not complete the CRF test in the second survey. The remaining 1795 (82.4%) children (901 boys and 894 girls; mean age: 10.2, SD: 0.8) provided CRF data in both surveys. They had similar age, height, and PA status with those lost to follow up, but there were more girls, and the children were significantly heavier, with higher BMI and lower CRF. There were only 4.5% and 2.1% missing values for PA in T1 and T2, respectively; therefore, the results may have not been significantly affected by the incomplete data. The children's characteristics stratified by BMI are presented in Table 2. CRF was significantly and inversely correlated with BMI in both surveys (r = −0.73, and −0.74 in T1 and T2, respectively; p b 0.001). Subsequent analyses showed similar trends in boys and girls. CRF in normal weight or Pa children were significantly higher than their peers (Table 3). CRF was also inversely associated with the changes in BMI over the study period (Table 4). Compared with those who had a high CRF at the baseline survey, boys with a low CRF had significantly higher odds of becoming or remaining overweight/obese in the follow-up study (Table 5). We have performed sensitivity tests by grouping the children into low, moderate, and high PA. No significant association was found between PA and the changes in BMI. Discussion In this paper we examined prospectively the relationship of CRF and PA with childhood obesity in 1795 Chinese schoolchildren. The main finding was that, regardless of gender, CRF was significantly inversely associated with subsequent body weight gain over an 18-month period. In addition, boys with low CRF had significantly increased risks of becoming or remaining overweight or obese. Although PA had no direct effects on BMI, active children showed significantly higher CRF than inactive children. As shown in previous studies (Ara et al., 2007; Dencker et al., 2007), our boys had significantly higher CRF than girls. Nevertheless, there is no consensus on the gender-specific effects of CRF on childhood obesity. We observed significant associations between CRF and BMI in boys, whereas the associations in girls were marginally significant. These concur with results by Byrd-Williams et al. (2008), who found that a high initial CRF in boys was inversely associated with changes in adiposity in a 4-year follow-up study. In contrast, others reported that increased BMI was significantly associated with lower CRF only in girls (Mota et al., 2006), or the effects of low CRF on the risk of becoming overweight were seen only among girls (Kim et al., 2005). The reason for the conflicting findings remains unclear. In the European Youth Heart Study, Moller et al. (2007) noticed a
Q. He et al. / Preventive Medicine 52 (2011) 109–113
111
Table 2 Subjects' characteristics of the follow-up study (Guangzhou, China, 2006 to 2008). T1
T2
Normal weight (n = 1538) Age, years ≤10 years, n (%) N10 years, n (%) Boys, n (%) Height, cm Weight, kg BMI, kg/m2 CRF, ml/kg/min Physically activea, n (%)
10.2(0.8) 1113(72.4) 425(27.6) 724(47.1) 137.8(7.0) 30.7(5.2) 16.1(1.7) 46.7(0.1) 551/1467(37.6)
Overweight/obese (n = 257)
Normal weight (n = 1508)
10.1(0.8) 183(71.2) 74(28.8) 177(68.9)⁎⁎⁎ 141.6(7.0)⁎⁎⁎ 45.4(7.6)⁎⁎⁎ 22.5(2.4)⁎⁎⁎ 39.6(0.2)⁎⁎⁎
Overweight/obese (n = 287)
11.7 (0.7) 93(6.2) 1415(93.8) 712(47.2) 148.4(8.1) 38.2(6.5) 17.2(1.9) 46.9(0.1) 596/1475(40.4)
93/248(37.5)
11.7(0.7) 19(6.6) 268(93.4) 189(65.9)⁎⁎⁎ 152.1(7.0)⁎⁎⁎ 55.6(8.6)⁎⁎⁎ 23.9(2.6)⁎⁎⁎ 38.7(0.2)⁎⁎⁎ 117/283(41.3)
Abbreviation: T1, baseline survey; T2, follow-up survey; BMI, body mass index; CRF, cardiorespiratory fitness. Data are present as mean (SD), mean (SE), or n (percentage) when appropriate. CRF were adjusted for district, school, sex, age, and physical activity. a There were some missing values. ⁎⁎⁎ p b 0.001 for comparisons between “normal weight” and “overweight/obese”.
