0750 Earlier bedtimes mediate the effect of a brief behavioral intervention on children’s BMIz

We demonstrated that a brief behavioral intervention enhanced children’s sleep; those with clinically meaningful improvements in sleep (> 30 m/night), had improvements in body mass index (BMI) and BMI z-scores (BMIz). Given emerging evidence regarding the potential importance of not only sleep duration but sleep timing (i.e., bedtimes) for obesity risk reduction, we explored whether sleep duration and/or sleep timing mediated effects of intervention on BMI and BMIz. We hypothesized that the effect of the intervention on 8-week BMI/BMIz would be mediated by earlier bedtimes and longer sleep duration at 2 weeks post-randomization.

Participants were 71 children 8-11 years old (mean (SD) age = 9.72 (1.00); 69% female; mean (SD) BMIz = 0.91 (0.935)) who slept < 9.5 h/night and were randomized to a 4-session behavioral intervention to increase nocturnal sleep duration (primarily via advancing bedtimes) or to a control (4 sessions; continue with sleep as usual). Sleep was assessed via 7-day actigraphy; height and weight were measured to calculate BMI/BMIz at baseline, 2- and 8-weeks post randomization. We assessed mediation using the medflex R package. Models predicting 8-week BMIz and BMI controlled for baseline BMIz and BMI, respectively. Duration (mean actigraph sleep period) and bedtime (mean actigraph sleep onset) were entered as continuous variables in models.

Relative to control, the behavioral intervention decreased children’s 8-week BMIz by -0.027 (SE = 0.013) via its effect on week 2 bedtimes (z = -2.066, p = 0.039). There was no direct effect of intervention on 8-week BMIz (z = 1.584, p = 0.113), and although of marginal significance, week 2 sleep duration did not mediate effects of intervention on 8-week BMIz (z = -1.937, p = 0.053). Findings focused on BMI, although consistent, did not reach statistical significance.

A behavioral intervention designed to enhance school-aged children’s nocturnal sleep had a positive impact on children’s weight status via its effect on bedtimes, and to a lesser degree, sleep duration. Findings add to emerging work supporting the potential importance of sleep timing in weight regulation.

R01HL092910; P20GM139743