Sleep duration during COVID-19 lockdown: systematic review and meta-analysis

Abstract

In attempts to slow down the spread of COVID-19 pandemic, countries took different measures including lockdowns. Several studies reported the effects of lockdowns on sleep mostly suggesting an increase in sleep duration during lockdowns. This is an interesting outcome as life in the modern world were associated with insufficient sleep. The present study is a systematic review and meta-analysis of work regarding sleep duration during lockdowns.

We searched PubMed using the terms “COVID-19”, “SARS-CoV-2”, “lockdown”, “stay at home”, “quarantine” and “sleep” and found 262 papers. After applying exclusion criteria, we identified 26 papers (with 35 discrete studies) for the meta-analysis. A fixed effect model was used with effect sizes estimated using Cohen’s d and heterogeneity of effect sizes tested using the Cochran’s Q test statistics.

Most studies (31/35) report an increase in sleep duration during lockdown periods with a mean (± STD) of 31.5 ± 21.2 minutes. Effect sizes (Cohen’s d) ranged between 0.08 and 3.34, which are considered between very small and huge. Q statistics was 4859.3 (p < 0.0001) and with no indication for publication bias (Egger’s test, p = 0.45). Eight studies also reported measures of “sleep quality” with 6/8 reporting worsening of sleep quality with small to large effect sizes Cohen’s d range between 0.09 and 1.86).

The study demonstrates increased sleep duration during lockdowns. Increased sleep duration is a positive change, but effects on well-being during lockdowns might be overshadowed by reduced sleep quality, increased stress, and lowered mood. It is interesting whether longer sleep duration habits may survive to post-COVID-19 days.

Introduction

Starting December 2019 our world experienced a major change with the appearance and fast spread of the COVID-19 virus. In attempts to slow down the spread of the disease, many countries took different measures at different times imposing social distancing regulations and mobility restrictions such as lockdowns (Caristia et al., 2020). Clearly, these regulations affected human behavior including sleep and eating habits, travel and social activities, with significant damaging consequences (Kumar et al., 2020; Schippers, 2020). One aspect of change that might be of significant importance is sleep, including sleep duration, timing and quality and indeed a significant number of studies in the last year examined sleep parameters in the context of the COVID-19 regulations [e.g. (Altena et al., 2020; Cellini, Canale, Mioni, & Costa, 2020)].

Whereas many studies emphasized the adverse effects of lockdowns on aspects of human health and behavior, including increased anxiety and stress (Oved et al., 2021; Violant-Holz et al., 2020), reduced activity (Violant-Holz et al., 2020) and reduced socialization, the results regarding sleep are more complex. Several studies concentrated on sleep disturbances during the pandemic. A recent meta-analysis based on 44 papers, involving a total of 54,231 participants from 13 countries reports that the prevalence of sleep problems during the COVID-19 pandemic is up to 40% of people from the general population (Jahrami et al., 2021), whereas another meta-analysis based on 6 studies and limited to India reports a lower prevalence of 26.7% (Singh, Bajpai, & Kaswan, 2021). These numbers may appear high, but it is important to remember that many studies show that even during “normal” days there is a high rate of sleep disturbances in the general population. For example, a meta-analysis of sleep quality in students (conducted before the COVID-19 outbreak) shows a 25% prevalence of subjects reporting low sleep quality (Chen, Zhang, & Zhou, 2020).

In general, it is repeatedly suggested that people in the modern society do not sleep enough (Chattu et al., 2018) and that disturbed and insufficient sleep can lead to a wide range of problems and pathologies ranging from increased chances for heart disease (Shi et al., 2021) to heightened emotional susceptibility (Hairston & Cohen-Zion, 2020). Within the range of sleep problems and disturbances, life in the modern world were repeatedly associated with insufficient sleep (CDC, 2012; Chattu et al., 2018) and insufficient sleep and other circadian and sleep disturbances had been repeatedly associated with a large variety of significant adverse effects ranging from somatic to mental diseases including (but not limited to) diabetes, hypercholesterolemia, heart disease, depression and more (Chattu et al., 2018; Shi et al., 2021; Zimmet et al., 2019). In that context, it is possible to suggest that amongst a range of adverse effects, lockdowns may also have at least one positive consequence, increased sleep duration. Yet, the results in different studies vary significantly and it is not simple to make general conclusions based on one or even a few studies.

To further explore the effects of COVID-19 lockdowns on sleep duration, the current study presents a systematic review and meta-analysis of recent studies that report changes in the duration of sleep in the general population.

