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Light exposure in the natural environment: Relevance to mood and sleep disorders
Abstract
In addition to being necessary for vision, light also plays a primary role in circadian physiology. Humans are diurnal animals and their biological clock synchronizes their physiological functions in such a way that functions associated with activity happen in the daytime while functions associated with rest occur at night. A misalignment between the endogenous circadian clock and the desired sleep schedule is the main cause of circadian sleep disorders; it may be involved in certain mood disorders as well. Since light is the main environmental cue used by the biological clock to set its own timing in relation to the day-night cycle, inappropriate light exposure can be involved in the physiopathology of circadian disorders. Conversely, when handled properly, controlled light exposure can be used to treat some mood and sleep disorders. While the earliest studies in the field focused solely on exposure to bright light, contemporary studies aim at understanding how the entire profile of light-dark exposure can influence the circadian clock and, consequently, mood, sleep, and vigilance quality. Following a brief summary of the main concepts underlying the non-visual effects of light, this paper presents some studies using ambulatory measurements of light exposure to illustrate how these concepts apply in real-life situations and discusses the clinical relevance of light exposure in the natural environment for mood, sleep, and circadian disorders.
... The illuminance, spectral distribution, duration, timing, previous lighting [48][49][50], the direction of light [51,52], visual fields [53] and other factors will affect human cognitive ...
... The illuminance, spectral distribution, duration, timing, previous lighting [48][49][50], the direction of light [51,52], visual fields [53] and other factors will affect human cognitive performance [54,55], sleep rhythm [56], emotional state [48], and even social behaviour [57]. In this experiment, under the condition of a simulated night shift in a confined space, the basic lighting requirements were firstly met, after which five lighting environments with different intensities of the circadian stimuli were created with different illuminances and spectra, aiming to allow for a comprehensive comparison across the effects caused by each condition over the whole night period on sleep quality, melatonin suppression and cognitive performance. ...
... The illuminance, spectral distribution, duration, timing, previous lighting [48][49][50], the direction of light [51,52], visual fields [53] and other factors will affect human cognitive performance [54,55], sleep rhythm [56], emotional state [48], and even social behaviour [57]. In this experiment, under the condition of a simulated night shift in a confined space, the basic lighting requirements were firstly met, after which five lighting environments with different intensities of the circadian stimuli were created with different illuminances and spectra, aiming to allow for a comprehensive comparison across the effects caused by each condition over the whole night period on sleep quality, melatonin suppression and cognitive performance. ...
Exposure to light during overtime work at night in confined spaces may disrupt the normal circadian clock, affect hormone secretion, sleep quality and performance, thereby posing great risks to the physical and mental health of night workers. Integrative lighting should be adopted to reduce the disturbance of normal physiological rhythm, while meeting the visual requirements of work. Through adjustable LED (CCT 6000 K/2700 K) and different vertical illuminance, five lighting patterns with different circadian stimuli (CS = 0.60, 0.30. 0.20, 0.10 and 0.05) were conducted, respectively, in a sleep lab using a within-subject design. Each lighting pattern lasted for 5 h every night. Eight healthy adults were recruited to complete the night work and their salivary melatonin, Karolinska sleepiness scale (KSS), Psychomotor Vigilance Task (PVT) and sleep quality were tested. The results showed that subjective sleepiness and melatonin concentration increased rapidly under low intervention (CS = 0.05) with the best sleep quality, while they decreased in high intervention (CS = 0.60) at night and led to significantly higher levels of sleepiness the next morning (p < 0.05). For the PVT, the middle intervention (CS = 0.30) showed the lowest response time and least errors (p < 0.05), suggesting that appropriate illuminance can improve visual performance. To reduce biorhythm disruptions, lower lighting stimulation is preferred during night work. For difficult visual tasks, high illuminances may not improve visual performance; just a slight increase in the existing lighting levels is adequate. Lighting interventions have a clear impact on sleep improvement and work capacity for those working overtime, and they may be translatable to other shift work scenarios.
