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Review
. 2021 Sep 28;18(19):10212.
doi: 10.3390/ijerph181910212.

Effects of a Short Daytime Nap on the Cognitive Performance: A Systematic Review and Meta-Analysis

Frédéric Dutheil  1 , Benjamin Danini  2 , Reza Bagheri  3 , Maria Livia Fantini  4 , Bruno Pereira  5 , Farès Moustafa  6 , Marion Trousselard  7 , Valentin Navel  8
Affiliations
Review

Effects of a Short Daytime Nap on the Cognitive Performance: A Systematic Review and Meta-Analysis

Frédéric Dutheil et al. Int J Environ Res Public Health. .

Abstract

Background: Napping in the workplace is under debate, with interesting results on work efficiency and well-being of workers. In this systematic review and meta-analysis, we aimed to assess the benefits of a short daytime nap on cognitive performance.

Methods: PubMed, Cochrane Library, ScienceDirect and PsycInfo databases were searched until 19 August 2021. Cognitive performance in working-aged adults, both before and following a daytime nap or under control conditions (no nap), was analysed by time and by type of cognitive function (alertness, executive function and memory).

Results: We included 11 studies (all in laboratory conditions including one with a subgroup in working conditions) for a total of 381 participants. Mean duration of nap was 55.4 ± 29.4 min. Overall cognitive performance did not differ at baseline (t0) between groups (effect size -0.03, 95% CI -0.14 to 0.07), and improved in the nap group following the nap (t1) (0.18, 0.09 to 0.27), especially for alertness (0.29, 0.10 to 0.48). Sensitivity analyses gave similar results comparing only randomized controlled trials, and after exclusion of outliers. Whatever the model used, performance mainly improved until 120 min after nap, with conflicting results during the sleep inertia period. Early naps in the afternoon (before 1.00 p.m.) gave better cognitive performance (0.24, -0.07 to 0.34). The benefits of napping were independent of sex and age. Duration of nap and time between nap and t1 did not influence cognitive performance.

Conclusions: Despite the fact that our meta-analyses included almost exclusively laboratory studies, daytime napping in the afternoon improved cognitive performance with beneficial effects of early nap. More studies in real work condition are warranted before implementing daytime napping at work as a preventive measure to improve work efficiency.

Keywords: cognitive performance; daytime nap; prevention; work.

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Conflict of interest statement

No conflicting relationship exists for any author.

Figures

Figure 1
Figure 1
Search strategy.
Figure 2
Figure 2
Methodological quality of included articles and summary bias risk. Using the “Scottish Intercollegiate Guidelines Network” (SIGN) Methodology checklist 2 Yes: +; No: − Can’t say: ?; Not applicable: NA; RCT: Randomized controlled trials; * item only for randomized studies.
Figure 3
Figure 3
Summary of meta-analysis on cognitive performance between groups (nap vs. control), for each cognitive function: before (left), after (middle) exclusion of studies not evenly distributed around the funnel plot and (right) non-randomised controlled trials. For details of the meta-analysis at each analysis time, please see Figure S3 for meta-analyses t1. For details of the meta-analysis on each cognitive function, please see Figure S1 for meta-analyses at t0, and Figure 4 for t1. For details of the meta-analysis on each group, please see Figure 4 and Figure S4 for the nap group, Figure 5 for the control group. t0: baseline; t1: after intervention (nap or no-nap). Each overall summary of a meta-analysis is represented in the graph by a dot on a vertical line. The black dots represent the overall pooled-effect estimate of individual meta-analyses (pooled effect size—ES), and the length of each vertical line around the dots represents their 95% confidence interval (95CI). Shorter lines represent a narrower 95CI thus higher precision around pooled-ES. Conversely, longer lines represent a wider 95CI and less precision around pooled-ES. The black solid horizontal line represents the null estimate (with a value of 0 for pooled-ES). Vertical lines that cross the null horizontal line represent a non-significant overall summary of the meta-analysis at each time analysed (t0 and t1).
Figure 4
Figure 4
Summary of meta-analyses on cognitive performance stratified on type of cognitive function and on time of analysis at t1 between groups. Each summary of meta-analysis is presented in three conditions: global model with all the studies, after exclusion of outliers (studies not evenly distributed around the funnel plot) and with only randomized controlled trials. Each summary of several meta-analyses is represented in the forest plot by a dot on a horizontal line. The black dots represent the pooled-effect estimate (pooled effect size—ES), and the length of each line around the dots represents their 95% confidence interval (95CI). Shorter lines represent a narrower 95CI thus higher precision around pooled-ES. Conversely, longer lines represent a wider 95CI and less precision around pooled-ES. An overall summary of the results of the meta-analyses pooled-estimate (result of the overall meta-analysis) is represented by a blue lozenge at the end of the graph. The black solid vertical line represents the null estimate (with a value of 0 for pooled-ES). Horizontal lines that cross the null vertical line represent the non-significant overall summary of the meta-analysis. Bold numbers represent the overall result of each meta-analysis.
Figure 5
Figure 5
Summary of sensitivity analysis: meta-analyses on cognitive performance at t1 compared with baseline (t0) within the nap group (left), meta-analyses on cognitive performance at t1 compared with baseline (t0) within the control group (middle), meta-analyses on changes in performance between t1 and t0 ((t1 − t0)/t0) between nap and control groups (right) Each summary of meta-analysis is presented in three conditions: global model with all the studies, after exclusion of outliers (studies not evenly distributed around the funnel plot) and with only randomized controlled trials For details of each meta-analysis, please see Figures S4, S6 and S7. Each summary of several meta-analyses is represented in the forest-plot by a dot on a horizontal line. The black dots represent the pooled-effect estimate (pooled effect size—ES), and the length of each line around the dots represents their 95% confidence interval (95CI). Shorter lines represent a narrower 95CI thus higher precision around pooled-ES. Conversely, longer lines represent a wider 95CI and less precision around pooled-ES. An overall summary of the results of the meta-analyses pooled-estimate (result of the overall meta-analysis) is represented by a blue lozenge at the end of the graph. The black solid vertical line represents the null estimate (with a value of 0 for pooled-ES). Horizontal lines that cross the null vertical line represent the non-significant overall summary of the meta-analysis.
Figure 6
Figure 6
Summary of meta-regressions: 95%CI: 95% confidence intervals; t0: baseline; t1: after nap (nap group) or rest without nap (control group) Results were presented before (left) and after (right) exclusion of non-randomized controlled trials The effect of each variable on the outcome is represented in the forest-plot by a dot on a horizontal line. The black dots represent the coefficient for each variable, and the length of each line around the dots represents their 95% confidence interval (95CI). The black solid vertical line represents the null estimate (with a value of 0). Horizontal lines that cross the null vertical line represent non-significant variables on the outcome. Bold numbers represent the significant results (p < 0.05).
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