The relationships between sex, age, geography and time in bed in adolescents: a meta-analysis of data from 23 countries.

Objectives: To quantify the relationships between age, sex and country of residence and sleep time (time in bed) in young people aged 9-18 years.

Methods: Thirty studies of sleep patterns in healthy adolescents from the last 30 years in 20 countries were reviewed. Monte Carlo simulation generated pseudo-data where only summary statistics were available. Raw and pseudo-data were combined, generating a total of 92,977 data points. A mixed model, clustering on countries, analysed data for school and non-school days separately.

Results: Sleep time varied with sex, age and geographical region. School day sleep differed slightly between boys and girls, girls sleeping 11 min/night more than boys (p = 0.003). On non-school days, girls slept 29 min more each day (p = 0.003). Sleep time declined with age, - 14 min/day per year of age (school days), and seven min/night per year of age (non-school days). Large differences between countries, showed adolescents from Asian countries sleeping 40-60 min less each night than Americans, and 60-120 min less than Europeans.

Conclusion: Sex, age, geographical region and day type interact and predict sleep patterns in adolescents. One consistent trend is the increasing gap between sleep on school days and non-school days as adolescents get older.