The evolution of human sleep: Technological and cultural innovation associated with sleep-wake regulation among Hadza hunter-gatherers

Low-to-Moderate Daytime Physical Activities Predicted Higher-Quality Sleep Among Habitually Active Agropastoralists

INTRODUCTION

The positive effects of physical activity (PA) on sleep are widely promoted by public health organizations and supported by abundant empirical evidence. Nonetheless, there remains a dearth of studies investigating the association between daytime PA and nighttime sleep among non-urban and nonindustrial populations that habitually engage in PA as part of their subsistence strategy.

METHODS

Here, we examined the bidirectional relationship between PA and sleep. We also looked at age, gender, and occupation-level differences in moderate-to-vigorous-intensity PA (MVPA), low-intensity PA (LPA), and sedentary activity durations among Basotho and Xhoxa agropastoralists residing in rural villages in the Eastern Cape, South Africa. We analyzed activity and sleep data collected from 113 individuals using MotionWatch actigraphy wristwatches across three field seasons (7111 individual days).

RESULTS

Percentage daily total MVPA decreased with age, though older participants maintained low activity levels and did not suffer from poorer sleep compared to younger participants. Herders spent more percentage of their day in higher-intensity activity than non-herders. Overall, women had greater daily percentage MVPA and lower percentage sedentary activity than men. Durations of total MVPA and LPA decreased total sleep time (TST) and improved sleep quality (increased sleep efficiency (SE), decreased fragmentation, and decreased percentage wake after sleep onset). Daytime PA measures were not affected by sleep duration or quality from the previous night.

CONCLUSIONS

Among this group of habitually active agropastoralists, low-to-moderate-intensity PA durations consistently predicted higher sleep quality. Our findings showed that sleep quality was more strongly affected by PA than sleep duration.

The Impact of Sleep: From Ancient Rituals to Modern Challenges

Although sleep is crucial for mental and physical health, insufficient sleep is a growing problem in our modern society. In general, adults need approximately eight hours of sleep per night, but this is often unfeasible nowadays. This sleep restriction has been observed, and it has worsened, throughout the past two centuries; therefore, it is more attributed to socioeconomic changes than to biological adaptations. The most important factors to contribute to this sleep restriction were the popularization of artificial light and industrialization. The present manuscript briefly overviews, from a socioanthropological perspective, the reasons why sleep has been impacted, disclosing its effects on individuals and on society.

Sleep in the wild: the importance of individual effects and environmental conditions on sleep behaviour in wild boar

Sleep serves vital physiological functions, yet how sleep in wild animals is influenced by environmental conditions is poorly understood. Here we use high-resolution biologgers to investigate sleep in wild animals over ecologically relevant time scales and quantify variability between individuals under changing conditions. We developed a robust classification for accelerometer data and measured multiple dimensions of sleep in the wild boar (Sus scrofa) over an annual cycle. In support of the hypothesis that environmental conditions determine thermoregulatory challenges, which regulate sleep, we show that sleep quantity, efficiency and quality are reduced on warmer days, sleep is less fragmented in longer and more humid days, while greater snow cover and rainfall promote sleep quality. Importantly, this longest and most detailed analysis of sleep in wild animals to date reveals large inter- and intra-individual variation. Specifically, short-sleepers sleep up to 46% less than long-sleepers but do not compensate for their short sleep through greater plasticity or quality, suggesting they may pay higher costs of sleep deprivation. Given the major role of sleep in health, our results suggest that global warming and the associated increase in extreme climatic events are likely to negatively impact sleep, and consequently health, in wildlife, particularly in nocturnal animals.

The Concurrent and Longitudinal Relationship between Perinatal Sleep Difficulties and Depression in a Large Sample of High-Risk Women in South Africa

INTRODUCTION

Perinatal depression and sleep difficulties are common among studies conducted in high income countries (HIC). This study examines the relationship between sleep difficulties and depression during the perinatal period and over an eight-year follow-up period in South Africa, a middle income country.

METHOD

A population cohort of 1238 pregnant women (mean age = 26.33) in 24 township neighborhoods in South Africa were recruited and reassessed six times over the next 8 years post birth with follow-up rates of 96-83%. The relationship between maternal depressed mood and sleep difficulties was examined over time, as well as the relationship of sleep with other socioeconomic, environmental, and psychiatric risk factors.

