Objective: To examine the association between family socioeconomic status (SES) and body mass index (BMI) z-score of children and adolescents, and the mediating effect of milk intake in this association.
Methods: In the study, 2 496 students and their parents were selected from 16 schools (4 urban middle schools, 4 rural middle schools, 4 urban primary schools, and 4 rural primary schools) using a stratified cluster sampling method. The frequency and amount of weekly milk intake from the 7-day Food Records reported by the students were extracted. The parents' education and household income were the indicators of family SES. The mediating effect of milk intake between family SES and BMI z-score of children and adolescents were tested using the PROCESS add-on SPSS software.
Results: Parents' education level and household income were positively correlated with BMI z-score of children and adolescents (P=0.001 and 0.038, respectively). The overall average daily intake of milk was (0.92±0.84) servings, and the frequency was (4.43±2.70) days per week. The students of primary school, in urban areas, with higher parents' education level, with higher household income, and being non-obese were likely to have higher frequency and amount of milk intake. Milk intake was one of the mediating factors in the relationship between family SES and BMI z-score of children and adolescents. Specifically, the mediating effect of the frequency of milk intake accounted for -6.57% and -10.21% of the total effects of the association between the parents' education and the household income with BMI z-score of children and adolescents, respectively. The mediating effect of the daily intake of milk accounted for -3.63% and -5.86% of the total effects of the association between the parents' education and the household income with BMI z-score of children and adolescents, respectively.
Conclusion: The milk intake of Chinese children and adolescents still needs to be improved. High family SES was found to contribute to high BMI z-score, mediated by the milk intake which was the protective factors of BMI z-score. Further research is needed to study other dietary or physical exercise behaviors that mediate the relationship between family SES and BMI z-score of children and adolescents in order to adopt more targeted interventions.
目的: 研究家庭社会经济状况(socio-economic status, SES)与儿童青少年体重指数(body mass index, BMI)z评分的关系，以及家庭SES如何通过影响儿童青少年的饮奶行为作用于儿童青少年的BMI z评分。
方法: 采用分层整群抽样的方法按城市中学、城市小学、乡村中学、乡村小学各抽取4所学校，共有2 496名学生及其家长作为研究对象。通过7 d饮食行为问卷得到学生每周饮奶次数和日均饮奶份数。采用父母最高文化程度和家庭月收入反映家庭SES。利用统计软件SPSS 18.0中PROCESS插件程序分析儿童青少年饮奶行为在家庭SES和儿童青少年BMI z评分关系中的中介作用。
结果: 父母最高文化程度、家庭月收入与儿童青少年BMI均呈正相关(P值分别为0.001, 0.038)。总人群的日均饮奶份数为(0.92±0.84)份，每周饮奶次数为(4.43±2.70)次。小学生、城市、父母最高文化程度、家庭月收入、非肥胖与每周饮奶次数和日均饮奶份数多有关(P值均 < 0.05)。儿童青少年饮奶行为在家庭SES与儿童青少年BMI z评分关系中起部分中介作用。每周饮奶次数在父母最高文化程度和家庭月收入与BMI z评分关系中的中介效应占总效应的比例分别为-6.57%和-10.21%。日均饮奶份数在父母最高文化程度和家庭月收入与BMI z评分关系中的中介效应占总效应的比例分别为-3.63%和-5.86%。
结论: 我国儿童青少年饮奶行为还有待提高; 儿童青少年饮奶行为在家庭高SES与儿童青少年高BMI z评分关系中起部分中介作用，为儿童青少年肥胖的保护因素; 未来还需对其他饮食或运动行为进行研究，以探索家庭SES与儿童青少年BMI z评分关系之间的机制，从而进行有针对性的干预。
Keywords: Body mass index; Family socioeconomic status; Milk intake.