Sleep and light exposure across different levels of urbanisation in Brazilian communities

Urbanisation negatively impacts sleep health and mood in adolescents: a comparative study of female students from city and rural schools of North India

This study investigated the impact of social settings on sleep, physical and mental health in female adolescents of North India (latitude 29.5 oN; longitude 77.5 oE). Using a battery of questionnaires, we compared the chronotype, sleep-wake pattern, sleep health (e.g. sleep quality, daytime sleepiness and fatigue) and mood (via depression, anxiety and stress symptoms) in female students (age 14-18 years) from rural (N = 719) and urban (N = 1033) schools separated by about 35 km, but families had almost similar socio-demographic details. The morning type was prevalent amongst rural, whilst the evening type was prevalent amongst urban students who also had access to smart phones, suggesting a possible greater use of the internet. There were greater negative sleep effects, daytime sleepiness, overall poor sleep quality, higher fatigue and anxiety levels in urban than the rural cohort. Interestingly, these measures also differed between school days and free days, suggesting an impact of the conflict between internal biological and social timings (= social jet lag). We also found a significant relationship between chronotype, internet addiction, mood-related parameters and measures of sleep health. Overall, these results suggest a possible impact of social settings on sleep health and mood-related behaviours in female adolescents.

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.

Photoperiod and metabolic health: evidence, mechanism, and implications

Circadian rhythms are evolutionarily programmed biological rhythms that are primarily entrained by the light cycle. Disruption of circadian rhythms is an important risk factor for several metabolic disorders. Photoperiod is defined as total duration of light exposure in a day. With the extended use of indoor/outdoor light, smartphones, television, computers, and social jetlag people are exposed to excessive artificial light at night increasing their photoperiod. Importantly long photoperiod is not limited to any geographical region, season, age, or socioeconomic group, it is pervasive. Long photoperiod is an established disrupter of the circadian rhythm and can induce a range of chronic health conditions including adiposity, altered hormonal signaling and metabolism, premature ageing, and poor psychological health. This review discusses the impact of exposure to long photoperiod on circadian rhythms, metabolic and mental health, hormonal signaling, and ageing and provides a perspective on possible preventive and therapeutic approaches for this pervasive challenge.

Multidimensions of sleep health among in-school adolescents in rural and urban areas in southwestern Nigeria

INTRODUCTION

Previous studies have focused on sleep inequities among disadvantaged populations in high-income countries. However, little is known about the differences in sleep health among adolescents in Africa. We aimed to compare the multidimensions of sleep health in adolescents living in rural vs. urban communities in Nigeria.

METHODS

This cross-sectional study enrolled adolescents aged 13-19 in six rural and six urban schools in Osun State, Nigeria. We measured the prevalence of poor sleep quality (Pittsburgh Sleep Quality Index score >5), daytime sleepiness (Epworth Sleepiness Scale for Children and Adolescents score >10), and risk of sleep apnea (Teen STOPBANG). We compared the sleep health variables between the rural and urban populations using multivariable logistic regression.

RESULTS

Of the 900 participants (51% rural; 59% female; average age (SD)= 15.1(1.4) years), 79% had short sleep duration (<8.5 hours), 14.9% poor sleep quality, 9.6% excessive daytime sleepiness and 9.8% risk of sleep apnea. Urban adolescents had a higher prevalence of poor sleep quality (p = .004), short sleep duration (p < .001), daytime sleepiness (p = .044), and risk of sleep apnea (p = .006) compared to rural adolescents. The adjusted odds of having poor sleep quality (p = .008) and daytime sleepiness (p = .007) were about 2-fold higher among urban compared to rural adolescents. Later school end time, having single/separated parent(s), absence of parental setting of bedtime were independently associated with poorer sleep health.

CONCLUSION

Adolescents in rural communities had better sleep health than adolescents in urban communities. There is a need to develop interventions to improve the sleep quality and overall sleep health of urban-dwelling adolescents.

Genome-wide gene by environment study of time spent in daylight and chronotype identifies emerging genetic architecture underlying light sensitivity

STUDY OBJECTIVES

Light is the primary stimulus for synchronizing the circadian clock in humans. There are very large interindividual differences in the sensitivity of the circadian clock to light. Little is currently known about the genetic basis for these interindividual differences.

METHODS

We performed a genome-wide gene-by-environment interaction study (GWIS) in 280 897 individuals from the UK Biobank cohort to identify genetic variants that moderate the effect of daytime light exposure on chronotype (individual time of day preference), acting as "light sensitivity" variants for the impact of daylight on the circadian system.

RESULTS

We identified a genome-wide significant SNP mapped to the ARL14EP gene (rs3847634; p < 5 × 10-8), where additional minor alleles were found to enhance the morningness effect of daytime light exposure (βGxE = -.03, SE = 0.005) and were associated with increased gene ARL14EP expression in brain and retinal tissues. Gene-property analysis showed light sensitivity loci were enriched for genes in the G protein-coupled glutamate receptor signaling pathway and genes expressed in Per2+ hypothalamic neurons. Linkage disequilibrium score regression identified Bonferroni significant genetic correlations of greater light sensitivity GWIS with later chronotype and shorter sleep duration. Greater light sensitivity was nominally genetically correlated with insomnia symptoms and risk for post-traumatic stress disorder (PTSD).

