Sensitivity of the human circadian pacemaker to nocturnal light: melatonin phase resetting and suppression

Circadian disruption upon painful peripheral nerve injury in mice: Temporal effects on transcriptome in pain-regulating sensory tissues

BACKGROUND

Neuropathic pain (NP) resulting from nerve damage shows diurnal fluctuation of intensity in patients, indicating circadian regulation. However, mechanisms linking NP and circadian regulation remain unclear. This study aimed to investigate time-dependent transcriptomic changes during a 24-hour period using a spared nerve injury (SNI) mouse model of NP.

METHODS

Pain-related behaviours were assessed at baseline and on days 7, 14, and 21 after SNI and control sham surgeries in C57BL/6JRJ mice. Spinal cord (SC) and periaqueductal gray (PAG) were collected 4-hourly over 24 h upon completion of behavioural testing.

RESULTS

RNA sequencing revealed 111 up- and 21 downregulated differentially expressed genes (DEGs) in the SC, and 35 up- and 33 downregulated DEGs in the PAG, across all six time points. The large majority of DEGs, 245 in the SC and 191 in the PAG, are involved in regulation of immunity. Among the top expressed genes, five DEGs in the SC, Atf3, Anxa10, Gpr151, Cxcl10, Sprr1a, and two DEGs in the PAG, Igf2 and Wnt6, were previously reported to regulate pain. Circadian analysis using CircaCompare identified 383 SC transcripts and 261 PAG transcripts with altered rhythmicity. Variability of gene expression during circadian day was increased in the SC and decreased in the PAG from the SNI mice.

CONCLUSION

These findings suggest that NP disrupts the circadian expression of rhythmic transcripts in the SC and PAG, potentially revealing new targets for chronotherapy of NP.

Association between outdoor artificial light at night and executive function among depressive patients: the mediating effect of sleep timing

Recent evidence highlights the potential impact of outdoor artificial light at night (ALAN) on sleep, and later sleep timing may be a risk factor for executive dysfunction. Depression is commonly associated with executive dysfunction, which significantly compromise prognosis. However, it remains unclear whether sleep-wake phase mediate the effects of outdoor ALAN on executive function. We assessed whether sleep timing mediated the association between outdoor ALAN and executive function among depressed patients. Between 2017 and 2023, 798 inpatients with depression were enrolled from the Fourth People's Hospital of Hefei. The outdoor ALAN exposure of patients was estimated using satellite images. All participants were assessed for sleep conditions using the Pittsburgh Sleep Quality Index (PSQI) and for executive function using the Behavior Rating Inventory of Executive Function-Adult Version (BRIEF-A). We employed multifactor linear regression models to investigate the association between outdoor ALAN exposure and executive function, adjusted for potential confounders. Additionally, mediation models were utilized to explore the mediating role of sleep timing in this association. Our study found that greater ALAN exposure was significantly associated with higher executive function scores. The exposure of participants at 12 months prior to enrollment had the greatest effect, for each interquartile range (IQR 29.93 nW/cm2/sr) increase in outdoor ALAN exposure, the Global Executive Composite (GEC) scores increased by 6.12 (95 % confidence interval [CI]: 2.49, 9.74). Mediation analysis indicated that sleep midpoint significantly mediated the relationship between outdoor ALAN and executive function, with a mediated proportion of 22.39 %. The study suggested that outdoor ALAN exposure has adverse effects on executive function in depressed patients, and sleep-wake phase may mediate the association between outdoor ALAN exposure and executive function.

The circadian rhythm of human body temperature - Clinical implications and review of the literature

Human body temperature remains an essential vital sign that had been used to judge our health given its strong correlation with human disease. Body temperature is also a manifestation of our circadian rhythm, with a predictable rise during the day peaking in the evenings and steady decrease during the night reaching a minimum around the time of awakening. Yet, the rhythm is believed to be endogenous and to exist independently of any external stimuli, including day light. Human illnesses such as infections, autoimmune conditions, and cancer had been associated with a disruption in the circadian rhythm. This is of significant clinical interest because measurements of the specific disruptions of the rhythm appear to carry diagnostic and prognostic value. This is a review of the literature with a focus on the determinants of human body temperature and the circadian rhythm of body temperature. The last section provides potential new research avenues in our search for chronotherapy clinical applications.

Improving children's alertness and neuromuscular response by using a blue-enriched white light in the kindergarten playroom

Preschool children, who spend most of their time indoors, and the effects of artificial light on children's health and performance are important. Previous studies show that blue-enriched white light (BWL) has significant effects on human bodies, but only a few studies have specifically examined its effects in young children. Moreover, due to the significant physiological differences between children and adults, findings from BWL studies in adults cannot be directly applied to children. Therefore, investigating the effects of BWL on young children living in indoor environments is crucial. We recruited 24 preschool children (age: 5 ± 0.8 years; 12 girls and 12 boys) to participate in a within-subject, randomized crossover study involving common white light (CWL) (450 lx, Melanopic EDI: 354.04 lx) and BWL (450 lx, Melanopic EDI: 746.05 lx) in a kindergarten playroom. Under different light conditions, the children underwent tests for cardiac activity and critical flicker fusion frequency (CFF), as well as psychomotor vigilance task (PVT) and ruler drop test (RDT). The results indicated that BWL had significant effects on preschool children. Compared to CWL exposure, BWL exposure significantly improved cardiac activity, alertness, and neuromuscular response but slightly increased visual fatigue. Our study reveals that BWL has significant potential to improve children's physiological and cognitive functions, particularly to improve cardiac activity, alertness, and neuromuscular response. This study broadens the understanding of the effects of indoor lighting on children and provides a theoretical basis for designing a healthy indoor environment for children.

Associations between light at night and mental health: A systematic review and meta-analysis

Light at night (LAN) disrupts the circadian rhythm by altering the natural light-dark cycle. With increasing interest in the relationship between LAN and mental health, there is value in an updated systematic review and meta-analysis considering prominent mental health conditions that also critically appraises LAN exposure assessment. We conducted a systematic review of six databases, two registries, and Google Scholar to identify studies examining the associations between indoor and outdoor LAN exposure (high vs. low exposure) and mental health outcomes (depression, bipolar disorder, anxiety, and schizophrenia), completing inverse-variance random-effects meta-analyses. Nineteen studies with a total population of 556,861 were included in the review. LAN exposure was associated with increased odds of depression prevalence (odds ratio [OR]: 1.18; 95 % confidence interval [CI]: 1.09 to 1.28), with stronger associations for bedside (OR: 1.45; 95 % CI: 1.03 to 2.04) or wrist-measured indoor LAN (OR: 1.30; 95 % CI: 1.22 to 1.38) than satellite-measured outdoor LAN exposure (OR: 1.10; 95 % CI: 1.04 to 1.17) and in older adults (OR: 1.56; 95 % CI: 1.24 to 1.96) compared to general adults (OR: 1.16; 95 % CI: 1.06 to 1.28) or youth (OR: 1.07; 95 % CI: 0.99 to 1.16). LAN exposure was also associated with an increased prevalence of bipolar disorder (OR: 1.19; 95 % CI: 1.08 to 1.31) and anxiety (OR: 1.10; 95 % CI: 1.02 to 1.20) and increased incidence of anxiety (hazard ratio [HR]: 1.08; 95 % CI: 1.02 to 1.15) and schizophrenia (HR: 1.55; 95 % CI: 1.01 to 2.39); however, the incidence of depression did not achieve statistical significance (HR: 1.53; 95 % CI: 0.98 to 2.38). Overall, our results suggest that LAN exposure influences adverse mental health conditions, with differences in results appreciated for depression prevalence depending on how LAN exposure was measured. Additional research is needed on the effects of LAN given its undoubted interest in the prevention and treatment of mental disorders.

Chronotherapeutic Treatments for Psychiatric Disorders: A Narrative Review of Recent Literature

PURPOSE OF THE REVIEW

This narrative review examines the newest findings from clinical trials of chronotherapeutics for psychiatric disorders. We reviewed the potential effects of the most commonly-studied chronotherapeutics such as bright light therapy, dark therapy, melatonin, and chronotherapy on the psychiatric disorders of depression, bipolar disorder, and anxiety disorders.

RECENT FINDINGS

The preponderance of recent clinical trials in chronotherapeutics has focused on bright light therapy in depression. However, there is an emerging body of preliminary studies testing chronotherapeutics in other psychiatric disorders, including bipolar disorder and post-traumatic stress disorder. Chronotherapeutics hold potential to improve sleep in adults with psychiatric conditions as well as psychiatric symptoms. Although the most recent literature demonstrates the promise of these interventions, the current body of work is limited by small sample sizes and relatively few studies outside of depression. Larger-scale trials are needed to refine treatment protocols, develop personalized treatment approaches, and inform dissemination. Studies in psychiatric conditions besides depression are particularly needed.

