Sleep, physical activity and BMI in six to ten-year-old children measured by accelerometry: a cross-sectional study

Mirjam Ekstedt,Claude Marcus,Michael Ingre,Gisela Nyberg,Örjan Ekblom

doi:10.1186/1479-5868-10-82

Abstract

BackgroundThe aim of this study is to describe the relationship between objective measures of sleep, physical activity and BMI in Swedish pre-adolescents. The day-to-day association between physical activity and sleep quality as well as week-day and weekend pattern of sleep is also described.MethodWe conducted a cross sectional study consisted of a cohort of 1.231 children aged six to ten years within the Stockholm county area. Sleep and physical activity were measured by accelerometry during seven consecutive days. Outcome measures are total sleep time, sleep efficiency, sleep start and sleep end; physical activity intensity divided into: sedentary (<1.5 METS), light (1.5 to 3 METS) and moderate-to-vigorous (> 3 METS); and Body Mass Index standard deviations score, BMIsds.ResultsTotal sleep time decreased with increasing age, and was shorter in boys than girls on both weekdays and weekends. Late bedtime but consistent wake-up time during weekends made total sleep time shorter on weekends than on weekdays. Day-to-day within-subject analysis revealed that moderate-to-vigorous intense physical activity promoted an increased sleep efficiency the following night (CI < 0.001 to 0.047), while total sleep time was not affected (CI -0.003 to 0.043). Neither sleep duration (CI -0.024 to 0.022) nor sleep efficiency (CI -0.019 to 0.028) affected mean physical activity level the subsequent day. The between-subject analysis indicates that the sleep of children characterized by high moderate-to-vigorous physical activity during the day was frequently interrupted (SE = -.23, P < .01). A negative association between BMIsds and sleep duration was found (-.10, p < .01).ConclusionsShort sleep duration was associated with high BMI in six to ten year old children. This study underscores the importance of consistent bedtimes throughout the week for promoting sleep duration in preadolescents. Furthermore, this study suggests that a large proportion of intensive physical activity during the day might promote good sleep quality.

Highlights

The aim of this study is to describe the relationship between objective measures of sleep, physical activity and BMI in Swedish pre-adolescents
Total sleep time decreased with increasing age, and was shorter in boys than girls on both weekdays and weekends
Day-to-day within-subject analysis revealed that moderate-to-vigorous intense physical activity promoted an increased sleep efficiency the following night (CI < 0.001 to 0.047), while total sleep time was not affected (CI −0.003 to 0.043)

Summary

Introduction

The aim of this study is to describe the relationship between objective measures of sleep, physical activity and BMI in Swedish pre-adolescents. Despite a growing body of evidence demonstrating an association between short sleep duration and current and future obesity in children aged 0–16 years [3,6,7,8,9,10,11], the causal relationship is still unclear. It is not known whether sleep loss affects the risk of obesity directly, through changes in function and levels of metabolic hormones such as glucagon-like peptide-1 [12] resulting in increased food intake, or if common behavioral or environmental factors such as hypo- or hyperactivity [13] and other types of stressors are involved, causing both sleep and weight disturbances [14,15]. Adults [16] and adolescents [17] seem more often to make up for a daily sleep deficit with longer weekend sleep, but the impact of sleep variability over the days of the week has rarely been studied among preadolescents

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