Sleep duration and overweight in adolescents: self-reported sleep hours versus time diaries.

OBJECTIVE: Studies of children have found an inverse association between sleep duration and overweight on the basis of parental report of sleep duration. Studies in adolescents have been inconsistent but used varied measures of sleep. We used a nationally representative sample of adolescents that included 2 different measures of sleep duration (24-hour time diaries and self-reported usual sleep hours) to examine whether the association with overweight is sensitive to how sleep is measured in a single study population. We expected that the 2 measures of sleep would be strongly correlated and that the time-diary sleep would be more strongly associated with overweight risk because it is likely the more accurate measure of sleep.
METHODS: In 2001-2002, adolescents from the Child Development Supplement of the Panel Study of Income Dynamics completed 24-hour time diaries on a random weekday and weekend. Adolescents also self-reported average sleep duration. Both sleep measures were categorized into quartiles. Height and weight were measured, and a BMI z score for age and gender was calculated. Overweight was defined as above the 95th percentile.
RESULTS: The final sample included 767 male and 779 female subjects who were aged 10 to 19 years. Mean time-diary sleep was nearly 9 hours on weekdays and >10 hours on weekends. Mean self-reported sleep duration was 8 hours. Time-diary sleep and self-reported sleep were weakly correlated. Time-diary sleep was not significantly associated with overweight. Self-reported sleep was associated with overweight, but the association was not linear. When both sleep measures were included in the same model, their effects on overweight were independent.
CONCLUSIONS: The weak correlation between self-reported sleep and time-diary sleep and the independence of their associations with overweight raise questions about what different measures of sleep duration in adolescents represent.