Analyzing the Interactions of Light and Melatonin Forcing in a Mathematical Model of the Human Circadian Oscillator

The pineal secretion of the hormone melatonin demonstrates a circadian (~24 h) rhythm with the onset of melatonin production at night and offset each morning under tight circadian control for entrained individuals. Melatonin exerts both acute sleep-promoting effects and phase-shifting effects on the circadian clock. Due to its hypnotic and chronobiotic (phase shifting) effects, exogenous melatonin supplements are increasingly being used as a treatment for a variety of sleep and circadian diseases and disorders. Phase shifting of the circadian clock can also be accomplished through ocular exposure to light. However, the interacting effects of light and melatonin on the circadian clock are not well understood. To analyze the dynamic behavior of both endogenous and exogenous melatonin's influence on the circadian clock, we extend a previously published mathematical model of the circadian clock to account for forcing due to both endogenous melatonin produced by the pineal gland and exogenous melatonin entering the system through ingested oral supplements. We fit model parameters using published melatonin pharmacokinetics, a melatonin suppression illuminance-response curve, and a 3-pulse 3 mg melatonin phase response curve (PRC). Simulated microscopic PRCs to light and melatonin are determined by the model fits and demonstrate a relative phase difference consistent with previous observations in experimental PRC data. Finally, we simulate a phase advancing experimental protocol utilizing both light exposure and exogenous melatonin to generate model predictions for the effects of interacting inputs to the clock. This modeling framework allows for the study of melatonin's dynamic properties and interaction with the circadian clock. Furthermore, it provides a framework for determining optimal light exposure and exogenous melatonin administration schedules to induce desired phase shifting of the circadian clock.

Circadian clock communication during homeostasis and ageing

Maintaining homeostasis is essential for continued health, and the progressive decay of homeostatic processes is a hallmark of ageing. Daily environmental rhythms threaten homeostasis, and circadian clocks have evolved to execute physiological processes in a manner that anticipates, and thus mitigates, their effects on the organism. Clocks are active in almost all cell types; their rhythmicity and functional output are determined by a combination of tissue-intrinsic and systemic inputs. Numerous inputs for a specific tissue are produced by the activity of circadian clocks of other tissues or cell types, generating a form of crosstalk known as clock communication. In mammals, the central clock in the hypothalamus integrates signals from external light-dark cycles to align peripheral clocks elsewhere in the body. This regulation is complemented by a tissue-specific milieu of external, systemic and niche inputs that modulate and cooperate with the cellular circadian clock machinery of a tissue to tailor its functional output. These mechanisms of clock communication decay during ageing, and growing evidence suggests that this decline might drive ageing-related morbidities. Dietary, behavioural and pharmacological interventions may offer the possibility to overcome these changes and in turn improve healthspan.

Characteristics of objectively-measured naturalistic light exposure patterns in U.S. adults: A cross-sectional analysis of two cohorts

Light is an environmental feature important for human physiology. Investigation of how light affects population health requires exposure assessment and personal biomonitoring efforts. Here, we derived measures of amount, duration, regularity, and timing from objective personal light (lux) measurement in >4000 participants across two United States (US)-based cohort studies, the Multi-Ethnic Study of Atherosclerosis (MESA) and the Hispanic Community Health Study / Study of Latinos (HCHS/SOL), encompassing eight geographic regions. Objective light and actigraphy data were collected over a week using wrist-worn devices (Actiwatch Spectrum). Cohort-stratified light exposure metrics were analyzed in relation to sex, season, time-of-day, location, and demographic and sleep health characteristics using Spearman correlation and linear and logistic regressions (separately by cohort) adjusted for age, sex (where applicable), and exam site. Light exposure showed sex-specific patterns and had seasonal, diurnal, geographic, and demographic and sleep health-related correlates. Results between independent cohorts were strongly consistent, supporting the utility and feasibility of light biomonitoring. These findings provide a fundamental first characterization of light exposure patterns in a large US sample and will inform future work to incorporate light as a biologically relevant exposure in environmental public health and key component of the human exposome.

Independent effects of the human circadian system and sleep/eating cycles on caloric intake in adolescents vary by weight status

Late-day eating is linked to increased obesity risk; however, whether the endogenous circadian system independently influences caloric intake and if this control differs among individuals based on weight status is unknown. Here, we investigated in adolescents the independent roles of the endogenous circadian system and of the behavioral sleep/wake cycle (sleep/wake, fasting/eating, rest/activity, dark/dim light, social interaction, posture, etc.) on self-selected caloric intake using a Forced Desynchrony protocol. Fifty-one male and female adolescents across three weight status categories (24 with healthy weight, 13 with overweight, and 14 with obesity) completed the protocol where participants lived on seven 28-h sleep/wake cycles in dim light during wake and complete darkness during sleep. Results suggest that the circadian system and the behavioral cycle each affected caloric intake, with a decrease across the wake episode and an increase from circadian morning to circadian evening in caloric intake. The endogenous circadian rhythm in caloric intake showed a circadian peak-to-trough difference of 196 [CI 95% 164, 226] kcal per meal with peak timing of 296° [288°, 304°; equivalent to ~17:30 in these participants]. In those with overweight/obesity, more calories were consumed later in the waking episode and later in the circadian cycle, and with blunted amplitudes compared to those with healthy weight. Results implicate both the endogenous circadian system and the behavioral cycle in shaping the daily rhythm of food intake. Furthermore, these results help explain the increased drive for caloric intake toward the evening, especially in those at risk for obesity.

Mental health and sleep correlates of self-reported outdoor daylight exposure in over 13,000 adults with depression

BACKGROUND

Increasing daylight exposure might be a simple way to improve mental health. However, little is known about daylight-symptom associations in depressive disorders.

METHODS

In a subset of the Australian Genetics of Depression Study (N = 13,480; 75% female), we explored associations between self-reported number of hours spent in daylight on a typical workday and free day and seven symptom dimensions: depressive (overall, somatic, psychological); hypo-manic-like; psychotic-like; insomnia; and daytime sleepiness. Polygenic scores for major depressive disorder (MDD); bipolar disorder (BD); and schizophrenia (SCZ) were calculated. Models were adjusted for age, sex, shift work status, employment status, season, and educational attainment. Exploratory analyses examined age-stratified associations (18-24 years; 25-34 years; 35-64 years; 65 and older). Bonferroni-corrected associations (p < 0.004) are discussed.

RESULTS

Adults with depression reported spending a median of one hour in daylight on workdays and three hours on free days. More daylight exposure on workdays and free days was associated with lower depressive (overall, psychological, somatic) and insomnia symptoms (p's<0.001), but higher hypo-manic-like symptoms (p's<0.002). Genetic loading for MDD and SCZ were associated with less daylight exposure in unadjusted correlational analyses (effect sizes were not meaningful). Exploratory analyses revealed age-related heterogeneity. Among 18-24-year-olds, no symptom dimensions were associated with daylight. By contrast, for the older age groups, there was a pattern of more daylight exposure and lower insomnia symptoms (p < 0.003) (except for 25-34-year-olds on free days, p = 0.019); and lower depressive symptoms with more daylight on free days, and to some extent workdays (depending on the age-group).

CONCLUSIONS

Exploration of the causal status of daylight in depression is warranted.

Efficacy of bright light therapy improves outcomes of perinatal depression: A systematic review and meta-analysis of randomized controlled trials

The efficacy of bright light therapy (BLT) in the context of perinatal depression remains underexplored. This meta-analysis aimed to systematically assess the effectiveness of BLT among perinatal depression. A comprehensive literature search was performed across several databases, including the Cochrane Central Register of Controlled Trials, PubMed, Embase, CNKI and the clinical trials registry platform, covering the period from the inception of each database up to January 2024. The Cochrane Collaboration's bias assessment tool was employed to evaluate the quality of the included studies. Review Manager 5.3 Software was utilized to conduct the meta-analysis. Six trials, encompassed a total of 167 participants diagnosed with perinatal depression were incorporated quantitative analysis, all of those have been published in English, with no restriction on publication year, and used BLT and dim light therapy (DLT) as intervention. The relative risk (RR) of BLT compared to DLT for perinatal depression is 1.46 (fixed effects model, p = 0.04, 95 % CI = [1.02, 2.10]), indicating a significant improvement in depression outcomes compared to DLT groups. The heterogeneity test yielded an I2 value of 41 % (p = 0.13), indicated a low degree of heterogeneity. Considering the small sample size, we conducted a sensitivity analysis, found RR increased to 2.33 (fixed effects model, p = 0.001, CI = 1.39-3.92). Cochrane Risk of Bias Tool showed only a single study was deemed high quality. This study indicates a beneficial impact of BLT on perinatal depression, subgroup analysis finds no significant mediation effects of different parameters after sensitivity analyses. It is recommended that future studies with larger samples be conducted to explore the effects of BLT on perinatal depression.

