Prevalence of adiposity and its association with sleep duration, quality, and timing among 9-12-year-old children in Guangzhou, China

Background: Short sleep duration has been reported to be associated with obesity in children, but findings are not consistent. Since few studies have examined the relationship between more complex sleep characteristics and obesity, we examined the association between adiposity and self-reported sleep duration, bedtime, and sleep quality in 9-12-year-old Chinese children using multilevel mixed models. Methods: 5518 children aged 9-12 years were recruited from 29 randomly selected primary schools in Guangzhou, China in 2014. Standardized questionnaires were used to obtain data to estimate sleep duration on typical weekdays and weekends. Sleep quality data were collected using the Children's Sleep Habits Questionnaire (CSHQ). Trained researchers undertook measurements of weight, height, and waist circumference (WC) for all participating children. Body mass index (BMI) z-scores were derived using the World Health Organization (WHO) child growth reference, and children were classified as overweight or obese using _1 and _2 SD as cut-offs, respectively. Percentage body fat (BF%) was calculated using bioelectrical impedance. Results: Longer sleep duration was inversely associated with BMI z-score (beta= -0.16, p < 0.05), WC (beta= -1.11, p < 0.05) and later bedtime was associated with higher BMI z-score (beta= 0.03, p < 0.05), WC (beta= 1.72, p < 0.001), and BF% (beta= 0.15, p < 0.05) in multivariable multilevel mixed models, after adjustment for age, gender, physical activity, parental education level, and average monthly income. No association was seen between sleep quality and adiposity. Conclusion: Shorter sleep duration and later bedtime are associated with higher adiposity indices in early adolescents from southern China. (C) 2017 The Authors. Publishing services by Elsevier B. V. on behalf of The Japan Epidemiological Association.