Effects of acute sleep deprivation on state anxiety levels: a systematic review and meta-analysis

Accepted Manuscript Title: Effects of acute sleep deprivation on state anxiety levels: a systematic review and meta-analysis Author: Gabriel Natan Pires, Andreia Gomes Bezerra, Sergio Tufik, Monica Levy Andersen PII: DOI: Reference:

S1389-9457(16)30136-8 http://dx.doi.org/doi: 10.1016/j.sleep.2016.07.019 SLEEP 3135

To appear in:

Sleep Medicine

Received date: Revised date: Accepted date:

16-4-2016 11-7-2016 20-7-2016

Please cite this article as: Gabriel Natan Pires, Andreia Gomes Bezerra, Sergio Tufik, Monica Levy Andersen, Effects of acute sleep deprivation on state anxiety levels: a systematic review and meta-analysis, Sleep Medicine (2016), http://dx.doi.org/doi: 10.1016/j.sleep.2016.07.019. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Effects of acute sleep deprivation on state anxiety levels: a systematic review and meta-analysis

Gabriel Natan Pires *, Andreia Gomes Bezerra, Sergio Tufik, Monica Levy Andersen

Department of Psychobioogy, Universidade Federal de São Paulo, São Paulo, Brazil

* Corresponding author: Departamento de Psicobiologia - Universidade Federal de São Paulo, Rua Napoleão de Barros, 925, Vila Clementino - SP- 04024-002, São Paulo, Brazil. Tel.: +55 11 21490155; fax: 55 11 5572 5092. E-mail address: [email protected] (G.N. Pires).

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Highlights 

Increased anxiety levels have been widely recognized as one of the most important consequences of sleep deprivation.



There are still aspects of this relationship, such as the extent of the anxiogenic potential and the specific effects of different types of sleep deprivation, which remain unclear.



We intended to evaluate the effects of acute sleep deprivation on state anxiety levels, by means of a systematic review and metaanalyses.



A significant increase in state anxiety levels was observed as a consequence of sleep deprivation, but not due to sleep restriction.



The State-Trait Anxiety Inventory (STAI) seems to be the best tool to measure sleep induced-anxiogenesis, while the Profile of Mood States (POMS) presented inconclusive results.

ABSTRACT Increased anxiety levels have been widely recognized as one of the most important consequences of sleep deprivation. However, despite this general consensus, there are still aspects of this relationship, such as the extent of the anxiogenic potential and the specific effects of different types of sleep deprivation, which remain unclear. As no broad review has been undertaken to evaluate this relationship, we performed a systematic review and meta-analysis regarding the effects of sleep deprivation on state anxiety. Our search strategy encompassed two databases—Pubmed/Medline and Scopus—through which we were able to identify 756 articles. After the selection process, 18 articles, 2

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encompassing 34 experiments, composed our final sample. Our analyses indicate that sleep deprivation, whether total or not, leads to a significant increase in state anxiety levels, but sleep restriction does not. Regarding the effect of the length of the period of sleep deprivation, no significant results were observed, but there was a notable tendency for an increase in anxiety in longer sleep deprivations. With regard to tools, the State-Trait Anxiety Inventory (STAI) seems to be the best one to measure sleep-induced anxiogenesis, while the Profile of Mood States (POMS) presented inconclusive results. In conclusion, it can be affirmed that sleep deprivation induces a state of increased anxiety, with similar results also in the case of total sleep deprivation; however, results in more specific experimental conditions are not definitive.

Keywords: Sleep Sleep deprivation Anxiety Anxiogenesis Meta-analysis

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INTRODUCTION Sleep deprivation is a condition classically related to neurobehavioral consequences, being able to modify behavioral patterns and even modulate psychiatric disorders in a ubiquitous manner [1,2]. One of the pioneers who described some of the consequences of sleep deprivation was Daniel Dement, who in his classic report about rapid eye movement (REM) sleep deprivation noticed the appearance of a triad of neurobehavioral co-morbidities: attention deficit, increased irritability and increased anxiety levels [3]. Since Dement’s report, research on the effects of sleep deprivation has evolved, with anxiety standing out as one of the most frequently reported neurobehavioral issues [4]. As both lack of sleep and anxiety (either as a psychiatric disorder or as an acute state) are highly frequent conditions, the importance of the association between these factors is evident. Sleep deprivation and anxiety are related in at least two different ways. The first possible relationship concerns the effects of anxiety disorders on sleep. Insomnia and lack of sleep are reported as common symptoms, consequences or co-morbidities of pre-established anxiety disorders, including generalized anxiety disorder, post-traumatic stress disorder, panic disorder and obsessive-compulsive disorder [5,6]. The second is the opposite relationship, in which sleep deprivation affects anxiety. In this case, acute or short-term sleep deprivation is considered as an anxiogenic condition, leading to increased state anxiety [7–10]. However, despite the common assumption of the bi-directionality between sleep deprivation and anxiety, the amount of evidence about these two possible relationships is very different. Among the studies addressing sleep deprivation and anxiety, the vast majority of them deal with anxiety disorders generating sleep loss and being associated with insomnia. As a consequence of 4

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this relationship, sleep complaints are generally considered as diagnostic criteria for anxiety disorders, with this relationship being the focus of at least two different meta-analyses [11,12]. Conversely, studies addressing the potential anxiogenic effects of sleep deprivation are not so numerous, with some aspects of this relationship still needing to be better understood. Most of these studies consider the general anxiolytic effect of sleep deprivation, but there has been little consideration of factors such as the effect of different types of sleep deprivation (eg, total or partial sleep deprivation), variation in duration of sleep deprivation or the sensitivity of the methods used to address sleep-deprivationinduced anxiety. Recently, it was suggested that a meta-analysis of the studies addressing the effects of sleep deprivation on state anxiety in humans could be an important step in solving some of the key questions on the overall relationship between sleep and anxiety [13]. Indeed, this is the most appropriate way to summarize data regarding the anxiogenic potential of sleep deprivation, as well as to provide evidence regarding its general effects and all related issues. Thus, the present article intends to comprehensively approach the effects of sleep deprivation on state anxiety levels, by means of a systematic review and meta-analysis.