The Effect of an Improved Environment According to Watson's Theory of Human Care on Sleep, Anxiety, and Depression in Patients Undergoing Open Heart Surgery: A Randomized Controlled Trial

Background/Objectives: According to Watson's Human Care Theory, an improved environment influences patients' care processes. The purpose of this study was to examine the effect of an improved environment, according to Watson's Human Care Theory, on sleep quality, anxiety, and depression in patients undergoing open heart surgery. Methods: Upon admission to the ward from the postoperative intensive care unit, the experimental group underwent environmental remediation for three days. The environmental arrangements ensured that the patient's room maintained an appropriate temperature range of 18-26 °C and humidity values of 30-50%. Monitoring took place at 21:00, 22:00, and 23:00 on Days 1, 2, and 3, at which times, the brightness of the patient rooms gradually decreased. On the morning of the fourth day, the patients were interviewed face to face, and research questionnaires were filled out (ClinicalTrials.gov identifier of the manuscript: NCT06744023). Results: After the implementation of an improved environment in accordance with Watson's Human Care Theory, the sleep duration of the patients in the experimental group (5.91 h) was higher than that of the control group (4.1 h). At the same time, the mean sleep quality score was measured as 300 ± 15.33 in the experimental group and 116.33 ± 14.94 in the control group. In addition, anxiety and depression levels were lower in the experimental group (5.63 ± 0.59; 4.53 ± 0.42) compared with the control group (12.03 ± 0.85; 10.03 ± 0.82). Conclusions: We recommend implementing improved environmental arrangements in accordance with Watson's Human Care Theory to improve sleep quality and reduce anxiety and depression levels in patients undergoing open heart surgery.

Circadian rhythm disorders in the blind

Non-24-h sleep-wake disorder in blind patients without light perception is an orphan circadian rhythm sleep-wake disorder and is extremely rare in sighted people. Non-24-h sleep-wake disorder is characterized by insomnia and daytime sleepiness alternating with asymptomatic episodes. The frequency of symptomatic periods depends on the daily desynchronization of endogenous circadian pattern of each patient. Diagnosis requires anamnesis, a sleep diary, and actigraphy, if possible; in addition, repeated 24-h measures of circadian markers such as melatonin secretion are also required. Treatment consists of sleep hygiene, behavioral therapy, and melatonin/melatonin agonist administration. Melatonin treatment should start when the circadian rhythm of the patient is in phase with the solar cycle. Efficacy of treatment may be evident after weeks even months from the beginning. There is often a relapse when the medication is stopped.

Sleep and circadian rhythms modeling: From hypothalamic regulatory networks to cortical dynamics and behavior

Sleep and circadian rhythms are regulated by dynamic physiologic processes that operate across multiple spatial and temporal scales. These include, but are not limited to, genetic oscillators, clearance of waste products from the brain, dynamic interplay among brain regions, and propagation of local dynamics across the cortex. The combination of these processes, modulated by environmental cues, such as light-dark cycles and work schedules, represents a complex multiscale system that regulates sleep-wake cycles and brain dynamics. Physiology-based mathematical models have successfully explained the mechanisms underpinning dynamics at specific scales and are a useful tool to investigate interactions across multiple scales. They can help answer questions such as how do electroencephalographic (EEG) features relate to subthalamic neuron activity? Or how are local cortical dynamics regulated by the homeostatic and circadian mechanisms? In this chapter, we review two types of models that are well-positioned to consider such interactions. Part I of the chapter focuses on the subthalamic sleep regulatory networks and a model of arousal dynamics capable of predicting sleep, circadian rhythms, and cognitive outputs. Part II presents a model of corticothalamic circuits, capable of predicting spatial and temporal EEG features. We then discuss existing approaches and unsolved challenges in developing unified multiscale models.

Effects of light on biological functions and human sleep

The nonvisual effects of light in humans are mainly conveyed by a subset of retinal ganglion cells that contain the pigment melanopsin which renders them intrinsically photosensitive (= intrinsically photosensitive retinal ganglion cells, ipRGCs). They have direct connections to the main circadian clock in the suprachiasmatic nuclei (SCN) of the hypothalamus and modulate a variety of physiological processes, pineal melatonin secretion, autonomic functions, cognitive processes such as attention, and behavior, including sleep and wakefulness. This is because efferent projections from the SCN reach other hypothalamic nuclei, the pineal gland, thalamus, basal forebrain, and the brainstem. The ipRGCs also directly impact the prefrontal cortex and the perihabenular nucleus (mood). In particular, light suppresses the secretion of melatonin in a dose-dependent manner, mainly depending on irradiance and spectral composition of light. There is evidence that exposure to light-emitting devices from luminaires and screens before bedtime can impact on sleep onset latency, sleep duration, and sleep quality. Likewise, light exposure during daytime modulates sleep architecture, duration, and sleep quality during the subsequent night. Therefore, the integration of acute, circadian, and long-term effects of light together influence sleep-wake quality and behavior in healthy individuals, as well as in patients with psychiatric or medical disorders.

Personal light treatment devices: a countermeasure to improve sleep, fatigue, and circadian misalignment in an operational setting

Carefully timed light exposure is a promising countermeasure to overcome the negative sleep and circadian implications of shift work. However, many lighting interventions are static and applied at the group level (e.g. light banks, changes to ambient lighting), which is not appropriate for all populations or settings. This study investigates whether individualized lighting exposure, via personal light treatment devices (PLTDs), can improve sleep, sustain projected performance, and entrain circadian rhythms with the work schedules of US Navy submariners. Submarines are a unique testbed for PLTD intervention because they provide a self-contained environment with little influence from outside schedules or lighting. Forty-two submariners were pseudo-randomly assigned to either the PLTD or Control group. PLTD group participants wore blue-light exposure glasses for ~40 minutes upon waking and blue-blocking glasses for ~2 hours before sleep; Control group participants did not use PLTDs. Both groups completed questionnaires assessing subjective sleep and mood before and after the 12-day intervention, and wore wrist actigraphy devices to objectively assess sleep, projected performance, and predicted circadian phase outcomes. Compared with the Control group, several objective and subjective sleep outcomes and projected performance scores were improved in the PLTD group. The PLTD group's predicted circadian phase (modeled from actigraphy-derived accelerometer data) more rapidly shifted to align with scheduled work periods. Compliance with PLTD use was high, with no major disruptions to operational duties reported. These data provide initial support for the use of PLTDs as a flexible and customizable countermeasure for fatigue, sleep loss, and circadian misalignment in an operational environment.

Let's Talk About It in the Morning: How Circadian Rhythms Impact Information Sharing on Social Media

This study investigated the role of circadian rhythms in online information sharing. We gathered 416,914 posts from the social media platform X (formerly Twitter). We identified daily patterns of collective positive and negative affect in these posts, consistent with previous research on social media and circadian rhythms. We created predicted values of positive and negative affect for each post, based on the time a post was created. We then used these predicted values for each post to estimate that post's likelihood of being reshared. We controlled for a range of possible confounders, such as the actual positive and negative affect expressed in a specific post and the number of existing followers and previous posts of the user who created the post, as well as whether the post contained hashtags, mentions, and quotes. The results support a strong relationship between the predicted positive and negative affect of a post-based on circadian patterns of collective positive and negative affect-and the likelihood of a post being shared. We further examine seasonal changes and design a natural experiment, in which we compare patterns of positive and negative affect and information sharing before and after the clocks change, i.e., "spring forward" and "fall back." The results suggest that these daily collective patterns of positive and negative affect on social media are influenced, at least partly, by hormonal influences and not only collective daily routines.

Does gaming keep subjects awake?: Subjective and objective sleep parameters following gaming in comparison to a passive control

OBJECTIVES

Gaming is a global phenomenon often associated with impaired health and sleep patterns. Although the research activities are growing, the evidence to date is rare due to the various gaming titles and inconsistent study designs. Thus, this study aimed to examine the impact of excessive gaming in the evening on subjective as well as objective sleep parameters by focusing on specific game titles and assessing several evenings/nights using a mixed-methods approach.

METHODS

A total of 33 experienced young male adults (23.00 ± 3.53 years old, ranked players in League of Legends or Counter-Strike: Global Offensive) took part. The individuals' sleep parameters were assessed via diary and actigraphy. In randomized order, one week apart and for a duration of 120 min each, two study evenings were spent gaming, while the other two evenings were spent without digital media and gaming, but instead watching a nature documentary.

RESULTS

No significant difference between the conditions were found (p > 0.05) in either the sleep duration nor the sleep quality. Daytime sleepiness was significantly increased after watching the documentary movie, when compared to gaming (p < 0.001).

CONCLUSIONS

These results indicate that, one the one hand, the gaming activity leads to higher arousal and alertness as it requires concentration and dedication. On the other hand, this impact seems only short-term and does not necessarily affect sleep patterns. Future studies are needed to gain deeper insights, especially regarding the long-term health effects of gaming.

