OBJECTIVES To study the association between early-life factors (including birth weight, method of birth, gestational age, and history of gestational metabolic disorders) and pubertal timing in girls. METHODS The stratified cluster sampling method was used to select the girls in grades 2-3 and 7-8 from three primary schools and three middle schools in Guangzhou, China from March to December, 2019, and breast development was examined for all girls. A questionnaire survey was performed to collect the information on early-life factors. The multivariate logistic regression model was used to evaluate the association of gestational metabolic disorders, birth weight, method of birth, and gestational age with pubertal timing in girls. The Bootstrap method was used to assess the mediation effect of body mass index (BMI) (Z score) between high birth weight (≥4 000 g) and pubertal timing. RESULTS A total of 1 665 girls were enrolled, among whom 280 (16.82%) were judged to have early pubertal timing. The multivariate logistic regression analysis showed that high birth weight was associated with the increased risk of early pubertal timing (OR=2.12, 95%CI: 1.19-3.66, P=0.008). Nevertheless, no significant association was observed between other early-life factors and pubertal timing (P>0.05). The OR for the mediation effect of BMI (Z score) between high birth weight and early pubertal timing was 1.25 (95%CI: 1.09-1.47), accounting for 29.33% of the total effect of high birth weight on early pubertal timing. CONCLUSIONS High birth weight is associated with the increased risk of early pubertal timing in girls, and overweight/obesity may play a partial mediating role in the association between high birth weight and early pubertal timing in girls.

Objective An ongoing debate surrounds the relationship between body composition and pubertal timing, in particular for boys. This cross-sectional study aimed to investigate the association of body composition with pubertal timing among children and adolescents. Methods A total of 1,493 boys and 1,261 girls who entered puberty were enrolled in Guangzhou, China. Tanner stages were evaluated by examination of breast development for girls and testicular volume for boys. Fat mass (FM) and fat-free mass (FFM) were determined by bioelectrical impedance analysis. Parameters for body composition were transformed into age-and gender-specific Z-scores. The association of body composition with pubertal timing was examined using multinomial logistic regression with inverse probability weighting (IPW) based on the propensity score. Results For boys, IPW analysis showed Z-scores of body fat percentage (BF%) and FM index (FMI) were negatively associated with early puberty (OR = 0.75, 95% CI = 0.64–0.87; OR = 0.74, 95% CI = 0.63–0.88). As for girls, in contrast to boys, positive associations were seen between BF% and FMI with early puberty (OR = 1.39, 95% CI = 1.19–1.64; OR = 1.59, 95% CI = 1.33–1.90). With respect to appendicular skeletal muscle mass index (ASMI), there was a positive association with early puberty and a negative one with late puberty in boys (OR = 1.26, 95% CI = 1.07–1.49; OR = 0.82, 95% CI = 0.69–0.99). Conclusion There is a positive association of FM with early puberty for girls while negative for boys. FFM yields a positive association with early puberty and a negative one with late puberty in boys, but not in girls. Our findings highlight the gender differences in the connection between body composition and pubertal onset.

目的 探讨出生体重及分娩方式对小学生超重肥胖和腹型肥胖的影响,为预防儿童肥胖提供依据.方法 依托广州市中小学生常规体检,采用分层整群抽样方法,抽取3所小学3 361名学生,对学生及家长进行问卷调查.应用Logis-tic回归模型分析分娩方式、出生体重与学生超重肥胖和腹型肥胖的关系.应用相乘交互项和Delta法探讨交互作用.结果 广州市小学生的超重肥胖率为21.33％,腹型肥胖率为12.08％.多因素Logistic分析表明,与顺产的学生相比,经剖宫产者的超重肥胖风险增加了44％(OR= 1.44,95％CI=1.16～1.80);高出生体重的学生超重肥胖风险较正常体重者增加62％(OR=1.62,95％CI=1.09～2.42).调整多因素后,未观察到出生体重和出生方式与学生腹型肥胖之间的关联性(P值均＞0.05).经剖宫产出生与父母肥胖对学生的超重肥胖(RERI=0.33,95％CI=0.02～0.65)和腹型肥胖(RER1=0.39,95％CI= 0.12～0.65)存在相加交互作用.结论 剖宫产及高出生体重与小学生超重肥胖风险增高有关联.剖宫产出生方式与父母肥胖可能协同促进儿童肥胖发生.

Objective:To analyze the current status of body composition and development patterns of children and adolescents aged 6-17 years in Guangzhou.Methods:This was a cross-sectional study involving 8 169 school students from 3 elementary schools and 3 middle schools in Guangzhou from March to December 2019.The fat-free mass (FFM) and fat mass (FM) were measured by the bioelectrical impedance analysis.The fat-free mass index (FFMI) and fat mass index (FMI) were calculated via the height standardization. T test was used to compare quantitative variables between groups.The growth pattern of body composition was described using the Hattori chart. Results:A total of 4 431 boys (54.24%) and 3 738 girls (45.76%) were involved in this study.FFM and FM both increased with age between boys and girls.Except for boys aged 11 years, FFM in boys were significantly higher than that in girls with the same age (all P<0.05). In the age of 7-10 years, FM in boys were significantly higher than that in girls with the same age, while it was significantly higher in girls aged 12 years and older than that of boys at the same age (all P<0.05). The Hattori chart showed that the difference in body composition between genders occurred after 11 years old.In contrast to girls, increases in the weight and body mass index (BMI) in boys were mainly attributed to the FFM development. Conclusions:The development of FFM and FM in children and adolescents varies with age, accompanied with the gender-specific features.FFM in boys is higher than that of girls at the same age.The weight gain in boys is mainly attributed to the development of fat-free tissues, and thus the utility of BMI may lead to the overestimation of obesity.