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METHODS Search strategy and article selection In order to identify studies addressing the effects of sleep deprivation on anxiety, a systematic bibliographic search was performed in two different databases: Pubmed/Medline and Scopus. The primary search strategy used was [("sleep deprivation" OR "sleep curtailment" OR "sleep restriction" OR "sleep loss") AND (anxi* OR "elevated plus-maze")] (with an additional filter for “article or review” in Scopus). The search process was concluded in July 2014. The term “elevated plus-maze” was intended to add specificity to a concurrent systematic review for the effects of sleep deprivation in rodent models of anxiety [14], having no impact on the present analysis. Articles were selected in a twophase process. In the first phase, titles and abstracts of articles resulting from the search described above were screened for suitability with the aims of the review. The second step encompassed full-text evaluations and was followed by data extraction. Additionally, relevant original studies cited by the articles selected in the primary search, as well as studies suggested by colleagues and experts in the field, were also included. Both selection phases were conducted and checked by different investigators (GNP and AGB, respectively). Any disagreements were resolved by consensus.

Inclusion and exclusion criteria Only

original

clinical

articles

addressing

the

effects

of

acute

experimentally or laboratory-induced sleep deprivation on state anxiety in humans were selected. Inclusion and exclusion criteria involved four different aspects: type of report, population, sleep deprivation, and anxiety assessment.

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Type of report: Only original, longitudinal, interventional and comparative articles were included. Any non-original or theoretical article (eg, reviews, opinion, letters or correspondence) were excluded. Also, observational or transversal studies and case reports were excluded. Population: Articles considering non-human species were excluded. Additionally, only studies conducted with healthy individuals were considered eligible. No restrictions regarding gender and age were applied. Sleep deprivation: To be included, studies should have addressed sleep deprivation as an intervention (independent variable). Sleep deprivation was defined as any kind of lack of sleep, which included total sleep deprivation (complete absence of sleep), partial sleep deprivation (deprivation of one specific sleep stage, such as REM sleep), sleep restriction (reduction in total time of sleep) and sleep fragmentation (intermittent awakenings through the sleep period). Only studies in which sleep deprivation was induced by experimental and controlled methods were included. This means that natural observation of lack of sleep, occupational sleep restriction (shiftwork or extended work periods), jet lag, lack of sleep due to disease or sleep disorder or any other non-experimental sleep deprivation study were not considered. Anxiety assessment: To be included, studies should have addressed state anxiety levels as an outcome. Studies addressing self-assessed or selfreported state anxiety levels by any tool in which the outcome is measured by a continuous numeric variable were eligible. Studies using dichotomous or categorical evaluation of anxiety (presence or absence of anxiety) or considering anxiety assessed by someone else but the volunteer (eg, physician’s diagnosis, parental scales, etc.) were excluded. Anxiety should have been assessed right after the periods of sleep deprivation. 7

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Studies that did not address only sleep deprivation as an intervention, but had at least one clear and unequivocal control group and one experimental group, or that presented clear and unbiased control and experimental time points, all free of confounding factors were also included. Of note, not only randomized controlled trials, but other interventional comparative designs that met the above criteria were included. Articles that presented incompatible study designs, with a significant lack of data (even after contacting authors), and those for which we could not find the full text were excluded.

Data extraction Each selected article was subdivided into experiments, which were defined as any case when a control group is compared to an experimental group (or a control time point compared to an experimental time point). Thus, for this systematic review, the analytical units are experiments, rather than the articles themselves. This is useful considering that it is normal in sleep medicine to compare a control group concomitantly with totally sleep-deprived or sleeprestricted groups, for example. In these cases, sleep-deprived and sleeprestricted individuals cannot be joined in a generic sleep-deprived group, since they entail completely different experimental contexts and, thus, are considered as different experiments. The number of experiments per article is equal to the number of independent groups compared to a correlated control group. For each experiment, we extracted data related to the study description, type of sleep deprivation and anxiety assessment. We also extracted data related to post-sleep-deprivation sleepiness, since it might reflect the extent and impact of sleep deprivation. However, sleepiness data were considered as a secondary outcome, were not included in our search strategy, are not a 8

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conditional inclusion criterion and are not expected to be found in all selected articles. For each subject, we extracted the following data: Study description: Article metadata (first author’s name, publication year, full reference), gender, age, sample size per group and study design type. Sleep deprivation: Type of sleep deprivation (total sleep deprivation, partial sleep deprivation, sleep restriction—first or second half of night—or sleep fragmentation) and duration of sleep deprivation. Anxiety

assessment:

Name

or

type

of

the

employed

anxiety-

measurement tool, mean and standard deviation for any measure of anxiety as outcome (provided that it is in accordance with the inclusion and exclusion criteria) and time of anxiety assessment. Regarding the outcome variables, only those related and sensible to state anxiety fluctuations were extracted. As examples, on the State-Trait Anxiety Index (STAI) only the state scale score was considered, while on the on the Profile of Mood States (POMS) only the tension-anxiety scale was considered. In the case of total sleep deprivation, only anxiety assessments acquired after 24 h of lack of sleep were extracted. In the case of repeated measures, the first and the last available measures were always extracted; but intermediate assessments were only extracted if multiples of 12 (eg, 36 h, 48 h). Sleepiness: The name of the chosen sleepiness-assessment tool (provided that it was used at least once after sleep deprivation), mean and standard deviation of sleepiness measure. Preferably, data were extracted directly from the full-text article, based on textual descriptions and tables. For outcome data, whenever the selected articles employed figures and charts to present results, data was extracted using a digital ruler. Alternatively, when mean and standard deviation data were 9

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not available, it was calculated or estimated based on imputable available information, such as standard error of the mean, sample sizes, p-values and tor F-statistics [15]. As a last alternative, when data were not directly extractable, authors were contacted and asked to provide experimental results or raw data. After two unsuccessful contact attempts, at least 2 weeks apart, the article was excluded.

Data synthesis and analyses For each experiment, we calculated the standardized mean difference based on Hedge’s G-method as a measure of effect size. This method standardizes the magnitude of the effect of the intervention in units of standard deviation, which allows comparisons among studies even if they employed different anxiety assessment tools. We then used a DerSimonian and Laird random effects weighted mean difference meta-analysis to calculate an overall effect size for each analysis. Whenever two different experiments from the same article and sharing a same control group were included in the same comparison, the sample size of the control group was adjusted by dividing it by the number of comparisons, avoiding overestimation of results. In the case of cohorts with pre- and post-sleep-deprivation anxiety assessments, only one sleep-deprived time point per comparison was included; and as a default, the last measurement in a row was selected. Data from intermediate time points were also extracted, but it was used only in the case of subgroup analyses intending to evaluate the duration of the sleep-deprivation protocol. Analyses were performed at four different levels: initially, in order to evaluate the overall and unspecific effect of sleep deprivation on state anxiety, we performed an analysis considering all selected experiments (first-level 10

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analysis). Second-level analyses were composed of stratifications according to the type of sleep deprivation, providing more specific results within the scope of lack of sleep, and according to the anxiety measurement tool employed in each experiment. Third-level analyses were composed by combinations of secondlevel analyses, together with information regarding duration of sleep deprivation. Finally, an independent analysis was performed for evaluation of post-sleepdeprivation sleepiness (fourth-level analysis). A minimal amount of two articles and two experiments per analysis was used. Heterogeneity of effect sizes within each comparison was tested using both Cochran’s Q-test and I2 statistic. In these tests, p-values lower than 0.05 and results higher than 50%, respectively, may represent substantial heterogeneity. Data are presented as effect size ± confidence intervals at 95% and are displayed in forest plots for first-level analyses and as comparative charts for second- and third-level analyses. The data analysis was designed in a way that meant that positive effect sizes denote anxiogenesis and negative effect sizes denote anxiolysis. Results were considered as significant when the confidence interval range was all lower or higher than zero and p<0.05. Analyses were performed with RevMan5.

Risk of bias and publication bias Possible biases affecting the selected articles were evaluated using a screening tool adapted from the Cochrane risk of bias tool [15]. This adaptation was intended to adjust the original screening tool to deal with some peculiarities of the study of experimental sleep deprivation, and encompassed both the exclusion of original items and the inclusion of a new one. Items related to allocation concealment (selection bias), blinding of participants and personnel 11

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(performance bias), and blinding of outcome assessment (detection bias) were excluded. This was due to the difficulty of concealing or blinding sleep deprivation as an intervention under laboratory-controlled conditions, since it is necessary to have investigators together with the volunteers to assure the extent of the sleep deprivation, and because sleep-deprived individuals may easily be recognized by their physical aspect. Conversely, a new item concerning baseline sleep habits was added to the screening tool. Since nonregular sleep habits, presence of sleep disorders or episodes of lack of sleep may impact and confound the results, an additional item was intended to evaluate whether there was any experimental concern about adequate sleep characteristics prior to the beginning of the experiments, which could be measured by actigraphs, sleep logs, sleep questionnaires, polysomnography, and other methods. Each article was considered of high, low or unclear risk for each potential bias source. For publication bias, all the selected articles were evaluated using a visual analysis of a funnel plot [16]. The funnel plot was constructed on the relationship between study precision (standard error) and effect size. In the absence of publication bias, the less precise studies would be expected to be spread widely at the upper part of the graph, while more precise studies would concentrate near the estimated effect size value in the bottom of the chart.

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RESULTS Selected studies and sample description Our search strategy resulted in 756 articles, 407 of which were retrieved from Pubmed/Medline and 349 exclusively found on Scopus. After title and abstract screening, according to our inclusion and exclusion criteria, 710 articles were excluded and 46 articles were considered eligible. From these 46 records, 28 articles were excluded during full-text evaluation. The remaining 18 articles composed our final sample and included 34 experiments [7,10,17–32]. No article was included based on reference-list evaluation. The selection process is detailed in Fig. 1. Among the final sample, 12 articles and 16 experiments addressed total sleep deprivation; seven articles and 17 experiments addressed sleep restriction and only one article with a single experiment addressed REM sleep deprivation. No record about sleep fragmentation was included. The majority of these articles were cohort studies (nine), followed by randomized controlled trials (five) and cross-over randomized control trials (four). Articles considering both men and women indistinctly composed most of our sample (53%), while male samples represented about 44% and female sample represented only 3%. Only one article was conducted on adolescents, while all the remaining were performed with adult individuals. Regarding the anxiety assessment tools, the most often used was the state scale on STAI, employed in 11 articles, POMS anxiety-tension scale, used in six articles. Three other tools were also used, each of them in a single article. Finally, post-sleep-deprivation sleepiness was assessed in only six articles. A detailed sample description is available in Table 1 and a list of inserted articles and experiments are available in Table 2.