Behavioural determinants of physiologically-relevant light exposure

Light exposure triggers a range of physiological and behavioural responses that can improve and challenge health and well-being. Insights from laboratory studies have recently culminated in standards and guidelines for measuring and assessing healthy light exposure, and recommendations for healthy light levels. Implicit to laboratory paradigms is a simplistic input-output relationship between light and its effects on physiology. This simplified approach ignores that humans actively shape their light exposure through behaviour. This article presents a novel framework that conceptualises light exposure as an individual behaviour to meet specific, person-based needs. Key to healthy light exposure is shaping behaviour, beyond shaping technology.

Chronobiological disruptions: unravelling the interplay of shift work, circadian rhythms, and vascular health in the context of stroke risk

Shift work, particularly night shifts, disrupts circadian rhythms and increases stroke risk. This manuscript explores the mechanisms connecting shift work with stroke, focusing on circadian rhythms, hypertension, and diabetes. The circadian system, controlled by different mechanisms including central and peripheral clock genes, suprachiasmatic nuclei (SCN), and pineal gland (through melatonin production), regulates body functions and responds to environmental signals. Disruptions in this system affect endothelial cells, leading to blood pressure issues. Type 2 diabetes mellitus (T2DM) is significantly associated with night shifts, with circadian disturbances affecting glucose metabolism, insulin sensitivity, and hormone regulation. The manuscript examines the relationship between melatonin, insulin, and glucose balance, highlighting pathways that link T2DM to stroke risk. Additionally, dyslipidemia, particularly reduced HDL-c levels, results from shift work and contributes to stroke development. High lipid levels cause oxidative stress, inflammation, and endothelial dysfunction, increasing cerebrovascular risks. The manuscript details the effects of dyslipidemia on brain functions, including disruptions in blood flow, blood-brain barrier integrity, and neural cell death. This comprehensive analysis emphasizes the complex interplay of circadian disruption, hypertension, diabetes, and dyslipidemia in increasing stroke risk among shift workers. Understanding these mechanisms is essential for developing targeted interventions to reduce stroke susceptibility and improve cerebrovascular health in this vulnerable population.

Impact of Modern Lifestyle on Circadian Health and Its Contribution to Adipogenesis and Cancer Risk

BACKGROUND

Recent research underscores a crucial connection between circadian rhythm disruption and cancer promotion, highlighting an urgent need for attention.

OBJECTIVES

Explore the molecular mechanisms by which modern lifestyle factors-such as artificial light exposure, shift work, and dietary patterns-affect cortisol/melatonin regulation and cancer risk.

METHODS

Employing a narrative review approach, we synthesized findings from Scopus, Google Scholar, and PubMed to analyze lifestyle impacts on circadian health, focusing on cortisol and melatonin chronobiology as molecular markers. We included studies that documented quantitative changes in these markers due to modern lifestyle habits, excluding those lacking quantitative data or presenting inconclusive results. Subsequent sections focused solely on articles that quantified the effects of circadian disruption on adipogenesis and tumor microenvironment modifications.

RESULTS

This review shows how modern habits lead to molecular changes in cortisol and melatonin, creating adipose microenvironments that support cancer development. These disruptions facilitate immune evasion, chemotherapy resistance, and tumor growth, highlighting the critical roles of cortisol dysregulation and melatonin imbalance.

CONCLUSIONS

Through the presented findings, we establish a causal link between circadian rhythm dysregulation and the promotion of certain cancer types. By elucidating this relationship, the study emphasizes the importance of addressing lifestyle factors that contribute to circadian misalignment, suggesting that targeted interventions could play a crucial role in mitigating cancer risk and improving overall health outcomes.

The interplay among sleep patterns, social habits, and environmental cues: insights from the Spanish population and implications for aligning daily rhythms

Introduction

The interplay among sleep patterns, social habits and environmental cues is becoming increasingly more important for public health and wellbeing due to its connection to circadian desynchronization. This paper explores said connections in Spain (which has an official and solar time mismatch), introducing the "Three Times Score" ‒which is based on questions widely used in the field‒ as a complementary tool for exploring the interplay of daily rhythms.

Methods

The questionnaire covers sleep-related habits, social time, and environmental time. The study includes 9,947 participants (34.89 ± 12.15 y/o, mean ± SD; 5,561 women) from different Spanish regions. Sleep parameters were obtained for work and free days, as well as a modified version of the sleep-corrected midsleep on free days (MBFbc) and a parameter similar to social jet lag, both derived from bed time rather than sleep time. A number of indexes were computed to compare bed and work-related habits, together with natural light/dark cycle, along with the Three Times Score. Mixed-effect regression analysis was used to test whether the biological, social and environmental factors included in the study significantly predicted the sleep-related parameters: bedtime, wake-up time, time in bed and mid-bedtime.

Results and discussion

Temporal differences were found between work and free days, with waking-up occurring 2 h earlier on work days (7:10 ± 0:01) than on free days (9:15 ± 0:01). Bed times were 1 h earlier on work days (23:46 ± 0:01) than on free days (00:45 ± 0:01), whereas time in bed was over 1 h shorter on work (7 h 23 min) versus free (8 h 29 min) days. Strong correlations were found between work starting time and waking-up and bedtimes on workdays. Women went to bed earlier and woke up later, spending more time in bed. Differences in sleep habits were observed between work and free days across all age groups. The group of younger adults (18-30) reported going to bed later than older and younger groups, especially on free days. Adolescents and young adults also woke-up later than other age groups, especially on free days. Social jet lag (relative to bed time) and desynchronization indexes also varied with age, with younger adult participants exhibiting higher levels. Seasonal differences were limited, with minor variations between winter and summer. According to the multiple regression analysis, social (day type, work start time, alarm clock usage), biological (age, gender, in most cases related to sex) and environmental (sunset time) factors significantly contribute to predicting sleep/bed related schedules. This study provides insights into sleep habits in the Spanish population, introducing the Three Times Score as a complementary tool for exploring the interactions between sleep/bed-related habits, natural darkness and work-related schedules. Understanding this interplay is crucial for developing tailored interventions to improve sleep and wellbeing.

Sleep Matters in Chronotype and Mental Health Association: Evidence from the UK and Germany

BACKGROUND

There is considerable evidence supporting the elevated risk of mental health problems in individuals with evening chronotype relative to those with morning or intermediate chronotypes. Recent data, however, suggest that this risk may be explained, at least partially, by poor sleep quality.

METHODS

This study aimed to further clarify the roles of chronotype and sleep quality in mental health outcomes (depression, anxiety, stress) in young individuals (18-40 years) living in the UK (n = 185) or Germany (n = 209).

RESULTS

Consistent with our recent observations in a comparable North Indian sample, we found that poor quality of sleep had significantly positive associations with adverse mental health outcomes both in the UK and Germany-based samples. Significant associations between evening chronotype and poor mental health were also evident, but these associations were fully mediated by poor quality of sleep in both samples.

CONCLUSIONS

These observations suggest that efforts to identify sleep disruption in a timely manner and promotion of good sleep may prevent mental health problems, especially in individuals with evening chronotype and other known risks for mental disorders.

Investigating the effects of indoor lighting on measures of brain health in older adults: protocol for a cross-over randomized controlled trial

BACKGROUND

The worldwide number of adults aged 60 years and older is expected to double from 1 billion in 2019 to 2.1 billion by 2050. As the population lives longer, the rising incidence of chronic diseases, cognitive disorders, and behavioral health issues threaten older adults' health span. Exercising, getting sufficient sleep, and staying mentally and socially active can improve quality of life, increase independence, and potentially lower the risk for Alzheimer's disease or other dementias. Nonpharmacological approaches might help promote such behaviors. Indoor lighting may impact sleep quality, physical activity, and cognitive function. Dynamically changing indoor lighting brightness and color throughout the day has positive effects on sleep, cognitive function, and physical activity of its occupants. The aim of this study is to investigate how different indoor lighting conditions affect such health measures to promote healthier aging.

METHODS

This protocol is a randomized, cross-over, single-site trial followed by an exploratory third intervention. Up to 70 older adults in independent living residences at a senior living facility will be recruited. During this 16-week study, participants will experience three lighting conditions. Two cohorts will first experience a static and a dynamic lighting condition in a cluster-randomized cross-over design. The static condition lighting will have fixed brightness and color to match lighting typically provided in the facility. For the dynamic condition, brightness and color will change throughout the day with increased brightness in the morning. After the cross-over, both cohorts will experience another dynamic lighting condition with increased morning brightness to determine if there is a saturation effect between light exposure and health-related measures. Light intake, sleep quality, and physical activity will be measured using wearable devices. Sleep, cognitive function, mood, and social engagement will be assessed using surveys and cognitive assessments.