RESULTS

Thirty-five percent of the women reported sleep difficulties during the perinatal period; whereas only 8% reported sleep difficulties at 8-year follow-up. Perinatal sleep difficulties were associated with lower income, lower educational attainment, less access to electricity, more food insecurity, higher rates of interpersonal violence and HIV, alcohol consumption, and depressed mood at 8 years. However, the severity of depressed mood was the strongest predictor of sleep problems longitudinally and cross-sectionally, after accounting for all other risk factors.

CONCLUSIONS

We found that the severity of depressed mood is highly associated with sleep difficulties from pregnancy to 8 years post-birth and in a linear relationship, so that higher depressed mood is associated with more sleep problems.

TRIAL REGISTRATION

ClinicalTrials.gov registration: # NCT00996528.

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.

Mediation of the association between multi-morbidity and sleep problems by pain and depressive symptoms among older adults: Evidence from the Longitudinal Aging Study in India, wave- 1

BACKGROUND

There could be several possible mechanisms on how chronic conditions relate to sleep problems in older persons; for instance, pain and sleep have a strong link and depressive symptoms are similarly associated with sleep problems. The present study explored whether pain and depressive symptoms are mediators in the relationship between multi-morbidity and sleep problems among older adults.

METHODS

Study utilized data from the Longitudinal Aging Study in India (LASI) with a sample of 31,464 older adults age 60 years and above. Multivariable logistic regression along with mediation analysis using Karlson-Holm-Breen (KHB) method was conducted.

RESULTS

A proportion of 14.8% of the participants suffered from sleep problems, whereas, 22.5% and 8.7% of older adults had multi-morbidity and had depressive symptoms, respectively. Also, around 10.3% of older adults reported pain and received no medication for the relief of pain, whereas 29.3% of older adults reported pain and received some type of medication for the relief of pain. Older adults with multi-morbidity had higher odds of suffering from sleep problems [adjusted odds ratio (aOR):1.26, confidence interval (CI):1.10-1.45] than those who had no multi-morbidity. Older adults who reported pain but received no medication for the relief of pain [aOR: 1.90, CI: 1.64-2.22] or reported pain and received medication for the relief of pain [aOR: 1.82, CI:1.62-2.04] and those who had depressive symptoms [aOR: 2.21, CI:1.89-2.57%] had higher odds of suffering from sleep problems compared to those who did not report pain and had no depressive symptoms, respectively. Around 11.2% of the association of multi-morbidity with sleep problems was mediated by pain and 4.3% of such association was mediated by depressive symptoms.

CONCLUSION

Pain and depressive symptoms were found to mediate the association between multi-morbidity and sleep problems; therefore, reducing pain and depressive symptoms may be considered to improve sleep in older multi-morbid patients.

Sleep deprivation among adolescents in urban and indigenous-rural Mexican communities

Comparing the nature of adolescent sleep across urban and more isolated, rural settings through an ecological, cross-cultural perspective represents one way to inform sleep nuances and broaden our understanding of human development, wellbeing and evolution. Here we tested the Social Jetlag Hypothesis, according to which contemporary, urban lifestyles and technological advances are associated with sleep insufficiency in adolescents. We documented the adolescent sleep duration (11-16 years old; X̅ = 13.7 ± 1.21; n = 145) in two small agricultural, indigenous and one densely urban context in Mexico to investigate whether adolescents in socio-ecologically distinct locations experience sleep deprivation. Sleep data was assembled with actigraphy, sleep diaries and standardized questionnaires. We employed multilevel models to analyze how distinct biological and socio-cultural factors (i.e., pubertal maturation, chronotype, napping, gender, working/schooling, access to screen-based devices, exposure to light, and social sleep practices) shape adolescent sleep duration. Results suggest that the prevalence of adolescent short sleep quotas is similar in rural, more traditional environments compared to highly urbanized societies, and highlight the influence of social activities on the expression of human sleep. This study challenges current assumptions about natural sleep and how adolescents slept before contemporary technological changes occurred.

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.