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Risk of bias and publication bias A low risk of bias was detected among the studies, as can be observed in Table 3. Among the five items, the highest percentage was for the item “Random sequence generation”, showing that half of the selected articles did not randomly allocate the volunteers into their groups (or did not explicitly state that they had). With respect to the other items, none of them appeared in more than one-third of the articles, indicating a low risk of bias. According to the funnel plot (Fig. 2) a low risk of publication bias was observed, as it seems that there were no omissions of unpublished data. This seems to be a characteristic of the articles on the current field, since there is no clear negative result. The opposite of a significant anxiolysis is an equally significant and equally publishable anxiogenesis. However, experiments are spread differently to the expected funnel-shaped scattered plot, with no obvious relationship between studies’ precision and effect size. This distribution may be a direct result of sample heterogeneity, given the variety of interventions and protocols employed in the selected studies.

Analyses A total of 16 meta-analyses were performed. In first-level analysis, a significant anxiogenesis was observed as a result of lack of sleep (analysis #1: 0.39 (0.67; 0.11); I2 = 0.72; p <0.01). A forest plot with results and experiments included in first level analysis is available in Fig. 3. In second level analysis (Fig. 4), similar anxiogenesis was observed following total sleep deprivation (analysis #2: 0.47 (0.86; 0.08); I2 = 0.76; p <0.01], but not following sleep restriction (analysis #3: 0.19 (0.61; -0.22); I2 = 0.67; p <0.01) (Fig. 4). Regarding the methods for evaluating anxiety, studies employing the STAI show increased 14

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anxiety as the ultimate result of sleep deprivation (analysis #6: 0.65 (0.86; 0.43); I2: 0.00; p <0.01), but those employing POMS resulted in non-significant effects [analysis #7: 0.02 (0.63; -0.59); I2 = 0.88; p <0.01]. All second-level analyses are presented in Fig. 4. In third-level analyses (Fig. 5), no significant result was observed in stratifications by sleep loss duration, either due to overall effect size crossing zero (analysis #8 and #12) or to high heterogeneity (analysis #9 and #13). Similarly, no significant result was observed in stratifications combining type of sleep loss and anxiety measurement tools, again either due to overall effect size crossing zero (analysis #11 and #15) or to high heterogeneity (analysis #10 and #14). Finally, fourth level analysis showed a significant sleepiness as consequence of sleep deprivation (analysis #16: 1.84 (2.61; 1.08); I2 = 0.75; p <0.01]. Results for all other analyses are available in Table 4 and further details in Table 2.

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DISCUSSION Increased state anxiety has been widely related to lack of sleep, probably since Dement’s first report 3. However, such an association is mostly based on empirical experience. Evidence about the real anxiogenic potential of sleep deprivation is hard to compile in non-systematic ways, because studies in this field are not so numerous, the methodological variability among these studies is remarkable, and anxiety is no more than a secondary outcome in some sleep deprivation trials. Thus, the only way to properly gather studies that have assessed the effects of sleep deprivation on state anxiety and to extract a reliable conclusion is by means of a meta-analysis. To the best of our knowledge, such an analysis has never been made, with our report being the first attempt to do so. In a first overall analysis (analysis #1), our data corroborates the empirical sense, indicating a significant increase in state anxiety following sleep deprivation. Such a conclusion was based on a good sample size, composed of 24 experiments and including 764 volunteers, which gives consistency to this analysis. It should be noted that this is the widest analysis among all analyses performed, encompassing different kinds of sleep deprivation, all used anxiety measurement tools and distinct protocols durations. Thus, conclusions drawn from this first case should be treated with caution, in order not to overgeneralize the effects of sleep deprivation to more specific cases. If sleep deprivation in general can generate an acute state of anxiety, the same might not be true for more specific conditions, in which lack of sleep may not lead to a proper anxiogenesis, or in which data may still be inconclusive even after this metaanalysis. Indeed, for most of the stratified analysis (analyses #2 to #14), there are some flaws or concerns that prevent a proper conclusion (discussed below). 16

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Regarding the type of sleep manipulation, a significant anxiogenesis can be observed as a result of total sleep deprivation (analysis #2), but not in the case of sleep restriction (analysis #3). Similarly, results remain non-significant when sleep restriction conducted in the first and in the second half of the night are taken separately (analyses #4 and 5). The reasons for the discrepancy between total sleep deprivation and sleep restriction are uncertain, but we can speculate about two different possibilities, one quantitative and the other qualitative. For the first, one may hypothesize that total sleep deprivation and sleep restriction are the same phenomena, but differentiate in total duration and severity. Thus, the reason for the observation of anxiogenesis in totally sleep deprived individuals is because this is a longer and more severe protocol than sleep restriction, which is milder and shorter, allowing some amount of sleep per night, and not being enough to increase anxiety levels. The second possibility would be to consider sleep deprivation and sleep restriction as qualitatively different phenomena, each leading to different consequences. In this sense, anxiogenesis would be only observed in sleep-deprived but not in sleep-restricted individuals, regardless of total time of lack of sleep or of their sleep pressure. In the stratification by protocol duration (analyses #8, #9, #12 and #13) significant results were not observed in any case. This is surprising, particularly in the case of total sleep deprivation, in which significant results would be expected in at least one time point, explaining the results obtained in analysis #2. The most probable explanation for the lack of significant results is the limited number of experiments in each of these cases, leading to increased heterogeneity. As examples, analyses #9 and #14 (respectively, sleep deprivation for 36 h or more and sleep restriction during 4–5 days) had only four 17

