Elsevier

Sleep Medicine Reviews

Volume 28, August 2016, Pages 69-85
Sleep Medicine Reviews

Clinical review
Has adult sleep duration declined over the last 50+ years?

https://doi.org/10.1016/j.smrv.2015.08.004Get rights and content

Summary

The common assumption that population sleep duration has declined in the past few decades has not been supported by recent reviews, which have been limited to self-reported data. The aim of this review was to assess whether there has been a reduction in objectively recorded sleep duration over the last 50+ years.

The literature was searched for studies published from 1960 to 2013, which assessed objective sleep duration (total sleep time (TST)) in healthy normal-sleeping adults. The search found 168 studies that met inclusion criteria, with 257 data points representing 6052 individuals ages 18–88 y. Data were assessed by comparing the regression lines of age vs. TST in studies conducted between 1960 and 1989 vs. 1990–2013. Weighted regression analyses assessed the association of year of study with age-adjusted TST across all data points. Regression analyses also assessed the association of year of study with TST separately for 10-y age categories (e.g., ages 18–27 y), and separately for polysomnographic and actigraphic data, and for studies involving a fixed sleep schedule and participants' customary sleep schedules.

Analyses revealed no significant association of sleep duration with study year. The results are consistent with recent reviews of subjective data, which have challenged the notion of a modern epidemic of insufficient sleep.

Introduction

It has been widely stated that modern industrialized societies have become sleep-deprived. Some studies have suggested that average sleep duration has declined over the last few decades [1], [2], [3], [4]. Such findings, combined with extensive epidemiologic evidence associating short sleep with health risks *[5], [6], *[7] and experimental evidence of adverse effects of sleep deprivation [8], [9], [10], have provoked widespread concern that chronic insufficient sleep has become a public health crisis.

However, recent reviews of self-reported data have cast doubt on whether nighttime sleep or 24-h sleep has decreased in recent decades, and whether there has been an increased prevalence of short sleep (<6 h), for which risks have been most clearly established. For example, a review of eight studies by Knutson et al. found no significant 31-y trend (1975–2006) towards a higher prevalence of self-reported nighttime sleep of ≤6 h [11]. Bin et al. reviewed 12 studies from 15 countries assessed from the 1960s–2000s, and found that sleep duration had increased in seven countries, decreased in six countries, and had not clearly changed in two countries [12]. In a subsequent meta-analysis of 38 studies conducted in 10 countries in the 1970s–2000s, Bin et al. [13] found that average 24-h sleep duration had increased in most countries (including the US), and that the prevalence of sleeping ≤ 6 h had decreased in most countries (including the US). Rowshan Ravan et al. studied 36-y trends (1968–2004) in sleep duration among Swedish women, and found no change in 50-y old women, and a decline of only 15 min in 38-y old women [14]. Moreover, Bonke reviewed five representative time-use studies spanning 1964–2009, and concluded that “the same number of hours is slept today as in the mid-1960s, with nearly the same prevalence of short and long sleepers” [15].

Discrepancies between studies of population temporal trends in sleep duration can be attributed to multiple factors, including characteristics and representativeness of the respondents, wording of the questions, and instructions given to respondents [16], [17]. Perhaps the biggest limitation of this literature is that it has been limited to self-reports of sleep duration (some of which were retrospective), which can be inaccurate [18], [19] due in part to response biases. The aim of this review was to examine whether there has been a decline over the past five decades in sleep duration, as indexed by objective data.

Section snippets

Methods

The search of the literature was modeled after a previous meta-analysis by Ohayon et al., which assessed objective sleep patterns across age [20]. PubMed, PsychLit, selected journals, and reference lists of located manuscripts were searched for studies published between 1960 and 2013 which met the following criteria: 1) inclusion of presumably healthy adults (as described by the authors), participant ages ≥18 y without sleep problems; 2) report of all-night average total sleep time (TST)

Results

The intercepts and slopes of the regression lines of age vs. TST did not differ for studies conducted between 1960–1989 and 1990–2013 (Fig. 1). In the regression analysis across all data points (n = 257), there was no significant association of year of study with TST (b = 0.03, p = 0.56) (Fig. 2), nor was there a significant association of study year with TST for any of the 10-y age categories (Fig. 3) (p = 0.40–0.92). Likewise, there was no significant association of year of study in analyses

Discussion

The results indicate relative stability of objectively-recorded sleep durations in healthy sleepers assessed over the last half-century. Similar results were found across all age groups, in both men and women, for both PSG and actigraphic data, and under conditions of fixed sleep periods and participants' usual sleep schedules. These data are consistent with recent comprehensive reviews that found no consistent or compelling evidence of significant decrements in self-reported sleep duration

Conflict of interest

The authors do not have any conflicts of interest to disclose.

Acknowledgments

This manuscript is dedicated to Dr. Richard R. Bootzin, our dear friend and colleague who passed away on December 4, 2014. Dr. Bootzin contributed to earlier drafts of this manuscript. Research supported by RO1-HL095799; R01-MD007716; R01-AG034588; R01-AG026364; R01-CA160245; R01-DA032922 the Cousins Center for Psychoneuroimmunology. Susan Noh assisted with this study.

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