Lee Stroner, Nicholas Castro, Leigh Signal, Paula Skidmore, James Faulkner, Michelle Williams, Sally Lark
Why did you do this study?
Poor sleep behaviour, along with physical inactivity and poor diet, has been associated with childhood obesity. Several aspects of sleep may be important, including sleep duration, sleep disorders and, more recently, something called “social jet lag”. A recent meta-analysis, which included 35,540 children, reported that in children short sleep (i.e., below the recommend number of hours recommend by the National Sleep Foundation) was associated with a 71% (odds ratio [OR]: 1.71, 95%CI: 1.36-2.14) greater likelihood of obesity. Similarly, several studies have reported an association between sleep disorders and obesity in children. However, while social jetlag has been associated with being overweight (OR: 3.30, 95%CI: 2.51-4.33) in a group of over 65,000 European adults, no known studies have examined whether obesity is associated with social jetlag in children, nor has any study in Children simultaneously examined the importance of sleep duration, sleep disorders and social jetlag.
Sleep–wake and metabolism cycles, which are tightly interconnected at the molecular level, are regulated by the circadian clock. In modern society, the rhythmicity of the circadian clock is often disrupted by social obligations, including work and school schedules. Social jetlag is the discrepancy between an individual’s circadian clock and social rhythms, and is measured as the difference in hours between the midpoint of sleep at work/school and free days. Social jetlag is simple to measure, and a potentially simple health behaviour for which public health policy can be developed. Therefore, the purpose of this study was investigate whether sleep duration, sleep disorders and social jetlag are associated with body composition in pre-adolescent children
What did you do and what did you find in this study?
This cross-sectional study recruited 341 children (50% Female) aged 8–10 years from three representative sample sites across New Zealand. Body composition was estimated four ways: body fat (%), fat mass index (FMI, kg/m2), waist to hip ratio (WHR), and body mass index (BMI, kg/m2). The three sleep variables of interest were: average sleep duration, sleep disorders, and social jetlag. Sleep duration was recorded using a parent-reported, single item habitual school/weekday sleep survey. Sleep disorders were estimated using the Children’s Sleep Habits Questionnaire. Social jetlag was calculated as the absolute difference between the midpoints of sleep on weekdays versus weekend days.
Following adjustment for possible confounders, sleep duration was only associated WHR (β = -0.008, 95%CI: -0.015, 0.000), and sleep disorders was only associated with FMI (β = -0.034, 95%CI: 0.002, 0.067 kg/m2), while social jetlag was associated with all four body composition variables. A one hour increase in social jetlag was associated with a 2.98 % (95%CI: 0.41, 5.55 %) increase in body fat, 0.51 kg/m2 (95%CI: 0.11, 0.91 kg/m2) increase in FMI, a 0.90 kg/m2 95%CI: 0.21, 1.58 kg/m2) increase in BMI, and a 0.13 (95%CI: 0.003, 0.023 increase in WHR.
How do these findings impact the public?
While sleep duration, sleep disorders and social jetlag were all found to be associated with body composition in pre-adolescent children, the association between social jetlag and body composition was found to be particularly strong. This finding is important, because social jetlag is something which is relatively easy to fix, and this simple fix may result in important improvements in childhood health.
The goal of the Cardiometabolic Lab is continue this important work, and identify other simple lifestyle factors which improve the health of children.