Accelerometer-measured sleep habits in Danish children and adolescents aged 3 to 17 years: a pooled analysis with 9,000 participants from six cross-sectional population-based studies

Mar 18, 2026Sleep

Sleep patterns measured by activity trackers in 3- to 17-year-old Danish children and teens from six studies with 9,000 participants

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Abstract

A total of 8,948 children and adolescents aged 3-17 years were monitored for sleep habits using accelerometers.

Total sleep time (TST) increased slightly from ages 3 to 5 years but declined through adolescence.
Girls consistently adhered to sleep duration recommendations more than boys.
Bedtime and wake time became increasingly later with age.
Sleep variability was highest among the youngest children and oldest adolescents.
Girls exhibited earlier changes in sleep habits compared to boys, who showed a more rapid progression during adolescence.

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STUDY OBJECTIVES: Sleep is vital for health and development, yet inadequate sleep among children and adolescents has risen in recent decades, constituting a pressing public health problem. However, much of the existing research is predominantly based on self- or parent-report, which can be prone to bias. This study used accelerometry-based measures to describe age- and sex-specific sleep habits.

METHODS: Thigh-mounted accelerometers were used to measure nocturnal total sleep time (TST), adherence to sleep duration recommendations, bedtime, wake time, chronotype, and sleep variability among 8,948 children and adolescents aged 3-17 years. Mixed-effects linear and quantile regression models fitted with fractional polynomials were used to explore the effects of age and sex on sleep.

RESULTS: Sleep habits differed significantly from childhood through adolescence, with consistent differences between weekdays and weekends. TST rose slightly from ages 3 to 5 years and then declined through adolescence, with consistently higher adherence among girls than boys. Chronotype, bedtime and wake time became increasingly later with age. TST variability was greatest among the youngest children and oldest adolescents, bedtime variability declined with age, whereas wake time variability increased. Overall, girls exhibited earlier changes in sleep habits compared to boys, whereas boys showed a more rapid progression of sleep habit shifts during adolescence.

CONCLUSIONS: Nocturnal sleep showed gradual and continuous differences from 3 to 17 years of age, indicating stability only within relatively narrow age intervals. Variations in the rate and timing of differences between boys and girls underscore the need for refined age- and sex-specific sleep duration recommendations.

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Accelerometer-measured sleep habits in Danish children and adolescents aged 3 to 17 years: a pooled analysis with 9,000 participants from six cross-sectional population-based studies

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