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experiments each, both presenting increased heterogeneity (as can be seen in Cochran’s p-value; Table 4). Analyses at other time points could not be performed due to lack of a minimal amount of articles and experiments, such as in the cases of sleep deprivation for more than 48 h and sleep restriction over 2–3 days. However, in a visual analysis regardless of heterogeneity and number of studies, one may note a tendency of increase in anxiety levels with time. Such improvement in the anxiogenic potential can be noted comparing analyses #8 and #9 (TSD 24 and ≤36 h) and analyses #12 and #13 (SR 1 day and 4–5 days). In both cases longer periods (ie ≤36 h and 4–5 days) present results that may be indicative of anxiogenesis, with bigger effect sizes and values crossing the zero value. Despite not being a reliable analysis, as it disregards the potential impact of heterogeneity, it may be indicative of the importance of the time of lack of sleep, more than the type of sleep manipulation,

in

generating

anxiety,

corroborating

the

aforementioned

hypothesis of quantitative effects. With respect to the tools used for anxiety measurement, analyses could be performed only with the data collected using STAI and POMS (analyses #6 and #7) which encompassed nine and 14 experiments, respectively. In these analyses, the use of state scale of STAI proved successful in detecting anxiogenesis following sleep deprivation, while POMS tension-anxiety provided non-significant data. Additional third-level analysis on the use of different anxiety measurement tools, when each questionnaire was evaluated separately for total sleep deprivation and sleep restriction, provided only non-significant data (analyses #10, #11, #14 and #15). However, a tendency for significant results can be observed in the stratified analysis using STAI for total sleep deprivation, in which effect size indicates anxiogenesis but p-value is only 18

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marginal to significance (analysis #10; p = 0.12). Data collected using STAI in the case of sleep restriction were non-significant, and in the case of POMS were not significant for both sleep conditions, either due to effect sizes crossing zero (analyses #11 and #15) or increased heterogeneity (analysis #14). These analyses were performed in order to evaluate whether different anxietymeasurement tools would have different sensibilities in detecting sleepdeprivation-induced anxiogenesis. Based on this, one may conclude that STAI has a higher sensitivity to detect outcomes, while POMS fails in this purpose. In order to properly understand this result, both measurement tools should be put in context. Despite being built upon different constructs and structured very differently among each other, both STAI and POMS are reliable tools to detect transient state-depended fluctuations in anxiety (for a review, see Rossi and Pourtois [33]). Thus, the distinct results obtained on our results are not due to the actual characteristics of each of these assessment tools, but by how they were employed on the selected studies. Two important considerations should be made in this sense: first, the number of articles using POMS was much smaller than those using STAI, consequently decreasing the power of the analysis related to this assessment toll. Second, the article from Selvi et al. [30], whose results point to anxiolysis, may have biased the analysis on the use of POMS (analysis #7), since it accounted for about 45% of this analysis’ effect size. Thus, while it is safe to conclude that STAI is a reliable and sensitive tool in detecting anxiogenesis due to sleep deprivation, data on the use of POMS are still inconclusive. It should be noted that studies on the relationship between sleep loss and anxiety are much more focused on sleep deprivation and sleep restriction than on REM sleep deprivation and sleep fragmentation. One may observe that 19

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among our sample only one article addressed REM sleep deprivation [21], resulting in a significant anxiogenesis. However, in light of the previous cases in which we had at least four experiments and hundreds of volunteers, it would be unwise to draw general conclusions based on a single experiment. Regarding sleep fragmentation, no article was included. Despite the fact that one may consider total sleep restriction and sleep deprivation as similar phenomena, differentiating only in total duration and severity, the same cannot be said about REM sleep deprivation and sleep fragmentation. These modes of lack of sleep are categorically different, being more specific and affecting sleep differently than total sleep restriction and total sleep deprivation. Unfortunately, no metaanalyses could be performed for REM sleep deprivation and sleep fragmentation due to the lack of articles. Thus, further research is needed on these two modes of lack of sleep. An interesting parallel can be traced between the present results and what would be expected in the case of sleep disorders. Taking the characteristics of each considered type of sleep manipulation, total sleep deprivation and sleep restriction resemble what is observed in insomnia, while REM sleep deprivation and sleep fragmentation are more related to obstructive sleep apnea syndrome (OSAS). In cases of insomnia, the difficulty to start or sustain sleep may lead to the observation of total sleep deprivation, or most often, sleep restriction, since the patient is unable to acquire a sufficient amount of sleep. Insomnia is actually one of the most common co-morbidities in patients affected by generalized anxiety disorder [11,34]; lack of sleep or difficulty getting to sleep being considered diagnostic criteria for three different anxiety disorders (generalized anxiety disorder, post-traumatic stress disorder and acute stress disorder [35]). The evidence of this current report reinforces the 20