CONCLUSIONS

This study is the first to assess light as an important exposure in the genomics of chronotype and is a critical first step in uncovering the genetic architecture of human circadian light sensitivity and its links to sleep and mental health.

Daytime light exposure is a strong predictor of seasonal variation in sleep and circadian timing of university students

In the absence of electric light, sleep for humans typically starts soon after dusk and at higher latitudes daily sleep timing changes seasonally as photoperiod changes. However, access to electric light shields humans from natural photoperiod changes, and whether seasonal changes in sleep occur despite this isolation from the natural light-dark cycle remains a matter of controversy. We measured sleep timing in over 500 university students living in the city of Seattle, WA (47.6°N) throughout the four seasons; we show that even when students are following a school schedule, sleep timing is delayed during the fall and winter. For instance, during the winter school days, students fell asleep 35 min later and woke up 27 min later (under daylight-savings time) than students during the summer school days, a change that is an hour larger relative to solar midnight. Furthermore, chronotype defined by mid-sleep on free days corrected for oversleep (MSFc), an indirect estimate of circadian phase, was more than 30 min later in the winter compared with the summer. Analysis of the effect of light exposure showed that the number of hours of light exposure to at least 50 lux during the daytime was a stronger predictor of MSFc than the exposure time to this illuminance after dusk. Specifically, MSFc was advanced by 30 min for each additional hour of light exposure during daytime and delayed by only 15 min for each additional hour of postdusk exposure to light. Additionally, the time of the day of exposure to high light intensities was more predictive of MSFc when daytime exposure was considered than when exposure for the full 24-h day was considered. Our results show that although sleep time is highly synchronized to social time, a delayed timing of sleep is evident during the winter months. They also suggest that daily exposure to daylight is key to prevent this delayed phase of the circadian clock and thus circadian disruption that is typically exacerbated in high-latitude winters.

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.

Technological infrastructure, sleep, and rest-activity patterns in a Kaqchikel Maya community

Sleep duration, quality, and rest-activity pattern-a measure for inferring circadian rhythm-are influenced by multiple factors including access to electricity. Recent findings suggest that the safety and comfort afforded by technology may improve sleep but negatively impact rest-activity stability. According to the circadian entrainment hypothesis, increased access to electric lighting should lead to weaker and less uniform circadian rhythms, measured by stability of rest-activity patterns. Here, we investigate sleep in a Maya community in Guatemala who are in a transitional stage of industrialization. We predicted that (i) sleep will be shorter and less efficient in this population than in industrial settings, and that (ii) rest-activity patterns will be weaker and less stable than in contexts with greater exposure to the natural environment and stronger and more stable than in settings more buffered by technologic infrastructure. Our results were mixed. Compared to more industrialized settings, in our study population sleep was 4.87% less efficient (78.39% vs 83.26%). We found no significant difference in sleep duration. Rest-activity patterns were more uniform and less variable than in industrial settings (interdaily stability = 0.58 vs 0.43; intradaily variability = 0.53 vs 0.60). Our results suggest that industrialization does not inherently reduce characteristics of sleep quality; instead, the safety and comfort afforded by technological development may improve sleep, and an intermediate degree of environmental exposure and technological buffering may support circadian rhythm strength and stability.

Relationship between multimorbidity and composite lifestyle status in Shenzhen, China

Objective

The study aimed to understand multimorbidity among adults in a high-tech city in southern coastal China that has undergone rapid economic development and to investigate its relationship with lifestyle status.

Methods

A population-based survey was conducted among 24 community centers in the Nanshan District of Shenzhen from February to December of 2018. Participants were recruited using a stratified random sampling approach. A self-administered questionnaire on typical chronic diseases, lifestyle factors, body composition, and social demographics was used to collect data. Multimorbidity was defined as two or more chronic diseases coexisting in a single person. An algorithm on body mass index, physical activity, drinking, smoking, and sleep quality was used to calculate lifestyle scores (0-9), with higher scores predicting a healthier lifestyle.

Results

A total of 2,905 participants were included in the analysis, with men accounting for 52.4%, and single for 25%. The prevalence of multimorbidity was 4.8%, and the mean lifestyle score was 4.79 ± 1.55. People who were old, retired, married, and had less education were more likely to have multimorbidity (all P < .05). A higher prevalence of multimorbidity was found among those who were obese, less engaged in physical activity, consumed more alcohol, and had poorer sleep quality (all p < .05). After adjusting for age, employment, education, and marital status, one unit increase in lifestyle score was associated with 0.74 times lower to have multimorbidity (OR: 0.74; 95% CI: 0.63-0.87, p < .05).

Conclusion

The prevalence of multimorbidity was relatively low in economically developed Shenzhen. Keeping a healthy lifestyle was related to the lower possibility of suffering from multiple chronic diseases.

Development and testing of methods for detecting off-wrist in actimetry recordings

Study Objectives

In field studies using wrist-actimetry, not identifying/handling off-wrist intervals may result in their misclassification as immobility/sleep and biased estimations of rhythmic patterns. By comparing different solutions for detecting off-wrist, our goal was to ascertain how accurately they detect nonwear in different contexts and identify variables that are useful in the process.

