Sleep duration and overweight in European children: is the association modified by geographic region?

STUDY OBJECTIVES: To investigate differences and a possible effect modification by geographical region in the association between sleep duration and overweight. DESIGN: Cross-sectional. SETTING: Primary schools and preschools in 8 European countries. PARTICIPANTS: 7867 children aged 2 to 9 years. INTERVENTIONS: Not applicable. MEASUREMENTS: Nocturnal sleep duration was assessed as part of a parental 24-h recall. Height and weight were measured by standardized procedures across centers. Data on personal, social, environmental and behavioral factors were collected using a standardized parental questionnaire. RESULTS: Sleep duration differed (P < 0.001) between European regions and normal vs. overweight children. A dose-dependent inverse association between sleep duration and overweight could be seen, with crude odds ratios ranging from 1.73 (99% CI 1.33; 2.25) for sleeping between 10 and 11 h to 3.81 (99% CI 2.85; 5.09) for sleeping less than 9 h (reference category > 11 h). This persisted after adjustment, but remained significant only for sleeping less than 9 h per night (north: OR = 1.70; 99% CI 1.13; 2.58 vs. south: OR = 2.84; 99% CI 1.57; 5.12) if stratified by region. No effect modification by region could be found, but adjustment for region accounted for changes in the effect estimate for sleeping less than 9 h (OR = 2.22; 99% CI 1.64; 3.02). The association was stronger in school children than in preschool children. CONCLUSION: Geographic region and related aspects-even if they do not seem to modify the association between sleep and overweight-should in any case be taken in consideration as a confounding factor on this association.