Association of outdoor activity time and screen time with sleep for 36 to 54 months children in Kaifu District, Changsha: A birth cohort study.

Objectives: The prevalence rate of sleep problems in children in China is increasing in recent years. There are inconsistencies in the relationship between physical activity and sleep, and the impact of screen time on young children seems more obvious.This study aims to understand the current situation of outdoor activity time, screen time and sleep (total sleep duration, bedtime, and wake-up time) and the associations between outdoor activity time and screen time with sleep for children aged 36-54 months in Kaifu District of Changsha.
Methods: Using the cluster sampling method, 1 286 newborns delivered in 3 community health service centers in Kaifu District, Changsha from January to December 2015 were selected as the research subjects to establish a prospective birth cohort. According self-designed questionnaire and household follow-up to select 36, 42, 48, 54 months Children's data. The mixed linear model was used to explore the associations of outdoor activity time and screen time with sleep.
Results: The 36-54 months children's total sleep duration was decreased from 11.60 h/d to 10.92 h/d ( P <0.001); bedtime time delayed from 21:58 to 22:00 ( P =0.124); wake-up time advanced from 7:52 to 7:37 ( P <0.001); outdoor activity time was decreased from 2.58 h/d to 1.94 h/d ( P <0.001), and screen time was decreased from 1.28 h/d to 1.09 h/d ( P <0.001). With aging, the prevalence of sleep <10 h/d and outdoor activity time <2 h/d was increased significantly, and the prevalence of screen time ≥1 h/d was decreased ( P <0.05). Mixed linear models showed that longer outdoor activity time was related to increased total sleep duration ( β =0.22, 95% CI 0.00 to 0.44) and delayed wake-up time ( β =0.16, 95% CI 0.00 to 0.32), and longer screen time was related to delayed bedtime ( β =0.22, 95% CI 0.05 to 0.39) and wake-up time ( β =0.24, 95% CI 0.08 to 0.41). These associations were different in gender. Longer outdoor activity time was related to delayed wake-up time ( β =0.37, 95% CI 0.14 to 0.59) in boys, but not in girls ( β =-0.16, 95% CI -0.33 to 0.01). Longer screen time was associated with delayed bedtime ( β =0.40, 95% CI 0.09 to 0.63) and wake-up time ( β =0.33, 95% CI 0.15 to 0.51) in girls, but only related to delayed wake-up time ( β =0.29, 95% CI 0.06 to 0.52) in boys, and the degree of association was lower than that of girls.
Conclusions: Among children aged 36-54 months in Kaifu District, Changsha, there are problems including going to bed late and getting up late, insufficient physical activity, and long screen time. Outdoor activity time and screen time are related to sleep. Increasing outdoor activity time and reducing screen time can help to improve children's sleep.