Methods

We developed algorithms using heuristic (HA) and machine learning (ML) approaches. Both were tested using data from a protocol followed by 10 subjects, which was devised to mimic contexts of actimeter wear/nonwear in real-life. Self-reported data on usage according to the protocol were considered the gold standard. Additionally, the performance of our algorithms was compared to that of visual inspection (by 2 experienced investigators) and Choi algorithm. Data previously collected in field studies were used for proof-of-concept analyses.

Results

All methods showed similarly good performances. Accuracy was marginally higher for one of the raters (visual inspection) than for heuristically developed algorithms (HA, Choi). Short intervals (especially &lt; 2 h) were either not or only poorly identified. Consecutive stretches of zeros in activity were considered important indicators of off-wrist (for both HA and ML). It took hours for raters to complete the task as opposed to the seconds or few minutes taken by the automated methods.

Conclusions

Automated strategies of off-wrist detection are similarly effective to visual inspection, but have the important advantage of being faster, less costly, and independent of raters’ attention/experience. In our study, detecting short intervals was a limitation across methods.

The Effect of Light Therapy on Electroencephalographic Sleep in Sleep and Circadian Rhythm Disorders: A Scoping Review

Light therapy is used to treat sleep and circadian rhythm disorders, yet there are limited studies on whether light therapy impacts electroencephalographic (EEG) activity during sleep. Therefore, we aimed to provide an overview of research studies that examined the effects of light therapy on sleep macro- and micro-architecture in populations with sleep and circadian rhythm disorders. We searched for randomized controlled trials that used light therapy and included EEG sleep measures using MEDLINE, PubMed, CINAHL, PsycINFO and Cochrane Central Register of Controlled Trials databases. Five articles met the inclusion criteria of patients with either insomnia or delayed sleep−wake phase disorder (DSWPD). These trials reported sleep macro-architecture outcomes using EEG or polysomnography. Three insomnia trials showed no effect of the timing or intensity of light therapy on total sleep time, wake after sleep onset, sleep efficiency and sleep stage duration compared to controls. Only one insomnia trial reported significantly higher sleep efficiency after evening light therapy (>4000 lx between 21:00−23:00 h) compared with afternoon light therapy (>4000 lx between 15:00−17:00 h). In the only DSWPD trial, six multiple sleep latency tests were conducted across the day (09:00 and 19:00 h) and bright light (2500 lx) significantly lengthened sleep latency in the morning (09:00 and 11:00 h) compared to control light (300 lx). None of the five trials reported any sleep micro-architecture measures. Overall, there was limited research about the effect of light therapy on EEG sleep measures, and studies were confined to patients with insomnia and DSWPD only. More research is needed to better understand whether lighting interventions in clinical populations affect sleep macro- and micro-architecture and objective sleep timing and quality.

Factors associated with sleep problems and sleeping pill use in Brazilians

OBJECTIVE

To estimate the prevalence of sleep problems and sleeping pill use and associated factors in the Brazilian population.

METHODS

This study was conducted with data from the 2019 Brazilian National Health Survey. Our sample consisted of 94,114 participants and the outcomes analyzed were sleep problems and sleeping pill use. Sociodemographic, lifestyle, and health characteristics were explored in a descriptive and multivariate analysis with Poisson regression, robust variance, and 5% significance.

RESULTS

We found a 35.1% (95%CI: 34.5–35.7) and 8.5% (95%CI: 8.2–8.9) prevalence of sleep problems and sleeping pill use, respectively. Sleep problems were associated with women (PR = 1.41; 95%CI: 1.36–1.46), individuals who self-assess their health as regular/poor/very poor (PR = 1.56; 95%CI: 1.51–1.62), those with chronic diseases (PR = 1.70; 95%CI: 1.64–1.78), those who use alcohol excessively (PR = 1.14; 95%CI: 1.09–1.20), and smokers (PR = 1.16; 95%CI: 1.10–1.22). Sleeping pill use was associated with women (PR = 1.57; 95%CI: 1.43–1.73), divorcees (PR = 1.46; 95%CI: 1.30–1.65), urban denizens (PR = 1.32; 95%CI: 1.21–1.45) those who self-assess their health as regular/poor/very poor (PR = 1.79; 95%CI: 1.64–1.95), those with chronic diseases (PR = 4.07; 95%CI: 3.48–4.77), and smokers (PR = 1.49; IC95%: 1.33–1.67).

CONCLUSION

This study found that the prevalence of sleep problems and sleeping pill use in Brazilians indicates the need for attention and sleep care for this population, especially in women and those with lifestyle and health conditions associated with the analyzed outcomes.

