Shining evolutionary light on human sleep and sleep disorders

A Cross Sectional Survey of Factors Related to Cannabis Use as a Sleep Aid Among Canadian Cancer Survivors

OBJECTIVES

Poor sleep is a common side effect of cancer. Cannabis is increasingly used to manage cancer treatment-related symptoms, including sleep. This study investigated factors related to cannabis use for sleep among Canadian cancer survivors.

METHOD

Adult Canadian cancer survivors (N = 940) were recruited via the Angus Reid Institute and completed an online, cross-sectional survey. Univariate and multiple binomial logistic regression models identified factors associated with cannabis use for sleep.

RESULTS

Of the participants (Mage = 64.5 yrs; Women = 51.1%; White = 92.9%), 25.1% (n = 236) currently use cannabis for sleep. Participants were at greater odds of using cannabis for sleep if they identified as a gender other than man or woman (AOR = 11.132), were diagnosed with multiple medical conditions (2:AOR = 1.988; 3+:AOR = 1.902), two psychological conditions (AOR = 2.171), multiple sleep disorders (AOR = 2.338), insomnia (AOR = 1.942), bone (AOR = 6.535), gastrointestinal (AOR = 4.307), genitourinary (AOR = 2.586), hematological (AOR = 4.739), or an unlisted cancer (AOR = 3.470), received hormone therapy only (AOR = 3.054), drink heavily (AOR = 2.748), or had mild insomnia (AOR = 1.828). Older participants (AOR=.972) and those with sleep apnea were less likely to use cannabis for sleep (AOR=.560).

CONCLUSION

Given its prevalence, research is needed to understand how factors associated with cannabis use as a sleep aid among Canadian cancer survivors may influence its use and effectiveness and whether these factors are barriers to accessing evidence-based treatments.

Childhood unpredictability and sleep quality in adulthood: the mediating roles of life history strategy and perceived stress

Background

Early environmental risk have been found to be related to lifelong health. However, the impact of childhood unpredictability, a type of early environmental risk, on health, especially on sleep quality in adulthood, has not been adequately studied. The present study aimed to examine the relationship between childhood unpredictability and sleep quality in adulthood and to explore the possible mediating roles of life history strategy and perceived stress.

Methods

A cross-sectional study was conducted on 472 participants from a university in Zhejiang Province, China. The questionnaire inquired about demography, childhood unpredictability, life history strategy (Mini-K), perceived stress (14-item Perceived Stress Scale), and Sleep Quality (Pittsburgh Global Sleep Quality Index).

Results

Higher childhood unpredictability was significantly associated with worse sleep quality in adulthood. Moreover, the link between higher childhood unpredictability and worse sleep quality in adulthood was explained by the chain mediation of life history strategy and perceived stress.

Conclusion

In line with the life history theory, individuals who have experienced higher unpredictability in childhood tend to develop a faster life history strategy and become more sensitive to stress in adulthood, and subsequently suffer a decrease in sleep quality.

Individual sleep need is flexible and dynamically related to cognitive function

Given that sleep deprivation studies consistently show that short sleep causes neurocognitive deficits, the effects of insufficient sleep on brain health and cognition are of great interest and concern. Here we argue that experimentally restricted sleep is not a good model for understanding the normal functions of sleep in naturalistic settings. Cross-disciplinary research suggests that human sleep is remarkably dependent on environmental conditions and social norms, thus escaping universally applicable rules. Sleep need varies over time and differs between individuals, showing a complex relationship with neurocognitive function. This aspect of sleep is rarely addressed in experimental work and is not reflected in expert recommendations about sleep duration. We recommend focusing on the role of individual and environmental factors to improve our understanding of the relationship between human sleep and cognition.

Animal models of human insomnia

Insomnia disorder (chronic sleep continuity disturbance) is a debilitating condition affecting 5%-10% of the adult population worldwide. To date, researchers have attempted to model insomnia in animals through breeding strategies that create pathologically short-sleeping individuals or with drugs and environmental contexts that directly impose sleeplessness. While these approaches have been invaluable for identifying insomnia susceptibility genes and mapping the neural networks that underpin sleep-wake regulation, they fail to capture concurrently several of the core clinical diagnostic features of insomnia disorder in humans, where sleep continuity disturbance is self-perpetuating, occurs despite adequate sleep opportunity, and is often not accompanied by significant changes in sleep duration or architecture. In the present review, we discuss these issues and then outline ways animal models can be used to develop approaches that are more ecologically valid in their recapitulation of chronic insomnia's natural aetiology and pathophysiology. Conditioning of self-generated sleep loss with these methods promises to create a better understanding of the neuroadaptations that maintain insomnia, including potentially within the infralimbic cortex, a substrate at the crossroads of threat habituation and sleep.

Sleep tight! Adolescent sleep quality across three distinct sleep ecologies

Background and objectives

Good sleep quality, associated with few arousals, no daytime sleepiness and self-satisfaction with one's sleep, is pivotal for adolescent growth, maturation, cognition and overall health. This article aims to identify what ecological factors impact adolescent sleep quality across three distinct sleep ecologies representing a gradient of dense urbanity to small, rural environments with scarce artificial lighting and no Internet.

Methodology

We analyze variation of sleep efficiency, a quantitative measure of sleep quality-defined as the ratio of total time spent asleep to total time dedicated to sleep-in two agricultural indigenous populations and one post-industrial group in Mexico (Campeche = 44, Puebla = 51, Mexico City = 50, respectively). Data collection included actigraphy, sleep diaries, questionnaires, interviews and ethnographic observations. We fit linear models to examine sleep efficiency variation within and between groups.

Results

We found that sleep efficiency varied significantly across sites, being highest in Mexico City (88%) and lowest in Campeche (75%). We found that variation in sleep efficiency was significantly associated with nightly exposure to light and social sleep practices.

Conclusions and implications

Our findings point toward contextual cost-benefits of sleep disruption in adolescence. We highlight the need to prioritize research on adolescent sleep quality across distinct developmental ecologies and its impact on health to improve adolescent wellbeing through evidence-based health practices.

