[Developmental characteristics on body composition in Chinese urban children and adolescents aged 3-17 years old].

Objective: To describe the body composition related developmental characteristics in Chinese children and adolescents aged 3-17 years. Methods: Data were obtained from the 'China Child and Adolescent Cardiovascular Health (CCACH) cross-sectional survey' in 2015, which including seven cities. Questionnaire survey, anthropometric measurements were carried out with body composition also measured, using the Hologic Discovery Dual Energy X-ray Absorptiometry (DXA) scanner. BMI, fat mass percentage (FMP), fat mass index (FMI) and fat free mass index (FFMI) were calculated. SAS 9.4 and SPSS 20.0 softwares were used for data analysis. Results: A total of 10 867 participants aged 3-17 years were involved in this study, including 5 512 boys (50.7%). FMP in boys decreased obviously between 10-15 years old[beta=-1.811 (95%CI: -1.987 - -1.635)]. FMP in girls decreased between 3-7 years old[beta=-0.896 (95%CI: -1.100 - -0.691)] and increased obviously between 12-15 years old [beta=0.989 (95%CI: 0.753-1.224)]. In general, FMP in girls were higher than that in boys in every age group, except for the 9 and 10 years old groups ( all P<0.05). FFMI of boys was higher than that in girls at all ages. Differences on FFMI were getting bigger between boys and girls in the 11 years old group and above. FMI increased with age [boys: beta=0.033 (95%CI: 0.018-0.048); girls: beta=0.192 (95%CI: 0.181-0.204)] and intersected between genders. Adiposity rebound age was earlier in the obese group than that in both overweight and normal weight groups. FMI in normal weight boys decreased with age and remained lower than 5 kg/m(2), while FMI in overweight [beta=0.114 (95%CI: 0.091-0.136)] and obese [beta=0.211 (95%CI: 0.176-0.245)] boys increased with age. FMP in boys decreased with age from 10 years old in all weight status groups [normal weight: beta=-0.836 (95%CI: -0.924 - -0.748); overweight: beta=-1.090 (95%CI: -1.269 - -0.910); obese: beta=-1.144 (95%CI: -1.321- -0.967)]. BMI, FFMI, FMI in girls changed with age similarly in all weight status groups and increased from 8 years old[normal weight: beta=0.174 (95%CI: 0.165- 0.182); overweight: beta=0.325 (95%CI: 0.304-0.346); obesity: beta=0.447 (95%CI: 0.406-0.488)]. Changes in FMP in girls increased significantly with age after 12 years old [normal weight: beta=0.963 (95%CI: 0.851-1.074); overweight: beta=0.910 (95%CI: 0.695-1.125); obesity: beta=0.895 (95%CI: 0.569-1.221)]. In total, correlation indexes of BMI and FMI were strong (boys: r=0.767; girls: r=0.873) and were different in various weight status groups. Conclusions: The growth chart of BMI presented inconsistently with the different developmental characteristics of body fat, and gender. Measurement on body composition needs to be developed for children and adolescents to give more precisely assessment on growth and development of children.