Clocks & Sleep, Vol. 1, Pages 280-289: How to Report Light Exposure in Human Chronobiology and Sleep Research Experiments Exposure to light has short- and long-term impacts on non-visual responses in humans. While many aspects related to non-visual light sensitivity have been characterised (such as the action spectrum for melatonin suppression), much remains to be elucidated. Here, we provide a set of minimum reporting guidelines for reporting the stimulus conditions involving light as an intervention in chronobiology, sleep research and environmental psychology experiments. Corresponding to the current state-of-the-art knowledge (June 2019), these are (i) measure and report the spectral power distribution of the acute stimulus from the observer’s point of view; (ii) measure and report the spectral power distribution of the background light environment from the observer’s point of view; (iii), make spectra available in tabulated form, (iv) report α-opic (ir)radiances and illuminance; (v) describe the timing properties of stimulus (duration and pattern); (vi) describe the spatial properties of stimulus (spatial arrangement and extent), and (vii) report measurement conditions and equipment. We supplement the minimum reporting guidelines with optional reporting suggestions and discuss limitations of the reporting scheme.

Clocks & Sleep, Vol. 1, Pages 273-279: The Effect of Shift Work and Poor Sleep on Self-Reported Skin Conditions: A Survey of Call Center Agents in the Philippines Night shift workers may have a disrupted circadian rhythm, which may contribute to the development of skin disease. The purpose of this study was to determine whether there is a significant difference in the prevalence and severity of self-reported skin disease between “regular” day shift workers compared to “graveyard” night shift workers. We conducted surveys from 630 call center agents in Manila, the Philippines, and they were analyzed regarding demographics, medical history, dermatologic history, lifestyle, and sleep. No difference was found in the prevalence of skin disease between shifts. However, night shift workers were worse sleepers. When compared to good sleepers, poor sleepers had a higher prevalence of skin disease with worse severity. Graveyard shift workers with poor sleep may have increased skin disease severity.

Clocks & Sleep, Vol. 1, Pages 259-272: Considering Sleep, Mood, and Stress in a Family Context: A Preliminary Study Background: During the first years of life, parental sleep strongly depends on child’s sleep quality. Poor parental sleep may relate to increased stress and negative mood. However, there is a lack of sleep studies focusing on all family members. This study aimed to investigate the relationship between sleep, mood, and stress in mothers, fathers and children. Methods: Data were obtained from 65 parental couples and 65 children (2 to 36 months). Data on sleep for all family members and stress of parents were completed by both mothers and fathers through questionnaires and sleep diaries. Results: Toddlers’ positive mood before nocturnal sleep was significantly associated with reduced wake times after sleep onset. Mothers reported worse sleep quality compared to fathers. Shorter sleep onset latency in fathers and better sleep efficiency in mothers were linked with better self-reported mood upon awakening. In mothers, but not in fathers, poor sleep quality was associated with higher perceived stress. Conclusion: Results suggest bidirectional relationships between sleep and mood in children, mothers and fathers. Moreover, results evidence poorer sleep in mothers, compared to fathers, which was linked with increased parenting stress. This gender gap should be further considered in studies with larger samples and in clinical contexts.

Clocks & Sleep, Vol. 1, Pages 240-258: Steady-State Pupil Size Varies with Circadian Phase and Sleep Homeostasis in Healthy Young Men Pupil size informs about sympathovagal balance as well as cognitive and affective processes, and perception. It is also directly linked to phasic activity of the brainstem locus coeruleus, so that pupil measures have gained recent attention. Steady-state pupil size and its variability have been directly linked to sleep homeostasis and circadian phase, but results have been inconsistent. Here, we report robust changes in steady-state pupil size during 29 h of continuous wakefulness in healthy young men (N = 20; 18–30 years old) maintained in dim-light in strictly controlled constant routine conditions. These variations were associated with variations in motivation and sustained attention performance. Pupil size variability did not significantly change during the protocol. Yet, pupil size variability was linearly associated with subjective fatigue, sociability, and anguish. No associations were found between neither steady-state pupil size nor pupil size variability, and objective EEG measure of alertness and subjective sleepiness. Our data support therefore the notion that, compared with its variability, steady-state pupil size is strongly influenced by the concomitant changes in sleep need and circadian phase. In addition, steady-state pupil size appears to be related to motivation and attention, while its variability may be related to separate affective dimensions and subjective fatigue.

Clocks & Sleep, Vol. 1, Pages 226-239: Burnout, Sleep, and Sleepiness during Day and Night Shifts in Transition from 8- to 12-Hour Shift Rosters among Airline Ground Crew Managers Organizational changes in shift scheduling provide rare opportunities for field studies aimed at investigating the effects of such changes on health and wellbeing. We studied the effects of a transition from 8-hour (8-h) to 12-hour (12-h) shift rosters in 39 airline ground crew managers on burnout, sleep quality, and sleepiness. Assessments were collected during the 8-h and were repeated three months after the transition to 12-h shift rosters. These assessments included the Shirom-Melamed Burnout Measure (SMBM), the Pittsburgh Sleep Quality Index (PSQI), actigraphy, the Karolinska Sleepiness Scale (KSS) completed hourly during one day and two night shifts, and caffeine intake. Findings demonstrated lower burnout, improved sleep quality, improved quality of naps, and increased afternoon sleepiness during the 12-h day shift. Napping was reported during 12-h night shifts by 36% of the sample. In nappers, increased night shift sleepiness was associated with increased caffeine intake on 8- and 12-h shifts. In non-nappers, increased night shift sleepiness was associated with decreased caffeine intake on the 8-h shift only. Change in shift length affects other structural and behavioral parameters in the workplace, making it challenging to isolate distinct characteristics of the two rosters and their relative effects on study outcomes. Individual differences in adaptation to shiftwork may also play a role.