Sleep Pathologies and Eating Disorders: A Crossroad for Neurology, Psychiatry and Nutrition

The intricate connection between eating behaviors and sleep habits is often overlooked in clinical practice, despite their profound interdependence. Sleep plays a key role in modulating psychological, hormonal and metabolic balance and exerting an influence on food choices. Conversely, various eating disorders may affect sleep continuity, sometimes promoting the development of sleep pathologies. Neurologists, nutritionists and psychiatrists tend to focus on these issues separately, resulting in a failure to recognize the full extent of the clinical conditions. This detrimental separation can lead to underestimation, misdiagnosis and inappropriate therapeutic interventions. In this review, we aim to provide a comprehensive understanding of the tangled relationship between sleep, sleep pathologies and eating disorders, by incorporating the perspective of sleep experts, psychologists and psychiatrists. Our goal is to identify a practical crossroad integrating the expertise of all the involved specialists.

A cross-sectional survey of the prevalence and patterns of using cannabis as a sleep aid in Canadian cancer survivors

PURPOSE

Poor sleep is one of the most common side effects of cancer. It can persist for years beyond treatment and negatively impact quality of life and health. Cannabis is increasingly used to manage cancer treatment-related symptoms, including sleep. This study investigated the use and perceived effects of cannabis as a sleep aid in Canadian cancer survivors.

METHODS

Adult Canadian cancer survivors (N = 1464) were recruited via the Angus Reid Institute and completed an online, cross-sectional survey including the Insomnia Severity Index and questions about cannabis use for sleep. Standard descriptive statistics, such as means, standard deviations, and ranges were produced for measured variables to assess the ways cancer survivors use cannabis for sleep. Frequencies were tabulated for categorical and ordinal variables.

RESULTS

On average, participants (Mage = 61.1 years; Women = 50%: Men = 48%) received their cancer diagnosis 12.5 years prior. Of participants, 23.5% (n = 344) currently use cannabis as a sleep aid, with reported benefits including relaxation, reduced time to fall asleep, fewer nocturnal awakenings and improved sleep quality. Two thirds (68.3%, n = 235) only began using cannabis for sleep after their cancer diagnosis. Over a third of participants (36.3%, n = 125) use cannabis as a sleep aid every day. Among the 344, the most common other reasons for using cannabis were pain (31.4%, n = 108), recreational use (24.4%, n = 84), and anxiety (12.5%, n = 43).

CONCLUSIONS

Given the prevalence and potential impact, research is needed to examine the actual efficacy of cannabis as a sleep aid.

IMPLICATIONS FOR CANCER SURVIVORS

It is important that cancer survivors have information on methods to help their sleep to avoid impairments to quality of life and health.

Nocturnal selective pressures on the evolution of human musicality as a missing piece of the adaptationist puzzle

Human musicality exhibits the necessary hallmarks for biological adaptations. Evolutionary explanations focus on recurrent adaptive problems that human musicality possibly solved in ancestral environments, such as mate selection and competition, social bonding/cohesion and social grooming, perceptual and motor skill development, conflict reduction, safe time-passing, transgenerational communication, mood regulation and synchronization, and credible signaling of coalition and territorial/predator defense. Although not mutually exclusive, these different hypotheses are still not conceptually integrated nor clearly derived from independent principles. I propose The Nocturnal Evolution of Human Musicality and Performativity Theory in which the night-time is the missing piece of the adaptationist puzzle of human musicality and performing arts. The expansion of nocturnal activities throughout human evolution, which is tied to tree-to-ground sleep transition and habitual use of fire, might help (i) explain the evolution of musicality from independent principles, (ii) explain various seemingly unrelated music features and functions, and (iii) integrate many ancestral adaptive values proposed. The expansion into the nocturnal niche posed recurrent ancestral adaptive challenges/opportunities: lack of luminosity, regrouping to cook before sleep, imminent dangerousness, low temperatures, peak tiredness, and concealment of identity. These crucial night-time features might have selected evening-oriented individuals who were prone to acoustic communication, more alert and imaginative, gregarious, risk-taking and novelty-seeking, prone to anxiety modulation, hedonistic, promiscuous, and disinhibited. Those night-time selected dispositions may have converged and enhanced protomusicality into human musicality by facilitating it to assume many survival- and reproduction-enhancing roles (social cohesion and coordination, signaling of coalitions, territorial defense, antipredatorial defense, knowledge transference, safe passage of time, children lullabies, and sexual selection) that are correspondent to the co-occurring night-time adaptive challenges/opportunities. The nocturnal dynamic may help explain musical features (sound, loudness, repetitiveness, call and response, song, elaboration/virtuosity, and duetting/chorusing). Across vertebrates, acoustic communication mostly occurs in nocturnal species. The eveningness chronotype is common among musicians and composers. Adolescents, who are the most evening-oriented humans, enjoy more music. Contemporary tribal nocturnal activities around the campfire involve eating, singing/dancing, storytelling, and rituals. I discuss the nocturnal integration of musicality's many roles and conclude that musicality is probably a multifunctional mental adaptation that evolved along with the night-time adaptive landscape.

Hormone physiology and sleep dynamics among BaYaka foragers of the Congo Basin: Gendered associations between nighttime activity, testosterone, and cortisol

Sleep quality is an important contributor to health disparities and affects the physiological function of the immune and endocrine systems, shaping how resources are allocated to life history demands. Past work in industrial and post-industrial societies has shown that lower total sleep time (TST) or more disrupted nighttime sleep are linked to flatter diurnal slopes for cortisol and lower testosterone production. There has been little focus on these physiological links in other socio-ecological settings where routine sleep conditions and nighttime activity demands differ. We collected salivary hormone (testosterone, cortisol) and actigraphy-based sleep data from Congolese BaYaka foragers (N = 39), who have relatively short and fragmented nighttime sleep, on average, in part due to their typical social sleep conditions and nighttime activity. The hormone and sleep data collections were separated by an average of 11.23 days (testosterone) and 2.84 days (cortisol). We found gendered links between nighttime activity and adults' hormone profiles. Contrary to past findings in Euro-American contexts, BaYaka men who were more active at night, on average, had higher evening testosterone than those with lower nighttime activity, with a relatively flat slope relating nighttime activity and evening testosterone in women. Women had steeper diurnal cortisol curves with less disrupted sleep. Men had steeper cortisol diurnal curves if they were more active at night. BaYaka men often hunt and socialize when active at night, which may help explain these patterns. Overall, our findings indicate that the nature of nighttime activities, including their possible social and subsistence contexts, are potentially important modifiers of sleep quality-physiology links, meriting further research across contexts.