... Various effects of excessive ALAN exposure on health have been reported, such as increased risks of cancer, obesity, skin and other diseases, mood disorders, and sleep disorders. One of the most salient known effects of exposure to bright light at night on humans and animals is delay and disturbance in the biological clock and confusing circadian rhythm (Dumont and Beaulieu, 2007). Melatonin suppression is believed to disturb the circadian rhythm and balance of endocrine hormones, which leads to negative consequences in physical and mental health conditions (Nelson and Chbeir, 2018). ...
... For example, light treatment is considered an option that reduces depressive symptoms. Properly controlled artificial light exposure can be used to treat some mood and sleep disorders (Dumont and Beaulieu, 2007), especially during dark winters in high latitude countries (Adamsson et al., 2018). A lab experiment study has shown that even a short-time (30 min) exposure to natural bright light during daytime is effective to increase positive emotions and reduce subjective sleepiness (Kaida et al., 2007). ...
... Another study revealed that an increase in outdoor ALAN exposure due to shale gas plant development reduced sleep time and subjective well-being in a US sample (Boslett et al., 2021). In sum, the light condition at night is crucially important in ensuring good mental health conditions (Dumont and Beaulieu, 2007). Adults living in areas exposed to higher levels had a higher likelihood of depressive symptoms or suicidal behaviors. ...
The quality of life of human beings has improved tremendously through improved productivity, convenience, safety, and livability due to nighttime lights that illuminate outdoor work, leisure, and mobility. Recently, however, concerns have been growing over outdoor artificial light at night (ALAN) and its effects on human beings as well as ecosystems including animals and plants. This literature review aims to deliver a critical overview of the findings and the areas for future research on the effects of outdoor ALAN on human health and behaviors. Through a narrative literature review, we found that scientific research crucially lacks studies on the effects of outdoor ALAN on human behaviors and health, including social interaction, which may be more widespread compared to what is recognized so far. This review also highlights the importance of investigating the causal and complex relationships between outdoor ALAN, health, and behaviors with sleep as a key mediating factor. We elucidate that outdoor ALAN has both positive and negative effects on human life. Therefore, it is important for societies to be able to access facts and evidence about these effects to plan, agree to, and realize the optimal usage of nighttime lighting that balances its merits and demerits. Researchers in related areas of study must investigate and deliver the science of outdoor ALAN to various stakeholders, such as citizens, policymakers, urban and landscape planners, relevant practitioners, and industries. We believe that our review improves the understanding of outdoor ALAN in relation to human life and contributes to sustainable and thriving societies.
... In the majority of these studies, the focus was on the light effect (e.g. sleep, [21][22][23][24][25][26][27][28] vitality, 24,29 circadian phase, 22,30-32 mood, 22,23,25,26,28 or social behaviour 33 ). Very rarely, no outcome measure was directly linked to the actual lighting conditions. ...
... In the majority of these studies, the focus was on the light effect (e.g. sleep, [21][22][23][24][25][26][27][28] vitality, 24,29 circadian phase, 22,30-32 mood, 22,23,25,26,28 or social behaviour 33 ). Very rarely, no outcome measure was directly linked to the actual lighting conditions. ...
... gender, age, chronotype), 29,51,52 sleep behaviour, preferences, 53 job tasks and behaviour or the used workplace. 22,54,55 In addition, differences in personal lighting conditions between days were also found and may be explained by the weather 56 The work schedule of the office workers included in this study was demonstrated using the percentages of time spent at a certain location. Respectively 22%, 42% and 17% of the awake day was reported as time spent at home, at work and elsewhere. ...
