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

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: less than or equal to 10 h, 5.4% (95% Cl 4.1 - 7.0), 10.5 - 11.0 h, 2.8% (95% Cl 2.3 - 3.3), and greater than or equal to 11.5 h, 2.1% (95% Cl 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, socio-demographic and lifestyle factors. The adjusted odds ratio for obesity were: for sleeping 10.5 - 11.0 h, 0.52 (95% Cl 0.34 - 0.78) and 0.46 (95% Cl 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.