Delayed Sleep in Winter Related to Natural Daylight Exposure among Arctic Day Workers

Usability and feasibility of an online intervention for older adults to support changes to routines and the home ('Light, activity and sleep in my daily life')

BACKGROUND

Indoor lighting, exposure to outdoor daylight, physical activity and sleep interact to influence functioning, mood and cicadian rhythm. Older adults (≥ 65 years), who often spend more time at home, are less physically active and experience more sleep problems, could benefit from strategies to support behavioural change and self-managed modifications in the home. The study's primary objective was to assess the usability and feasibility of the 'Light, activity and sleep in my daily life' intervention, delivered as a web-based course.

METHODS

This 9-week intervention was delivered in a municipality in Sweden (55.70° N). Participants were eight healthy women (age 71-84), community-living in one-person households. We recruited through municipal staff and posters at senior citizen meeting points. Both qualitative and quantitative data were collected before and after the intervention. The outcome measures were intervention usability (ease of use, usefulness) and study feasibility (e.g., recruitment procedure, online engagement). Measures also included changes to routines and self-managed home adjustments to determine whether the participants applied what they had learnt.

RESULTS

All participants completed the intervention. Time logged in varied between 25 min and 3 h (M = 1 h 50 min) per week. Seven participants' system usability scores were between 90 and 100 ('Excellent') out of 100. When interviewed, participants reported overall high satisfaction with what they had learnt. Six participants were particularly satisfied with the modules targeting light. Seven participants made changes to their lighting or darkness conditions, such as replaced bulbs with either 3-step dimming or higher colour temperature LEDs (samples were included in the intervention test kit). One suggestion to improve the online delivery was to enable participants to add text comments to the weekly evaluation form.

CONCLUSIONS

The web-based intervention was feasible to deliver but time for recruitment should be extended and advertisement in the local newspaper should be considered. Participants' computer proficiency and access to the internet at home will be critical in a future study with a larger sample. Only minor changes to the online content of the intervention are needed based on participants' feedback. The intervention will be possible to evaluate in a future pilot study.

Effect of daily light exposure on sleep in polar regions: A meta-analysis

Although studies have shown that light affects sleep in polar populations, the sample size of most studies is small. This meta-analysis provides the first systematic review of the effects of summer glare, spring and fall moderate daylight, and artificial lighting on general sleep problems (sleep duration, efficiency, and delay). This analysis included 18 studies involving 986 participants. We calculated the random effect size via an evidence-based meta-analysis that analysed the effect of bright/auxiliary light on sleep and the effect of three different types of light on sleep compared with conventional light. There was no significant correlation between specific light types and sleep duration. Intense summer light has a negative effect on sleep time and efficiency. Moderate, natural light in spring and autumn effectively delayed sleep but could not improve sleep efficiency. For artificial fill light, neither blue light nor enhanced white light has been found to have a significant effect. In summary, summer light has a detrimental effect on sleep in polar populations, and moderate natural light may be superior to conventional light. However, specific strategies to improve sleep and artificial lighting in polar populations must be explored further.

Promoting adolescent sleep and circadian function: A narrative review on the importance of daylight access in schools

Adolescent sleep disturbances and circadian delays pose significant challenges to mood and daytime functioning. In this narrative review, we explore the impact of light on sleep and highlight the importance of monitoring and managing light exposure in adolescents throughout the day and night. The benefits of daylight exposure in mitigating sleep and circadian disruptions are well-established; however, interventions targeting access to daylight in adolescents remain understudied and underutilized. The primary aim of this narrative review is to bring attention to this gap in the literature and propose the need for institutional-level interventions that promote access to daylight, especially considering adolescents' early school start times and substantial time spent indoors on weekdays. School-led interventions, such as active commuting to school and outdoor curriculums, have promising effects on sleep and circadian rhythms. Additionally, practical measures to optimize natural light in classrooms, including managing blinds and designing conducive environments, should also be considered. While future studies are necessary to facilitate the implementation of interventions, the potential for these school-level interventions to support adolescent sleep health is evident. Aiming for integration of individual-level regulation and institutional-level intervention of light exposure is necessary for optimal outcomes.