significant secular decline in CRF in girls. Several differences have been found in CVD risk factors, including blood pressure, triglycerides, fasting total cholesterol, etc. between boys and girls in a study on CRF and body fatness (Eisenmann et al., 2007). In addition, the differences in physiological characteristics, and the physical developmental factors during the adolescence period may be related to the observed gender-difference. Furthermore, the difference in the onset of puberty, behavioral characteristics and environmental risk factors between boys and girls might also have an influence on the association between CRF and childhood obesity. Our results showing a significantly lower level of CRF in overweight/obese children compared with those with normal weight are in agreement with several population-based investigations (Kim et al., 2005; Hussey et al., 2007; McGavock et al., 2009). In addition, we found that initial CRF level was a significant predictor of body weight gain. Within the 18-month follow-up period, children with a low baseline CRF were 6.9–8.7 times (for boys, OR = 8.71, p b 0.001; and for girls, OR = 6.87; p = 0.055) more likely to remain or become overweight or obese than those who have a high CRF at baseline. These risk estimates were much higher than in several longitudinal studies conducted in Caucasian children, that ranged from 3 to 4 times (Kim et al., 2005; McGavock et al., 2009; Mota et al., 2009). However, the lack of a common definition for CRF makes comparison across these studies difficult. Our findings in Chinese children added more data to the limited list of longitudinal studies on the relationship of CRF and childhood obesity. A secular trend with declining CRF and increasing body fatness has been observed in children (Stratton et al., 2007; Moller et al., 2007). Moreover, childhood obesity has been suggested to be associated with increased risks of high blood pressure, dyslipidaemia, insulin resistance, and metabolic syndrome, etc.
(Jolliffe and Janssen, 2006). Our findings suggest that improving CRF in children might prevent overweight and obesity. Regular assessments of CRF would identify unfit children whose risks of developing several cardiovascular and lipid diseases could be reduced. Low levels of PA have been suggested to be associated with an increased risk of obesity. A meta-analysis of 50 studies by Rowlands et al. (2000) revealed a small to moderate relationship between body fatness and activity in children. The 2002 China national nutrition and health survey also showed that overweight children spent 0.5 h less on moderate/vigorous activities per week compared to those with normal weight (Li et al., 2007). The absence of any significant association between PA and the changes in BMI in our study might be due to inaccuracies in the estimation of the children's PA, or a weak association between PA and BMI changes. However, previous studies have also reported inconsistent findings (Harro, 1997). Gender differences have also been reported (Hussey et al., 2007). The intensity, frequency, and duration of PA should be taken into account when determining the effects of PA on children's body composition. Some authors have postulated that there may be a threshold of intensity of PA that is influential on body fatness (Abbott and Davies, 2004). Fulton et al. in their review summarized that several developed recommendations advocated 60 or more minutes of daily moderateto vigorous-intensity PA to promote health among youth. This is much higher than the cut-off points for the definition of ‘physically active’ in our study (Fulton et al., 2004). However, although PA was not associated with children's BMI and weight gain, we have demonstrated significantly higher CRF in physically active children than inactive children. CRF has been considered a better index of the activity level than direct and short-term measures of PA (Grund et al., 2000). Our findings of a significant inverse relationship of CRF with
Table 3 Comparisons of CRF in different BMI categories and physical activity groups (Guangzhou, China, 2006 to 2008). Physical activitya
BMI category Normal weight
Overweight/obese
Physically active
Physically inactive
n
Mean(SE)
n
Mean(SE)
n
Mean(SE)
n
Mean(SE)
T1 Boys Girls
724 814
48.17(0.11) 45.15(0.09)
177 80
40.75(0.23)⁎⁎⁎ 38.61(0.27)⁎⁎⁎
365 279
47.05(0.12) 44.85(0.11)
498 573
46.42(0.10)††† 44.43(0.08)††
T2 Boys Girls
712 796
49.06(0.13) 44.67(0.10)
189 98
40.41(0.25)⁎⁎⁎ 37.40(0.27)⁎⁎⁎
405 308
47.88(0.13) 44.22(0.10)
476 569
46.66(0.12)††† 43.69(0.08)†††
Abbreviation: T1, baseline survey; T2, follow-up survey; CRF, cardiorespiratory fitness; BMI, body mass index. BMI categories were adjusted for district, school, age, and physical activity. Compared with normal weight, ***: p b 0.001. “Physical activity” group was adjusted for district, school, age, and BMI. Compared with “physically active”, ††: p b 0.01; †††: p b 0.001. a There were some missing values.