Relationship Between Circadian Strain, Light Exposure, and Body Mass Index in Rural and Urban Quilombola Communities

Industrialization has greatly changed human lifestyle; work and leisure activities have been moved indoors, and artificial light has been used to illuminate the night. As cyclic environmental cues such as light and feeding become weak and/or irregular, endogenous circadian systems are increasingly being disrupted. These disruptions are associated with metabolic dysfunction, possibly contributing to increased rates of overweight and obesity worldwide. Here, we aimed to investigate how activity-rest rhythms, patterns of light exposure, and levels of urbanization may be associated with body mass index (BMI) in a sample of rural and urban Quilombola communities in southern Brazil. These are characterized as remaining social groups who resisted the slavery regime that prevailed in Brazil. Quilombola communities were classified into five groups according to their stage of urbanization: from rural areas with no access to electricity to highly urbanized communities. We collected anthropometric data to calculate BMI, which was categorized as follows: from ≥ 18.5 kg/m² to < 25 kg/m² = normal weight; from ≥ 25 kg/m² to < 30 kg/m² = overweight; and ≥ 30 kg/m² = obese. Subjects were asked about their sleep routines and light exposure on workdays and work-free days using the Munich Chronotype Questionnaire (N = 244 included). In addition, we analyzed actimetry data from 121 participants with seven consecutive days of recordings. Living in more urbanized areas and higher intradaily variability (IV) of activity-rest rhythms were associated with an increased risk of belonging to the overweight or obese group, when controlling for age and sex. These findings are consistent with preclinical data and point to potential strategies in obesity prevention and promotion of healthy metabolic profiles.

Current Insights into Optimal Lighting for Promoting Sleep and Circadian Health: Brighter Days and the Importance of Sunlight in the Built Environment

This perspective considers the possibility that daytime's intrusion into night made possible by electric lighting may not be as pernicious to sleep and circadian health as the encroachment of nighttime into day wrought by 20th century architectural practices that have left many people estranged from sunlight.

Sleep Under Preindustrial Conditions: What We Can Learn from It

Human sleep is regulated by light in two fundamental ways: The light-dark (LD) cycle entrains a circadian clock that in turn regulates sleep timing, and light per se can acutely inhibit sleep. Throughout evolution, these sleep regulatory systems became highly sensitive to the effects of light and they can be affected by the relatively low light intensities that are used indoors. Thus, postindustrial living conditions have created built environments that have isolated humans from the natural LD cycle and exposed them to an artificial one that can affect daily sleep timing. Studying indigenous communities that have differential access to electricity, as well as communities living in highly urbanized areas, we and others have shown that human access to artificial light has delayed the daily onset of sleep but has had a smaller effect on its offset, leading to an overall reduction in sleep duration that is pervasive in modern societies. In this chapter we discuss these studies, highlight their main findings, and point to their limitations.

Long-term cumulative light exposure from the natural environment and sleep: A cohort study

We analysed (A) the association of short-term as well as long-term cumulative exposure to natural light, and (B) the association of detailed temporal patterns of natural light exposure history with three indicators of sleep: sleep duration, sleep problems, and diurnal preference. Data (N = 1,962; 55% women; mean age 41.4 years) were from the prospective Young Finns Study, which we linked to daily meteorological data on each participant's neighbourhood natural light exposure using residential postal codes. Sleep outcomes were self-reported in 2011. We first examined associations of the sleep outcomes with cumulative light exposure of 5-year, 2-year, 1-year, and 2-month periods prior to the sleep assessment using linear and Poisson regression models adjusting for potential confounders. We then used a data-driven time series approach to detect clusters of participants with different light exposure histories and assessed the associations of these clusters with the sleep outcomes using linear and Poisson regression analyses. A greater cumulative light exposure over ≥1 year was associated with a shorter sleep duration (β = -0.10, 95% confidence interval [CI] -0.15 to -0.04), more sleep problems (incident rate ratio [IRR] 1.04, 95% CI 1.0-1.07) and diurnal preference towards eveningness (β = -0.09, 95% CI -0.14 to -0.03). The data-driven exposure pattern of "slowly increasing" light exposure was associated with fewer overall sleep problems (IRR 0.93, 95% CI 0.88-0.98) compared to a "recently declining" light exposure group representing the "average-exposure" group. These findings suggest that living in an area with relatively more intense light exposure for a longer period of time influences sleep.

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.

Outdoor daylight exposure and longer sleep promote wellbeing under COVID-19 mandated restrictions

Light is an important regulator of daily human physiology in providing time‐of‐day information for the circadian clock to stay synchronised with the 24‐hr day. The coronavirus disease 2019 (COVID‐19) pandemic led to social restrictions in many countries to prevent virus spreading, restrictions that dramatically altered daily routines and limited outdoor daylight exposure. We previously reported that sleep duration increased, social jetlag decreased, and mid‐sleep times delayed during social restrictions (Global Chrono Corona Survey, N = 7,517). In the present study, we investigated in the same dataset changes in wellbeing and their link to outdoor daylight exposure, and sleep–wake behaviour. In social restrictions, median values of sleep quality, quality of life, physical activity and productivity deteriorated, while screen time increased, and outdoor daylight exposure was reduced by ~58%. Yet, many survey participants also reported no changes or even improvements. Larger reductions in outdoor daylight exposure were linked to deteriorations in wellbeing and delayed mid‐sleep times. Notably, sleep duration was not associated with outdoor daylight exposure loss. Longer sleep and decreased alarm‐clock use dose‐dependently correlated with changes in sleep quality and quality of life. Regression analysis for each wellbeing aspect showed that a model with six predictors including both levels and their deltas of outdoor daylight exposure, sleep duration and mid‐sleep timing explained 5%–10% of the variance in changes of wellbeing scores (except for productivity). As exposure to daylight may extenuate the negative effects of social restriction and prevent sleep disruption, public strategies during pandemics should actively foster spending more daytime outdoors.