Light enables us to see and perceive our environment but it also initiates effects beyond vision, such as alertness. Literature describes that at least six factors are relevant for initiating effects beyond vision. The exact relationship between these factors and alertness is not yet fully understood. In the current field study, personal lighting conditions of 62 Dutch office workers (aged 49.7 ± 11.4 years) were continuously measured and simultaneously self-reported activities and locations during the day were gathered via diaries. Each office worker participated 10 working days in spring 2017. Personal lighting conditions were interpreted based on four of the six factors (light quantity, spectrum, timing, and duration of light exposure). Large individual differences were found for the daily luminous exposures, illuminances, correlated colour temperatures, and irradiances measured with the blue sensor area of the dosimeter. The average illuminance (over all participants and all days) over the course of the day peaked three times. The analysis of the duration of light exposure demonstrated that the participants were on average only exposed to an illuminance above 1000 lx for 72 minutes per day. The interpretation of personal lighting conditions based on the four factors provides essential information since all of these factors may be relevant for initiating effects beyond vision. The findings in the current paper give first in-depth insight in the possibilities to interpret personal lighting conditions of office workers.
... Studies of occupational light exposure at the northern hemisphere between 40° N and 50° N have reported average daytime light levels about 100 and 300 lux during office work in winter and summer, respectively (Hubalek et al., 2010;Figueiro and Rea, 2016), 100-800 lux during hospital work, 800-2000 lux during factory and railway work (Papantoniou et al., 2014) and about 3000 lux for people working mostly outdoors during summer (Dumont and Beaulieu, 2007). Hospital and ofce workers spend about 15 min above 1000 lux during summer, daytime working hours (Heil and Mathis, 2002;Hubalek et al., 2010), whereas people working mostly outdoors during summer spend about 3 h at more than 1000 lux (Dumont and Beaulieu, 2007). ...
... Studies of occupational light exposure at the northern hemisphere between 40° N and 50° N have reported average daytime light levels about 100 and 300 lux during office work in winter and summer, respectively (Hubalek et al., 2010;Figueiro and Rea, 2016), 100-800 lux during hospital work, 800-2000 lux during factory and railway work (Papantoniou et al., 2014) and about 3000 lux for people working mostly outdoors during summer (Dumont and Beaulieu, 2007). Hospital and ofce workers spend about 15 min above 1000 lux during summer, daytime working hours (Heil and Mathis, 2002;Hubalek et al., 2010), whereas people working mostly outdoors during summer spend about 3 h at more than 1000 lux (Dumont and Beaulieu, 2007). In a recent study in Denmark, latitude 55-56°N, with a partly overlapping study population with that of the current study, we showed that outdoor workers on average spent most daytime working hours above 2500 lux during summer and only brie y during winter, while this did not occur for indoor workers (Daugaard et al., 2019). ...
... For building construction laborers and garbage collectors, expected to work mainly outdoors, we observed all daytime, all year light intensities between approximately 1600 and 2000 lux. We are only aware of a single field study from Montreal, Canada, reporting that persons who mostly worked outdoors were exposed to about 3000 lux during summer (Dumont and Beaulieu, 2007). The differences between ours and the ndings from Spain and Canada could, in addition to a seasonal effect, at least partly be explained by differences in latitude. ...
High daytime light levels may reduce the risk of affective disorders. Outdoor workers are during daytime exposed to much higher light intensities than indoor workers. A way to study daytime light exposure and disease on a large scale is by use of a general population job exposure matrix (JEM) combined with national employment and health data. The objective of this study was to develop a JEM applicable for epidemiological studies of exposure response between daytime light exposure, affective disorders, and other health effects by combining expert scores and light measurements. We measured light intensity during daytime work hours 06:00-17:59 for 1-7 days with Philips Actiwatch Spectrum® light recorders (Actiwatch) among 695 workers representing 71 different jobs. Jobs were coded into DISCO-88, the Danish version of the International Standard Classification of Occupations 1988. Daytime light measurements were collected all year round in Denmark (55-56°N). Arithmetic mean white light intensity (lux) was calculated for each hour of observation (n = 15,272), natural log-transformed, and used as the dependent variable in mixed effects linear regression models. Three experts rated probability and duration of outdoor work for all 372 jobs within DISCO-88. Their ratings were used to construct an expert score that was included together with month of the year and hour of the day as fixed effects in the model. Job, industry nested within job, and worker were included as random effects. The model estimated daytime light intensity levels specific for hour of the day and month of the year for all jobs with a DISCO-88 code in Denmark. The fixed effects explained 37% of the total variance: 83% of the between-jobs variance, 57% of the between industries nested in jobs variance, 43% of the between-workers variance, and 15% of the within-worker variance. Modeled daytime light intensity showed a monotonic increase with increasing expert score and a 30-fold ratio between the highest and lowest exposed jobs. Building construction laborers were based on the JEM estimates among the highest and medical equipment operators among the lowest exposed. This is the first quantitative JEM of daytime light exposure and will be used in epidemiological studies of affective disorders and other health effects potentially associated with light exposure.
