Children who go to bed and wake up an average of 1 hour later on weekends vs. weekdays are more likely to have a higher body fat percentage, fat mass index, BMI and waist-to-hip ratio than children who maintain a consistent bedtime, according to findings from a cross-sectional study.
“In modern society, the rhythmicity of the circadian clock is often disrupted by social obligations, including work and school schedules,” Lee Stoner, PhD, MPH, of the department of exercise and sport science at the University of North Carolina at Chapel Hill, and colleagues wrote. “Social jet lag is simple to measure and may be a simple target for public health policy.”
Stoner and colleagues analyzed data from 341 children aged 8 to 10 years, recruited from schools in three major cities across New Zealand between April 2015 and April 2016 (50% girls; mean age, 10 years). Researchers assessed three sleep behaviors via parent/caregiver questionnaires: average sleep duration, sleep disturbances (estimated with the Children’s Sleep Habits Questionnaire) and social jet lag, measured as the difference in hours between the midpoint of sleep during work/school days and on weekend days. Researchers also assessed five dependent variables: body fat percentage, fat mass, fat mass index, waist-to-hip ratio and BMI.
Within the cohort, 29% of children were overweight and 40% had disturbed sleep. Most children (92%) slept for at least 9 hours per night, and total sleep duration did not differ between weekdays and weekend. However, all but two children went to bed a mean of 42 minutes later during weekends, and 97% awoke on average 42 minutes later during weekends vs. weekdays. Average social jet lag was 43 minutes, with 35% of children having at least 1 hour of social jet lag.
Researchers found that sleep duration was not associated with any variable, but sleep disturbances were associated with fat mass index (beta = 0.047; 95% CI, 0.002-0.093).
Social jet lag was associated with all adiposity variables, according to researchers. One hour of social jet lag was associated with a 3% increase in body fat, a 1.73-kg increase in fat mass, a 0.76-kg/m² increase in fat mass index, a 0.89-kg/m² increase in BMI and a 0.13 increase in waist-to-hip ratio, according to researchers.
“Independent of sleep duration or sleep disturbances, 1 hour of social jet lag was associated with five measures of adiposity, including 3% greater absolute body fat,” the researchers wrote. “While further studies are required to confirm causality, these preliminary findings suggest that social jet lag may be an important and measurable public health target in children.” – by Regina Schaffer
Disclosures: The authors report no relevant financial disclosures.