Archaic Introgression Shaped Human Circadian Traits

When the ancestors of modern Eurasians migrated out of Africa and interbred with Eurasian archaic hominins, namely, Neanderthals and Denisovans, DNA of archaic ancestry integrated into the genomes of anatomically modern humans. This process potentially accelerated adaptation to Eurasian environmental factors, including reduced ultraviolet radiation and increased variation in seasonal dynamics. However, whether these groups differed substantially in circadian biology and whether archaic introgression adaptively contributed to human chronotypes remain unknown. Here, we traced the evolution of chronotype based on genomes from archaic hominins and present-day humans. First, we inferred differences in circadian gene sequences, splicing, and regulation between archaic hominins and modern humans. We identified 28 circadian genes containing variants with potential to alter splicing in archaics (e.g., CLOCK, PER2, RORB, and RORC) and 16 circadian genes likely divergently regulated between present-day humans and archaic hominins, including RORA. These differences suggest the potential for introgression to modify circadian gene expression. Testing this hypothesis, we found that introgressed variants are enriched among expression quantitative trait loci for circadian genes. Supporting the functional relevance of these regulatory effects, we found that many introgressed alleles have associations with chronotype. Strikingly, the strongest introgressed effects on chronotype increase morningness, consistent with adaptations to high latitude in other species. Finally, we identified several circadian loci with evidence of adaptive introgression or latitudinal clines in allele frequency. These findings identify differences in circadian gene regulation between modern humans and archaic hominins and support the contribution of introgression via coordinated effects on variation in human chronotype.

Archaic Introgression Shaped Human Circadian Traits

Introduction

When the ancestors of modern Eurasians migrated out of Africa and interbred with Eurasian archaic hominins, namely Neanderthals and Denisovans, DNA of archaic ancestry integrated into the genomes of anatomically modern humans. This process potentially accelerated adaptation to Eurasian environmental factors, including reduced ultra-violet radiation and increased variation in seasonal dynamics. However, whether these groups differed substantially in circadian biology, and whether archaic introgression adaptively contributed to human chronotypes remains unknown.

Results

Here we traced the evolution of chronotype based on genomes from archaic hominins and present-day humans. First, we inferred differences in circadian gene sequences, splicing, and regulation between archaic hominins and modern humans. We identified 28 circadian genes containing variants with potential to alter splicing in archaics (e.g., CLOCK, PER2, RORB, RORC), and 16 circadian genes likely divergently regulated between present-day humans and archaic hominins, including RORA. These differences suggest the potential for introgression to modify circadian gene expression. Testing this hypothesis, we found that introgressed variants are enriched among eQTLs for circadian genes. Supporting the functional relevance of these regulatory effects, we found that many introgressed alleles have associations with chronotype. Strikingly, the strongest introgressed effects on chronotype increase morningness, consistent with adaptations to high latitude in other species. Finally, we identified several circadian loci with evidence of adaptive introgression or latitudinal clines in allele frequency.

Conclusions

These findings identify differences in circadian gene regulation between modern humans and archaic hominins and support the contribution of introgression via coordinated effects on variation in human chronotype.

Individual light history matters to deal with the Antarctic summer

The effect of light, main zeitgeber of the circadian system, depends on the time of day it is received. A brief trip to the Antarctic summer (ANT) allowed us to explore the impact of a sudden and synchronized increase in light exposure on activity-rest rhythms and sleep patterns of 11 Uruguayan university students, and to assess the significance of light history in determining individual circadian phase shift. Measurements collected in the peri-equinox in Montevideo, Uruguay (baseline situation, MVD) and in ANT, included sleep logs, actigraphy, and salivary melatonin to determine dim-light melatonin onset (DLMO), the most reliable marker of circadian phase. The increase in light exposure in ANT with respect to MVD (affecting both light-sensitive windows with opposite effects on the circadian phase) resulted in no net change in DLMO among participants as some participants advanced their DLMO and some others delayed it. The ultimate cause of each participant's distinctive circadian phase shift relied on the unique change in light exposure each individual was subjected to between their MVD and ANT. This study shows an association between the individual light history and the circadian phase shift.

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.

How Sleep Research in Extreme Environments Can Inform the Military: Advocating for a Transactional Model of Sleep Adaptation

PURPOSE OF REVIEW

We review the literature on sleep in extreme environments. Accordingly, we present a model that identifies the need for mitigating interventions to preserve sleep quality for military deployments.

RECENT FINDINGS

Situational factors that affect sleep in extreme environments include cold temperatures, isolated and confined areas, fluctuating seasonality, photoperiodicity, and extreme latitudes and altitudes. Results vary across studies, but general effects include decreased total sleep time, poor sleep efficiency, and non-specific phase delays or phase advances in sleep onset and sleep architecture. Considering habitability measures (e.g., light or temperature control) and individual differences such as variable stress responses or sleep need can mitigate these effects to improve mood, cognition, and operational performance. Although the situational demands during military missions inevitably reduce total sleep time and sleep efficiency, mitigating factors can attenuate sleep-related impairments, hence allowing for optimal mission success and personnel safety.