DISCUSSION

We hypothesize participants will have better sleep quality and greater physical activity during the dynamic lighting compared to the static lighting condition. Additionally, we hypothesize there is a maximal threshold at which health-outcomes improve based on light exposure. Study findings may identify optimal indoor lighting solutions to promote healthy aging for older adults.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT05978934.

Effect of Diurnal Light Conditions on Electroretinogram Responses to Red and Blue Flickering Light

Bright light impacts the human circadian system such that exposure to bright light at night can suppress melatonin secretion, and exposure to bright light in the morning prevents light-induced melatonin suppression at night. The preventive effect of morning light may attenuate the prior history of light sensitivity of intrinsically photosensitive retinal ganglion cells (ipRGCs) that regulate the circadian system. In this study, we evaluated electroretinogram (ERG) responses to red and blue flickering lights following dim and bright daylight conditions. Eleven healthy females underwent ERG measurements during exposure to 33 Hz flickering red or blue light under dim and bright daytime conditions. We averaged ERG waves for 50 flickering light pulses of the trigger signal data. We obtained the amplitude of the signal-averaged ERG by calculating the difference between the waves' peaks and bottoms. Although there was no significant dim and bright light difference in the amplitude of ERG waves, the ERG amplitude to flickering blue light under the bright light condition was significantly lower than to flickering blue light under the dim light condition. In this study, blue light stimulated mainly ipRGCs and S-cones. Since S-cones may contribute minimally to the light-adapted 33 Hz flicker ERG results, our findings suggest that bright light during the daytime attenuates the sensitivity of human ipRGCs.

The dynamic responses of mood and sleep physiology to chronic sleep restriction and subsequent recovery sleep

Healthy sleep of sufficient duration preserves mood and disturbed sleep is a risk factor for a range of psychiatric disorders. As adults commonly experience chronic sleep restriction (SR), an enhanced understanding of the dynamic relationship between sleep and mood is needed, including whether susceptibility to SR-induced mood disturbance differs between sexes. To address these gaps, data from N = 221 healthy adults who completed one of the two multi-day laboratory studies with identical 9-day SR protocols were analyzed. Participants randomized to the SR (n = 205) condition underwent 5 nights of SR to 4 hours of time-in-bed and were then randomized to one of the seven sleep doses that ranged from 0 to 12 hours in 2 hours increments; participants randomized to the control (n = 16) condition received 10 hours time-in-bed on all study nights. The Profile of Mood States (POMS) was used to assess mood every 2 hours during wakefulness and markers of sleep homeostasis (EEG slow-wave activity (SWA)) were derived via polysomnography. Mood progressively deteriorated across SR with marked disturbances in somatic mood components. Altered sleep physiology contributed to mood disturbance whereby increased EEG SWA was associated with increased POMS Total Mood Disturbance scores, a finding specific to males. The mood was restored in a dose-response fashion where improvements were greater with longer sleep doses. These findings suggest that when lifestyle and environmental factors are inhibited in the laboratory, the affective consequences of chronic sleep loss are primarily somatic mood disturbances. Altered sleep homeostasis may contribute to mood disturbance, yet sleep-dependent mechanisms may be sex-specific.

The effects of daylight duration on the multiple sleep latency test (MSLT) results: A pilot study

OBJECTIVE

MSLT results are known to be affected by multiple factors including sleep time, frequency of nighttime arousals, and medications intake. Although being the main synchronizer of sleep and wakefulness, daylight duration effects on MSLT have not been examined. Burlington, Vermont, USA experiences great variations in daylight duration, ranging from 8 h 50 min to 15 h 33 min of daylight. The aim of this study was to test the hypothesis that there would be photoperiod duration effects on MSLTs performed during short daylight (short daylight studies, SDS) vs. long daylight (long daylight studies, LDS) from 2013 to 2023 in our sleep laboratory.

METHODS

We identified and analyzed 37 SDS (daylight 530-560 min) and 36 LDS (daylight 903-933 min) from our database. Groups of SDS and LDS results were compared using non-paired student T test, Chi-Square and non-parametric Mann Whitney U Test.

RESULTS

Average daylight duration was 15 h 18 ± 14.6 min for LDS and 8 h 57 ± 18 min for SDS. Two groups did not differ in terms of the age, gender, BMI and race of patients studied. Mean total sleep time and sleep efficiency during PSG preceding MSLT, and MSLT mean sleep onset latency did not significantly differ for the two groups. However, SDS MSLT naps had significantly more sleep onset REM periods (SOREMP), and distribution of the number of SOREMP captured during MSLT was different for SDS and LDS groups. Differences of SDS and LDS results did not relate to sleep architecture of the overnight PSG as analysis of sleep and REM latency and relative percentages of N1, N2, REM, and N3 was not significantly different between SDS and LDS. The two groups showed difference in arousal indexes during N1 and REM sleep.

CONCLUSIONS

Daylight duration may impact MSLT results and should probably be accounted for in MSLT interpretation. Attention to photoperiod could be considered in MSLT guidelines, if our results are replicated in larger samples.

Daily light exposure profiles and the association with objective sleep quality in patients with Parkinson's disease: The PHASE study

STUDY OBJECTIVES

Light information crucially influences sleep initiation and continuity. The purpose of this study was to compare daily light exposure between patients with Parkinson's disease (PD) and non-PD older adults and evaluate the association of daily light exposure with objective sleep measures in patients with PD.

METHODS

In this cross-sectional study of 189 outpatients with PD and 1101 community-dwelling older adults (controls), daily light exposure was measured using wrist light meters during the daytime and light meters set in the bedrooms during the nighttime, and objective sleep quality was measured by wrist actigraphy.

RESULTS

The median duration of exposure to ≥ 1000 lux light was significantly shorter in patients with PD than in controls. The median nighttime light intensity was higher in patients with PD than in controls. Among patients with PD, multivariable analysis suggested that the highest quartile of exposure to ≥ 1000 lux light during the daytime was linked to significantly higher sleep efficiency (SE) by 8.0% and shorter wake after sleep onset (WASO) by 36.9 minutes than the lowest quartile. During the nighttime, the highest quartile of mean light intensity had significantly lower SE by 6.8%, longer WASO by 24.1 minutes, longer sleep onset latency, and higher fragmentation index, than the lowest quartile. Importantly, daytime and nighttime light levels were independently associated with objective sleep measures.

CONCLUSIONS

The present study illustrated that greater daytime light exposure and lower nighttime light exposure are significantly associated with better objective sleep measures in patients with PD.

A bidirectional model of sleep and technology use: A theoretical review of How much, for whom, and which mechanisms

The link between technology and sleep is more complex than originally thought. In this updated theoretical review, we propose a new model informed by the growing body of evidence in the area over the past 10 years. The main theoretical change is the addition of bi-directional links between the use of technology and sleep problems. We begin by reviewing the evidence to date for the originally proposed mechanisms of bright light, arousal, nighttime sleep disruptions, and sleep displacement. Then, in support of the new direction of effect (sleep problems preceding technology use), we propose two new mechanisms: technology before sleep might be used as a time filler and/or as an emotional regulation strategy to facilitate the sleep-onset process. Finally, we present potential moderators of the association between technology and sleep, in recognition of protective and vulnerability factors that may mitigate or exacerbate the effects of technology on sleep and vice versa. The goal of this theoretical review is to update the field, guide future public health messages, and to prompt new research into how much technology and sleep affect each other, for whom it may be problematic, and which mechanisms may explain their association.

Differences in the pupillary responses to evening light between children and adolescents

BACKGROUND

In the mammalian retina, intrinsically-photosensitive retinal ganglion cells (ipRGC) detect light and integrate signals from rods and cones to drive multiple non-visual functions including circadian entrainment and the pupillary light response (PLR). Non-visual photoreception and consequently non-visual sensitivity to light may change across child development. The PLR represents a quick and reliable method for examining non-visual responses to light in children. The purpose of this study was to assess differences in the PLRs to blue and red stimuli, measured one hour prior to bedtime, between children and adolescents.

METHODS

Forty healthy participants (8-9 years, n = 21; 15-16 years, n = 19) completed a PLR assessment 1 h before their habitual bedtime. After a 1 h dim-light adaptation period (< 1 lx), baseline pupil diameter was measured in darkness for 30 s, followed by a 10 s exposure to 3.0 × 1013 photons/cm2/s of either red (627 nm) or blue (459 nm) light, and a 40 s recovery in darkness to assess pupillary re-dilation. Subsequently, participants underwent 7 min of dim-light re-adaptation followed by an exposure to the other light condition. Lights were counterbalanced across participants.

RESULTS

Across both age groups, maximum pupil constriction was significantly greater (p < 0.001, ηp2 = 0.48) and more sustained (p < 0.001, ηp2 = 0.41) during exposure to blue compared to red light. For adolescents, the post-illumination pupillary response (PIPR), a hallmark of melanopsin function, was larger after blue compared with red light (p = 0.02, d = 0.60). This difference was not observed in children. Across light exposures, children had larger phasic (p < 0.01, ηp2 = 0.20) and maximal (p < 0.01, ηp2 = 0.22) pupil constrictions compared to adolescents.

