Sleep behavior in relation to body mass index in primary school students.

Objective: This study aims to examine the relationship between multiple sleep behaviors in elementary school students-including occasional late bedtimes, social jet lag, and weekend oversleeping-and subsequent changes in their body mass index over 1 year. Methods: A one-year cohort study was carried out in Yangzhou City, Jiangsu Province, China, involving 3,213 students in grades one through five. At baseline and follow-up, trained staff obtained height and weight through standardized on-site measurements, and body mass index (BMI) was calculated. According to changes in BMI, students were assigned to four categories. Different sleep behaviors were collected through self-reported questionnaires. Multiple logistic regression was applied to assess the association between these sleep behaviors and BMI change. Results: The normal weight persistence group (C1), overweight obesity reduction group (C2), overweight obesity increase group (C3), and overweight obesity persistence group (C4) consisted of 1,508 (46.93%), 678 (21.10%), 191 (5.94%), and 836 (26.02%) children, respectively. Social jet lag varied across different groups of lower-grade children. The monthly maximum weekend bedtime-defined as the latest time a child went to bed on any weekend night within that month-was identified as a contributing factor to overweight and obesity. Weekday and weekend sleep opportunities influenced overweight and obesity among upper-grade students. Conclusion: The monthly maximum weekend bedtime is an important indicator related to the development and continuation of overweight and obesity in elementary school students. Sleeping opportunity assessments should clearly separate school days from weekends.