... Average light intensities of ~50 lux have been measured during night work (Dumont et al., 2012;Papantoniou et al., 2014). A single study has shown that outdoor workers on average spend ~3 h >1000 lux during summer (Dumont and Beaulieu, 2007). Light exposure has constantly been reported higher on indoor workers' days off than on their work days (Koller et al., 1993;Borugian et al., 2005;aan het Rot et al., 2008;Hubalek et al., 2010;Crowley et al., 2015). ...
... Light intensity (lux) f No measurements >2500 lux. (Dumont and Beaulieu, 2007). Those workers reached a maximum exposure level of ~3000 lux and spent ~3 h >1000 lux during summer day work. ...
... This is reassuring. It should, however, be mentioned that night workers were exposed to lower levels of light during daylight hours and thus experienced a blunted circadian pattern of light and dark which may affect circadian adjustment (Dumont and Beaulieu, 2007). ...
Abstract
Objective
To assess light exposure during days with indoor, outdoor, and night work and days off work.
Methods
Light intensity was continuously recorded for 7 days across the year among indoor (n = 170), outdoor (n = 151), and night workers (n = 188) in Denmark (55–56°N) equipped with a personal light recorder. White light intensity, duration above 80, 1000, and 2500 lux, and proportion of red, green, and blue light was depicted by time of the day and season for work days and days off work.
Results
Indoor workers’ average light exposure only intermittently exceeded 1000 lux during daytime working hours in summer and never in winter. During daytime working hours, most outdoor workers exceeded 2500 lux in summer and 1000 lux in winter. Night workers spent on average 10–50 min >80 lux when working night shifts. During days off work, indoor and night workers were exposed to higher light intensities than during work days and few differences were seen between indoor, outdoor, and night workers. The spectral composition of light was similar for indoor, outdoor, and night workers during days at and off work.
Conclusion
The night workers of this study were during night hours on average exposed for a limited time to light intensities expected to suppress melatonin. The indoor workers were exposed to light levels during daylight hours that may reduce general well-being and mood, especially in winter. Outdoor workers were during summer daylight hours exposed to light levels comparable to those used for the treatment of depression.
... Disruption of the circadian system is closely linked to sleep disturbance [18][19][20] and mood disorders [20][21][22][23][24]. For example, depressed patients show reduced daytime activity and increased motor activity during sleep [25,26]. ...
... Disruption of the circadian system is closely linked to sleep disturbance [18][19][20] and mood disorders [20][21][22][23][24]. For example, depressed patients show reduced daytime activity and increased motor activity during sleep [25,26]. ...