112
Q. He et al. / Preventive Medicine 52 (2011) 109–113
Table 4 Mixed linear regression analysis of CRF and PA (in separate models) with the changes in BMI⁎ among children (Guangzhou, China, 2006 to 2008). Predictors
CRF, ml/kg/min PA
Boys
Girls
β
SE
p-value
β
SE
p-value
− 0.63 0.01
0.07 0.07
b0.001 0.989
− 0.64 − 0.07
0.09 0.09
b 0.001 0.355
Abbreviation: CRF, cardiorespiratory fitness. PA, physical activity. BMI, body mass index. ⁎ Adjusted for district, school, and age. District and school were taken as a random effect.
BMI changes in both genders suggest that promoting PA in children could reduce the development of obesity by improving their CRF levels. Several limitations should be noted when interpreting our results. Firstly, CRF and PA were both assessed indirectly. Although performance in the MFT may be affected by motivation, previous studies have shown that this test was reliable, and the predicted CRF was highly correlated with the measured values in the laboratory (Mahoney, 1992). Despite the problems of recall bias, self-reported PA is the most commonly used method in epidemiological studies. Reliable estimates of PA by self-reporting are generally found in children aged 11 years or more (Sallis et al., 1993). Estimated PA levels have been shown to be consistently higher than those measured by other instruments (Welk et al., 2000). However, direct determinations of CRF and PA level are impractical in populationbased studies. In our study, PA levels were dichotomized, but our results were broadly consistent with previous studies (Ara et al., 2007; Dencker et al., 2006). Secondly, BMI has been widely used to define overweight and obesity among children. However, it does not necessarily reflect body compositions that are related to fitness. Nevertheless, precise measures of body fat are not feasible for population surveys. Furthermore, overweight/obesity during childhood determined by BMI has been showed to be a strong predictor of obesity and coronary heart disease risk factors in young adulthood (Janssen et al., 2005). Thirdly, while several epidemiological studies have suggested that dietary energy intake was related to BMI (Obarzanek et al., 1994; Zaimin et al., 2003), we did not obtain these data. Finally, pubertal level was also not assessed. These potential confounders might have affected our results. In conclusion, this study documents significant negative relationships of CRF with the changes in BMI in Chinese children. The observed difference in CRF between physically active and inactive children may be clinically unimportant for the individual. However, given the high prevalence of childhood obesity, improving the CRF of children could result in substantial public health benefit. Future studies with a better documentation of PA and the inclusion of data on dietary intake, puberty and socioeconomic factors should elucidate the complex relationships.
Conflict of interest statement The authors declare that there are no conflicts of interest.
Table 5 Logistical regression analysis of becoming or remaining overweight/obese in the follow-up study (Guangzhou, China, 2006 to 2008).
Boys Girls
CRF at T1
n
Overweight/obese at T2
ORa (95% CI)
p-value
High Low High Low
451 450 447 447
72 117 33 65
1.0 8.71(2.59–29.26) 1.0 6.87(0.96–49.09)
b 0.001 0.055
Abbreviation: T1, baseline survey; T2, follow-up survey; CRF, cardiorespiratory fitness; OR, odds ratio; CI, confidence interval. a Adjusted for district, school, age, BMI at T1, and CRF difference between T1 and T2. District and school were taken as a random effect.
