Sleep duration, sleep-wake schedule regularity, and body weight in Hong Kong Chinese adolescents

The relationship between sleep duration and sleep-wake disturbances and body weight has been under-researched in adolescents. This is a cross-sectional school-based study of 327 adolescents with an average age of 14.5 years. Between-group, correlational, and hierarchical regression analyses were performed to investigate the relationship between body mass index (BMI) and sleep duration, sleep quality, daytime sleepiness, and sleep-wake schedule regularity. There was no significant difference between overweight/obese and normal weight adolescents in sleep quality, daytime sleepiness, sleep duration during the weekdays and weekend, and mean sleep duration; however, overweight/obese adolescents had significantly later bedtimes (average 25 min) during weekends than did normal weight subjects. After controlling for depression and sociodemographic and lifestyle factors, shorter mean time in bed and greater weekend delay in bedtime were independent predictors of higher BMI z-scores. The contribution of chronotype to sedentary lifestyle, eating behaviour, and body weight is worth further investigation.