Reduced risk for overweight and obesity in 5- and 6-y-old children by duration of sleep—a cross-sectional study

International Journal of Obesity (2002) 26, 710–716 ß 2002 Nature Publishing Group All rights reserved 0307–0565/02 $25.00 www.nature.com/ijo PAPER Reduced risk for overweight and obesity in 5- and 6-y-old children by duration of sleep — a cross-sectional study R von Kries1, AM Toschke1, H Wurmser1, T Sauerwald2 and B Koletzko2* 1 Institute for Social Paediatrics and Adolescent Medicine, Ludwig-Maximilians University of Munich, Munich, Germany; and 2Dr von Haunersches Kinderspital, Ludwig-Maximilians University of Munich, Munich, Germany OBJECTIVE: To assess the relationship between sleep duration and adiposity in 5- and 6-y-old Bavarian children. DESIGN: Cross-sectional study. SUBJECTS: A total of 6862 German children aged 5 – 6 y participating in the obligatory health examination in Bavaria, southern Germany. MEASUREMENTS: Routine data were collected on the height and weight of children at the time of school entry in six public health offices in 1999 and in another two in 2000. Body fat mass was estimated by BIA performed in three of those offices. An extensive questionnaire was given to all children’s parents in order to assess risk factors for overweight and obesity. The main outcome measures were overweight, defined by a body mass index (BMI) above the 90th centile and obesity, defined by a BMI above the 97th centile for the German children in Bavaria. Excessive body fat was defined as fat mass above the 90th centile for all German children seen in this survey. The main exposure was usual sleeping hours on week days. RESULTS: The prevalence of obesity decreased by duration of sleep:
10 h, 5.4% (95% CI 4.1 – 7.0), 10.5 – 11.0 h, 2.8% (95% CI 2.3 – 3.3), and  11.5 h, 2.1% (95% CI 1.5 – 2.9). Similar relations were found with the prevalence of overweight and excessive body fat. These effects could not be explained by confounding due to a wide range of constitutional, sociodemographic and lifestyle factors. The adjusted odds ratio for obesity were: for sleeping 10.5 – 11.0 h, 0.52 (95% CI 0.34 – 0.78) and 0.46 (95% CI 0.28 – 0.75) for sleeping 11.5 h. CONCLUSION: The effect of sleep duration on obesity in children reflects a higher body fat composition and appears to be independent of other risk factors for childhood obesity. International Journal of Obesity (2002) 26, 710 – 716. DOI: 10.1038=sj=ijo=0801980 Keywords: primary prevention; body mass index; Bavaria; Germany; epidemiology; logistic models  Introduction Obesity is associated with sleep disorders and with changes in the sleep structure.1 Recent studies reported an association between a short duration of sleep and overweight and obesity in 3-2 and 5-y-old children.3 The aim of our study was to answer the following questions: *Correspondence: Professor B Koletzko, Dr von Haunersches Kinderspital, Ludwig-Maximilians University of Munich, Lindwurmstr 4, 80337 Munich, Germany. E-mail: Received 17 March 2001  Is the link between longer total sleeping hours and overweight/obesity in children independent of other known risk factors for childhood obesity? Can this association for body mass index (BMI) be confirmed for high body fat estimated from bioelectrical impedance analysis (BIA) measurement, a better indicator of true adiposity? We analysed the association between sleep duration and overweight=obesity defined by BMI in a cross-sectional study enrolling 6862 children aged 5 – 6 y. A wide range of potentially confounding constitutional and constitutional, sociodemographic and lifestyle risk factors for childhood obesity were considered to estimate the independent impact of sleep duration. BIA measurements were performed in a subset (n ¼ 1706) of the population. Sleep duration and childhood obesity R von Kries et al Methods Study population and data sources Public health offices in eight out of 76 communities in Bavaria, who were willing to collaborate and were not involved in other studies, were invited to a questionnaire study on possible causes of childhood obesity during the 1999 (n ¼ 6) and the 2000 (n ¼ 2) school entrance health examinations. Two communities were excluded because of return rates of 25.5 and 49.1%. In six communities the return rates of the questionnaires were above 60%, allowing the data to be considered for further analyses. In these six communities the distributions of BMI, gender and number of siblings in the 1997 compulsory school entry health examination were similar to those in all regions of Bavaria, suggesting that the study region is representative for Bavarian children. The study region consists of one densely populated area (847 inhabitants=km2), the city of Ingolstadt, a population on the outskirts of the city of Augsburg (214 inhabitants=km2), and four rural areas (Miesbach, Günzburg, Kitzingen, and areas surrounding Regensburg) all with less than 200 inhabitants=km2. In these communities the overall return rate of the questionnaires was 75.9%. The total number of completed questionnaires was 7754. The analysis was confined to the 5-y-old (5.00 – 5.99 y; n ¼ 2109) and 6-y-old (6.00 – 6.99 y; n ¼ 4753) German children with information on height and weight, which were measured as part of the routine health examination, leaving 6862 questionnaires for the analyses. Overweight was defined as BMI > 90th percentile and obesity as BMI > 97th percentile. The reference values for BMI were based on the age- and sex-specific distribution in 115 530 German children aged 5.00 – 6.99 y investigated during the 1997 school health examination in Bavaria.4 The BMI cut-off values for the 90th and 97th percentile in the widely used reference values from France5 were below the respective actual BMI cut-off values in Bavaria, which are likely to reflect a BMI increase in German children.6 We attempted to analyse the relationship of sleeping hours to the extremes of the present distribution of BMI-values ( > 90th= > 97th percentile) in Bavarian children. Fat mass was estimated by BIA (Tanita, TBF-300) in three of eight public health offices according to Deurenberg et al.7 High body fat was defined as fat mass above the 90th age- and gender-specific percentile in the population studied here (n ¼ 1706). Questionnaire The questions on sleep were: ‘When does your child usually go to bed during the week? with the options (a) before 8 pm, (b) between 8 and 9 pm, (c) between 9 and 10 pm, (d) between 10 pm and 11 pm and (e) later than 11 pm; and ‘When does your child usually get up in the morning during the week?’ with the options (a) before 6 am, (b) between 6 and 7 am, (c) between 7 and 8 am and (d) after 8 am. If the bedtime or time for getting up had been given as the 711 interval, for example, ‘between 7 and 8 am’, the time was set as the lower figure plus 30 min. If the time had been given as before or after an hour the time was set as this specific hour (eg before 6 am was set as 6 am). The sleeping time was calculated by the difference between bedtime and time for getting up. We c (...truncated)