The influence of sleep on job satisfaction: examining a serial mediation model of psychological capital and burnout

Introduction

This study draws on the conservation of resources theory to investigate whether the loss of sleep can trigger the loss of additional resources that are necessary for work.

Methods

Using cross-sectional design of 322 call center employees working at a government-owned public bank in South Korea, we test the study hypotheses using regression and bootstrapping indirect effects analyses.

Results

The results of analyses show that insufficient sleep increases employee burnout and that psychological capital mediates this relationship. We also find that insufficient sleep decreases job satisfaction via a serial mediation model such that insufficient sleep reduces psychological capital, which in turn increases burnout, and ultimately results in lower job satisfaction.

Discussion

The findings reinforce the previous assessment that although sleep is a non-work factor, its impact spills over to the workplace. Theoretically, this study goes beyond direct effect to uncover the underlying or mediating mechanisms that account for the impact of the sleep-burnout relationship and the sleep-job satisfaction relationship. For managers, the results highlight the significance of sleep to employees' overall health and well-being and thus underscore the need to foster a work culture that recognizes and prioritizes employee sleep needs.

Sound reasons for unsound sleep: Comparative support for the sentinel hypothesis in industrial and nonindustrial groups

Background and objectives

Sleep is a vulnerable state in which individuals are more susceptible to threat, which may have led to evolved mechanisms for increasing safety. The sentinel hypothesis proposes that brief awakenings during sleep may be a strategy for detecting and responding to environmental threats. Observations of sleep segmentation and group sentinelization in hunter-gatherer and small-scale communities support this hypothesis, but to date it has not been tested in comparisons with industrial populations characterized by more secure sleep environments.

Methodology

Here, we compare wake after sleep onset (WASO), a quantitative measure of nighttime awakenings, between two nonindustrial and two industrial populations: Hadza hunter-gatherers (n = 33), Malagasy small-scale agriculturalists (n = 38), and Hispanic (n = 1,531) and non-Hispanic White (NHW) (n = 347) Americans. We compared nighttime awakenings between these groups using actigraphically-measured sleep data. We fit linear models to assess whether WASO varies across groups, controlling for sex and age.

Results

We found that WASO varies significantly by group membership and is highest in Hadza (2.44 h) and Malagasy (1.93 h) and lowest in non-Hispanic Whites (0.69 h). Hispanics demonstrate intermediate WASO (0.86 h), which is significantly more than NHW participants. After performing supplementary analysis within the Hispanic sample, we found that WASO is significantly and positively associated with increased perception of neighborhood violence.

Conclusions and implications

Consistent with principles central to evolutionary medicine, we propose that evolved mechanisms to increase vigilance during sleep may now be mismatched with relatively safer environments, and in part responsible for driving poor sleep health.

Links between household and family social dynamics with sleep profiles among BaYaka foragers of the Congo Basin

Given the contributions of sleep to a range of health outcomes, there is substantial interest in ecological and environmental factors, including psychosocial contexts, that shape variation in sleep between individuals and populations. However, the links between social dynamics and sleep are not well-characterized beyond Euro-American settings, representing a gap in knowledge regarding the way that local socio-ecological conditions interrelate with sleep profiles across diverse settings. Here, we focused on data from a subsistence-level society in Republic of the Congo to test for links between the household/family social environment and sleep measures. Specifically, we used actigraphy-derived sleep data (N = 49; 318 nights) from two community locations (a village and rainforest camp) among BaYaka foragers, who are members of a remote, non-industrialized subsistence society in the Congo Basin. We drew on social dynamics that have been previously linked to sleep variation in Euro-American contexts, including: household crowding, same surface cosleeping, and marital conflict. We examined the following sleep measures: total sleep time (TST), total 24-h sleep time (TTST), and sleep quality (fragmentation). BaYaka adults had shorter and lower quality sleep when their shared sleeping space was more crowded. In the village, parents with breastfeeding-aged infants had longer TTST and higher quality sleep than adults without infants, contrasting with results from other cultural contexts. Based on peer rankings of marital conflict, husbands showed longer and higher quality sleep in less conflicted marriages. Women showed the opposite pattern. These counter-intuitive findings for women may reflect the limitations of the measurement for wives' marital experiences. In total, these results point to the importance of considering local socio-ecological conditions to sleep profiles and underscore the need for expanded study of sleep and health outcomes in settings where shared sleep in constrained space is routine practice.

Adaptive Solutions to the Problem of Vulnerability During Sleep

Sleep is a behavioral state whose quantity and quality represent a trade-off between the costs and benefits this state provides versus the costs and benefits of wakefulness. Like many species, we humans are particularly vulnerable during sleep because of our reduced ability to monitor the external environment for nighttime predators and other environmental dangers. A number of variations in sleep characteristics may have evolved over the course of human history to reduce this vulnerability, at both the individual and group level. The goals of this interdisciplinary review paper are (1) to explore a number of biological/instinctual features of sleep that may have adaptive utility in terms of enhancing the detection of external threats, and (2) to consider relatively recent cultural developments that improve vigilance and reduce vulnerability during sleep and the nighttime. This paper will also discuss possible benefits of the proposed adaptations beyond vigilance, as well as the potential costs associated with each of these proposed adaptations. Finally, testable hypotheses will be presented to evaluate the validity of these proposed adaptations.