Sleep Habits in Pairs of Japanese High School Students and Their Mothers in Summer and Autumn

This study aimed to examine the sleep habits in pairs of Japanese high school students and their mothers in the summer and autumn. Nineteen pairs of high school students and their mothers participated in this study. Wrist actigraphy, subjective sleep evaluations, and bedroom environmental measurements (temperature, humidity, and light) were performed for a duration of one week. The results of a split-plot analysis of variance revealed no significant difference in the actigraphically evaluated time spent in bed (TIB) between the seasons and between the mothers and students. The TIB was approximately 6 h on weekdays, and significantly lengthened to approximately 7 h on weekends (p < 0.05). The average sleep efficiency values recorded were higher than 90%. The mothers showed significantly advanced sleep phases compared to those of the students (p < 0.05). In addition, the waking time on Monday morning was significantly correlated between the mothers and students in the summer and autumn (p < 0.05). A perceived sleep loss “almost every day” or “several times per week” was reported by approximately half of the mothers and students in each season. The students occasionally fell into nocturnal sleep with the room light turned on. These results suggest that sleep hygiene education considering life habit characteristics is required to ensure sufficient sleep time.

No improvement of sleep from vitamin D supplementation: insights from a randomized controlled trial

Background

Vitamin D has been linked to sleep health in observational studies. Data from randomized controlled trials (RCTs) with vitamin D is scarce.

Methods

This study presents the results of a secondary analysis of 189 vitamin D insufficient participants (47.1% women) in a previously performed RCT, of which 92 were randomized to vitamin D (100,000 IU (2500 μg) as a bolus dose followed by 20,000 IU (500 μg) per week), and 97 to placebo. At baseline and after 4 months at the end of the study serum 25-hydroxyvitamin D (s-25(OH)D) was measured, and the study questionnaire assessing sleep duration, daytime sleepiness, and symptoms of insomnia, was completed.

Results

At baseline, mean s-25(OH)D was 35.0 ± 11.8 and 35.5 ± 13.3 nmol/L in the vitamin D and placebo groups, respectively. After four months, we found no statistically significant differences between the intervention groups in any of the assessed sleep outcomes, neither when stratified by sex, nor when performed in subgroups based on baseline or end of study s-25(OH)D level or presence of sleep complaints at baseline.

Conclusions

We were not able to demonstrate a significant effect of vitamin D supplementation on sleep in this vitamin D insufficient population.

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RCT investigating vitamin D for 4 months in participants with low vitamin D status.

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Vitamin D did not improve sleep duration, excessive daytime sleepiness or insomnia.

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The role of vitamin D in sleep health remains controversial.

Reappraisal of the historical myopia epidemic in native Arctic communities

PURPOSE

This study was developed to explain the extraordinary rise in myopia prevalence beginning after 1950 in Indigenous Arctic communities considering recent findings about the risk factors for school myopia development. Myopia prevalence changed drastically from a historical low of less than 3% to more than 50% in new generations of young adults following the Second World War. At that time, this increase was attributed to concurrent alterations in the environment and way of life which occurred in an aggressive programme of de-culturalization and re-acculturation through residential school programmes that introduced mental, emotional and physical stressors. However, the predominant idea that myopia was genetic in nature won the discussion of the day, and research in the area of environmental changes was dismissed. There may have also been an association between myopia progression and the introduction of extreme mental, emotional and physical stressors at the time.

RECENT FINDINGS

Since 1978, animal models of myopia have demonstrated that myopiagenesis has a strong environmental component. Furthermore, multiple studies in human populations have shown since 2005 how myopia could be produced by a combination of limited exposure to the outdoors and heavy emphasis on academic subjects associated with intense reading habits. This new knowledge was applied in the present study to unravel the causes of the historical myopia epidemics in Inuit communities.

SUMMARY

After reviewing the available published data on myopia prevalence in circumpolar Inuit populations in the 20th century, the most likely causes for the Inuit myopia epidemic were the combination of increased near work (from almost none to daily reading) and the move from a mostly outdoor to a much more indoor way of life, exacerbated by fewer hours of sunshine during waking hours, the lower illuminance in the Arctic and the extreme psychophysical stress due to the conditions in the Residential Schools.

