Objective: To understand the association between body fat distribution and calcaneal bone mineral density (BMD) in children and adolescents aged 6-16 years in Beijing. Methods: Children and adolescents were selected in 30 schools (8 primary schools, 21 middle schools and one 12-year education school) from Dongcheng, Tongzhou, Fangshan and Miyun districts of Beijing by using a stratified cluster sampling method from November 2017 to January 2018. A total of 15 030 students in grade 1 to 4 of primary school, grade 1 of junior and senior middle school were enrolled after excluding subjects who were not able to participate into this study due to trauma or other uncomfortable physical conditions or with missing key values or with diabetes and kidney diseases. Questionnaire survey, body composition and calcaneus bone mineral density were conducted. The relation of fat mass percentage (FMP), trunk to total fat ratio (TrTFR), trunk to limb fat ratio (TrLFR), limb to total fat ratio (LTFR) and viscera to total fat ratio (VTFR) with calcaneus BMD were assessed using the multivariate linear regression models after adjusting for possible confounding effects. The central fat distribution types were divided into 4 groups including type 1: both trunk fat and visceral fat greater than the sex-and age-specific internal P(75); type 2: barely trunk fat greater than P(75); type 3: barely visceral fat greater than P(75); type 4: both trunk fat and visceral fat greater than P(75). The central fat distribution types were included into the model in the form of dummy variables to analyze its relationship with calcaneal BMD. The sex-and age-specific z-scores of fat distribution indicators and BMD were calculated. Results: A total of 15 030 participants aged (11.4±3.3) years (50.2% boys) were involved in the analysis. In both genders, after adjusting for age, height, lean mass index, smoking, drinking, physical activity, milk intake, vitamin D and calcium supplementation, FMP, TrTFR, TrLFR and VTFR were negatively correlated with calcaneal BMD (all P value<0.05), while LTFR was positively associated with calcaneal BMD (all P values<0.05). Compared to the central fat distribution type 1, the regression coefficients (95% CI) of type 2, 3 and 4 were -0.253 (-0.418, -0.087), -0.385 (-0.567, -0.204) and -0.428 (-0.487, -0.369) in boys, respectively; the regression coefficients (95% CI) of type 3 and 4 were -0.158 (-0.301, -0.015) and -0.226 (-0.290, -0.163), respectively. Conclusion: Body fat distribution and central fat distribution in children and adolescents were correlated with calcaneus bone mineral density.
目的： 了解北京6~16岁儿童青少年体脂分布与跟骨骨密度的关联性。 方法： 于2017年11月至2018年1月，采用分层整群抽样的方法在北京市东城、房山、密云以及通州区选择30所学校（包括8所小学，21所中学和1所12年制学校），将小学1~4年级、初中1年级和高中1年级6~16岁学生作为研究对象，排除因外伤等身体不适不能参加体检及关键变量缺失和患有糖尿病、肾脏疾病的学生后，共纳入15 030名研究对象。进行问卷调查，测量体脂和跟骨骨密度。以跟骨骨密度为因变量，分别以体脂率（FMP）、躯干-全身脂肪比（TrTFR）、躯干-四肢脂肪比（TrLFR）、四肢-全身脂肪比（LTFR）、内脏-全身脂肪比（VTFR）为自变量，调整相关混杂因素后，采用多元线性回归进行分析；将中心性脂肪分布类型分成4组：分布类型1为躯干脂肪和内脏脂肪均<其相应性别-年龄别脂肪量的P(75)；分布类型2为单纯躯干脂肪≥其相应性别-年龄别脂肪量的P(75)；分布类型3为单纯内脏脂肪≥其相应性别-年龄别脂肪量P(75)；分布类型4为躯干脂肪和内脏脂肪均≥其相应性别-年龄别脂肪量P(75)，将分布类型采用哑变量形式纳入模型分析其与跟骨骨密度的关系。各体脂指标、跟骨骨密度均计算经性别-年龄别标准化转换后的Z评分。 结果： 15 030名研究对象年龄为（11.4±3.3）岁，男童占50.2%。调整年龄、身高、肌肉质量指数、吸烟、饮酒、运动、奶类摄入、维生素D和钙剂补充情况后，男童和女童FMP、TrTFR、TrLFR及VTFR与跟骨骨密度均呈负向关联（P<0.05），LTFR与跟骨骨密度呈正向关联（P< 0.05）；与分布类型1相比，男童中心性脂肪分布类型2、3和4与跟骨骨密度的β（95%CI）值分别为-0.253（-0.418，-0.087）、-0.385（-0.567，-0.204）和-0.428（-0.487，-0.369）；女童中心性脂肪分布类型3和4与跟骨骨密度的β（95%CI）值分别为-0.158（-0.301，-0.015）和-0.226（-0.290，-0.163）。 结论： 儿童青少年体脂分布和中心性脂肪分布与跟骨骨密度均有关联。.
Keywords: Body fat distribution; Bone mineral density; Child; Cross-sectional study.