Sleep duration or bedtime? Exploring the association between sleep timing behaviour, diet and BMI in children and adolescents

Objective:To determine whether sleep timing behaviour is associated with energy intake and diet quality in children and adolescents.Design:Cross- sectional analysis of nationally representative survey data.Sample:A total of 2200 participants of the 2007 Australian National Children's Nutrition and Physical Activity Survey aged 9-16 years with 2 days of food intake data, 4 days of use of time data and complete anthropometry. Participants were grouped into one of four sleep-wake behaviour categories: early bed-early rise (EE); early bed-late rise (EL); late bed-early rise (LE) and late bed-late rise (LL). The four categories were compared for body mass index (BMI) z-score, energy intake and diet quality assessed using the Dietary Guideline Index for Children and Adolescents. Analyses were adjusted for survey design, sociodemographic characteristics, sleep duration and physical activity level (PAL).Results:In adjusted multivariate regression models with sleep timing behaviour group as the independent variable, the 'LL' category compared with the 'EE' category had a higher BMI z-score (β=0.20, 95% confidence interval (CI) 0.06 to 0.34, P=0.007), and lower diet quality (β=-4.0, 95% CI-5.7 to-2.3, P<0.001). Children and adolescents who went to bed late also had a higher intake of extra foods (that is, energy-dense, nutrient-poor foods) while those whom went to bed early consumed more fruit and vegetables. Energy intake was associated with sleep duration (β=-4.5 kJ, 95% CI-6.7 to-2.4, P<0.001), but not sleep timing behaviour.Conclusion:Late bedtimes and late wake up times are associated with poorer diet quality, independent of sleep duration, PAL and child and sociodemographic characteristics.