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.

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.

Effectiveness of a Cool Bed Linen for Thermal Comfort and Sleep Quality in Air-Conditioned Bedroom under Hot-Humid Climate

Comfort temperature and sleep quality involving 20 participants were determined in two cases: Case A (arbitrary, controlled air-conditioner setting) and Case B (adjustment of 3 °C higher than the setting of Case A with cool bed linen). Data of indoor thermal comfort and electricity consumption were collected every night throughout the measurement period. Questionnaires on thermal comfort and sleep quality were distributed twice a night for a duration of three nights for each case; the first night was for respondents’ adaptation and the following two nights were for measurement. The sleep quality of the respondents was objectively measured using a commercially available activity tracker. Results found that most respondents were thermally comfortable in both cases, with 39% lower energy consumption reported for Case B compared to Case A. The thermal conditions of Case B were found to be more tolerable than those of Case A. Most respondents reported to have a calm and satisfied sleep for both cases. Comfort temperature and Sleep Efficiency Index (SEI) were found to be maintained in both cases.

Taking the sleep lab to the field: Biometric techniques for quantifying sleep and circadian rhythms in humans

OBJECTIVES

Remarkably, the specifics of sleep along the human lineage have been slow to emerge, which is surprising given our distinct mental and behavioral capacity and the importance of sleep for individual health and cognitive performance. Largely due to difficultly of measuring sleep outside a controlled, clinical, and laboratory study in ambulatory individuals, human biologists have yet to undergo a thorough examination of sleep in ecologically diverse settings. Here, I outline the procedures and methods for generating sleep data in a broader ecological context with the goal of facilitating the integration of sleep and circadian analyses into human biology research.

METHODS

I describe the steps involved in participant recruitment, screening by way of survey instruments, and sample collection. In addition to describing field use of the traditional (but invasive) equipment such as the gold-standard application of electroencephalography (EEG), I demonstrate leading-edge noninvasive techniques for biometric devices (ie, wrist-worn actigraphy, ring worn arterial pulsometry) to generate sleep and circadian rhythms data.

RESULTS

I outline best approaches to process and analyze data-including variables such as sleep duration, 24-hour sleep time (ie, summation of night and day sleep), sleep efficiency, sleep fragmentation, and nonparametric circadian rhythms analysis to quantify circadian amplitude. Finally, I discuss comparative statistical methods that are optimized for the use of time-series data.

CONCLUSIONS

This review serves as an introduction to the best practices for studying sleep-wake patterns in humans-with the goal of standardizing tools for launching new human sleep biology research initiatives across the globe.

The R Language as a Tool for Biometeorological Research

R is an open-source programming language which gained a central place in the geosciences over the last two decades as the primary tool for research. Now, biometeorological research is driven by the diverse datasets related to the atmosphere and other biological agents (e.g., plants, animals and human beings) and the wide variety of software to handle and analyse them. The demand of the scientific community for the automation of analysis processes, data cleaning, results sharing, reproducibility and the capacity to handle big data brings a scripting language such as R in the foreground of the academic universe. This paper presents the advantages and the benefits of the R language for biometeorological and other atmospheric sciences’ research, providing an overview of its typical workflow. Moreover, we briefly present a group of useful and popular packages for biometeorological research and a road map for further scientific collaboration on the R basis. This paper could be a short introductory guide to the world of the R language for biometeorologists.

Healthy Eating, Physical Activity, and Sleep Hygiene (HEPAS) as the Winning Triad for Sustaining Physical and Mental Health in Patients at Risk for or with Neuropsychiatric Disorders: Considerations for Clinical Practice

Neuropsychiatric disorders stem from gene-environment interaction and their development can be, at least in some cases, prevented by the adoption of healthy and protective lifestyles. Once full blown, neuropsychiatric disorders are prevalent conditions that patients live with a great burden of disability. Indeed, the determinants that increase the affliction of neuropsychiatric disorders are various, with unhealthy lifestyles providing a significant contribution in the interplay between genetic, epigenetic, and environmental factors that ultimately represent the pathophysiological basis of these impairing conditions. On one hand, the adoption of Healthy Eating education, Physical Activity programs, and Sleep hygiene promotion (HEPAS) has the potential to become one of the most suitable interventions to reduce the risk to develop neuropsychiatric disorders, while, on the other hand, its integration with pharmacological and psychological therapies seems to be essential in the overall management of neuropsychiatric disorders in order to reduce the disability and improve the quality of life of affected patients. We present an overview of the current evidence in relation to HEPAS components in the prevention and management of neuropsychiatric disorders and provide suggestions for clinical practice.