Daily light exposure, sleep-wake cycle and attention in adolescents from different urban contexts

OBJECTIVE

to compare daily light exposure, activity-rest rhythm, sleep-wake cycle (SWC) and attention in Brazilian students living in different levels of urbanization.

METHODS

115 adolescents (74 girls), aged 14-18 years (mean 15.5 ± 0.7 years), from the first years of high school have participated. The SWC was evaluated by actimetry and a Sleep Diary for 10 days. Besides, the "Health and Sleep" Questionnaire, the Morningness and Eveningness Scale for adolescents, the Pittsburgh Sleep Quality Index, and the Pediatric Daytime Sleepiness Scale were answered. Attention was assessed by a Continuous Performance Task.

RESULTS

In the less urbanized region, there were a greater exposure to light during the day accompanied by a higher proportion of morning-types and less occurrence of excessive daytime sleepiness. Otherwise, in the more urbanized region, adolescents showed a trend to sleep less in weekdays and presented more irregularity in sleep duration between weekdays and weekend, with 83 ± 15% of sleep efficiency, 01:04 ± 1:30 h of WASO and 7 ± 6.7 awakenings per night on the weekdays, suggestive of poor sleep quality. Despite of this, they showed better attentional performance: more correct responses (tonic and phasic alertness, and sustained attention) and less omissions (for all components). Regardless of the degree of urbanization, there was partial sleep deprivation, irregular sleep schedules and poor sleep quality in adolescents.

CONCLUSIONS

The daily light exposure and activity-rest profiles, SWC and attention in adolescents varied according to the degree of urbanization. Besides, the negative impacts of early school starting times leading to sleep deprivation, irregular sleep times and poor sleep quality were observed irrespective of the degree of urbanization, reinforcing that the early school starting time at morning is a strong temporal challenge for teenagers, having negative impacts on cognition and academic performance.

Circadian Strain, Light Exposure, and Depressive Symptoms in Rural Communities of Southern Brazil

Irregular light-dark cycles and circadian/sleep disturbances have been suggested as risk or co-occurring factors in depression. Among a set of metrics developed to quantify strain on the circadian system, social jetlag (SJL) has been put forward as a measure of the discrepancy between biological and social clocks. Here, we approached the question on whether light exposure and SJL would also be associated with depressive symptoms in Quilombola communities in Southern Brazil. These rural communities are void of potential confounders of modern lifestyles and show low levels of SJL. 210 Quilombolas (age range 16-92; 56% women) were asked about their sleep times and light exposure using the Munich ChronoType Questionnaire (MCTQ). The Beck Depression Inventory (BDI) was used to assess depressive symptoms. Additionally, we analyzed 7-day actimetry recordings in 124 subjects. BDI scores higher than 10 (having clinically significant depressive symptoms; controlled for age and sex in the multivariate analysis) were positively associated with SJL >1 h and negatively associated with median light exposure during the day, especially in the morning from 8:00 to 10:00. Our results suggest that low light exposure during the day, and higher levels of SJL are associated with depressive symptoms; longitudinal and experimental studies are needed to understand the underlying mechanisms. Nevertheless, we highlight the potential of treatment strategies aimed at decreasing circadian strain and insufficient light exposure, which are suggested as areas of further research in Psychiatry.

Moonstruck sleep: Synchronization of human sleep with the moon cycle under field conditions

Before the availability of artificial light, moonlight was the only source of light sufficient to stimulate nighttime activity; still, evidence for the modulation of sleep timing by lunar phases is controversial. Here, we use wrist actimetry to show a clear synchronization of nocturnal sleep timing with the lunar cycle in participants living in environments that range from a rural setting with and without access to electricity in indigenous Toba/Qom communities in Argentina to a highly urbanized postindustrial setting in the United States. Our results show that sleep starts later and is shorter on the nights before the full moon when moonlight is available during the hours following dusk. Our data suggest that moonlight likely stimulated nocturnal activity and inhibited sleep in preindustrial communities and that access to artificial light may emulate the ancestral effect of early-night moonlight.

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.

Evening home lighting adversely impacts the circadian system and sleep

The regular rise and fall of the sun resulted in the development of 24-h rhythms in virtually all organisms. In an evolutionary heartbeat, humans have taken control of their light environment with electric light. Humans are highly sensitive to light, yet most people now use light until bedtime. We evaluated the impact of modern home lighting environments in relation to sleep and individual-level light sensitivity using a new wearable spectrophotometer. We found that nearly half of homes had bright enough light to suppress melatonin by 50%, but with a wide range of individual responses (0–87% suppression for the average home). Greater evening light relative to an individual’s average was associated with increased wakefulness after bedtime. Homes with energy-efficient lights had nearly double the melanopic illuminance of homes with incandescent lighting. These findings demonstrate that home lighting significantly affects sleep and the circadian system, but the impact of lighting for a specific individual in their home is highly unpredictable.