Centrality and bridge symptoms of anxiety, depression, and sleep disturbance among college students during the COVID-19 pandemic-a network analysis

Symptoms of depression and anxiety usually co-occur and are inextricably linked to sleep disturbance. However, little is known about the symptom-to-symptom relationships among these three mental disorders. Hence, to improve our understanding of concurrent depression, anxiety, and sleep disturbance, we used the network analysis approach to construct an interplay relationship among the above three mental disorders and identify which specific symptoms bridge these aggregations. We collected data from a large sample (N = 6710, male = 3074, female = 3636; mean age = 19.28) at a university. We estimated the symptom network structure of depression, anxiety, and sleep disturbance as assessed by the Patient Health Questionnaire-9, Generalized Anxiety Disorder-7, and Youth Self-Rating Insomnia Scale during the COVID-19 lockdown. We further investigated four goals: first, identifying the individual core symptoms in the network by the index of "expected influence"; second, determining the bridge symptoms that play roles in linking different mental disorders by the index of bridge expected influence (1-step); third, examining the robustness of all results; and fourth, providing an overall structure that may or may not differ by sex. The network structure was stable, accurate, and predictable. Items referring to sleep dissatisfaction, poor sleep quality, and uncontrollable worry were potentially core symptoms in the interplay among depression, anxiety, and sleep disturbance. Sleep, guilt, restlessness, irritability, and feeling afraid can function as bridges among depression, anxiety, and sleep disturbance, which is clinically relevant and theoretically important. The results suggested that the network structures significantly differed between the female and male networks. Robustness tests also revealed that the results were reliable.

Ecological and social pressures interfere with homeostatic sleep regulation in the wild

Sleep is fundamental to the health and fitness of all animals. The physiological importance of sleep is underscored by the central role of homeostasis in determining sleep investment – following periods of sleep deprivation, individuals experience longer and more intense sleep bouts. Yet, most sleep research has been conducted in highly controlled settings, removed from evolutionarily relevant contexts that may hinder the maintenance of sleep homeostasis. Using triaxial accelerometry and GPS to track the sleep patterns of a group of wild baboons (Papio anubis), we found that ecological and social pressures indeed interfere with homeostatic sleep regulation. Baboons sacrificed time spent sleeping when in less familiar locations and when sleeping in proximity to more group-mates, regardless of how long they had slept the prior night or how much they had physically exerted themselves the preceding day. Further, they did not appear to compensate for lost sleep via more intense sleep bouts. We found that the collective dynamics characteristic of social animal groups persist into the sleep period, as baboons exhibited synchronized patterns of waking throughout the night, particularly with nearby group-mates. Thus, for animals whose fitness depends critically on avoiding predation and developing social relationships, maintaining sleep homeostasis may be only secondary to remaining vigilant when sleeping in risky habitats and interacting with group-mates during the night. Our results highlight the importance of studying sleep in ecologically relevant contexts, where the adaptive function of sleep patterns directly reflects the complex trade-offs that have guided its evolution.

Sex differences in childhood sleep and health implications

CONTEXT

Sleep is critical for optimal childhood metabolic health and neurodevelopment. However, there is limited knowledge regarding childhood sex differences in sleep, including children with neurodevelopmental disorders, and the impact of such differences on metabolic health.

OBJECTIVE

To evaluate if sex differences in childhood sleep exist and if sleep associates with metabolic health outcomes equally by sex. Using autism spectrum disorder (ASD) as a case study, we also examine sleep sex differences in children with a neurodevelopmental disorder.

METHODS

A narrative review explored the literature focussing on sex differences in childhood sleep.

RESULTS

Sex differences in sleep were not detected among pre-adolescents. However, female adolescents were more likely to report impaired sleep than males. Childhood obesity is more common in males. Shorter sleep duration may be associated with obesity in male pre-adolescents/adolescents; although findings are mixed. ASD is male-predominant; yet, there was an indication that pre-adolescent female children with ASD had more impaired sleep.

CONCLUSION

Sex differences in sleep appear to emerge in adolescence with more impaired sleep in females. This trend was also observed among pre-adolescent female children with ASD. Further research is needed on sex differences in childhood sleep and metabolic health and the underlying mechanisms driving these differences.

The subthalamic corticotropin-releasing hormone neurons mediate adaptive REM-sleep responses to threat

When an animal faces a threatening situation while asleep, rapid arousal is the essential prerequisite for an adequate response. Here, we find that predator stimuli induce immediate arousal from REM sleep compared with NREM sleep. Using in vivo neural activity recording and cell-type-specific manipulations, we identify neurons in the medial subthalamic nucleus (mSTN) expressing corticotropin-releasing hormone (CRH) that mediate arousal and defensive responses to acute predator threats received through multiple sensory modalities across REM sleep and wakefulness. We observe involvement of the same neurons in the normal regulation of REM sleep and the adaptive increase in REM sleep induced by sustained predator stress. Projections to the lateral globus pallidus (LGP) are the effector pathway for the threat-coping responses and REM-sleep expression. Together, our findings suggest adaptive REM-sleep responses could be protective against threats and uncover a critical component of the neural circuitry at their basis.

Increased digital media use is associated with sleep problems among university students: A study during the COVID-19 pandemic in Japan

This retrospective cohort study investigates the association between the incidence of sleep problems and changes in digital media use among university students during the COVID-19 pandemic. It used data from annual health check-ups performed at a Japanese university in 2019 and 2020. Students undergoing these check-ups were identified to respond to questions about sleep problems, digital media use, breakfast and exercise habits, and stress. In total, 3,869 students were included in the analysis. The association between the incidence of sleep problems in 2020 and the changes in digital media use between 2019 and 2020 was assessed using logistic regression models. The rate of long digital media use (≥ 2 hours) in 2019 was 42.6%, while in 2020 it was 53.6%. Incidence of sleep problems was observed in 244 students (6.3%) in 2020. There were 786 students (20.3%) who used digital media for ≤ 2 h in 2019 and ≥ 2 h in 2020. From the sample, 66 students (8.4%) reported incidence of sleep problems in 2020. Additionally, those respondents who specifically reported increased digital media use between 2019 and 2020 (increased use) where at greater risk (OR: 1.76; 95% CI: 1.21, 2.55) of reporting sleep problems in 2020, even after controlling for other study variables. Thus, this study provides evidence that the incidence of sleep problems has had a significant association with an increase in digital media use among university students throughout the COVID-19 pandemic. These findings highlight the importance of ensuring appropriate digital media use among students for improved quality of sleep.