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association between lack of sleep and anxiety. Conversely, patients suffering from OSAS do not present a significant reduction in total sleep time, but actually present significant sleep fragmentation [36,37]. In this syndrome, respiratory events tend to be concentrated in REM sleep, as a consequence of the reduced muscle tonus during this sleep phase. Each of these respiratory events leads to an arousal, culminating in a marked fragmentation of sleep, as well as a discrete reduction in REM sleep duration. Clinical studies on the relationship between sleep apnea and anxiety have shown a positive correlation between these conditions [38,39] and continuous positive airway pressure (CPAP) therapy seems to decrease anxiety symptoms after 3 months of treatment [40]. However, these studies are not able to show whether the increased anxiety in OSAS patients is due to the changes in sleep pattern or due to other features of this syndrome. Thus, it corroborates the need for new experimental studies on the effects of REM sleep deprivation and sleep fragmentation on anxiety, as a way of evaluating the nature of OSAS-related increased anxiety. The association between increased anxiety and sleep deprivation in a causal relationship may have some important implications. The first implication concerns overall mental and physical health: modern lifestyle and all its related features have been leading to both a chronic sleep-restricted condition [41,42] and to an increase in anxiety on a population level [43,44], which in turn are both related to a wide range of chronic and acute diseases [42]. Considering the causal relationship addressed in the present review, the introduction of sleep hygiene measures, aimed at maintaining adequate sleep duration and proper sleep quality, may lead to an increased quality of life, both by directly preventing sleep-related disorders, as well as by indirectly reducing anxiety-related comorbidities. The second implication is related to occupational health: lack of 21

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sleep has been related to general impaired decision-taking ability [45,46] and to reduced professional performance in several different contexts, encompassing health professionals, professional drivers, airline pilots and workers in general [47–50]. Anxiety alone has also been related to impaired decision taking as well as to reduced professional performance and an increased number of working accidents [51,52]. One may think about a potential causal sequence, in which sleep

deprivation

leads

to

anxiety,

which

would

ultimately influence

performance during the day. Such intuitive reasoning allows us to conclude that the prevention of sleep deprivation would consequently prevent the negative effects of anxiety on professional performance. Obviously, this is not the general rule for every case in which anxiety occurs, but it may be true for at least a part of these events. Thus, one may consider the avoidance of sleep deprivation as a matter of importance in occupational medicine. Finally, the last implication regards research: despite the overall conclusion of increased anxiety due to sleep deprivation, acquired in analysis #1, the data and conclusions of most of the subsequent analyses (analyses #2 to #15) were right on the edge between the reliable and the inconclusive. Thus, future research on the relationship between sleep deprivation and anxiety are still needed, mainly in the areas in which few or no studies were observed, such as those considering REM sleep deprivation, sleep fragmentation, and with exclusively female samples. Finally, for a proper understanding of the extent of the above-presented results, some final considerations are needed. One may consider the nature of the sleep deprivation in the studies included in this systematic review. Only studies in which sleep deprivation was experimentally induced were included, which means that cases in which lack of sleep was due to shiftwork, jet lag, 22

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substance-

or

disease-induced

sleep

deprivation,

or

any other

non-

experimentally induced methods were excluded. The reason for this was to assure a minimal amount of homogeneity among the results. By including studies on shiftwork or jet lag, we would have to deal with and manage several additional variables, which would act as potential confounders and incur increased heterogeneity. Additionally, experimentally induced sleep deprivation is naturally different from shiftwork, jet lag and other non-experimental conditions, which is per se a reason to separate them. By including only experiments with experimental sleep deprivation, we could analyze the effects of pure sleep deprivation in a decontextualized way. Now, as its primary effects have been disclosed in the present report, meta-analysis in each of these contexts can be performed and are encouraged. Regarding age, one might note that the vast majority of the selected studies was conducted with adult individuals, while only two were conducted with adolescents and none with children or elderly samples. The lack of studies in children or the elderly is reasonable and relies on ethical and procedural aspects. Considering that we were evaluating exclusively the effects of experimental sleep deprivation (ie, sleep deprivation actively induced under laboratory-controlled conditions), it would be completely unacceptable to submit individuals younger than 14 or older than 60 to such conditions. Consequently, the results of this meta-analysis should be valid only for adult populations. Another point that deserves attention is the fact that only articles reporting tests conducted with healthy volunteers were considered eligible. Thus, the conclusions of the present study cannot be extrapolated to any potential effects of sleep deprivation on patients suffering from generalized anxiety disorders or any other anxiety disorder. Healthy volunteers and patients affected by anxiety disorders are distinct in regards to 23

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their behavioral phenotype and neurobiological milieu, factors that lead one to expect possible different effects of sleep deprivation on these two distinct populations. Interestingly, sleep deprivation has presented anti-depressive effects in cases of major depression [53], which may allow us to question whether sleep deprivation would lead to anxiolysis in cases of generalized anxiety disorder. Thus, in order to address the effects of sleep deprivation on patients presenting anxiety disorders, a separate and independent metaanalysis should be performed. In conclusion, the present meta-analysis showed that sleep deprivation leads to an indubitable increase in anxiety levels. This anxiogenic potential can also be observed when considering only total sleep deprivation, but the data is questionable in the case of sleep restriction. Additionally, the duration of the period of lack of sleep seems to be a determinant for the rise in anxiety levels. Regarding the anxiety assessment tools, STAI appears to be a reliable method to measure anxiety following sleep deprivation, while data on POMS and other questionnaires are still not definitive. Future research on the topic should consider the points that still have not provided consistent data, in particular research on REM sleep deprivation and sleep fragmentation.

Conflict of interest GNP is a current employee of Springer Nature; this position has no relation with the present article, nor with any of this author’s academic activities. Other authors have no conflicts of interest to disclose. Acknowledgments Funding for this study was provided by AFIP, CNPq and FAPESP.

