Melyssa Roy1, Jillian J Haszard2, Jennifer S Savage3, Kimberly Yolton4, Dean W Beebe4, Yingying Xu4, Barbara Galland5, Ian M Paul6, Jodi A Mindell7, Seema Mihrshahi8, Li Ming Wen8,9, Barry Taylor10, Rosalina Richards11, Lisa Te Morenga12, Rachael W Taylor1. 1. Department of Medicine, University of Otago, Dunedin, New Zealand. 2. Biostatistics Centre, University of Otago, Dunedin, New Zealand. 3. Center for Childhood Obesity Research and Department of Nutritional Sciences, Pennsylvania State University, State College, Pennsylvania, USA. 4. Department of Pediatrics, Cincinnati Children's Hospital Medical Center and University of Cincinnati College of Medicine, Cincinnati, Ohio, USA. 5. Department of Women's and Children's Health, University of Otago, Dunedin, New Zealand. 6. Department of Pediatrics, Penn State College of Medicine, Hershey, Pennsylvania, USA. 7. Saint Joseph's University and Children's Hospital of Philadelphia, Philadelphia, Pennsylvania, USA. 8. Centre of Research Excellence in the Early Prevention of Obesity in Childhood, School of Public Health University of Sydney, New South Wales, Sydney, Australia. 9. Health Promotion Unit, Population Health Research and Evaluation Hub, Sydney, New South Wales, Australia. 10. Office of the Dean, University of Otago, Dunedin, New Zealand. 11. Centre for Pacific Health, Va'a o Tautai, University of Otago, Dunedin, New Zealand. 12. School of Health, Victoria University of Wellington, Wellington, New Zealand.
Abstract
BACKGROUND: Although sleep duration is a risk factor for obesity in young children, less is known about other aspects of sleep health, including bedtime, on obesity risk. OBJECTIVE: To determine whether bedtime is associated with body mass index (BMI) z-score or obesity risk in children ages 2 to 5 years, and to determine if associations are independent of sleep duration. METHODS: Cohort analyses were undertaken using three early life obesity prevention trials (POI, INSIGHT, Healthy Beginnings) and a longitudinal cohort study (HOME). Bedtime was assessed by questionnaire and BMI through clinical measurement between 2 and 5 years in 1642 children. Adjusted regression models examined whether BMI z-score and obesity (BMI z-score ≥ 2) were associated with bedtime, nocturnal sleep time and 24-hour sleep time. A discrete mixture model categorized children into bedtime trajectory groups across time points. RESULTS: Bedtime was inconsistently associated with BMI z-score. Although each hour later of bedtime was associated with greater odds of obesity at ages 3 (OR; 95% CI: 1.05; 1.003, 1.10) and 5 (1.35; 1.08, 1.69) years, odds were attenuated after adjustment for nocturnal or 24-hour sleep time. Longer nocturnal sleep duration at 2 years was associated with lower odds of obesity (OR 0.90; 0.86, 0.94), as was longer 24-hour sleep duration at 3 years in girls (0.70; 0.62, 0.78). BMI z-score and odds of obesity were not significantly different between 'early to bed' and 'late to bed' trajectory groups. CONCLUSIONS: Timing of bedtime appears inconsistently related to obesity in young children, possibly via influencing overall sleep duration.
BACKGROUND: Although sleep duration is a risk factor for obesity in young children, less is known about other aspects of sleep health, including bedtime, on obesity risk. OBJECTIVE: To determine whether bedtime is associated with body mass index (BMI) z-score or obesity risk in children ages 2 to 5 years, and to determine if associations are independent of sleep duration. METHODS: Cohort analyses were undertaken using three early life obesity prevention trials (POI, INSIGHT, Healthy Beginnings) and a longitudinal cohort study (HOME). Bedtime was assessed by questionnaire and BMI through clinical measurement between 2 and 5 years in 1642 children. Adjusted regression models examined whether BMI z-score and obesity (BMI z-score ≥ 2) were associated with bedtime, nocturnal sleep time and 24-hour sleep time. A discrete mixture model categorized children into bedtime trajectory groups across time points. RESULTS: Bedtime was inconsistently associated with BMI z-score. Although each hour later of bedtime was associated with greater odds of obesity at ages 3 (OR; 95% CI: 1.05; 1.003, 1.10) and 5 (1.35; 1.08, 1.69) years, odds were attenuated after adjustment for nocturnal or 24-hour sleep time. Longer nocturnal sleep duration at 2 years was associated with lower odds of obesity (OR 0.90; 0.86, 0.94), as was longer 24-hour sleep duration at 3 years in girls (0.70; 0.62, 0.78). BMI z-score and odds of obesity were not significantly different between 'early to bed' and 'late to bed' trajectory groups. CONCLUSIONS: Timing of bedtime appears inconsistently related to obesity in young children, possibly via influencing overall sleep duration.
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