CONCLUSIONS

Blue light elicited a greater and more sustained pupillary response than red light in children and adolescents. However, the overall amplitude of the rod/cone-driven phasic response was greater in children than in adolescents. Our findings using the PLR highlight a higher sensitivity to evening light in children compared to adolescents, and continued maturation of the human non-visual photoreception/system throughout development.

A Mixed-Methods, Multimedia Pilot Study to Investigate Sleep Irregularity Determinants Among Undergraduate Students

PURPOSE

To pilot a novel approach investigating the interplay of social and institutional determinants influencing university undergraduate student sleep patterns.

DESIGN

A two-part, three-phase mixed-methods approach.

SETTING

A mid-size US university conducted in spring and fall 2020.

PARTICIPANTS

191 undergraduate students (69 first-years, 43 second-years, 48 third-years, 31 fourth-years).

METHOD

For Part A, participants texted their activities and emotions in real time, producing a data-rich, weeklong diary of comprehensive activity logs, emoticons, multimedia submissions, and juxtapositions of ideal vs real schedules. Semi-structured contextual interviews were also conducted. For Part B, a one-time survey examined Part A insights across all class years. These diverse datasets were triangulated using thematic, comparative, and content analyses through MAXQDA software and visual mapping methods.

RESULTS

Three preliminary themes were identified as encouraging an irregular sleep schedule: a prevailing academic ethos emphasizing busyness, time management challenges, and the rhythm of institutional schedules and deadlines. An overarching theme suggests that perceptions of peer sleep habits and academic prioritization above all else could be influential across factors.

CONCLUSION

This pilot study indicates that sleep regularity among undergraduates is potentially shaped by individual choices combined with broader institutional paradigms. While it is limited by its exploratory nature, timing, and small sample size, the results highlight the promise of this methodology for more extensive studies and suggest that future interventions should emphasize systemic changes that prioritize sleep.

Circadian photoentrainment varies by season and depressed state: associations between light sensitivity and sleep and circadian timing

STUDY OBJECTIVES

Altered light sensitivity may be an underlying vulnerability for disrupted circadian photoentrainment. The photic information necessary for circadian photoentrainment is sent to the circadian clock from melanopsin-containing intrinsically photosensitive retinal ganglion cells (ipRGCs). The current study tested whether the responsivity of ipRGCs measured using the post-illumination pupil response (PIPR) was associated with circadian phase, sleep timing, and circadian alignment, and if these relationships varied by season or depression severity.

METHODS

Adult participants (N = 323, agem = 40.5, agesd = 13.5) with varying depression severity were recruited during the summer (n = 154) and winter (n = 169) months. Light sensitivity was measured using the PIPR. Circadian phase was assessed using Dim Light Melatonin Onset (DLMO) on Friday evenings. Midsleep was measured using actigraphy. Circadian alignment was calculated as the DLMO-midsleep phase angle. Multilevel regression models covaried for age, gender, and time since wake of PIPR assessment.

RESULTS

Greater light sensitivity was associated with later circadian phase in summer but not in winter (β = 0.23; p = 0.03). Greater light sensitivity was associated with shorter DLMO-midsleep phase angles (β = 0.20; p = 0.03) in minimal depression but not in moderate depression (SIGHSAD < 6.6; Johnson-Neyman region of significance).

CONCLUSIONS

Light sensitivity measured by the PIPR was associated with circadian phase during the summer but not in winter, suggesting ipRGC functioning in humans may affect circadian entrainment when external zeitgebers are robust. Light sensitivity was associated with circadian alignment only in participants with minimal depression, suggesting circadian photoentrainment, a possible driver of mood, may be decreased in depression year-round, similar to decreased photoentrainment in winter.

Decreased Memory and Learning Ability Mediated by Bmal1/M1 Macrophages/Angptl2/Inflammatory Cytokine Pathway in Mice Exposed to Long-Term Blue Light Irradiation

Humans are persistently exposed to massive amounts of blue light via sunlight, computers, smartphones, and similar devices. Although the positive and negative effects of blue light on living organisms have been reported, its impact on learning and memory remains unknown. Herein, we examined the effects of widespread blue light exposure on the learning and memory abilities of blue light-exposed mice. Ten-week-old male ICR mice were divided into five groups (five mice/group) and irradiated with blue light from a light-emitting diode daily for 6 months. After 6 months of blue light irradiation, mice exhibited a decline in memory and learning abilities, assessed using the Morris water maze and step-through passive avoidance paradigms. Blue light-irradiated mice exhibited a decreased expression of the clock gene brain and muscle arnt-like 1 (Bmal1). The number of microglia and levels of M1 macrophage CC-chemokine receptor 7 and inducible nitric oxide synthase were increased, accompanied by a decrease in M2 macrophage arginase-1 levels. Levels of angiopoietin-like protein 2 and inflammatory cytokines interleukin-6, tumor necrosis factor-α, and interleukin-1β were elevated. Our findings suggest that long-term blue light exposure could reduce Bmal1 expression, activate the M1 macrophage/Angptl2/inflammatory cytokine pathway, induce neurodegeneration, and lead to a decline in memory.

Estimating dim light melatonin onset time in children using delta changes in melatonin

We aimed to establish a method for estimating dim light melatonin onset (DLMO) using mathematical slopes calculated from melatonin concentrations at three sampling points before and after sleep in children. The saliva of 30 children (mean age ± SD: 10.2 ± 1.3 years old) was collected under dim-light conditions up to six times every hour starting at 17:30 (t17), namely, 18:30 (t18), 19:30 (t19), 20:30 (t20), 21:30 (t21), 22:30 (t22), and 23:30 (t23), in the evening, and at 6:00 (t30) the following morning. We calculated SLOPE on (mathematical slope between melatonin concentrations at t18 and t20, t21 or t22), SLOPE off (the slope between t20, t21 or t22, and t30), and Δ S L O P E , which is generated by subtracting SLOPE on from SLOPE off . DLMO was estimated by multiple regression analysis with the leave-one-out cross-validation (LOOCV) method using SLOPE on and SLOPE off , and Δ S L O P E . The intraclass correlation coefficient (ICC) between the estimated and measured DLMOs was used as the index of estimation accuracy. DLMOs estimated using multiple regression equations with SLOPE on and SLOPE off yielded significant ICCs for the measured DLMOs, with the largest ICC at t20 (ICC = 0.634). Additionally, the ICC between the estimated and measured DLMOs using the equation with Δ S L O P E was significant, with a larger ICC at t20 (ICC = 0.726) than that of the equation with SLOPE on and SLOPE off . Our results showed that DLMO could be estimated with a certain level of accuracy from salivary melatonin levels at three time points before and after sleep in children.

Supplementary Information

The online version contains supplementary material available at 10.1007/s41105-023-00493-x.

Insomnia symptoms and related factors in a community-based population: The Yamagata Cohort study

Objective/background

Insomnia is prevalent and is a risk factor for the development of lifestyle-related diseases and early death. To improve insomnia, it is necessary to identify the factors that affect it. This study investigated the associations between insomnia symptoms and mental, physical, and environmental factors in the general Japanese population.

Patients/methods

The study participants were 7,873 individuals who responded to the Health and Lifestyle Survey questionnaire that included sleep-related items between December 2021 and March 2022. Insomnia symptoms were defined as a score of 6 or higher on the Athens Insomnia Scale (AIS). A multivariate logistic regression analysis was performed to identify factors independently associated with insomnia symptoms.

Results

Of all subjects, 23.4% had insomnia symptoms. Factors associated with insomnia symptoms were older age, female sex, very difficult living conditions on current income, pain/discomfort, anxiety, lack of happiness, frequent nocturia, long duration from bathing time to bedtime, bedroom lighting, and short walking duration. The subgroup analysis showed stronger associations between walking time in men, higher body mass index in women, time from bathing time to bedtime, and daily walking duration in older adults.

Conclusions

Insomnia symptoms were common in community-based populations and were independently associated with three different factor groups including physical, psychological, and environmental factors. Improvements in insomnia symptoms require appropriate practical support tailored to an individual's situation.

The cognitive impact of light: illuminating ipRGC circuit mechanisms

Ever-present in our environments, light entrains circadian rhythms over long timescales, influencing daily activity patterns, health and performance. Increasing evidence indicates that light also acts independently of the circadian system to directly impact physiology and behaviour, including cognition. Exposure to light stimulates brain areas involved in cognition and appears to improve a broad range of cognitive functions. However, the extent of these effects and their mechanisms are unknown. Intrinsically photosensitive retinal ganglion cells (ipRGCs) have emerged as the primary conduit through which light impacts non-image-forming behaviours and are a prime candidate for mediating the direct effects of light on cognition. Here, we review the current state of understanding of these effects in humans and mice, and the tools available to uncover circuit-level and photoreceptor-specific mechanisms. We also address current barriers to progress in this area. Current and future efforts to unravel the circuits through which light influences cognitive functions may inform the tailoring of lighting landscapes to optimize health and cognitive function.