[Thoughts about Light and Sleep]

Thoughts about Light and Sleep Abstract. Many aspects of health and disease are mainly determined by the constant change between light and darkness during a solar day. The resulting physiological rhythms correspond to the circadian rhythm, which was one of the most central drivers in the evolution of humans. However, over the last 20-30 years, these natural rhythms of the change of light and darkness are being increasingly ignored by modern societies. It is well known that these rhythms are modulators of many physiological pathways and any desynchronization or misalignment will activate different pathophysiological pathways, which contribute to the risk of chronic diseases. Light pollution by widespread illumination of our environment and the night sky and uncontrolled man-made use of any light source plays a key role in the pathogenesis of sleep disturbances. Blue light exposure in the evening from any artificial light source (especially from electronic device screens) is of special relevance in this context. In this article a few key facts concerning light, sleep and diseases are presented. We should by all means account for the effects of light and darkness and stop any further light pollution.

Sleep variability and nighttime activity among Tsimane forager-horticulturalists

OBJECTIVES

A common presumption in sleep research is that "normal" human sleep should show high night-to-night consistency. Yet, intra-individual sleep variation in small-scale subsistence societies has never been studied to test this idea. In this study, we assessed the degree of nightly variation in sleep patterns among Tsimane forager-horticulturalists in Bolivia, and explored possible drivers of the intra-individual variability.

METHODS

We actigraphically recorded sleep among 120 Tsimane adults (67 female), aged 18-91, for an average of 4.9 nights per person using the Actigraph GT3X and Philips Respironics Actiwatch 2. We assessed intra-individual variation using intra-class correlations and average deviation from each individual's average sleep duration, onset, and offset times ( ɛ¯).

RESULTS

Only 31% of total variation in sleep duration was due to differences among different individuals, with the remaining 69% due to nightly differences within the same individuals. We found no statistically significant differences in Tsimane sleep duration by day-of-the-week. Nightly variation in sleep duration was driven by highly variable sleep onset, especially for men. Nighttime activities associated with later sleep onset included hunting, fishing, housework, and watching TV.

CONCLUSIONS

In contrast to nightly sleep variation in the United States being driven primarily by "sleeping-in" on weekends, Tsimane sleep variation, while comparable to that observed in the United States, was driven by changing "bedtimes," independent of day-of-the-week. We propose that this variation may reflect adaptive responses to changing opportunity costs to sleep/nighttime activity.

The influence of age- and sex-specific labor demands on sleep in Namibian agropastoralists

OBJECTIVE

To understand the basics of sleep quality in a pastoralist population and to explore predictors of this variation.

DESIGN

Cross-sectional.

SETTING

Northern Namibia, dry seasons of 2016 and 2017.

PARTICIPANTS

The Himba, a nonindustrial seminomadic agropastoralist population without access to the electrical grid.

MEASUREMENTS

Using Actiwatch-2 devices, 75 participants completed 721 days of wear. We calculated sleep duration, efficiency, and activity counts before and after sunset/sunrise and onset/offset. Participants were also interviewed about sleeping arrangements and nighttime disruptions.

RESULTS

Himba show lower sleep duration and efficiency than other populations studied, and men had substantially lower duration and efficiency than women. Sex differences were not attenuated when napping was included with total sleep time. Age predicted longer sleep duration and lower evening and morning activity levels. Number of adult co-sleepers predicted increased sleep duration and efficiency in women. Livestock disturbance was not a commonly reported cause of nighttime waking.

CONCLUSIONS

These findings support predictions that pastoralist groups may have lower sleep quality than other subsistence populations, but this does not appear to be a consequence of noise from livestock. Instead, lower sleep quality appears to be the result of subsistence and social activities, particularly for men and young adults overall.

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.