Objective: To evaluate the consistency between bioelectrical impedance analysis (BIA) and dual-energy X-ray absorptiometry (DXA) in the measurement of body composition in children and adolescents aged 7-17 years. Methods: Fat-free mass (FFM) and fat mass (FM) were measured by both BIA and DXA in 1 431 children. The consistency between the methods was evaluated by intra-class correlation coefficients (ICCs) and Bland-Altman analysis. Logarithmic transformation of both measurements was performed before Bland-Altman analysis. Results: The ICCs for FFM were 0.986 and 0.974 and ICCs for FM were 0.854 and 0.926 in boys and girls respectively. In boys, the mean ratio of FFMs by BIA and DXA was 1.04, with limits of Agreement (LoA) of 0.95-1.14, and in girls, the mean ratio of FFMs by BIA and DXA was 1.02, with the LoA of 0.90-1.15. The LoA of FFM became narrower with age in both boys and girls. Both boys and girls had the wide LoAs for FM (0.40-1.27 and 0.48-1.48, respectively). Additionally, the LoA ranges for FFM and FM narrowed with the increase of BMI level in both boys and girls. Conclusion: For all children, BIA showed good consistency with DXA for FFM, whereas significant errors occurred in FM measurement. The consistency between BIA and DXA was better for obese children than for underweight or normal-weight children.

目的 探讨母亲孕期被动吸烟及女生超重肥胖对女生月经初潮年龄(age at menarche,AAM)的影响,为促进儿童青少年健康成长提供参考.方法 基于2016年中学新生体检工作,采用方便抽样法对广州市城区26所中学的2 722名初一女生进行问卷调查和体格检查.应用Logistic回归模型分析女生超重肥胖、母亲孕期被动吸烟与女生AAM的关系,采用四向分解法探讨女生超重肥胖在母亲孕期被动吸烟对女生AAM提前中的中介效应.结果 女生月经来潮率为90.82％(2 472/2 722).月经初潮中位年龄为12.00岁,初潮提前率为34.91％(863/2 472).与母亲孕期无被动吸烟的女生相比,母亲孕期被动吸烟≤3d/周的女生AAM提前的风险增加32％(OR调整=1.32,95％CI=1.06～ 1.65),母亲孕期被动吸烟＞3 d/周的女生AAM提前的风险增加58％(OR调整=1.58,95％CI=1.21～2.07).超重肥胖女生AAM提前的风险比非超重肥胖的女生增加77％(OR调整=1.77,95％CI=1.36～2.31).四向分解结果显示,母亲孕期被动吸烟导致女儿AAM提前的风险中,79.60％归因于母亲孕期被动吸烟的直接效应(P＜0.01).结论 女生超重肥胖和母亲孕期被动吸烟与女生AAM提前关联.母亲孕期被动吸烟对女生AAM提前的影响方式可能以直接作用为主.

目的 分析广州市中小学生奶及奶制品的摄入现状及其影响因素,为广州市促进学生奶及奶制品的摄入提供实证依据.方法 于2019年4-12月对广州市3所小学和3所中学的7 948名学生及其家长进行问卷调查,收集一般人口学信息及学生近1个月奶及奶制品(包括纯牛奶、酸奶、奶粉、奶酪和其他奶制品)的摄入频次和摄入量.采用x2检验和多因素Logistic回归模型对调查对象的奶及奶制品摄入量及其影响因素进行分析.结果 76.12％的学生奶及奶制品摄入频次＜7次/周,78.88％奶及奶制品摄入量不足(＜300 g/d),奶及奶制品摄入者每天摄入量的中位数为178.57 g/d.多因素Iogistic回归分析显示,女生、高中生奶及奶制品摄入量不足的风险更高[OR值(OR值95％CI)分别为1.42(1.26～1.60),1.86(1.51～2.28)];而父亲文化程度为大专及以上(OR=0.75,95％CI=0.59～ 0.94)、母亲文化程度为高中及以上(高中:OR=0.75,95％CI=0.61～0.93;大专及以上:OR=0.58,95％CI=0.46～ 0.72)和家庭年收入≥20万元(OR=0.77,95％CI=0.64～0.92)的学生更可能足量摄入奶及奶制品.结论 广州市中小学生奶及奶制品摄入率高,但摄入量明显不足.应加强对学生和家长的营养健康教育,重点关注女生和高年级学生,促进中小学生奶及奶制品的摄入.