Effects of light therapy on sleep and circadian rhythm in older type 2 diabetics living in long-term care facilities: a randomized controlled trial

Background

Light influences the secretion of melatonin in the body and regulates circadian rhythms, which play an important role in sleep and mood. The light level of rooms in long-term care facilities is usually far below the threshold required to regulate the body's circadian rhythm, and insufficient light can easily lead to sleep and mood disturbances among older residents in nursing homes. Therefore, the objective of this study was to investigate the effects of light therapy on sleep and circadian rhythm in older adults with type 2 diabetes residing in long-term care facilities.

Methods

This study was a prospective, single-blind, randomized controlled trial. Participants were randomly assigned to either the light therapy (LT) group or the control group and received the intervention for four weeks. Primary outcomes included the Pittsburgh Sleep Quality Index (PSQI) and objective sleep parameters recorded by a sleep monitoring bracelet, Morningness-Eveningness Questionnaire (MEQ). The secondary outcome included glycated serum protein (GSP). Data was collected at three time points: at baseline (T0), immediate post-treatment (T1), and 4-week follow-up (T2). A linear mixed model analysis was used to analyzed the data.

Results

We enrolled 45 long-term care residents. Compared with the control group, significant reductions in PSQI scores were observed at T1 and T2. At T2, the sleep score of objective sleep parameters was significantly higher in the LT group compared to the control group. Additionally, compared to the baseline T0, MEQ scores were significantly lower in the LT group at T1 and T2, with no significant difference in the control group. There was no significant difference between groups in glycated serum protein values at T1 and T2. However, compared to T0, glycated serum protein values decreased in the LT group while increased in the control group at T2.

Conclusion

Light therapy had a positive effect on subjective sleep quality and circadian rhythm time type in long-term care residents with type 2 diabetes, and had a possible delayed effect on objective sleep. However, no discernible alterations in blood glucose levels were detected in this study.

The Negative Effects of Travel on Student Athletes Through Sleep and Circadian Disruption

Collegiate athletes must satisfy the academic obligations common to all undergraduates, but they have the additional structural and social stressors of extensive practice time, competition schedules, and frequent travel away from their home campus. Clearly such stressors can have negative impacts on both their academic and athletic performances as well as on their health. These concerns are made more acute by recent proposals and decisions to reorganize major collegiate athletic conferences. These rearrangements will require more multi-day travel that interferes with the academic work and personal schedules of athletes. Of particular concern is additional east-west travel that results in circadian rhythm disruptions commonly called jet lag that contribute to the loss of amount as well as quality of sleep. Circadian misalignment and sleep deprivation and/or sleep disturbances have profound effects on physical and mental health and performance. We, as concerned scientists and physicians with relevant expertise, developed this white paper to raise awareness of these challenges to the wellbeing of our student-athletes and their co-travelers. We also offer practical steps to mitigate the negative consequences of collegiate travel schedules. We discuss the importance of bedtime protocols, the availability of early afternoon naps, and adherence to scheduled lighting exposure protocols before, during, and after travel, with support from wearables and apps. We call upon departments of athletics to engage with sleep and circadian experts to advise and help design tailored implementation of these mitigating practices that could contribute to the current and long-term health and wellbeing of their students and their staff members.

Mood correlates with circadian alignment in healthy individuals

OBJECTIVE

To determine whether there is a correlation between mood and the alignment between the timing of the circadian pacemaker (circadian phase) and the timing of sleep in healthy, euthymic individuals.

METHODS

Participants were 25 first-year medical students (25.9 ± 3.3years, 16 females). Mood (Profile of Mood States, brief form) and circadian phase (salivary dim light melatonin onset) were assessed 4 times over 7weeks. Circadian alignment was determined using the dim light melatonin onset to average midsleep interval (phase angle difference).

RESULTS

Profile of Mood States, brief form score and phase angle difference were correlated: later dim light melatonin onset relative to midsleep (shorter phase angle differences) was associated with worse mood (F1,75 =10.953, p = .001). There was no difference in Profile of Mood States, brief form score between female and male participants and no interaction between gender and phase angle difference.

CONCLUSIONS

There is a correlation between circadian alignment and mood among healthy individuals as has been found in individuals with seasonal and nonseasonal depression. This finding has implications for the development, prevention and treatment of mood disorders.

Contributions of the light environment and co-sleeping to sleep consolidation into nighttime in early infants: A pilot study

BACKGROUND

Sleep consolidation into nighttime is considered the primary goal of sleep development in early infants. However, factors contributing to sleep consolidation into nighttime remain unclear.

AIM

To clarify the influences of the light environment and nighttime co-sleeping on sleep consolidation into nighttime in early infants.

STUDY DESIGN

Cross-sectional study.

SUBJECTS AND METHODS

Sleep-wake time and light stimulation were measured in infants for 4 consecutive days using actigraphy. The infants' mothers were asked to complete a sleep events diary and a questionnaire about childcare, including "co-sleeping", defined as when the infant and mother slept on the same surface throughout the night.

OUTCOME MEASURES

The data were analyzed with a focus on daytime and nighttime sleep parameters.

RESULTS

Daytime light stimulation reduced daytime "active sleep", tended to reduce daytime sleep, and increased daytime waking. Nighttime light stimulation reduced nighttime "quiet sleep" and nighttime sleep and increased nighttime waking. Co-sleeping reduced nighttime waking, and, as a result, nighttime sleep time and sleep efficiency increased. Co-sleeping reduced daytime sleep and tended to increase daytime waking. Consequently, co-sleeping tended to increase the ratio of nighttime sleep to daytime sleep.

CONCLUSIONS

The present findings suggest that an appropriate light environment promotes daytime waking and nighttime sleep in early infants, but it does not contribute to sleep consolidation into nighttime by itself. On the other hand, co-sleeping may promote sleep consolidation into nighttime. Therefore, further methods for safe co-sleeping need to be established while avoiding risk factors for sudden unexpected death in infancy/sudden infant death syndrome.

Circadian neurogenetics and its implications in neurophysiology, behavior, and chronomedicine

The circadian rhythm affects multiple physiological processes, and disruption of the circadian system can be involved in a range of disease-related pathways. The genetic underpinnings of the circadian rhythm have been well-studied in model organisms. Significant progress has been made in understanding how clock genes affect the physiological functions of the nervous system. In addition, circadian timing is becoming a key factor in improving drug efficacy and reducing drug toxicity. The circadian biology of the target cell determines how the organ responds to the drug at a specific time of day, thus regulating pharmacodynamics. The current review brings together recent advances that have begun to unravel the molecular mechanisms of how the circadian clock affects neurophysiological and behavioral processes associated with human brain diseases. We start with a brief description of how the ubiquitous circadian rhythms are regulated at the genetic, cellular, and neural circuit levels, based on knowledge derived from extensive research on model organisms. We then summarize the latest findings from genetic studies of human brain disorders, focusing on the role of human clock gene variants in these diseases. Lastly, we discuss the impact of common dietary factors and medications on human circadian rhythms and advocate for a broader application of the concept of chronomedicine.

Effects of a violet-excitation light-emitting diode on melatonin secretion and sleepiness: preliminary findings from a randomized controlled trial

STUDY OBJECTIVES

A new type of lighting using violet-excitation light-emitting diodes (LEDs) with an action spectrum centered at approximately 405 nm was developed. Although violet-excitation LEDs can reduce melatonin suppression compared with blue-excitation LEDs, no studies have compared the effects of violet-excitation LEDs with those of blue-excitation LEDs on melatonin suppression. This study was designed to compare the effects of violet-excitation LEDs with those of blue-excitation LEDs on melatonin suppression, psychomotor vigilance, and sleepiness.

METHODS

Sixteen healthy Japanese males aged 20-39 years were exposed to violet- and blue-excitation LEDs for 3 hours in a crossover randomized manner. The primary outcome was changes in salivary melatonin levels compared with the baseline levels. The secondary outcomes were changes in psychomotor vigilance and the Karolinska Sleepiness Scale. Melatonin suppression was calculated from the difference in the area under the curves between the baseline and intervention.

RESULTS

Of the 16 participants, 15 completed the measurements. The baseline characteristics did not differ significantly between the 2 groups. After adjusting for age, a difference of 16.28 pg/mL in mean melatonin suppression was observed between the violet- and blue-excitation LED groups (-2.15 pg/mL vs -18.43 pg/mL; P = .006). The overall melatonin suppression by violet-excitation LEDs was 48.6% smaller than that by blue-excitation LEDs. No significant differences in psychomotor vigilance and sleepiness were observed between the 2 groups.