Exposure to light at night (LAN) can disrupt the circadian system, thereby altering neuroimmune reactivity and related behavior. Increased exposure to LAN affects people of all ages – and could have particularly detrimental effects during early-life and adolescence. Despite this, most research on the behavioral and physiological effects of LAN has been conducted in adult animals. Here we evaluated the effects of dim LAN during critical developmental windows on adulthood neuroimmune function and affective/sickness behaviors. Male and female C57BL/6 J mice were exposed to dim LAN [12:12 light (150 lux)/dim (15 lux) cycle] during early life (PND10-24) or adolescence (PND30-44) [control: 12:12 light (150 lux)/dark (0 lux) cycle]. Behaviors were assessed during juvenile (PND42-44) and adult (PND60) periods. Contrary to our hypothesis, juvenile mice that were exposed to dim LAN did not exhibit changes in anxiety- or depressive-like behaviors. By adulthood, adolescent LAN-exposed female mice showed a modest anxiety-like phenotype in one behavioral task but not another. Adolescent LAN exposure also induced depressive-like behavior in a forced swim task in adulthood in both male and female mice. Additionally, developmental LAN exacerbated the hippocampal cytokine response (IL-1β) following peripheral LPS in female, but not male mice. These results suggest female mice may be more susceptible to developmental LAN than male mice: LAN female mice had a modest anxiety-like phenotype in adulthood, and upon LPS challenge, higher hippocampal IL-1β expression. Taken together, developmental LAN exposure in mice promotes a modest increase in susceptibility to anxiety- and depressive-like symptoms.
... In the majority of these studies, the focus was on the light effect itself. Sleep, vitality, circadian phase, mood, and social behaviour have been investigated often (Appleman, Figueiro, & Rea, 2013;Dumont & Beaulieu, 2007;Figueiro, Plitnick, & Rea, 2014;Figueiro et al., 2017;Hsu, Moskowitz, & Young, 2014;. Very rarely, no outcome measure was directly linked to the actual lighting conditions. ...
... Even though this study only included participants from one office building and was performed in spring 2017, large individual differences were found. These individual differences in personal lighting conditions may be caused by fixed personal characteristics (e.g., gender, age, chronotype) (Emens et al., 2009;Goulet, Mongrain, Desrosiers, Paquet, & Dumont, 2007;, sleep behaviour, preferences , job tasks and behaviour, or the used workplace Dumont & Beaulieu, 2007; . In addition, differences in personal lighting conditions between days were found and may be explained by the weather (Kimball & Hand, 1922) or possibly varying work schedules including flexible workplaces of office workers. ...
Lighting controls in offices are still mainly focused on energy savings.
However, focusing on a potential productivity increase of office
workers would lead to much higher savings in company costs. A less
alert office worker performs a task worse compared to a more alert
office worker. This project aimed at developing input for intelligent
systems to optimize subjective alertness of office workers. A systematic approach has been developed which comprises of four parts: gathering personal lighting conditions, interpreting personal lighting conditions, identifying predictors of personal lighting conditions, and relating personal lighting conditions to subjective alertness.
First, this thesis focused on exploring the advantages and
disadvantages of three methods to gather personal lighting
conditions: Person-Bound Measurements (PBM), Location-Bound
Measurements (LBM), and Location-Bound Estimations (LBE). Second, measured personal lighting conditions were interpreted according to light factors identified to initiate effects beyond vision. Third, multiple predictors were identified to influence personal lighting conditions. And fourth, the relationship between personal lighting conditions and alertness was found to be negligible in two separate field studies.
The above-mentioned systematic approach conveys input to be
inserted in intelligent systems to optimize alertness of office workers.
Such systems would provide recommendations for office workers to
adjust their own personal lighting conditions. This type of system may
be both energy efficient and practical. The system can be used by
companies to support their office workers. The office workers would
feel more alert whereas the employers would see productivity gains to
help them reducing their company costs.
... Collectively, we expect services irrespective of time of day (including emergency services, transportation and healthcare), which demands that humans are awake and functioning during the night when we are biologically programmed to sleep. For workers (and other members of society) who are required to be awake during the night, this often results in circadian disruption 56 . ...
... For example, 90-150 lux does not seem to alter the onset of evening melatonin even though it seems to promote an earlier sleep period 55 . Moreover, some studies claim that a 30 minute daily dosage of natural daylight for healthy individuals is enough to maintain a stable diurnal rhythm 56) . In the laboratory, a stable diurnal rhythm may be encountered using a strict and stable electric lighting environment 57) . ...