Clocks & Sleep, Vol. 1, Pages 220-225: The Association between Sexual Orientation and Sleep Problems: Are there Racial and Ethnic Differences? Using the 2013–2017 National Health Interview Survey, this study examined whether there were significant sexual orientation differences in sleep problems in specific racial and ethnic populations. The analysis had a large sample size and enough statistical power to evaluate any sexual orientation differences or non-differences in sleep problems in Latinx, non-Latinx Black, non-Latinx Asian and Pacific Islander, and non-Latinx White populations. Consistent with recent studies on sexual orientation and sleep problems, this analysis revealed that, for most racial and ethnic groups, there was no significant sexual orientation difference in non-normal sleep duration. Sexual minority adults were significantly more likely to report not feeling rested, trouble falling asleep, trouble staying asleep, and taking medications for sleep than heterosexual adults. There were two notable exceptions in the findings. The first exception was that Latinx sexual minority adults were significantly more likely to report non-normal sleep duration when compared with Latinx heterosexual adults. The second exception was that there was no significant sexual orientation difference in not feeling rested among Asian and Pacific Islander adults.

Clocks & Sleep, Vol. 1, Pages 209-219: Predictors of Excessive Daytime Sleepiness in Medical Students: A Meta-Regression Excessive daytime sleepiness (EDS) is highly prevalent among medical students and can have serious negative outcomes for both students and their patients. Little is known about the magnitude and predictors of EDS among medical college students. A meta-regression analysis was conducted to achieve these two targets. A systematic search was performed for English-language studies that reported the prevalence of EDS among medical students using the Epworth sleepiness scale (ESS), age, sex, sleep duration and sleep quality as predictive variables. A total of nine observational studies (K = 9, N = 2587) were included in the analyses. Meta-regression analyses were performed using mean age (years), sex (proportion of male subjects), sleep duration (hours/night) and sleep quality index score (continuous scale) as moderators for EDS—with the prevalence of EDS as an outcome variable. An interaction term of sleep duration X sleep quality was created to assess if these two variables simultaneously influenced the outcome variable. Utilizing the ESS, the pooled prevalence of EDS among medical students was 34.6% (95% Confidence Interval (CI) 18.3–50.9%). Meta-regression models of age, sex, sleep duration and sleep quality alone revealed poor predictive capabilities. Meta-regression models of sleep duration–sleep quality interaction revealed results with high statistical significance. The findings from this review contribute supporting evidence for the relationship between sleep duration and sleep quality scores (i.e., sleep duration X sleep quality score) in predicting EDS in medical students.

Clocks & Sleep, Vol. 1, Pages 193-208: Light Modulation of Human Clocks, Wake, and Sleep Light, through its non-imaging forming effects, plays a dominant role on a myriad of physiological functions, including the human sleep–wake cycle. The non-image forming effects of light heavily rely on specific properties such as intensity, duration, timing, pattern, and wavelengths. Here, we address how specific properties of light influence sleep and wakefulness in humans through acute effects, e.g., on alertness, and/or effects on the circadian timing system. Of critical relevance, we discuss how different characteristics of light exposure across the 24-h day can lead to changes in sleep–wake timing, sleep propensity, sleep architecture, and sleep and wake electroencephalogram (EEG) power spectra. Ultimately, knowledge on how light affects sleep and wakefulness can improve light settings at home and at the workplace to improve health and well-being and optimize treatments of chronobiological disorders.

Clocks & Sleep, Vol. 1, Pages 185-192: The Impact of on-Call Work for Partners’ Sleep, Relationship Quality and Daytime Functioning The on-call schedule is a common work arrangement that allows for the continuance of services during periods of low demand or emergencies. Even though 17%–25% of the world’s population participate in on-call work, the human impacts of on-call are generally poorly described in the literature. Of the studies available on the effects of on-call work on workers, disturbances to sleep duration and sleep quality are the most commonly reported, along with negative sleep-related consequences on sleepiness, fatigue, stress and mood. Research has shown that for couples sharing a bed, disturbances to sleep can impair relationship conflict resolution and reduce relationship quality. In the ‘off-site’ on-call scenario where workers are sleeping at home, their co-sleeping partner may be at risk of sleep disturbances and the subsequent detrimental consequences of this disturbed sleep for themselves and their relationship. To date, few studies have investigated the impact of on-call work for partners’ sleep and the potential sleep-related consequences. Therefore, further studies are needed to specifically address whether on-call work impacts the sleep of partners and whether these sleep disturbances also impact the partner’s daily performance and relationship quality. Our aim was to provide a narrative around the existing, relevant literature that both investigate and inform the potential impact of on-call for workers’ partners’ sleep and related consequences.

Clocks & Sleep, Vol. 1, Pages 166-184: Sleep Modelling across Physiological Levels Sleep and circadian rhythms are regulated across multiple functional, spatial and temporal levels: from genes to networks of coupled neurons and glial cells, to large scale brain dynamics and behaviour. The dynamics at each of these levels are complex and the interaction between the levels is even more so, so research have mostly focused on interactions within the levels to understand the underlying mechanisms—the so-called reductionist approach. Mathematical models were developed to test theories of sleep regulation and guide new experiments at each of these levels and have become an integral part of the field. The advantage of modelling, however, is that it allows us to simulate and test the dynamics of complex biological systems and thus provides a tool to investigate the connections between the different levels and study the system as a whole. In this paper I review key models of sleep developed at different physiological levels and discuss the potential for an integrated systems biology approach for sleep regulation across these levels. I also highlight the necessity of building mechanistic connections between models of sleep and circadian rhythms across these levels.