上海市初中生课余时间安排与骨密度的关系

Relationship between the after-school schedule and bone mineral density in middle-school students in Shanghai

目的了解上海初中预备班学生课余时间安排与学生骨密度的关系,为采取针对性的干预措施提供依据。方法 2017年11月—2018年4月,分层随机整群抽取上海市3个区(市区、城郊结合区、郊区)6所初中共18个班级初中预备班518名学生,对学生和家长分别进行问卷调查,对学生进行体格检查和超声骨密度测定。结果学生周末校外文化课培训时间为4.0(2.0,6.0)h,骨密度Z值为0.3(-0.7,1.0)。平滑曲线拟合显示,周末校外文化课培训时间与学生骨密度Z值呈非线性相关。根据拟合结果,采用两段式多元线性回归分析发现,当周末校外文化课培训时间<4.5 h,培训时间与骨密度呈负相关(β=-0.11,P=0.01);当周末校外文化课培训时间≥4.5 h,培训时间与骨密度的相关无统计学意义(β=0.02,P=0.65)。家长问卷和学生问卷均显示,学生课余户外活动时间与骨密度Z值呈非线性关系。当每天户外活动时间≥45 min,户外活动时间与骨密度呈正相关(P<0.05);当每天户外活动时间<45 min,户外活动时间与骨密度相关无统计学意义(P>0.05)。结论学生周末校外文化课培训时间短或平时户外活动时间长,与骨密度值水平升高相关。建议合理安排初中生课余时间,校外文化课培训时间要适量,并加强户外运动,促进学生的体格发育。

Objective To investigate the relationship between after-school schedule and bone mineral density in middle-school students in Shanghai, to provide a reference for taking targeted measures. Methods From November 2017 to April 2018,eighteen classes of six middle schools in Shanghai(from urban districts, urban-suburb combined districts and suburban districts, respectively) were selected based on cluster random sampling. In each school, 2-4 classes were further randomly chosen in the 6 th grade. Questionnaires were completed by 518 students and their parents, as well as physical examination and bone mineral density assessment. Results The average time spent on after-school academic learning during weekends was 4.0(IQR: 2.0, 6.0) h. The Z-score of bone density was 0.3(IQR:-0.7, 1.0). The smooth curve fit model showed a non-linear relationship between after-school academic learning time during weekends and the Z-scores of bone mineral densities. A two-stage multiple linear regression analysis was further applied according to the fit results, and the results showed that when total after-school academic learning time <4.5 hours during weekends, the learning time was inversely correlated with the bone density Z-scores(β=-0.11,P=0.01), and when the learning time ≥4.5 hours, there was no significant correlation between the learning time and bone density Z-scores(β=0.02, P=0.65). Parent and student questionnaires showed that there was a non-linear relationship between students’ daily time spent on outdoor sports-related activities and bone density Z-scores. When time spent on the outdoor activities ≥45 minutes per day, outdoor activities were positively correlated with bone density Z-scores(P<0.05). However, when the time spent on outdoor activities <45 minutes per day, there was no significant relationship between outdoor activities and bone density Z-scores(P>0.05). Conclusion Too much time on after-school academic learning during weekends or limited time on outdoor activities are both related to impaired bone mineral densities. Therefore, a reasonable after-school schedule for middle-school students is important for physical development, especially during weekends.