Access to electric light is associated with delays of the dim-light melatonin onset in a traditionally hunter-gatherer Toba/Qom community

Key to the transition of humans from nomadic hunting-gathering groups to industrialized and highly urbanized societies was the creation of protected and artificially lit environments that extended the natural daylight hours and consolidated sleep away from nocturnal threats. These conditions isolated humans from the natural regulators of sleep and exposed them to higher levels of light during the evening, which are associated with a later sleep onset. Here, we investigated the extent to which this delayed timing of sleep is due to a delayed circadian system. We studied two communities of Toba/Qom in the northern region of Argentina, one with and the other without access to electricity. These communities have recently transitioned from a hunting-gathering subsistence to mixed subsistence systems and represent a unique model in which to study the potential effects of the access to artificial light on sleep physiology. We have previously shown that participants in the community with access to electricity had, compared to participants in the community without electricity, later sleep onsets, and shorter sleep bouts. Here, we show they also have a delayed dim-light melatonin onset (DLMO). This difference is present during the winter but not during the spring when the influence of evening artificial light is likely less relevant. Our results support the notion that the human transition into artificially lit environments had a major impact on physiological systems that regulate sleep timing, including the phase of the master circadian clock.

Measuring circadian function in bipolar disorders: Empirical and conceptual review of physiological, actigraphic, and self-report approaches

BACKGROUND

Interest in biological clock pathways in bipolar disorders (BD) continues to grow, but there has yet to be an audit of circadian measurement tools for use in BD research and practice.

PROCEDURE

The International Society for Bipolar Disorders Chronobiology Task Force conducted a critical integrative review of circadian methods that have real-world applicability. Consensus discussion led to the selection of three domains to review-melatonin assessment, actigraphy, and self-report.

RESULTS

Measurement approaches used to quantify circadian function in BD are described in sufficient detail for researchers and clinicians to make pragmatic decisions about their use. A novel integration of the measurement literature is offered in the form of a provisional taxonomy distinguishing between circadian measures (the instruments and methods used to quantify circadian function, such as dim light melatonin onset) and circadian constructs (the biobehavioral processes to be measured, such as circadian phase).

CONCLUSIONS

Circadian variables are an important target of measurement in clinical practice and biomarker research. To improve reproducibility and clinical application of circadian constructs, an informed systematic approach to measurement is required. We trust that this review will decrease ambiguity in the literature and support theory-based consideration of measurement options.

Early chronotype with advanced activity rhythms and dim light melatonin onset in a rural population

Studying communities at different stages of urbanisation and industrialisation can teach us how timing and intensity of light affect the circadian clock under real-life conditions. We have previously described a strong tendency towards morningness in the Baependi Heart Study, located in a small rural town in Brazil. Here, we tested the hypothesis that this morningness tendency is associated with early circadian phase based on objective measurements (as determined by dim light melatonin onset, DLMO, and activity) and light exposure. We also analysed how well the previously collected chronotype questionnaire data were able to predict these DLMO values. The average DLMO observed in 73 participants (40 female) was 20:03 ± 01:21, SD, with an earlier average onset in men (19:38 ± 01:16) than in women (20:24 ± 01:21; P ≤ .01). However, men presented larger phase angle between DLMO and sleep onset time as measured by actigraphy (4.11 hours vs 3.16 hours; P ≤ .01). Correlational analysis indicated associations between light exposure, activity rhythms and DLMO, such that early DLMO was observed in participants with higher exposure to light, higher activity and earlier light exposure. The strongest significant predictor of DLMO was morningness-eveningness questionnaire (MEQ) (beta=-0.35, P ≤ .05), followed by age (beta = -0.47, P ≤ .01). Sex, light exposure and variables derived from the Munich chronotype questionnaire were not significant predictors. Our observations demonstrate that both early sleep patterns and earlier circadian phase have been retained in this small rural town in spite of availability of electrification, in contrast to metropolitan postindustrial areas.

Validation of the Portuguese Variant of the Munich Chronotype Questionnaire (MCTQPT)

Introduction

Differences in the manner circadian clocks entrain to the 24-h day are expressions of different chronotypes that can range from extreme early to extreme late, from proverbial larks to owls. The Morningness Eveningness Questionnaire (MEQ) was one of the first to assess daily preference based on subjective self-assessment – a psychological construct. The later developed Munich Chronotype Questionnaire (MCTQ) uses instead the actual sleep timing to assess chronotype. It calculates the mid-sleep point, halfway between onset and offset on work-free days (MSF), which is then corrected for potential oversleep on free days compensating for sleep debt accumulated over the workweek (MSF_sc). MSF_sc is expressed in local time and is thought to be a proxy for “phase of entrainment” of the circadian clock. The MCTQ-derived chronotype is therefore a biological construct. In the present report, we validate the Portuguese variant (MCTQ^PT) of the MCTQ. Portugal is of particular interest, since it is thought to consist of especially late chronotypes.

Methods

We have used three methods to assess the timing of daily behavior, namely, the chronotype (MCTQ), the daily preference (rMEQ), and a simple self-assessment (time-of-day type). A total of 80 healthy adults living in Portugal, with age and sex distributed according to the Portuguese population, were recruited. We analyzed 4 weeks of continuous records of actimetry data to validate the MCTQ^PT and used the rMEQ to compare between a biological chronotype (sleep timing) and a psychological chronotype (daily preference). MCTQ variables were analyzed by descriptive statistics; correspondence between measurements was done by Spearman correlations or cross-tabulation; in a subset of 41 individuals, test–retest reliability was assessed.

