Clinical Review
In search of lost sleep: Secular trends in the sleep time of school-aged children and adolescents

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Summary

Background

Sleep deficits are associated with a wide range of detrimental physical and mental health outcomes. There is concern that children are not getting enough sleep, and that sleep duration has been declining. However, evidence is sparse.

Methods

A systematic review of world literature was conducted to locate studies reporting the sleep duration of children aged 5–18 years. Monte Carlo simulation was used to generate pseudodata from summary data, which were combined with raw data and analysed by linear regression of sleep duration on year of measurement at the age × sex × day type × country level.

Results

Data were available on 690,747 children from 20 countries, dating from 1905 to 2008. From these data, 641 regressions were derived. The sample-weighted median rate of change was −0.75 min nightly per year, indicating a decrease of more than 1 h per night over the study period. Rates of change were negative across age, sex and day type categories, but varied according to region, with Europe, the USA, Canada and Asia showing decreases and Australia, the UK and Scandinavia showing increases.

Conclusion

Over the last 103 years, there have been consistent rapid declines in the sleep duration of children and adolescents.

Introduction

Adequate sleep is important for the growth, maturation and health of children and insufficient sleep has been associated with an array of physical and psychosocial health deficits.1 These include an impaired ability to concentrate2, 3 and retain information,4, 5 mood disorders including anxiety, depression and hyperactivity4, 6 as well as impaired motor skills7 and poorer overall health and immune function.8 Inadequate sleep has also been associated with impaired academic performance,2 an increased risk of injuries and accidents,9 suicide ideation10 and drug and alcohol use.11 It has been suggested that short sleep duration increases the risk of obesity by increasing sympathetic activity, elevating cortisol and ghrelin levels, decreasing leptin levels and/or impairing glucose tolerance.12, 13 Both cross-sectional and prospective cohort studies on children support this association.14, 15, 16 In light of this connection, together with the growing prevalence of obesity worldwide,17 secular declines in sleep duration have been linked to the secular rise in obesity.16, 17

The notion that children are sleeping less than they used to is widespread both in the scientific literature and the popular media, and is “moving out of the bedroom, home and neighbourhood, and into the courts, boardrooms and even parliament”.18 This secular decline, variously ascribed to electrification,14, 19 increased use of technology,20, 21 and modern lifestyle,15, 22, 23 is believed to have resulted in many children not getting enough sleep.24, 25, 26 Declines in children’s sleep duration over recent decades have been reported in the scholarly literature. Dollman and colleagues27 noted a 30 min decline between the years 1985 and 2004 for 10–15 year-old Australian children on school nights while Iglowstein et al.28 reported declines for 1–16 year-old Swiss children between 1974 and 1993. Similar trends have also been reported for children from Japan29 and Iceland.30

In spite of such findings, there is also evidence to suggest that that the sleep duration of children has not declined over the years. Hofferth and Sandberg31 reported an increase in the sleep duration of 3–12 year-old American children between the years 1981 and 1997, while Huysmans et al.32 reported no change for 15-18 year-old children in the Netherlands between 1980 and 2000. Pääkönen33 found that children in Finland were getting more sleep on weekends and less sleep on weekdays in 2000 compared with 1987. Randler,34 on the other hand, noted that the sleep duration of German children had increased from 1907 up until the 1970s at which time a decline commenced.

The belief that children are getting less sleep than they should, and that this deficit is due to “modernism”, has persisted for at least a century. Given the conflicting evidence around secular trends in children’s sleep and the apparent scarcity of scientific evidence,35 we have undertaken a comprehensive review of historical studies of children’s sleep durations in order to chart changes in sleep duration over the last century.

Section snippets

Data location

A systematic literature review was conducted to locate relevant data. A pilot search determined the scope and relevance of candidate databases. The Scopus, EbscoHost, Ovid and Web of Science platforms were searched. Table 1 shows the search terms used.

Studies returned from the database search were initially included and read in full if the abstract stated that the self- or proxy-reported sleep duration of children was measured. Papers were excluded if the abstract explicitly stated that the

Data collected

Search strategies employed in this study identified a total of 218 studies (Fig. 1) and 44 raw datasets. Sleep duration data were available for 822,105 children from 35 different countries at the age × sex × country × day type level. These data were collected between 1892 and 2008.

Data included for trend analysis

From the data collected, it was possible to derive 641 regressions at the age × sex × country × day type level, encompassing 690,747 children from 20 countries (Australia, Belgium, Brazil, Canada, China, Denmark,

Main findings

This study identified a secular decline of 0.75 min per year in children’s sleep duration over the last 100 years. Significant differences were identified across most age groups, between sexes and regions, and on the different day types. The greatest rate of decline in sleep occurred for older children, boys and on schooldays. Regional analyses indicated secular declines in Asia, Canada the USA and Europe, while increases were identified in Australia and in the other parts of Europe (the UK and

Financial support

This study received no financial support.

Disclosures

The authors declare no conflict of interest.

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