ENIGMA-Sleep: Challenges, opportunities, and the road map

Neuroimaging and genetics studies have advanced our understanding of the neurobiology of sleep and its disorders. However, individual studies usually have limitations to identifying consistent and reproducible effects, including modest sample sizes, heterogeneous clinical characteristics and varied methodologies. These issues call for a large-scale multi-centre effort in sleep research, in order to increase the number of samples, and harmonize the methods of data collection, preprocessing and analysis using pre-registered well-established protocols. The Enhancing NeuroImaging Genetics through Meta-Analysis (ENIGMA) consortium provides a powerful collaborative framework for combining datasets across individual sites. Recently, we have launched the ENIGMA-Sleep working group with the collaboration of several institutes from 15 countries to perform large-scale worldwide neuroimaging and genetics studies for better understanding the neurobiology of impaired sleep quality in population-based healthy individuals, the neural consequences of sleep deprivation, pathophysiology of sleep disorders, as well as neural correlates of sleep disturbances across various neuropsychiatric disorders. In this introductory review, we describe the details of our currently available datasets and our ongoing projects in the ENIGMA-Sleep group, and discuss both the potential challenges and opportunities of a collaborative initiative in sleep medicine.

The Human Sleep Paradox: The Unexpected Sleeping Habits of Homo sapiens

The human sleep pattern is paradoxical. Sleep is vital for optimal physical and cognitive performance, yet humans sleep the least of all primates. In addition, consolidated and continuous monophasic sleep is evidently advantageous, yet emerging comparative data sets from small-scale societies show that the phasing of the human pattern of sleep–wake activity is highly variable and characterized by significant nighttime activity. To reconcile these phenomena, the social sleep hypothesis proposes that extant traits of human sleep emerged because of social and technological niche construction. Specifically, sleep sites function as a type of social shelter by way of an extended structure of social groups that increases fitness. Short, high-quality, and flexibly timed sleep likely originated as a response to predation risks while sleeping terrestrially. This practice may have been a necessary preadaptation for migration out of Africa and for survival in ecological niches that penetrate latitudes with the greatest seasonal variation in light and temperature on the planet.

Gender differences in BaYaka forager sleep-wake patterns in forest and village contexts

Sleep studies in small-scale subsistence societies have broadened our understanding of cross-cultural sleep patterns, revealing the flexibility of human sleep. We examined sleep biology among BaYaka foragers from the Republic of Congo who move between environmentally similar but socio-ecologically distinct locations to access seasonal resources. We analyzed the sleep-wake patterns of 51 individuals as they resided in a village location (n = 39) and a forest camp (n = 23) (362 nights total). Overall, BaYaka exhibited high sleep fragmentation (50.5) and short total sleep time (5.94 h), suggestive of segmented sleep patterns. Sleep duration did not differ between locations, although poorer sleep quality was exhibited in the village. Linear mixed effect models demonstrated that women's sleep differed significantly from men's in the forest, with longer total sleep time (β ± SE =  - 0.22 ± 0.09, confidence interval (CI) = [- 0.4, - 0.03]), and higher sleep quality (efficiency; β ± SE =  - 0.24 ± 0.09, CI = [- 0.42, - 0.05]). These findings may be due to gender-specific social and economic activities. Circadian rhythms were consistent between locations, with women exhibiting stronger circadian stability. We highlight the importance of considering intra-cultural variation in sleep-wake patterns when taking sleep research into the field.

The Impact of Earplugs and Eye Masks on Sleep Quality in Surgical ICU Patients at Risk for Frequent Awakenings

OBJECTIVES

Sleep disturbances may contribute to the development of delirium, prolonged ICU stay, and increased mortality. There is conflicting data on the effectiveness of earplugs and eye masks for sleep promotion in the ICU. This study evaluates the impact of earplugs and eye masks on sleep quality in postoperative surgical ICU patients at risk for frequent awakenings.

DESIGN

Prospective randomized controlled trial.

SETTING

Surgical ICU within the University of Texas Southwestern Medical Center.

PATIENTS

Adult, female patients admitted to the surgical ICU requiring hourly postoperative assessments following breast free flap surgery between February 2018 and October 2019.

INTERVENTIONS

Patients were randomized into an intervention group or a control group. The intervention group received earplugs and eye masks in addition to standard postoperative care, whereas the control group received standard postoperative care.

MEASUREMENTS AND MAIN RESULTS

The primary outcome was overall sleep quality assessed via the Richards-Campbell Sleep Questionnaire. Secondary outcomes of patient satisfaction and rates of ICU delirium were assessed with a modified version of the Family Satisfaction in the ICU survey and the Confusion Assessment Method for the ICU. After a planned interim analysis, the study was stopped early because prespecified criteria for significance were attained. Compared with the control group's average Richards-Campbell Sleep Questionnaire total score of 47.3 (95% CI, 40.8-53.8), the intervention group's average Richards-Campbell Sleep Questionnaire total score was significantly higher at 64.5 (95% CI, 58.3-70.7; p = 0.0007). There were no significant between-group differences for Confusion Assessment Method for the ICU scores or modified Family Satisfaction in the ICU survey scores.

CONCLUSIONS

These results suggest that earplugs and eye masks are effective in improving sleep quality in ICU patients undergoing frequent assessments. The results strengthen the evidence for nonpharmacologic sleep-promoting adjuncts in the ICU.

The Evolutionarily Mismatched Impact of Urbanization on Insomnia Symptoms: a Short Review of the Recent Literature

PURPOSE OF REVIEW

For the most part of human existence, individuals have been living a rural lifestyle in a rural setting. However, such sleep-conducive conditions have largely been transformed dramatically by urbanization within a relatively short span of time in recent history, and the resulting evolved mechanisms-environment mismatch is theorized to bring about an increased risk for insomnia symptoms. This brief review of the recent literature is designed to evaluate the veracity of this proposition.