Results

MCTQ-derived variables (MSF, MSW, MSF_sc) correlated highly with their counterparts calculated from actimetry (MSW: rho = 0.697; MSF: rho = 0.747; MSF_sc: rho = 0.646; all p < 0.001). The MCTQ assessment of the chronotype showed good test–retest reliability (rho = 0.905; p < 0.001). The rMEQ score correlates with MSF_sc (rho = −0.695; p < 0.001), and the agreement for the self-assessment with the MSF_sc was fair (kw = 0.386; p < 0.001).

Conclusion

The Portuguese variant of the MCTQ revealed to be a reliable questionnaire to assess the chronotype for the Portuguese adult population, as previously reported for other countries.

Clocks in the Wild: Entrainment to Natural Light

Entrainment denotes a process of coordinating the internal circadian clock to external rhythmic time-cues (Zeitgeber), mainly light. It is facilitated by stronger Zeitgeber signals and smaller period differences between the internal clock and the external Zeitgeber. The phase of entrainment ψ is a result of this process on the side of the circadian clock. On Earth, the period of the day-night cycle is fixed to 24 h, while the periods of circadian clocks distribute widely due to natural variation within and between species. The strength and duration of light depend locally on season and geographic latitude. Therefore, entrainment characteristics of a circadian clock vary under a local light environment and distribute along geoecological settings. Using conceptual models of circadian clocks, we investigate how local conditions of natural light shape global patterning of entrainment through seasons. This clock-side entrainment paradigm enables us to predict systematic changes in the global distribution of chronotypes.

[Factors associated with sleep disorders in university students]

The objective was to investigate sleep disorders and associated sociodemographic and behavioral factors. A census of university students was carried out. Questions extracted from the Munich Chronotype Questionnaire investigated: insufficient sleep duration (< 6 hours/day for < 65 years and < 5 hours/day for other ages), long latency (> 30 minutes), low self-rated sleep quality, nocturnal awakenings (involuntary, in the middle of the night), and daytime sleepiness (difficulty concentrating). Independent variables included sociodemographic and behavioral characteristics. Adjusted analyses were performed with Poisson regression. Of the 1,865 students, 32% exhibited insufficient sleep on class days, 8.2% insufficient sleep on weekends, 18.6% long latency on class days, 17.2% long latency on weekends, 30% low self-rated sleep quality, 12.7% nocturnal awakenings, and 32.2% daytime sleepiness. Higher alcohol consumption was associated with insufficient sleep duration and long latency on class days, low quality sleep, awakenings, and daytime sleepiness. Smoking was associated with insufficient sleep duration on weekends, awakenings, and low-quality sleep. Black and brown skin color were associated with insufficient sleep duration on class days, low-quality sleep, and awakenings. Morning classes were associated with insufficient sleep and daytime sleepiness. Female gender was associated with low-quality sleep and awakenings. The most frequent sleep disorders were insufficient sleep on class days, low self-rated quality of sleep, and daytime sleepiness. Alcohol consumption and smoking and black and brown skin color were the principal factors associated with sleep disorders.

Eating Behavior (Duration, Content, and Timing) Among Workers Living under Different Levels of Urbanization

Urbanization has contributed to extended wakefulness, which may in turn be associated with eating over a longer period. Here, we present a field study conducted in four groups with different work hours and places of living in order to investigate eating behavior (duration, content, and timing). Anthropometric measures were taken from the participants (rural (n = 22); town (n = 19); city-day workers (n = 11); city-night workers (n = 14)). In addition, a sociodemographic questionnaire was self-answered and 24-h food recalls were applied for three days. The 24-h food recalls revealed that fat intake varied according to the groups, with the highest consumption by the city-day workers. By contrast, city-day workers had the lowest intake of carbohydrate, whereas the rural group had the highest. In general, all groups had some degree of inadequacy in food consumption. Eating duration was negatively correlated with total energy intake, fat, and protein consumption in the rural and town groups. There was a positive correlation between body mass index and eating duration in both city groups. The rural group had the earliest start time of eating, and this was associated with a lower body mass index. This study suggested that food content and timing, as well as eating duration, differed according to place of living, which in turn may be linked to lifestyle.

Poor sleep quality associates with self-reported psychiatric and cardiometabolic symptoms independently of sleep timing patterns in a large sample of rural and urban workers

Poor sleep associates with mental and cardiometabolic pathological outcomes. The participation of sleep timing features in the pathways by which this relationship occurs is not clear. This study aims to evaluate the interrelationship between sleep quality and self-reported psychiatric/cardiometabolic symptoms, considering mediation and moderation effects of sleep timing patterns, and urban versus rural work environment, respectively; and to verify the association between sleep quality and polymorphisms of AANAT, RORA and TIMELESS genes. An epidemiological survey was performed in a rural area in southern Brazil. Eight-hundred and twenty-nine subjects were evaluated for sleep quality using the Pittsburgh Sleep Quality Index, and sleep timing patterns using the Munich Chronotype Questionnaire. Work characteristics and psychiatric/cardiometabolic symptoms were assessed using a structured self-report questionnaire. Three polymorphisms of AANAT, RORA and TIMELESS (rs3760138, rs782931 and rs774045, respectively) were genotyped in blood samples. We found statistically significant associations of poor sleep quality with self-reported psychiatric symptoms (B = 0.382; 95% CI 0.289-0.476; adjusted p-value <.001), and with self-reported cardiometabolic symptoms (B = 0.079; 95% CI 0.013-0.151; adjusted p-value = .048). The genetic analysis showed that RORA GA/AA genotype was associated to poor sleep quality (B = 0.146, 95% CI 0.054-0.239; adjusted p-value = .004). No moderated mediation effects were observed in the conditional analysis. TIMELESS polymorphism was not included in the analysis due to the low frequency of risk genotypes. These results yield new insights regarding the interrelationship between sleep characteristics and psychiatric/cardiometabolic self-reported symptoms, taking into account genes related to the biological clocks and melatonin pathways.