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Fig. 1. Flowchart of articles selection. Fig. 2. Funnel plot, considering experiments presented in analysis #1. Each point represents one single experiment. The vertical dotted lined represents the overall effect size and the gray-shaded band represents the 95% confidence interval. SE, standard error; SMD, standardized mean difference. Fig. 3. Forest plot and included studies in analysis #1. Positive effect sizes denote anxiogenesis and negative effect sizes denote anxiolysis. Results are represented as the effect size ± 95% confidence interval. Fig. 4. Results of second-level analyses. The horizontal shadedgray band represents the overall estimated effect size as calculated in analysis #1. Data are represented as the effect size ± 95% confidence interval. POMS, Profile of Mood States; SR, sleep restriction; SR-1, sleep restriction in the first half of the night; SR-2, sleep restriction in the second half of the night; STAI, State-Trait Anxiety Index; TSD, total sleep deprivation. *Effect size not crossing zero line and p < 0.05. Fig. 5. Results of third-level analyses. The horizontal shadedgray band represents the overall estimated effect size as calculated in analysis #1. Information regarding each numbered analysis can be checked in Table 1.

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Table 1. Sample description. Gender Male Female Both

Articles Experiments 6 1 12

15 1 18

Adolescent (14–18 years) Adult (>18 years)

2 18

2 34

Type of study RCT

5

9

CO-RCT

4

4

Cohort

9

21

12 1 7 4 3 1

16 1 17 9 7 1

Age

Sleep manipulation Total sleep deprivation REM sleep deprivation Sleep restriction Awake on first half Awake on second half Other

Duration TSD 24 h TSD ≤36 h TSD >36 h SR 1 day SR 2–3 days SR 4–5 days REM SD Anxiety assessment STAI—state score POMS—tension anxiety MASQ—anxiety arousal PAI—anxiety scale Hamilton Anxiety Scale Sleepiness assessment Visual analytic scale SSS

Articles Experiments 9 4 1 5 1

11 4 1 9 4

3 1

4 1

11

22

6

11

1 1 1

1 1 1

3 3

4 4

29

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CO-RCT, cross-over randomized controlled trial; MASQ, Mood and Anxiety Symptom Questionnaire; PAI, Personality Assessment Inventory; POMS, Profile of Mood States; RCT, randomized controlled trial; SR, sleep restriction; SSS, Stanford Sleepiness Scale; STAI, State-Trait Anxiety Inventory; TSD, total sleep deprivation.

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Table 2. List and description of selected articles. Article

Exp Gender

Age

Sleep manipulation

Duration

Screening tools

Study design

Meta-analyses

Total sleep deprivation

24 h 6.5 h of sleep—5 days

MASQ-AA

RCT

1, 2, 8

POMS

CO-RCT

1, 3, 7, 13, 15

Sleep restriction (wake on second half)

Sleep until 3 a.m.

STAI

Cohort

1, 3, 5, 6, 12, 14

Total sleep deprivation

24 h

STAI; SSS

CO-RCT

1, 2, 6, 8, 10

POMS

Cohort

1, 7

POMS

Cohort

none

POMS

Cohort

none

Sleep restriction (wake on first half)

24 h 4 h of sleep (3–7 a.m.) 4 h of sleep (3–7 a.m.) 4 h of sleep (3–7 a.m.)

POMS

Cohort

1, 3, 4, 7, 12, 15

Total sleep deprivation

77 h

PAI-AA

Cohort

1, 2

Adults

Total sleep deprivation

32 h

STAI; HAM-A

Cohort

1, 2, 6, 9, 10

Both

Adults

Total sleep deprivation

24 h

STAI; SSS

Cohort

8

2

Both

Adults

Total sleep deprivation

36 h

STAI; SSS

Cohort

1, 2, 6, 9, 10

Matzner et al., 2013

1

Male

Adults

Total sleep deprivation

24 h

STAI

RCT

1, 2, 6, 8, 10

Matzner et al., 2013

2

Female

Adults

Total sleep deprivation

24 h

STAI

RCT

1, 2, 6, 8, 10

Minkel et al., 2012

1

Both

Adults

Total sleep deprivation

24 h

POMS

RCT

1, 2, 7, 8, 11

Motomura et al., 2013

1

Male

Adults

Sleep restriction (wake on first half)

4 h of sleep—5 days

STAI; POMS; SSS

RCT

1, 3, 4, 6, 7, 13, 14, 15

Peeke et al., 1980

1

Male

Adults

Total sleep deprivation

24 h

STAI

CO-RCT

1, 2, 6, 8, 10

Sagaspe et al., 2006

1

Male

Adults

Total sleep deprivation

24 h

STAI; VAS

Cohort

8

Sagaspe et al., 2006

2

Male

Adults

Total sleep deprivation

36 h

STAI

Cohort

1, 2, 6, 9, 10

Schuh-Hofer et al., 2013

1

Both

Adults

Total sleep deprivation

24 h

STAI; VAS

CO-RCT

1, 2, 6, 8, 10

Selvi et al., 2007

1

Both

Adults

Total sleep deprivation

24 h

POMS

RCT

1, 2, 7, 8, 11

Selvi et al., 2007

2

Both

Adults

Total sleep deprivation

24 h

POMS

RCT

1, 2, 7, 8, 11

Babson et al., 2010

1

Both

Adults

Baum et al., 2014

1

Both

Clark and Golshan, 2008

1

Both

Adults

Goldstein et al., 2013

1

Both

Adults

Greenberg et al., 1972

1

Both

Irwin et al., 2012

1

Both

Adults

Sleep restriction (wake on first half)