RECENT FINDINGS

The majority of recent findings have suggested that most proposed evolutionarily mismatched urban factors are indeed related to the presence of insomnia symptoms. However, there is a general paucity of longitudinal evidence (and for some other factors, a lack of enough evidence of any kind). Although there is a preponderance of recent findings indicating a link between evolutionarily mismatched urban phenomena and insomnia symptoms, more longitudinal data are needed before any causative conclusion can be drawn.

COVID-19 Pandemic on Fire: Evolved Propensities for Nocturnal Activities as a Liability Against Epidemiological Control

Humans have been using fire for hundreds of millennia, creating an ancestral expansion toward the nocturnal niche. The new adaptive challenges faced at night were recurrent enough to amplify existing psychological variation in our species. Night-time is dangerous and mysterious, so it selects for individuals with higher tendencies for paranoia, risk-taking, and sociability (because of security in numbers). During night-time, individuals are generally tired and show decreased self-control and increased impulsive behaviors. The lower visibility during night-time favors the partial concealment of identity and opens more opportunities for disinhibition of self-interested behaviors. Indeed, individuals with an evening-oriented chronotype are more paranoid, risk-taking, extraverted, impulsive, promiscuous, and have higher antisocial personality traits. However, under some circumstances, such as respiratory pandemics, the psychobehavioral traits favored by the nocturnal niche might be counter-productive, increasing contagion rates of a disease that can evade the behavioral immune system because its disease cues are often nonexistent or mild. The eveningness epidemiological liability hypothesis presented here suggests that during the COVID-19 pandemic, the evening-oriented psychobehavioral profile can have collectively harmful consequences: there is a clash of core tendencies between the nocturnal chronotype and the recent viral transmission-mitigating safety guidelines and rules. The pandemic safety protocols disrupt much normal social activity, particularly at night when making new social contacts is desired. The SARS-CoV-2 virus is contagious even in presymptomatic and asymptomatic individuals, which enables it to mostly evade our evolved contagious disease avoidance mechanisms. A growing body of research has indirectly shown that individual traits interfering with social distancing and anti-contagion measures are related to those of the nocturnal chronotype. Indeed, some of the social contexts that have been identified as superspreading events occur at night, such as in restaurants, bars, and nightclubs. Furthermore, nocturnal environmental conditions favor the survival of the SARS-CoV-2 virus much longer than daytime conditions. We compare the eveningness epidemiological liability hypothesis with other factors related to non-compliance with pandemic safety protocols, namely sex, age, and life history. Although there is not yet a direct link between the nocturnal chronotype and non-compliance with pandemic safety protocols, security measures and future empirical research should take this crucial evolutionary mismatch and adaptive metaproblem into account, and focus on how to avoid nocturnal individuals becoming superspreaders, offering secure alternatives for nocturnal social activities.

Sleep duration is related to increased mortality risk through white blood cell counts in a large national sample

OBJECTIVES

Sleep, like many biological processes, is linked with immunity and inflammation such that "abnormal" sleep is associated with changes in circulating immune cells. These sleep patterns are also associated with increased mortality risk, and it may be that altered immune cell counts are one biological pathway through which sleep affects mortality. We used NHANES survey data to examine the associations between sleep duration, total white blood cell (WBC) count, and mortality from biological causes.

METHODS

Several waves of public NHANES data (2005-2011; n = 11 353, ages 18+) were analyzed using bivariate statistics and causal mediation models including corrections for complex survey design.

RESULTS

Deceased individuals were characterized by higher WBC but lower monocyte counts relative to surviving individuals. Significant associations between sleep duration, total WBC count, monocytes and mortality were found, as were marginally significant relationships between sleep and these cell counts. Significant mediated effects of sleep on mortality were found. Including covariates known to affect mortality, such as BMI, age, and self-reported health resulted in a nonsignificant mediated effect of sleep on mortality for monocytes, while mediated effects for total WBC count remained.

CONCLUSIONS

This large, cross-sectional analysis suggests that sleep duration is associated with changes in mortality risk through-in part-effects on leukocyte count. These findings support an immunological/inflammatory pathway linking sleep and mortality. Further research in populations with quantitatively different sleep patterns can determine whether this sleep-immune-mortality pathway is restricted to Western, industrial samples or is characteristic of humans in general.

Nondipping Blood Pressure: Predictive or Reactive Failure of Renal Sodium Handling?

Blood pressure follows a daily rhythm, dipping during nocturnal sleep in humans. Attenuation of this dip (nondipping) is associated with increased risk of cardiovascular disease. Renal control of sodium homeostasis is essential for long-term blood pressure control. Sodium reabsorption and excretion have rhythms that rely on predictive/circadian as well as reactive adaptations. We explore how these rhythms might contribute to blood pressure rhythm in health and disease.

Live fast, die young and sleep later: Life history strategy and human sleep behavior

Background and objectives

Life History Theory (LHT) describes trade-offs that organisms make with regard to three investment pathways: growth, maintenance and reproduction. In light of the reparative functions of sleep, we examine sleep behaviors and corresponding attitudes as proximate manifestations of an individual's underlying relative prioritization of short-term reproduction versus long-term maintenance.

Methodology

We collected survey data from 568 participants across two online studies having different participant pools. We use a mixture of segmented and hierarchical regression models, structural equation modeling and machine learning to infer relationships between sleep duration/quality, attitudes about sleep and biodemographic/psychometric measures of life history strategy (LHS).

Results

An age-mediated U- or V-shaped relationship appears when LHS is plotted against habitual sleep duration, with the fastest strategies occupying the sections of the curve with the highest mortality risk: < 6.5 hr (short sleep) and > 8.5 hr (long sleep). LH 'fastness' is associated with increased sleepiness and worse overall sleep quality: delayed sleep onset latency, more wakefulness after sleep onset, higher sleep-wake instability and greater sleep duration variability. Hedonic valuations of sleep may mediate the effects of LHS on certain sleep parameters.