Daylight Saving Time: Pros and Cons

The original rationale for the adoption of daylight saving time (DST) was to conserve energy; however, the effects of DST on energy consumption are questionable or negligible. Conversely, there is substantial evidence that DST transitions have the cumulative effect on sleep deprivation with its adverse health effects. In light of current evidence, the European Commission in 2018 decided that biannual clock change in Europe would be abolished. Current indirect evidence supports the adoption of perennial standard time, which aligns best with the human circadian system and has the potential to produce benefits for public health and safety.

Sleep Quality and Duration in European Adolescents (The AdolesHealth Study): A Cross-Sectional, Quantitative Study

Sleep is a vital element of adolescents' overall health; it influences their body and mind and thus affects their quality of life. Adequate sleep quality and duration are essential for maintaining optimal metabolic health and lowering the risk of developing several medical conditions, such as cardiovascular disease. The current study aimed to assess the perceived sleep quality and duration of 1717 European adolescents from three different European countries (Spain, Iceland and Estonia) aged 13- to 16-years (900 boys, 817 girls) using the Pittsburgh Sleep Quality Index (PSQI). A multivariate analysis of variance (MANOVA) was performed to examine differences between groups and two-factor analysis of variance (ANOVA) was used to analyze city and age differences. The probability of having poor sleep quality and duration was calculated by Odd-Ratio (OR). Our study found poor sleep quality in 44% of the boys and 53% of the girls, whereas 68% and 69%, respectively did not get the recommended hours of sleep (i.e., 8-10 h). No difference was found between adolescents from Estonia, Iceland and Spain regarding sleep duration. In contrast, Spanish and Estonian adolescents reported higher probabilities of having poor sleep quality. Finally, girls had a significantly higher probability of poor sleep quality than boys.

Sleep in the land of the midnight sun and polar night: The Tromsø study

While some diseases and human behaviors fluctuate consistently with season, the extent of seasonal variations in sleep, especially at high latitudes, is less consistent. We used data from a geographic region (69º North) with extremely large seasonal differences in daylight that had the participants blinded for the current study's hypotheses. Data were derived from the Tromsø Study (2015-2016), an ongoing population-based study in Northern Norway comprising citizens aged 40 years and older (n = 21,083, participation = 64.7%). The sleep parameters included bedtime, rise time, sleep onset latency (SOL), and total sleep time. Insomnia was defined according to recent diagnostic criteria (International Classification of Sleep Disorders; ICSD-3). We found some evidence of monthly or seasonal variation in sleep problems. Insomnia was most common during the winter months among men, but not women. No seasonal or monthly effects were observed for sleep duration. SOL was slightly longer during the winter months, but the differences were small and hardly of any clinical relevance. The small or non-existing seasonal variation in sleep and sleep difficulties indicate that extreme seasonal variation in daylight is of little influence on sleep status. The city of Tromsø is a modern city with considerable level of artificial light, which may contribute to the observed rather stabile sleep patterns throughout the year.

Sleep Timing in Late Autumn and Late Spring Associates With Light Exposure Rather Than Sun Time in College Students

Timing of the human sleep-wake cycle is determined by social constraints, biological processes (sleep homeostasis and circadian rhythmicity) and environmental factors, particularly natural and electrical light exposure. To what extent seasonal changes in the light-dark cycle affect sleep timing and how this varies between weekdays and weekends has not been firmly established. We examined sleep and activity patterns during weekdays and weekends in late autumn (standard time, ST) and late spring (daylight saving time, DST), and expressed their timing in relation to three environmental reference points: clock-time, solar noon (SN) which occurs one clock hour later during DST than ST, and the midpoint of accumulated light exposure (50% LE). Observed sleep timing data were compared to simulated data from a mathematical model for the effects of light on the circadian and homeostatic regulation of sleep. A total of 715 days of sleep timing and light exposure were recorded in 19 undergraduates in a repeated-measures observational study. During each three-week assessment, light and activity were monitored, and self-reported bed and wake times were collected. Light exposure was higher in spring than in autumn. 50% LE did not vary across season, but occurred later on weekends compared to weekdays. Relative to clock-time, bedtime, wake-time, mid-sleep, and midpoint of activity were later on weekends but did not differ across seasons. Relative to SN, sleep and activity measures were earlier in spring than in autumn. Relative to 50% LE, only wake-time and mid-sleep were later on weekends, with no seasonal differences. Individual differences in mid-sleep did not correlate with SN but correlated with 50% LE. Individuals with different habitual bedtimes responded similarly to seasonal changes. Model simulations showed that light exposure patterns are sufficient to explain sleep timing in spring but less so in autumn. The findings indicate that during autumn and spring, the timing of sleep associates with actual light exposure rather than sun time as indexed by SN.