CONCLUSIONS

Melatonin suppression in healthy Japanese males exposed to violet-excitation LEDs was significantly smaller than that in those exposed to blue-excitation LEDs. Our preliminary findings indicate that violet-excitation LEDs may have the potential to reduce the magnitude of blue-excitation LED-induced melatonin suppression.

CITATION

Mitsui K, Saeki K, Sun M, Yamagami Y, Tai Y, Obayashi K. Effects of a violet-excitation light-emitting diode on melatonin secretion and sleepiness: preliminary findings from a randomized controlled trial. J Clin Sleep Med. 2024;20(1):101-109.

Association Between Bedroom Light Pollution With Subjectively and Objectively Measured Sleep Parameters Among Chinese Young Adults

PURPOSE

To investigate the cross-sectional associations between real-world multiperiod bedroom light at night and sleep parameters among 365 Chinese young adults.

METHODS

Bedroom light exposure was estimated at the individual level for two consecutive days using a portable illuminance meter. Subjective sleep parameters were measured with the Pittsburgh Sleep Quality Index, and objective sleep parameters were assessed by wrist-worn ActiGraph accelerometers for seven consecutive days.

RESULTS

Compared with the low-exposure group (average light intensity < 3lx), the high-exposure group (average light intensity ≥ 3lx) was associated with decreased 1.15% in sleep efficiency (sleep efficiency, 95% CI: -1.78, -0.52; p < .001), increased 3.94 minutes in wake after sleep onset (wake after sleep onset, 95% CI: 1.55, 6.33; p = .001), increased 1.05 unit in movement index (95% CI: 0.20, 1.89; p = .015), and increased 2.16 unit in sleep fragmentation index ( 95% CI: 0.63, 3.68; p = .006). In comparison, each interquartile increase in 2h-average and 1h-average intensity of preawake light (PAL) (PAL-2h and PAL-1h) was associated with 7.04 minutes of increases in total sleep time (95% CI: 0.87, 13.22; p = .025) and 6.69 minutes of increases in total sleep time (95% CI: 0.51, 12.87; p = .034), respectively.

DISCUSSION

Altogether, our results support the role of bedroom light exposure in sleep and imply the importance of bedroom light exposure management as a potential strategy to reduce the public health burden of sleep problems. Keeping the bedroom environment dark at night and allowing moderate morning light exposure may be important measures for improving the sleep quality of young adults.

Two oscillatory components detected by forced splitting of the sleep-wake cycle in humans

The sleep-wake cycle of human subjects was artificially split into two episodes by imposing an 8-h light and 4-h dark cycle (LD 8:4) twice a day for 7 days, which was followed by a 3-day free-running session. Sleep was permitted only in the dark period. The subjects in the ordinary group were exposed to ordinary light (ca. 500 lx) in the 8-h light period, and those in the bright light group to bright (ca. 5,000 lx) and ordinary light alternatively with bright light after the first dark period (2400-400). Split sleeps persisted in the free-running session with the major episode around the first dark period and the minor episode around the second dark period. By contrast, circadian melatonin rhythm in the free-running session significantly phase delayed in the ordinary light group, but phase advanced in the bright light group, keeping the melatonin rhythm unsplit. The length of nocturnal melatonin secretion (NMS) was significantly shortened in the bright light group. Interestingly, the falling phase of NMS advanced significantly further than the rising phase. Such a difference was not detected in the ordinary light group. Similar differences were observed in the body temperature rhythm. These findings indicated oscillatory mechanisms underlying split sleeps distinct from the circadian pacemaker and suggested an involvement of different circadian oscillators in the rising and falling phases of NMS, which is consistent with the dual oscillator model proposed for the circadian system of nocturnal rodents.NEW & NOTEWORTHY The present study demonstrated that human sleep was separated into two essentially identical components, which persisted under constant conditions, suggesting circadian oscillator underlying split-sleep episodes. The study also indicated differential light sensitivities in the rising and falling phases of circadian melatonin rhythm, indicating the involvement of two different oscillators. These results consisted of the evening and morning dual-oscillator hypothesis for the circadian pacemaker and the hierarchical model for the pacemaker and sleep-wake cycle.

Method to determine whether sleep phenotypes are driven by endogenous circadian rhythms or environmental light by combining longitudinal data and personalised mathematical models

Sleep timing varies between individuals and can be altered in mental and physical health conditions. Sleep and circadian sleep phenotypes, including circadian rhythm sleep-wake disorders, may be driven by endogenous physiological processes, exogeneous environmental light exposure along with social constraints and behavioural factors. Identifying the relative contributions of these driving factors to different phenotypes is essential for the design of personalised interventions. The timing of the human sleep-wake cycle has been modelled as an interaction of a relaxation oscillator (the sleep homeostat), a stable limit cycle oscillator with a near 24-hour period (the circadian process), man-made light exposure and the natural light-dark cycle generated by the Earth's rotation. However, these models have rarely been used to quantitatively describe sleep at the individual level. Here, we present a new Homeostatic-Circadian-Light model (HCL) which is simpler, more transparent and more computationally efficient than other available models and is designed to run using longitudinal sleep and light exposure data from wearable sensors. We carry out a systematic sensitivity analysis for all model parameters and discuss parameter identifiability. We demonstrate that individual sleep phenotypes in each of 34 older participants (65-83y) can be described by feeding individual participant light exposure patterns into the model and fitting two parameters that capture individual average sleep duration and timing. The fitted parameters describe endogenous drivers of sleep phenotypes. We then quantify exogenous drivers using a novel metric which encodes the circadian phase dependence of the response to light. Combining endogenous and exogeneous drivers better explains individual mean mid-sleep (adjusted R-squared 0.64) than either driver on its own (adjusted R-squared 0.08 and 0.17 respectively). Critically, our model and analysis highlights that different people exhibiting the same sleep phenotype may have different driving factors and opens the door to personalised interventions to regularize sleep-wake timing that are readily implementable with current digital health technology.

The sleep, circadian, and cognitive performance consequences of watchkeeping schedules in submariners: A scoping review

Watchkeeping schedules are essential for maintaining submarine operations, but come with human risk factors including, disrupted sleep, circadian misalignment, and cognitive deficits. There is now an emerging literature examining the strengths and weaknesses of submarine watchkeeping schedules trialled in the field and under simulated laboratory conditions. The aim of this scoping review was to summarise this literature. A systematic search of peer-reviewed journal articles and industry reports listed in MEDLINE, PsychINFO, PubMed, Scopus, Embase and Google Scholar undertaken in May 2023 returned 7298 papers. Following screening procedures, 13 studies were identified for inclusion. The findings revealed that sleep was sufficiently preserved regardless of watchkeeping schedule (total sleep time = 5.46-7.89 h), circadian misalignment was greater for non-24 h schedules, and longer off-watch periods were associated with better cognitive performance. Taken together, when comparing between watchkeeping schedules, the present findings suggest that the 4 h-on/8 h-off and 8 h-on/16 h-off schedules may be a good compromise when balancing human risk factors and operational demands. However, submarines are complex and challenging environments to study and there is a need to expand the literature. More research comparing watchkeeping schedules is needed. Future studies should focus on cognitive performance measures, such as problem-solving, prioritisation and executive decision-making to address present shortcomings, and an examination of sleep and circadian countermeasures to assist with adaptation either initiated pre-deployment or by modifying the submarine environment itself should be considered.

Sleep regularity and mortality: a prospective analysis in the UK Biobank

Background

Irregular sleep-wake timing may cause circadian disruption leading to several chronic age-related diseases. We examined the relationship between sleep regularity and risk of all-cause, cardiovascular disease (CVD), and cancer mortality in 88,975 participants from the prospective UK Biobank cohort.

Methods

The sleep regularity index (SRI) was calculated as the probability of an individual being in the same state (asleep or awake) at any two time points 24 hr apart, averaged over 7 days of accelerometry (range 0-100, with 100 being perfectly regular). The SRI was related to the risk of mortality in time-to-event models.

Results

The mean sample age was 62 years (standard deviation [SD], 8), 56% were women, and the median SRI was 60 (SD, 10). There were 3010 deaths during a mean follow-up of 7.1 years. Following adjustments for demographic and clinical variables, we identified a non-linear relationship between the SRI and all-cause mortality hazard (p [global test of spline term]<0.001). Hazard ratios, relative to the median SRI, were 1.53 (95% confidence interval [CI]: 1.41, 1.66) for participants with SRI at the 5th percentile (SRI = 41) and 0.90 (95% CI: 0.81, 1.00) for those with SRI at the 95th percentile (SRI = 75), respectively. Findings for CVD mortality and cancer mortality followed a similar pattern.

Conclusions

Irregular sleep-wake patterns are associated with higher mortality risk.

Funding

National Health and Medical Research Council of Australia (GTN2009264; GTN1158384), National Institute on Aging (AG062531), Alzheimer's Association (2018-AARG-591358), and the Banting Fellowship Program (#454104).