Conclusions and implications

The costs of deprioritizing maintenance can be parameterized in the domain of sleep, where 'life history fastness' corresponds with sleep patterns associated with greater senescence and mortality. Individual differences in sleep having significant health implications can thus be understood as components of lifelong trajectories likely stemming from calibration to developmental circumstances. Relatedly, hedonic valuations of sleep may constitute useful avenues for non-pharmacological management of chronic sleep disorders.Lay Summary: Sleep is essential because it allows the body to repair and maintain itself. But time spent sleeping is time that cannot be spent doing other things. People differ in how much they prioritize immediate rewards, including sociosexual opportunities, versus long-term goals. In this research, we show that individual differences in sleep behaviors, and attitudes toward sleep, correspond with psychological and behavioral differences reflecting such differing priorities. Orientation toward sleep can thus be understood as part of the overall lifetime strategies that people pursue.

The Jaw Epidemic: Recognition, Origins, Cures, and Prevention

Contemporary humans are living very different lives from those of their ancestors, and some of the changes have had serious consequences for health. Multiple chronic "diseases of civilization," such as cardiovascular problems, cancers, ADHD, and dementias are prevalent, increasing morbidity rates. Stress, including the disruption of traditional sleep patterns by modern lifestyles, plays a prominent role in the etiology of these diseases, including obstructive sleep apnea. Surprisingly, jaw shrinkage since the agricultural revolution, leading to an epidemic of crooked teeth, a lack of adequate space for the last molars (wisdom teeth), and constricted airways, is a major cause of sleep-related stress. Despite claims that the cause of this jaw epidemic is somehow genetic, the speed with which human jaws have changed, especially in the last few centuries, is much too fast to be evolutionary. Correlation in time and space strongly suggests the symptoms are phenotypic responses to a vast natural experiment-rapid and dramatic modifications of human physical and cultural environments. The agricultural and industrial revolutions have produced smaller jaws and less-toned muscles of the face and oropharynx, which contribute to the serious health problems mentioned above. The mechanism of change, research and clinical trials suggest, lies in orofacial posture, the way people now hold their jaws when not voluntarily moving them in speaking or eating and especially when sleeping. The critical resting oral posture has been disrupted in societies no longer hunting and gathering. Virtually all aspects of how modern people function and rest are radically different from those of our ancestors. We also briefly discuss treatment of jaw symptoms and possible clinical cures for individuals, as well as changes in society that might lead to better care and, ultimately, prevention.

Sleep, brain vascular health and ageing

Sleep maintains the function of the entire body through homeostasis. Chronic sleep deprivation (CSD) is a prime health concern in the modern world. Previous reports have shown that CSD has profound negative effects on brain vasculature at both the cellular and molecular levels, and that this is a major cause of cognitive dysfunction and early vascular ageing. However, correlations among sleep deprivation (SD), brain vascular changes and ageing have barely been looked into. This review attempts to correlate the alterations in the levels of major neurotransmitters (acetylcholine, adrenaline, GABA and glutamate) and signalling molecules (Sirt1, PGC1α, FOXO, P66^shc, PARP1) in SD and changes in brain vasculature, cognitive dysfunction and early ageing. It also aims to connect SD-induced loss in the number of dendritic spines and their effects on alterations in synaptic plasticity, cognitive disabilities and early vascular ageing based on data available in scientific literature. To the best of our knowledge, this is the first article providing a pathophysiological basis to link SD to brain vascular ageing.

(Pre)Modern sleep. New evidence from the Antwerp criminal court (1715-1795)

Lately, experts have turned to historical evidence to uncover the default mode of our sleep pattern. Even though there are some notable exceptions, most historians use a qualitative methodology based on scattered evidence in diaries, letters, novels, medical treatise and other literary sources. To provide fresh perspective in the debate, the present article develops a more quantitative approach. Drawing fresh evidence from early modern criminal records - viz the eyewitness reports of the Hoge Vierschaer or the local criminal court in Antwerp - we are able to debunk some classic stereotypes about premodern sleep patterns. Data reveal that most 18^th -century Antwerpers slept fewer hours than we would expect, slumbered in a monophasic way and rarely if ever took a nap during the day. Moreover, the start and end of sleep were less attuned to the solar cycle than we would imagine. Last but not least, the pattern also shows some fascinating weekly and seasonal variations.

Sleep problems among Chinese adolescents and young adults during the coronavirus-2019 pandemic

OBJECTIVE

To assess the prevalence and sociodemographic correlates of insomnia symptoms among Chinese adolescents and young adults affected by the outbreak of coronavirus disease-2019 (COVID-19).

METHODS

This cross-sectional study included Chinese adolescents and young adults 12-29 years of age during part of the COVID-19 epidemic period. An online survey was used to collect demographic data, and to assess recognition of COVID-19, insomnia, depression, and anxiety symptoms using the Pittsburgh Sleep Quality Index (PSQI), the Patient Health Questionnaire (PHQ-9), and the Generalized Anxiety Disorder (GAD-7) questionnaires, respectively. The Social Support Rate Scale was used to assess social support.

RESULTS

Among 11,835 adolescents and young adults included in the study, the prevalence of insomnia symptoms during part of the COVID-19 epidemic period was 23.2%. Binomial logistic regression analysis revealed that female sex and residing in the city were greater risk factors for insomnia symptoms. Depression or anxiety were risk factors for insomnia symptoms; however, social support, both subjective and objective, was protective factors against insomnia symptoms. Furthermore, anxiety and depression symptoms were mediators of social support and insomnia symptoms.

CONCLUSIONS

Results of this study revealed a high prevalence of sleep problems among adolescents and young adults during the COVID-19 epidemic, especially senior high school and college students, which were negatively associated with students' projections of trends in COVID-19. The adverse impact of COVID-19 was a risk factor for insomnia symptoms; as such, the government must devote more attention to sleep disorders in this patient population while combating COVID-19.