Interventions and strategies to improve health through the management of circadian (re)adaptation have been explored in the field, and in both human and animal laboratory manipulations of shiftwork. As part of an initiative by the Working Time Society (WTS) and International Committee on Occupational Health (ICOH), this review summarises the literature on the management of circadian (re)adaption using bright light treatment. Recommendations to maximise circadian adaptation are summarised for practitioners based on a variety of shiftwork schedules. In slowly rotating night shift schedules bright light appears most suitable when used in connection with the first three night shifts. These interventions are improved when combined with orange glasses (to block blue-green light exposure) for the commute home. Non-shifting strategies involve a lower dosage of light at night and promoting natural daylight exposure during the day (also recommended for day shifts) in acordance with the phase and amplitude response curves to light in humans.
... Under real-world, lifelike conditions, light exposure is highly variable, not only for a given individual but also between individuals differing in health status, geographical location, socioeconomic status, and occupation (Campbell et al., 1988;Crowley et al., 2015;Dumont & Beaulieu, 2007;Okudaira et al., 1983;Reid et al., 2014;Savides et al., 1986;Smolders et al., 2013). While some targeted studies have generated pair-wise or factor-wise comparisons in light exposure between different groups, a generalist framework for measuring and predicting light exposure across demographic groups currently does not exist. ...
Beyond visual function, specialized light-sensitive retinal circuits involving the photopigment melanopsin drive critical aspects of human physiology and behavior, including sleep–wake rhythms, hormone production, mood, and cognition. Fundamental discoveries of visual neurobiology dating back to the 1990s have given rise to strong interest from the lighting industry in optimizing lighting to benefit health. Consequently, evidence-based recommendations, regulations, and policies need to translate current knowledge of neurobiology into practice. Here, reviewing recent advances in understanding of NIF circuits in humans leads to proposed strategies to optimize electric lighting. Highlighted knowledge gaps must be addressed urgently, as well as the challenge of developing personalized, adaptive NIF lighting interventions accounting for complex individual differences in physiology, behavior, and environment. Finally, lighting equity issues appear in the context of marginalized groups, who have traditionally been underserved in research on both fundamental visual processes and applied lighting. Biologically optimal light is a fundamental environmental right.
... The exact light exposure that an individual receives over time depends on a range of factors [23,24]. At the individual level, light exposure depends on occupation [25][26][27], age [28,29], chronotype, and health status [28, [30][31][32]. ...
This article introduces a comprehensive metadata descriptor aimed at capturing crucial metadata information within personalized light exposure datasets. This metadata descriptor fills a critical gap in the field of personalized light exposure research by promoting standardized documentation of light exposure metadata. Light exposure profoundly impacts human physiology and behaviour, playing a central role in regulating the circadian system and influencing various physiological processes. As research on the real-world effects of light exposure gains momentum through the development of wearable sensors and light-logging technologies incorporating digital health approaches, there is a need to harmonize and standardize data collection and documentation across diverse studies and settings. The metadata descriptor was collaboratively developed by an international team of experts through a scoping exercise and synchronous discussions. It covers study-level, participant-level, dataset-level, and device-level metadata. The structure of the descriptor was designed to be modular, allowing for future expansions and customizations. The metadata descriptor comprises four main domains: study-level information, participant-level information, dataset-level information, and device-level information. Each domain includes specific metadata fields, ensuring comprehensive documentation of the data collection process. The metadata descriptor is available in JavaScript Object Notation (JSON) format, facilitating both human and machine readability. A user-friendly web interface has been developed for generating compliant JSON files, making it accessible to a wide range of users. The descriptor follows versioning principles to accommodate future updates and improvements. Following a description of the latest version, the article outlines several future directions for the metadata descriptor, including validation in real-world settings, independent evaluation, community-driven development, implementation in multiple software languages, and endorsement by scientific organizations. Integration with data repositories and platforms is also essential for streamlining data management and sharing. The metadata descriptor adheres to FAIR data principles, ensuring data is findable, accessible, interoperable, and reusable. Researchers are encouraged to adopt this descriptor to enhance the quality and utility of their light dosimetry datasets, ultimately advancing our understanding of the non-visual effects of light in real-world contexts.
