Validation of prediction equations for estimating resting energy expenditure in obese Chinese children.

OBJECTIVES: (1) To examine the validity of existing prediction equations (PREE) for estimating resting energy expenditure (REE) in obese Chinese children, (2) to correlate the measured REE (MREE) with anthropometric and biochemical parameters and (3) to derive a new PREE for local use. DESIGN: Cross-sectional study. SUBJECTS: 100 obese children (71 boys) were studied. MEASUREMENTS: All subjects underwent physical examination and anthropometric measurement. Upper and central body fat distribution was signified by centrality and conicity index respectively, and REE was measured by indirect calorimetry. Fat free mass (FFM) were measured by DEXA scan. Thirteen existing prediction equations for estimating REE were compared with MREE among these obese children. Fasting blood for glucose, lipid profile and insulin were obtained. RESULTS: The overall, male and female median MREEs were 7.1 mJ/d (IR 6.2-8.4), 7.3 mJ/d (IR 6.3-9.7) and 6.9 mJ/d (IR 5.6-8.1) respectively. No sex difference was noted in MREE (p=0.203). Most of the equations except Schofield equation underestimated REE of our children. By multiple linear regression, MREE was positively correlated with FFM (p<0.0001), conicity index (p<0.001) and centrality index (p=0.001). A new equation for estimating REE for local use was derived as: REE=(17.4*logFFM)+(11.4*conicity index)-(2.4*centrality index)-31.3. The mean difference of new PREE-MREE was -0.011 mJ/d (SD 1.51) with an interclass correlation coefficient of 0.91. CONCLUSION: None of the existing prediction equations were accurate in their estimation of REE, when applied to obese Chinese children. A new prediction equation has been derived for local use.

Body fat measured by bioelectrical impedance in Hong Kong Chinese children.

OBJECTIVE: To establish reference standards for percentage body fat measured in Hong Kong Chinese children, by methods involving bioelectrical impedance analysis. DESIGN: Cross-sectional study. SETTING: Thirty-six randomly selected primary and secondary schools and a teaching hospital in Hong Kong. PARTICIPANTS: A total of 14 842 students randomly selected from the schools and two additional small convenience samples of subjects. MAIN OUTCOME MEASURES: Percentage body fat was measured with the Tanita Body Composition Analyzer (Model no. BF-522) and percentile curves were constructed using the LMS method. In one separate small sample of children, repeatability of the percentage body fat measurement was assessed at different times of the day by BF-522 bioelectrical impedance analysis. In another sample, assessment was by the BF-522 and two other models (BC-418 and BF-401) consecutively to test the agreement of percentage body fat values obtained by the three different models. RESULTS. The percentage body fat values and percentile curves are presented. From the age of 6 to 18 years, the percentage body fat remained fairly stable in boys, but increased steadily in girls. The mean difference in percentage body fat measured with BF-522 at different times of the day was around 1% (95% limits of agreement: -4% to +8%). The mean differences in readings obtained from the BC-418 and BF-522 devices were -3.5% and 1% in boys and girls, respectively. The 95% limits of agreement were particularly wide in boys (-15% to 8%). CONCLUSIONS: Reference values for percentage body fat of Chinese children and adolescents are provided. Caution needs to be exercised however, given that readings obtained at different times of the day vary and data obtained by different makes and models of bioelectrical impedance analysis machines may not be interchangeable.

Waist circumference and waist-to-height ratio of Hong Kong Chinese children.

BACKGROUND: Central body fat is a better predictor than overall body fat for cardiovascular (CV) risk factors in both adults and children. Waist circumference (WC) has been used as a proxy measure of central body fat. Children at high CV risk may be identified by WC measurements. Waist-to-height ratio (WHTR) has been proposed as an alternative, conveniently age-independent measure of CV risk although WHTR percentiles have not been reported. We aim to provide age- and sex-specific reference values for WC and WHTR in Hong Kong Chinese children. METHODS: Cross sectional study in a large representative sample of 14,842 children aged 6 to 18 years in 2005/6. Sex-specific descriptive statistics for whole-year age groups and smoothed percentile curves of WC and WHTR were derived and presented. RESULTS: WC increased with age, although less after age 14 years in girls. WHTR decreased with age (particularly up to age 14). WHTR correlated less closely than WC with BMI (r = 0.65, 0.59 cf. 0.93, 0.91, for boys and girls respectively). CONCLUSION: Reference values and percentile curves for WC and WHRT of Chinese children and adolescents are provided. Both WC and WHTR are age dependent. Since the use of WHRT does not obviate the need for age-related reference standards, simple WC measurement is a more convenient method for central fat estimation than WHRT.

C-reactive protein in children with obstructive sleep apnea and the effects of treatment.

OBJECTIVE: To evaluate C-reactive protein (CRP) concentration in children with OSA and to determine the effects of treatment for OSA on its serum concentration. METHODS: Consecutive children with habitual snoring and symptoms suggestive of OSA were recruited. They completed a sleep apnea symptom questionnaire, underwent physical examination and an overnight polysomnography (PSG). Fasting serum CRP and lipid profile were taken after overnight PSG. OSA was diagnosed if obstructive apnea index (OAI)>1. RESULTS: One hundred forty-one children with a median (IQR) age of 10.8 (8.5-12.8) years were recruited. There were 96 boys and the commonest presenting symptoms were nocturnal mouth breathing, prone sleeping position and poor attention at school. Forty-five children were found to have OSA and those with moderate disease (OAI>5) had significantly higher CRP levels compared to their non-OSA counterparts [1.3 (0.8-3.6) vs. 0.7 (0.2-2.0), P=0.01]. Stepwise linear multiple regression analysis indicated that OAI was independently associated with CRP (beta coefficient=0.013, P=0.001). Sixteen children underwent treatment and there was significant reduction in their serum CRP after intervention [pre vs. post-CRP, 1.3 (0.6-4.1) vs. 0.4 (0.2-1.3), P=0.033]. A significant correlation was also demonstrated between change in CRP and change in OAI (r=0.593, P=0.042) following treatment for OSA. CONCLUSION: Children with OSA may have associated systemic inflammation as reflected by a raised CRP that decreased significantly following treatment.

Standard reference for the six-minute-walk test in healthy children aged 7 to 16 years.

RATIONALE: We have previously reported that the six-minute-walk test (6MWT) is a reliable and valid functional test for assessing exercise tolerance and endurance. There is a lack of pediatric standard reference for the 6MWT. OBJECTIVES: To construct height-specific standards for the 6MWT for children aged 7 to 16 years. METHODS: The anthropometric data, spirometric lung function, and six-minute-walk distance (6MWD) of Chinese children aged 7 to 16 years were prospectively measured using standardized protocols. The findings were used to construct height-specific standards for the 6MWT. The least mean square (LMS) method using maximum penalized likelihood was used to facilitate model fitting. Factors significantly associated with 6MWD were also determined. MEASUREMENTS AND MAIN RESULTS: From January 2005 to April 2006, a total of 1,445 subjects were studied. The measured variables showed a normal distribution. Height-specific reference standards for 6MWT were constructed for both male and female children. Forward stepwise multiple regression analysis revealed height and difference in heart rate before and after the walk test to be important clinical variables associated with 6MWD. CONCLUSIONS: These 6MWD standards will provide useful references for the care of pediatric patients.