Materials And Methods

Results

As shown in Table 1, 31/35 studies showed a significantly longer sleep duration during lockdown compared with pre-lockdown periods, whereas non-significant effects were demonstrated in four studies. Mean increase in sleep duration across all studies was 31.5 ± 3.6 (mean ± SEM) minutes and the range was 1.0 min to 96.0 minutes. Effect sizes (Cohen’s d) for the studies with significant effects ranged between 0.08 and 3.34 (Fig. 1). Mean effect size across all experiments comparing pre-lockdown to lockdown periods was 0.58 ± 0.11 (mean ± SEM) which is considered a medium effect size (Rosnow et al., 2000). Q statistics was 4859 (p < 0.001). There was no indication for publication bias in these studies (Egger’s test, p = 0.22). Seven of the studies examined children and youth (Table 1). Teenagers are expected to sleep longer than adults regardless of lockdown conditions (Kocevska et al., 2021; Ohayon, Carskadon, Guilleminault, & Vitiello, 2004) and this was the case here with the measures of sleep duration before lockdown where mean (± SEM) for adult studies was 446.3 ± 7.5 min and for the children and youth studies 522.7 ± 20.7 min [t-test: t(33) = 5.91, p < 0.001]. However, despite the differences in baseline, no differences between young and adult populations were demonstrated for the effects of lockdown on sleep duration. Six of the studies in young populations showed significant elongation of sleep duration during lockdown. Effect sizes in these studies ranged between 0.08 and 1.53, not different than effect sizes for the studies conducted in adults [t-test: t(33) = 0.18, p = 0.86].

Eight of the 35 studies also reported direct measures for sleep quality using either the PSQI questionnaire or measure of sleep efficiency. As shown in Table 2, six out of these papers report worse sleep quality during lockdown compared with pre-lockdown periods with a medium mean effect size (Cohen’s = 0.68).

Discussion

Short sleep duration and sleep disturbances are common in modern life and had been associated with a large scope of problems ranging from reduced functionality, well-being and increased susceptibility to many modern world diseases (CDC, 2012; Chattu et al., 2018; Shi et al., 2021; Zimmet et al., 2019). It is therefore interesting to note that amongst the multiple consequences of COVID-19 related lockdowns (Kumar et al., 2020; Schippers, 2020), one change that emerges as possibly positive is an increase in sleep duration. This change is emphasized in the current systematic review where nearly all studies demonstrated significant increase in sleep time.

Unfortunately, the possible advantages of increased sleep in these conditions may not be clear because several studies also report a reduction in sleep quality (Table 2). Accordingly, it is not clear if the advantage of sleeping more is not overshadowed by the reduction in the quality of sleep. Yet, some optimism could be appropriate as at least one study suggest that sleep quality recovers when the lockdown ends (Beck, Leger, Cortaredona, Verger, & Peretti-Watel, 2020).

One question regarding the studies of sleep is how well they reflect the actual situation rather than the subjective feeling of subjects. Most of the studies examined in this meta-analysis are based on self-reported questionnaires which suggests at least some level of inaccuracy in reporting past and present sleep duration (Matricciani, 2013). Only three papers (that included reports of 7 discrete studies) were based on data obtained using wearable devices or smartphone apps or both. A separate analysis of these few studies resulted in a smaller sleep duration increase (mean = 15.1 min) compared with the analysis of survey based studies (mean = 31.3). These differences may suggest that while answering sleep questionnaires, individuals may overestimate the changes that happen during lockdowns. However, as the number of studies that used wearable devices is small it is not possible to make any strong conclusion on this issue and it should be further investigated. Interestingly, a recent study that compared self-reports (using a dedicated smartphone app) with data from wearable devices during the COVID-19 lockdown reported shorter subjective sleep duration (app) than objective sleep duration (wearable devices) both before and during lockdown but the increase in sleep during lockdown was similar for subjective and objective measures (Oved et al., 2021). This same report (Oved et al., 2021) suggests differential effects of lockdown in sub-populations. Specifically, the study shows that both age and chronotype are factors that influence change in sleep duration under lockdown conditions. For the older age group, the increase in sleep duration was mainly expressed in early chronotypes, whereas for the younger age group, it was mainly expressed in late chronotypes (Oved et al., 2021). These data are important as they demonstrate that whereas most studies address the general population, further exploration of the consequences of lockdowns and other measures taken during the COVID-19 epidemic should really explore specific sub-populations.

In summary, the current meta-analysis suggests that amongst many other effects, lockdowns result in increased sleep duration but that this increase varies between studies. It is an open question how life in these odd times will affect future habits and human behavior and whether the habit of sleeping more will stay with us after the epidemic will end.

Declaration Of Interest Statement

Authors declare no conflict of interests.

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