... Light loggers can be used for a variety of purposes [29, [31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47][48][49], spanning both research (e.g., associational or intervention studies) and clinical (e.g., compliance to light therapy regime) settings. They differ in their ability to capture quantities related to light accurately [42], with some only capturing the photopic illuminance (lux). ...
Introduction
Exposure to light fundamentally influences human physiology and behaviour by synchronising our biological clock to the external light-dark cycle and controlling melatonin production. In addition to well-controlled laboratory studies, more naturalistic approaches to examining these “non-visual” effects of light have been developed in recent years. As naturalistic light exposure is quite unlike well-controlled stimulus conditions in the laboratory, it is critical to measure light exposure in a person-referenced way, the “spectral diet.” To this end, light loggers have been developed to capture personalised light exposure. As an alternative to light sensors integrated into wrist-worn actimeters, pendants, or brooch-based light loggers, a recently developed wearable light logger laterally attached to spectacle frames enables the measurement of biologically relevant quantities in the corneal plane.
Methods
Here, we examine the usability and acceptability of using the light logger in an undergraduate student sample (n = 18, mean±1SD: 20.1 ± 1.7 years; 9 female; Oxford, UK) in real-world conditions during a 24-h measurement period. We probed the acceptability of the light logger using rating questionnaires and open-ended questions.
Results
Our quantitative results show a modest acceptability of the light logger. A thematic analysis of the open-ended questions reveals that the form factor of the device, in particular, size, weight, and stability, and reactions from other people to the wearer of the light logger, were commonly mentioned aspects.
Conclusion
In sum, the results indicate the miniaturisation of light loggers and “invisible” integration into extant everyday objects as key areas for future technological development, facilitating the availability of light exposure data for developing personalised intervention strategies in both research, clinical and consumer contexts.
... Photic history may influence the individual physiological response to light and underlies plastic changes of the circadian phase across seasons (long-term light history) 69 , and less gradual transitions such as trans-latitudinal trips or between urban and natural environments (short-term light history) 17,21,24,70 . Although it is clear that photic history will affect subsequent response to light, only a few studies have focused on light exposure differences to assess phase shifts in real-life conditions 15,39,71 . Transitions between locations with artificial to natural lighting induce acute phase-advance shifts attributable to a concerted change in light exposure, which is simultaneously increased in the PAW and decreased in the PDW 17,21 . ...
The effect of light, main zeitgeber of the circadian system, depends on the time of day it is received. A brief trip to the Antarctic summer (ANT) allowed us to explore the impact of a sudden and synchronized increase in light exposure on activity-rest rhythms and sleep patterns of 11 Uruguayan university students, and to assess the significance of light history in determining individual circadian phase shift. Measurements collected in the peri-equinox in Montevideo, Uruguay (baseline situation, MVD) and in ANT, included sleep logs, actigraphy, and salivary melatonin to determine dim-light melatonin onset (DLMO), the most reliable marker of circadian phase. The increase in light exposure in ANT with respect to MVD (affecting both light-sensitive windows with opposite effects on the circadian phase) resulted in no net change in DLMO among participants as some participants advanced their DLMO and some others delayed it. The ultimate cause of each participant’s distinctive circadian phase shift relied on the unique change in light exposure each individual was subjected to between their MVD and ANT. This study shows an association between the individual light history and the circadian phase shift.
... One study comparing the effect of walking in a green versus urban environment found positive affect was only increased in the green environment (Legrand, Jeandet, Beaumont, & Polidori, 2022). Additionally, exercise performed in a naturalistic environment allows light exposure, which can improve affect (Dumont & Beaulieu, 2007). Moreover, several studies have shown that NA is lower and positive affect is higher when participants choose their preferred exercise modality (Daley & Maynard, 2003;Parfitt & Gledhill, 2004). ...
