DataSheet1_Seasonality of Children’s Height and Weight and Their Contribution to Accelerated Summer Weight Gain.pdf

Background: While children have been shown to have increased BMI during the summer compared to the school year, it is not known if this may be due to seasonal variations in height or weight separately.
Methods: Trained nurses measured heights (cm) and weights (kg) in a cohort of Kindergarteners (n = 7599) twice per year from the beginning of kindergarten through 5th grade. Variation in height and weight by season (school year vs. summer) was examined using separate mixed-effects models. Season, sex, and BMI trajectory group were tested as fixed effects. Random effects included repeated measurements of time, students nested within a school, intercept, and slope for growth over time. Similar models using BMIz as the outcome examined the interaction of height or weight with season.
Results: The rate of height gain was greater during the school year (∼Sept to April) compared to summer (∼April to Sept) (β = -0.05, SE = 0.013, p < 0.0001). The rate of weight gain did not differ seasonally. Height gain was more strongly associated with increased BMIz during summer compared to the school year (β =.02, SE = 0.005, p <0 .0001), mainly among children who remained healthy weight throughout elementary school (β = 0.014, SE = 0.003, p < 0.0001) and those who transitioned to a healthier weight status (β = 0.026, SE = 0.008, p = 0.004). We found a similar seasonal effect for the association between weight with BMIz among children who maintained a healthy weight status (β = 0.014, SE = 0.014, p < 0.0001). particularly among children who maintained a healthy weight status (β = 0.014, SE = 0.014, p < 0.0001).
Conclusion: This study indicates seasonality in children’s height gain, gaining height at a faster rate during the school year compared to the summer, while weight gain remained relatively more consistent throughout the year. Seasonality in height and weight gain had the greatest impact on BMIz among children with a healthy weight status. Future research with more frequent measurements is needed to better understand the seasonal regulation of children’s growth and weight gain.

研究背景：已有研究证实，儿童夏季的身体质量指数（BMI）高于学年期间，但目前尚不明确该差异是否分别由身高或体重的季节变化所导致。
研究方法：由经过培训的护士对7599名幼儿园儿童组成的队列进行身高（厘米，cm）与体重（千克，kg）测量，从幼儿园入园直至五年级阶段，每年开展两次测量。本研究采用独立的混合效应模型，分析身高与体重随季节（学年与夏季）的变化情况；将季节、性别及BMI轨迹组作为固定效应纳入模型，随机效应则包含重复测量时间、学校嵌套的学生群体、截距项以及随时间增长的生长斜率项。以BMI z分数（BMIz）为因变量的类似模型，用于检验身高或体重与季节的交互效应。
研究结果：学年期间（约9月至次年4月）的身高增长速率显著高于夏季（约4月至9月）（β=-0.05，标准误SE=0.013，p<0.0001）；而体重增长速率未呈现显著季节差异。与学年阶段相比，夏季的身高增长与BMIz升高的关联更强（β=0.02，SE=0.005，p<0.0001），该效应主要见于整个小学阶段均维持健康体重的儿童（β=0.014，SE=0.003，p<0.0001）以及体重状态向更健康方向转变的儿童（β=0.026，SE=0.008，p=0.004）。在维持健康体重状态的儿童中，体重与BMIz的关联也呈现类似的季节效应（β=0.014，SE=0.014，p<0.0001），尤其见于维持健康体重状态的儿童亚组（β=0.014，SE=0.014，p<0.0001）。
研究结论：本研究表明儿童身高增长存在季节节律，学年期间的身高增长速率快于夏季，而体重增长在全年相对更为稳定。身高与体重增长的季节效应对健康体重状态儿童的BMIz影响最为显著。未来需开展测量频率更高的研究，以更深入地阐明儿童生长与体重增长的季节调控机制。