The relationship between school day sleep duration and body mass index in Norwegian children (aged 10-12).

OBJECTIVE: To examine the relationship between sleep duration and body mass index (BMI) in Norwegian children (aged 10-12).

METHODS: Children and parents of a population of primary school children (N=9 430) were invited to complete a questionnaire containing questions about usual bedtimes, wake-up times, self and parent evaluations of pubertal maturation, parental education and economic status, and parent-reported height and weight of the child. Sixty per cent of parents and children participated. BMI was available for 4 158 children, 44% of the original sample.

RESULTS: A U-shaped relationship was found between sleep duration and age- and gender-adjusted BMI. Shorter and longer sleep durations were significantly related to high BMI. The percentage of obesity and overweight was higher in the shortest sleep duration group compared with intermediate sleep durations. Crude logistic regression analyses showed a significant association between early pubertal maturation and both obesity and overweight. Socio-economic status was significantly related to overweight. Short sleep duration showed a significant association with obesity but not with overweight. In an adjusted logistic regression model, short sleep duration was still significantly associated with obesity when controlling for physical maturation and socio-economic status.

CONCLUSIONS: High BMI was associated with short and long self and parent-reported duration of sleep. The percentage of obesity/overweight was higher in the shortest sleep duration group than for intermediate sleep durations. Short sleep duration was significantly associated with obesity but not with overweight. Adjusting for physical maturation and socio-economic status, short sleep duration still showed a significant association with obesity.