Associations of diarised sleep onset time, period and duration with total and central adiposity in a biethnic sample of young children : the Born in Bradford observational cohort study

OBJECTIVES: To investigate associations of parent-reported sleep characteristics with adiposity levels in a biethnic sample of young children. DESIGN: A cross-sectional observational study. SETTING: The Born in Bradford 1000 study, UK. PARTICIPANTS: Children aged approximately 18 months (n=209; 40.2% South Asian; 59.8% white) and 36 months (n=162; 40.7% South Asian; 59.3% white). PRIMARY AND SECONDARY OUTCOME MEASURES: Children's body mass index (BMI) z-score, sum of two-skinfolds (triceps and subscapular) and waist circumference. Adjusted regression was used to quantify associations of sleep parameters with adiposity stratified by ethnicity and age group. The results are beta coefficients (95% CIs) and unless otherwise stated represent the difference in outcomes for every 1-hour difference in sleep parameters. RESULTS: The average sleep onset time was markedly later in South Asian (21:26±68 min) than white children (19:41±48 min). Later sleep onset was associated with lower BMI z-score (-0.3 (-0.5 to -0.0)) and sum of two-skinfolds (-1.5 mm (-2.8 mm to -0.2 mm)) in white children aged 18 months and higher BMI z-score in South Asian children aged 36 months (0.3 (0.0-0.5)). Longer sleep duration on weekends than weekdays was associated with higher BMI z-score (0.4 (0.1-0.8)) and waist circumference (1.2 cm (0.3-2.2 cm)) in South Asian children aged 18 months, and later sleep onset on weekends than weekdays was associated with larger sum of two-skinfolds (1.7 mm (0.3-3.1 mm)) and waist circumference (1.8 cm (0.6-2.9 cm)). Going to sleep ≥20 min later on weekends than weekdays was associated with lower waist circumference in white children aged 18 months (-1.7 cm (-3.2 cm to -0.1 cm)). CONCLUSIONS: Sleep timing is associated with total and central adiposity in young children but associations differ by age group and ethnicity. Sleep onset times and regular sleep schedules may be important for obesity prevention.