Acknowledgments We thank Prof. Wilson Tam and Dr. Xin Gao for their excellent technical assistance. We are also very grateful to the students, their parents, the schools' principals and their teachers who participated in this study, and all of the field investigators. References Abbott, R.A., Davies, P.S., 2004. Habitual physical activity and physical activity intensity: their relation to body composition in 5.0–10.5-y-old children. Eur. J. Clin. Nutr. 58, 285–291. Ara, I., Moreno, L.A., Leiva, M.T., Gutin, B., Casajus, J.A., 2007. Adiposity, physical activity, and physical fitness among children from Aragon, Spain. Obesity 15, 1918–1924 (Silver Spring). Brewer, J., Ramsbottom, R., Williams, C., 1988. Multistage Fitness Test. National Coaching Foundation, Leeds. Byrd-Williams, C.E., Shaibi, G.Q., Sun, P., et al., 2008. Cardiorespiratory fitness predicts changes in adiposity in overweight Hispanic boys. Obesity 16, 1072–1077 (Silver Spring). Dencker, M., Thorsson, O., Karlsson, M.K., et al., 2006. Daily physical activity and its relation to aerobic fitness in children aged 8–11 years. Eur. J. Appl. Physiol. 96, 587–592. Dencker, M., Thorsson, O., Karlsson, M.K., et al., 2007. Gender differences and determinants of aerobic fitness in children aged 8–11 years. Eur. J. Appl. Physiol. 99, 19–26. Ding, Z.Y., 2008. National epidemiological survey on childhood obesity, 2006. Zhonghua Er Ke Za Zhi 46, 179–184. Dugan, S.A., 2008. Exercise for preventing childhood obesity. Phys. Med. Rehabil. Clin. N. Am. 19, 205–216. Eisenmann, J.C., Wickel, E.E., Welk, G.J., Blair, S.N., 2005. Relationship between adolescent fitness and fatness and cardiovascular disease risk factors in adulthood: the Aerobics Center Longitudinal Study (ACLS). Am. Heart J. 149, 46–53. Eisenmann, J.C., Welk, G.J., Ihmels, M., Dollman, J., 2007. Fatness, fitness, and cardiovascular disease risk factors in children and adolescents. Med. Sci. Sports Exerc. 39, 1251–1256. Ferris, B.G., 1978. Epidemiology Standardization Project (American Thoracic Society). Am. Rev. Respir. Dis. 118, 1–120. Flouris, A.D., Canham, C.H., Faught, B.E., Klentrou, P., 2007. Prevalence of cardiovascular disease risk in Ontario adolescents. Arch. Dis. Child. 92, 521–523. Fulton, J.E., Garg, M., Galuska, D.A., Rattay, K.T., Caspersen, C.J., 2004. Public health and clinical recommendations for physical activity and physical fitness: special focus on overweight youth. Sports Med. 34, 581–599. Grund, A., Dilba, B., Forberger, K., et al., 2000. Relationships between physical activity, physical fitness, muscle strength and nutritional state in 5- to 11-year-old children. Eur. J. Appl. Physiol. 82, 425–438. Harro, M., 1997. Validation of a questionnaire to assess physical activity of children ages 4–8 years. Res. Q. Exerc. Sport 68, 259–268. Haslam, D., Sattar, N., Lean, M., 2006. ABC of obesity. Obesity—time to wake up. BMJ 333, 640–642. He, Q.Q., Wong, T.W., Du, L., et al., 2008. Nutrition and children's respiratory health in Guangzhou, China. Public Health 122, 1425–1432. Hussey, J., Bell, C., Bennett, K., O'Dwyer, J., Gormley, J., 2007. Relationship between the intensity of physical activity, inactivity, cardiorespiratory fitness and body composition in 7–10-year-old Dublin children. Br. J. Sports Med. 41, 311–316. Janssen, I., Katzmarzyk, P.T., Srinivasan, S.R., et al., 2005. Utility of childhood BMI in the prediction of adulthood disease: comparison of national and international references. Obes. Res. 13, 1106–1115. Ji, C.Y., 2005. Report on childhood obesity in China (1)—body mass index reference for screening overweight and obesity in Chinese school-age children. Biomed. Environ. Sci. 18, 390–400. Johnson, M.S., Figueroa-Colon, R., Herd, S.L., et al., 2000. Aerobic fitness, not energy expenditure, influences subsequent increase in adiposity in black and white children. Pediatrics 106, E50. Jolliffe, C.J., Janssen, I., 2006. Vascular risks and management of obesity in children and adolescents. Vasc. Health Risk Manag. 