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