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Children's Daily Time Use and Its Associations with Obesity and Mental Health among Shanghai's Primary-School Students
Yunting Zhang, Donglan Zhang, Fan Jiang
Background
A report from the Program for International Student Assessment (PISA) showed Shanghai students topped international education ranking, while concerns about their academic stress and declining physical fitness have increased. A growing body of literature demonstrated the link between children’s daily activities and academic performance. However, few studies have assessed the overall pattern of children’s daily time use in these activities and its relationships to their health, besides academic outcomes. Therefore, this study describes the overall time-use in different types of activities of children in Shanghai, with the purpose to find an optimal time allocation strategy to improve children’s health.
Data and Method
We conducted the Shanghai Children's Health and Development Study (SCHDS) in 2014. SCHDS is a population-representative survey of Shanghai's primary school students. 17466 children from grade 1 to 5 in 26 primary schools were randomly sampled from 7 districts. Students’ time spent on vigorous to moderate physical activities (VMPA), screen viewing, homework was assessed using the international Children's Leisure Activities Study Survey Questionnaire. Sleep time and duration was reported by parents. Body Mass Index (BMI) was objectively measured by medical professionals. Children's mental and behavioral health was measured using the validated Strength and Difficulties Questionnaire. The study also investigated a comprehensive list of variables including children's demographic characteristics, family structure and environment and medical conditions.
In descriptive analysis, we calculate the average time spent on VMPA, screen viewing, sleep and homework on both weekday and weekend. We then perform probit regressions to examine the relationships between time use for each activity and obesity and mental health status, adjusting for a set of covariates. Finally, we apply linear optimization based on the predicted probabilities to identify an optimal time allocation strategy.
Results
A complete sample of 8699 subjects is used for the analysis. The population-weighted average time is 1.77 hours/day for VMPA, 1.07 hours/day for screen viewing, 9.24 hours/day for sleep, and 1.37 hours/day for homework. All time-uses differ significantly between weekday and weekend. More than 2 hours of screen time predicts 3.91% (95% confidence interval (CI): 1.24% - 6.58%) increase in obesity, comparing to less than 1 hour. More than 10 hours of sleep predicts 7.15% (95% CI: -9.77% - -4.54%) decrease in the likelihood of being obese, as compared to less than 9 hours of sleep. Time-use in VMPA, screen viewing, sleep and homework is significantly associated with mental health. Finally, to minimize the probability of obesity and mental health abnormality, given the assumption that students spending 10 hours on classes, meals and light physical activities, the optimal time allocation strategy is >=10 hours for sleep, 1-2 hours for VMPA, <2 hour for screen viewing and 1-2 hours for homework.
Conclusion
Results from SCHDS confirmed the relationships between children’s daily time use and their physical and mental health. Guidelines for school-aged children should consider the overall time-use to promote children’s health and development.