2, 171–187. Kim, J., Must, A., Fitzmaurice, G.M., et al., 2005. Relationship of physical fitness to prevalence and incidence of overweight among schoolchildren. Obes. Res. 13, 1246–1254. Li, Y., Zhai, F., Yang, X., et al., 2007. Determinants of childhood overweight and obesity in China. Br. J. Nutr. 97, 210–215. Mahoney, C., 1992. 20-MST and PWC170 validity in non-Caucasian children in the UK. Br. J. Sports Med. 26, 45–47. McGavock, J.M., Torrance, B.D., McGuire, K.A., Wozny, P.D., Lewanczuk, R.Z., 2009. Cardiorespiratory fitness and the risk of overweight in youth: the Healthy Hearts Longitudinal Study of Cardiometabolic Health. Obesity 17, 1802–1807 (Silver Spring). McMillan, C., Sattar, N., McArdle, C.S., 2006. ABC of obesity. Obesity and cancer. BMJ 333, 1109–1111. Moller, N.C., Wedderkopp, N., Kristensen, P.L., Andersen, L.B., Froberg, K., 2007. Secular trends in cardiorespiratory fitness and body mass index in Danish children: the European Youth Heart Study. Scand. J. Med. Sci. Sports 17, 331–339. Mota, J., Flores, L., Flores, L., Ribeiro, J.C., Santos, M.P., 2006. Relationship of single measures of cardiorespiratory fitness and obesity in young schoolchildren. Am. J. Hum. Biol. 18, 335–341.
Q. He et al. / Preventive Medicine 52 (2011) 109–113 Mota, J., Ribeiro, J.C., Carvalho, J., Santos, M.P., Martins, J., 2009. Cardiorespiratory fitness status and body mass index change over time: a 2-year longitudinal study in elementary school children. Int. J. Pediatr. Obes. 26, 1–5. Obarzanek, E., Schreiber, G.B., Crawford, P.B., et al., 1994. Energy intake and physical activity in relation to indexes of body fat: the National Heart, Lung, and Blood Institute Growth and Health Study. Am. J. Clin. Nutr. 60, 15–22. Perez Gomez, G., Huffman, F.G., 2008. Risk factors for type 2 diabetes and cardiovascular diseases in Hispanic adolescents. J. Adolesc. Health 43, 444–450. Rizzo, N.S., Ruiz, J.R., Hurtig-Wennlof, A., Ortega, F.B., Sjostrom, M., 2007. Relationship of physical activity, fitness, and fatness with clustered metabolic risk in children and adolescents: the European youth heart study. J. Pediatr. 150, 388–394. Rowlands, A.V., Ingledew, D.K., Eston, R.G., 2000. The effect of type of physical activity measure on the relationship between body fatness and habitual physical activity in children: a meta-analysis. Ann. Hum. Biol. 27, 479–497.
113
Sallis, J.F., Buono, M.J., Roby, J.J., Micale, F.G., Nelson, J.A., 1993. Seven-day recall and other physical activity self-reports in children and adolescents. Med. Sci. Sports Exerc. 25, 99–108. Stratton, G., Canoy, D., Boddy, L.M., Taylor, S.R., Hackett, A.F., Buchan, I.E., 2007. Cardiorespiratory fitness and body mass index of 9–11-year-old English children: a serial cross-sectional study from 1998 to 2004. Int. J. Obes. Lond. 31, 1172–1178. Welk, G.J., Corbin, C.B., Dale, D., 2000. Measurement issues in the assessment of physical activity in children. Res. Q. Exerc. Sport 71 (2 Suppl), 59–73. Yuko Takahashi, N.K., Matsuzaka, Akira, Yamazoe, Masayuki, Ikeda, Akiko, 2004. Validity of the multistage 20-m shuttle-run test for Japanese children, adolescents, and adults. Pediatr. Exerc. Sci. 16, 113–125. Zaimin, Wang, Patterson, Carla M., Hills, Andrew P., 2003. The relationship between BMI and intake of energy and fat in Australian youth: a secondary analysis of the National Nutrition Survey 1995. Nutr. Dietetics. 60, 23–29.