Sleep timing and duration in indigenous villages with and without electric lighting on Tanna Island, Vanuatu

It has been hypothesized that sleep in the industrialized world is in chronic deficit, due in part to evening light exposure, which delays sleep onset and truncates sleep depending on morning work or school schedules. If so, societies without electricity may sleep longer. However, recent studies of hunter-gatherers and pastoralists living traditional lifestyles without electricity report short sleep compared to industrialized population norms. To further explore the impact of lifestyles and electrification on sleep, we measured sleep by actigraphy in indigenous Melanesians on Tanna Island, Vanuatu, who live traditional subsistence horticultural lifestyles, in villages either with or without access to electricity. Sleep duration was long and efficiency low in both groups, compared to averages from actigraphy studies of industrialized populations. In villages with electricity, light exposure after sunset was increased, sleep onset was delayed, and nocturnal sleep duration was reduced. These effects were driven primarily by breastfeeding mothers living with electric lighting. Relatively long sleep on Tanna may reflect advantages of an environment in which food access is reliable, climate benign, and predators and significant social conflict absent. Despite exposure to outdoor light throughout the day, an effect of artificial evening light was nonetheless detectable on sleep timing and duration.

Daylight Saving Time and Artificial Time Zones - A Battle Between Biological and Social Times

Many regions and countries are reconsidering their use of Daylight Saving Time (DST) but their approaches differ. Some, like Japan, that have not used DST over the past decades are thinking about introducing this twice-a-year change in clock time, while others want to abolish the switch between DST and Standard Time, but don’t agree which to use: California has proposed keeping perennial DST (i.e., all year round), and the EU debates between perennial Standard Time and perennial DST. Related to the discussion about DST is the discussion to which time zone a country, state or region should belong: the state of Massachusetts in the United States is considering switching to Atlantic Standard Time, i.e., moving the timing of its social clock (local time) 1 h further east (which is equivalent to perennial DST), and Spain is considering leaving the Central European Time to join Greenwich Mean Time (GMT), i.e., moving its social timing 1 h further west. A wave of DST discussions seems to periodically sweep across the world. Although DST has always been a political issue, we need to discuss the biology associated with these decisions because the circadian clock plays a crucial role in how the outcome of these discussions potentially impacts our health and performance. Here, we give the necessary background to understand how the circadian clock, the social clock, the sun clock, time zones, and DST interact. We address numerous fallacies that are propagated by lay people, politicians, and scientists, and we make suggestions of how problems associated with DST and time-zones can be solved based on circadian biology.

Chronotype and Social Jetlag: A (Self-) Critical Review

The Munich ChronoType Questionnaire (MCTQ) has now been available for more than 15 years and its original publication has been cited 1240 times (Google Scholar, May 2019). Additionally, its online version, which was available until July 2017, produced almost 300,000 entries from all over the world (MCTQ database). The MCTQ has gone through several versions, has been translated into 13 languages, and has been validated against other more objective measures of daily timing in several independent studies. Besides being used as a method to correlate circadian features of human biology with other factors-ranging from health issues to geographical factors-the MCTQ gave rise to the quantification of old wisdoms, like "teenagers are late", and has produced new concepts, like social jetlag. Some like the MCTQ's simplicity and some view it critically. Therefore, it is time to present a self-critical view on the MCTQ, to address some misunderstandings, and give some definitions of the MCTQ-derived chronotype and the concept of social jetlag.

Seasonal synchronization of sleep timing in industrial and pre-industrial societies

Artificial light has reshaped human sleep/wake cycle in industrial societies and raised concern on the misalignment of this cycle relative to the light and dark cycle. This manuscript contrasts sleep timing in extratropical, industrial societies (data from eight national time use surveys in countries with Daylight Saving Time —DST— regulations) and Subtropical, pre-industrial societies with and without access to artificial light (data from nine locations coming from seven previous reports) against the cycle of light and dark. Within the two process model of sleep, results show sleep onset and sleep offset keep bound to each other by the homeostatic process. In winter, the photoreceptive process aligns the phase of the sleep/wake cycle to sunrise. As a result the phase increasingly lags with increasing latitude up to a delay of 120 min at 55° latitude. In summer, the homeostatic process still binds sleep onset to speep offset but DST rules in industrialized societies reduce the lag by one third to 40 min at 55° latitude. Sleep timing is then stationary with latitude. The phase of the sleep/wake cycle is then governed by natural trends and no clues of misalignment are revealed.