Sleep, circadian rhythms and health

At the core of human thought, for the majority of individuals in the developed nations at least, there is the tacit assumption that as a species we are unfettered by the demands imposed by our biology and that we can do what we want, at whatever time we choose, whereas in reality every aspect of our physiology and behaviour is constrained by a 24 h beat arising from deep within our evolution. Our daily circadian rhythms and sleep/wake cycle allow us to function optimally in a dynamic world, adjusting our biology to the demands imposed by the day/night cycle. The themes developed in this review focus upon the growing realization that we ignore the circadian and sleep systems at our peril, and this paper considers the mechanisms that generate and regulate circadian and sleep systems; what happens mechanistically when these systems collapse as a result of societal pressures and disease; how sleep disruption and stress are linked; why sleep disruption and mental illness invariably occur together; and how individuals and employers can attempt to mitigate some of the problems associated with working against our internal temporal biology. While some of the health costs of sleep disruption can be reduced, in the short-term at least, there will always be significant negative consequences associated with shift work and sleep loss. With this in mind, society needs to address this issue and decide when the consequences of sleep disruption are justified in the workplace.

Impacts of nocturnal breastfeeding, photoperiod, and access to electricity on maternal sleep behaviors in a non-industrial rural Bolivian population

OBJECTIVES

We tested 4 main predictions, derived from life history theory and self-evident human diurnality, regarding maternal sleep behaviors in a non-industrialized population in which mother-nursling co-sleeping is universal and prolonged: (1) Night breastfeeding incurs a sleep cost to co-sleeping mothers; (2) Night breastfeeding increases with infant age, causing mothers to sleep less; (3) Sleep duration co-varies with darkness duration; (4) Access to electricity reduces sleep duration.

DESIGN

Mothers self-recorded and reported nursing and sleep behaviors for a 48-hour period once per month (median = 5 months).

SETTING

Rural Bolivian altiplano homesteads, primarily reliant on agropastoralism, scattered throughout the countryside surrounding a main town (altitude 3800 m; 17°14'S, 65°55'W; darkness duration 10-12 hours over the year).

PARTICIPANTS

One hundred eighty-four co-sleeping mother-infant pairs (infant age 22-730 days).

MEASUREMENTS

Breastfeeding frequency, and retiring and rising times for 885 48-hour observation periods.

RESULTS

Maternal sleep duration covaried with darkness duration. Sleep duration was shorter in those with access to electricity (ie, living nearer to town) than those without access (more distant homesteads). Night breastfeeding rate was fairly steady until it began to decline after the first year postpartum. At a given infant age, higher night breastfeeding rates were associated with less maternal sleep. As their infants aged, mothers without electricity slept more, whereas mothers with access slept less.

CONCLUSIONS

During the first year postpartum, more frequent night nursing shortens maternal sleep more than any other predictor variable. For older infants, the effect of night nursing diminishes, and even modest "modernization" (eg, access to electricity) is associated with shorter maternal sleep.

An evolutionary perspective on night terrors

Night terrors, also known as sleep terrors, are an early childhood parasomnia characterized by screams or cries, behavioral manifestations of extreme fear, difficulty waking and inconsolability upon awakening. The mechanism causing night terrors is unknown, and a consistently successful treatment has yet to be documented. Here, we argue that cultural practices have moved us away from an ultimate solution: cosleeping. Cosleeping is the norm for closely related primates and for humans in non-Western cultures. In recent years, however, cosleeping has been discouraged by the Western medical community. From an evolutionary perspective, cosleeping provides health and safety benefits for developing children. We discuss night terrors, and immediate and long-term health features, with respect to cosleeping, room-sharing and solitary sleeping. We suggest that cosleeping with children (≥1-year-old) may prevent night terrors and that, under certain circumstances, cosleeping with infants (≤11-months-old) is preferable to room-sharing, and both are preferable to solitary sleeping.

Sleep in a comparative context: Investigating how human sleep differs from sleep in other primates

OBJECTIVES

Primates vary in their sleep durations and, remarkably, humans sleep the least per 24-hr period of the 30 primates that have been studied. Using phylogenetic methods that quantitatively situate human phenotypes within a broader primate comparative context, we investigated the evolution of human sleep architecture, focusing on: total sleep duration, rapid eye movement (REM) sleep duration, non-rapid eye movement (NREM) sleep duration, and proportion of sleep in REM.

MATERIALS AND METHODS

We used two different Bayesian methods: phylogenetic prediction based on phylogenetic generalized least squares and a multistate Onrstein-Uhlenbeck (OU) evolutionary model of random drift and stabilizing selection.

RESULTS

Phylogenetic prediction confirmed that humans sleep less than predicted for a primate of our body mass, predation risk, brain size, foraging needs, sexual selection, and diet. These analyses further revealed that humans pack an unexpectedly higher proportion of REM sleep within a shorter overall sleep duration, and do so by reducing NREM sleep (rather than increasing REM). The OU model generally confirmed these findings, with shifts along the human lineage inferred for TST, NREM, and proportion of REM, but not for REM.

DISCUSSION

We propose that the risks and opportunity costs of sleep are responsible for shorter sleep durations in humans, with risks arising from terrestrial sleep involving threats from predators and conspecifics, and opportunity costs because time spent sleeping could be used for learning, creating material objects, and socializing.

Chronotype variation drives night-time sentinel-like behaviour in hunter-gatherers

Sleep is essential for survival, yet it also represents a time of extreme vulnerability to predation, hostile conspecifics and environmental dangers. To reduce the risks of sleeping, the sentinel hypothesis proposes that group-living animals share the task of vigilance during sleep, with some individuals sleeping while others are awake. To investigate sentinel-like behaviour in sleeping humans, we investigated activity patterns at night among Hadza hunter-gatherers of Tanzania. Using actigraphy, we discovered that all subjects were simultaneously scored as asleep for only 18 min in total over 20 days of observation, with a median of eight individuals awake throughout the night-time period; thus, one or more individuals was awake (or in light stages of sleep) during 99.8% of sampled epochs between when the first person went to sleep and the last person awoke. We show that this asynchrony in activity levels is produced by chronotype variation, and that chronotype covaries with age. Thus, asynchronous periods of wakefulness provide an opportunity for vigilance when sleeping in groups. We propose that throughout human evolution, sleeping groups composed of mixed age classes provided a form of vigilance. Chronotype variation and human sleep architecture (including nocturnal awakenings) in modern populations may therefore represent a legacy of natural selection acting in the past to reduce the dangers of sleep.