Irwin et al., 2012

2

Both

Adults

Sleep restriction (wake on first half)

Irwin et al., 2012

3

Both

Adults

Kahn-Greene et al., 2007

1

Both

Adults

Labbate et al., 1998

1

Both

Lee et al., 2004

1

Lee et al., 2004

Adolescents Sleep restriction

Adolescents REM sleep deprivation

31

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Selvi et al., 2007

3

Both

Adults

Sleep restriction (wake on second half)

Sleep until 1:30 AM

POMS

RCT

1, 3, 5, 7, 12, 15

Selvi et al., 2007

4

Both

Adults

Sleep restriction (wake on second half)

Sleep until 1:30 AM

POMS

RCT

1, 3, 5, 7, 12, 15

Vardar et al., 2007

1

Male

Adults

Total sleep deprivation

30 h

STAI; VAS

Cohort

1, 2, 6, 9, 10

Vardar et al., 2007

2

Male

Adults

Sleep restriction (wake on first half)

5 h of sleep—1 day

STAI; VAS

Cohort

1, 3, 4, 6, 12, 14

Wu et al., 2008

1

Male

Adults

Sleep restriction (wake on second half)

3 h of sleep—1 day

STAI

Cohort

12

Wu et al., 2008

2

Male

Adults

Sleep restriction (wake on second half)

3 h of sleep—2 days

STAI

Cohort

none

Wu et al., 2008

3

Male

Adults

Sleep restriction (wake on second half)

3 h of sleep—3 days

STAI

Cohort

none

Wu et al., 2008

4

Male

Adults

Sleep restriction (wake on second half)

3 h of sleep—4 days

STAI

Cohort

1, 3, 5, 6, 13, 14

Wu et al., 2008

5

Male

Adults

Sleep restriction (wake on first half)

3 h of sleep—1 day

STAI

Cohort

12

Wu et al., 2008

6

Male

Adults

Sleep restriction (wake on first half)

3 h of sleep—2 days

STAI

Cohort

none

Wu et al., 2008

7

Male

Adults

Sleep restriction (wake on first half)

3 h of sleep—3 days

STAI

Cohort

none

Wu et al., 2008 8 Male Adults Sleep restriction (wake on first half) 3 h of sleep—4 days STAI Cohort 1, 3, 4, 6, 13, 14 CO-RCT, cross-over randomized controlled trial; HAM-A, Hamilton Anxiety Rating Scale; MASQ-AA, Mood and anxiety symptom questionnaire - Anxious Arousal scale; PAI-AA, Personality Assessment Inventory - anxiety arousal scale; POMS, Profile of Mood States; RCT, randomized controlled trial; SSS, Stanford Sleepiness Scale; STAI, State-Trait Anxiety Inventory; VAS, Sleepiness Visual Analytic Scale.

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Table 3. Risk of bias assessment. Low-risk of bias Unclear-risk of bias High-risk of bias Baseline sleep control 72.20% 0% 27.80% Random sequence generation 44.40% 5.60% 50.00% Incomplete outcome data 8.30% 0% 16.70% Selective reporting 100% 0% 0% Other bias 94.40% 0% 5.60% Adapted from the Cochrane risk of bias tool.

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Table 4. Description and results for all meta-analyses. CI-Lower CI-Upper I2 p 0.67 0.11 0.72 <0.01

Stratifications Overall analysis—no filters

Exp N-ctrl N-exp ES 24 384 410 0.39

2nd level 2* 3 4 5 6* 7

TSD SR SR—sleep in the first half SR—sleep in the second half STAI POMS

14 9 4 4 14 9

229 161 64 47 174 183

241 161 64 47 193 187

0.47 0.19 0.34 -0.18 0.65 0.02

0.86 0.61 0.70 0.80 0.86 0.63

0.08 -0.22 -0.02 -1.16 0.43 -0.59

0.76 0.67 0.04 0.81 0.00 0.87

<0.01 <0.01 0.37 <0.01 <0.01 <0.01

3rd level

TSD; 24 h TSD: ≤36 h TSD; STAI TSD; POMS SR; 1 day SR;4–5 days SR; STAI SR; POMS

11 4 9 3 7 4 5 5

174 67 134 54 97 84 54 121

186 67 139 58 97 84 54 121

0.42 0.89 0.74 -0.26 0.01 0.53 0.51 -0.09

0.90 1.44 1.06 1.35 0.53 0.84 0.89 0.53

-0.06 0.34 0.42 -1.87 -0.52 0.22 0.12 -0.72

0.79 0.55 0.37 0.93 0.68 0.00 0.00 0.81

<0.01 0.08 0.12 <0.01 <0.01 0.93 0.95 <0.01

1st level

# 1*

8 9 10 11 12 13 14 15

4th level 16* Sleepiness 7 94 94 1.84 2.61 -1.08 0.75 <0.01 CI-Lower, lower bound of confidence interval at 95%; CI-Upper, upper bound of confidence interval at 95%; ES, effect size; Exp, experiments; N-ctrl, sample size in control groups; N-exp, sample size in experimental group; POMS, Profile of Mood States; SR, sleep restriction; STAI, State-Trait Anxiety Index; TSD, total sleep deprivation. p values are referent to the Cochran's Q test. * Analysis in which effect size does not cross zero and p is lower than 5%. Description and results for all meta-analyses. 34

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35

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FIGURES

Figure 1.

36

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Figure 2.r.

37

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Figure 3.

38

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Figure 4.

39

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Figure 5.

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