People with schizophrenia (SCZ) have a shorter life expectancy than those without psychiatric conditions. Of note, people with SCZ have high rates of cigarette smoking, physical inactivity, and obesity. These factors all coalesce to contribute to compromised health in this population, with smoking as a primary contributor. Therefore, it is paramount to develop effective smoking cessation strategies for this population. The purpose of this study was to investigate whether walking at a brisk pace, relative to engaging in passive activity, would reduce acute cigarette craving, nicotine withdrawal, and negative affect (NA) among people with SCZ who smoke cigarettes. Using a within-subjects design, twenty participants completed four laboratory sessions with condition sequence counterbalanced: 1) exposure to smoking cues + treadmill walking, 2) exposure to neutral cues + treadmill walking, 3) exposure to smoking cues + passive/sedentary activity, 4) exposure to neutral cues + passive/sedentary activity. Relative to sedentary activity, walking resulted in greater decreases in nicotine withdrawal but did not significantly affect craving or NA. These results did not vary as a function of cue type. These findings suggest that walking may be a helpful strategy to reduce acute nicotine withdrawal symptoms among people with SCZ. However, it should be used in conjunction with other strategies for smoking cessation.
... This includes research primarily describing and characterizing the patterns of light exposure across seasons and in different populations, 26,[42][43][44][45][46][47] as well as studies associating light exposure and health-related outcomes. [48][49][50][51][52][53][54][55][56][57][58] The biological rationale for hypothesized associations between light exposure and health-related outcomes is clearly established through in-laboratory findings in humans and animals. 2,13 Monitoring light exposure as an outcome or mediator in clinical trials ...
Background
Light exposure is an important driver and modulator of human physiology, behavior and overall health, including the biological clock, sleep-wake cycles, mood and alertness. Light can also be used as a directed intervention, e.g., in the form of light therapy in seasonal affective disorder (SAD), jetlag prevention and treatment, or to treat circadian disorders. Recently, a system of quantities and units related to the physiological effects of light was standardized by the International Commission on Illumination (CIE S 026/E:2018). At the same time, biometric monitoring technologies (BioMeTs) to capture personalized light exposure were developed. However, because there are currently no standard approaches to evaluate the digital dosimeters, the need to provide a firm framework for the characterization, calibration, and reporting for these digital sensors is urgent.
Objective
This article provides such a framework by applying the principles of verification, analytic validation and clinical validation (V3) as a state-of-the-art approach for tools and standards in digital medicine to light dosimetry.
Results
This article describes opportunities for the use of digital dosimeters for basic research, for monitoring light exposure, and for measuring adherence in both clinical and non-clinical populations to light-based interventions in clinical trials.
... Compared with healthy controls, the circadian rhythm regulation mechanism has fewer effects on positive emotion, but it has strong effects on negative emotion (54). Another study showed that shift work is associated with bad moods and that shift workers have a higher chance of becoming depressed (56). Major life events, including divorce, death, shift work, childbirth and others affect daily lifestyle, which usually influences the circadian system; a disrupted circadian system may lead to sleep disorders, negative emotions and psychological distress (57). ...
Background
Psychiatric nurses often face abuse, attacks, escape, suicides, and other situations related to the care of patients with mental disorders, which are more likely to induce psychological distress.
Aims
This study aimed to examine the relationship between coping styles and psychological distress among Chinese psychiatric nurses in Shandong and the significance of sleep quality as a mediating factor.
Methods
A total of 812 psychiatric nurses in Shandong, China, were investigated using the Psychological Distress Scale (K10), Simplified Coping Style Questionnaire (SCSQ), Pittsburgh Sleep Quality Index (PSQI) and self-compiled general information questionnaire.
Results
Psychological distress was detected in 571 psychiatric nurses (70.3%). The psychological distress of psychiatric nurses was significantly different with respect to professional title (χ ² = 10.627, P < 0.05) and shift work (χ ² = 9.120, P < 0.01). Psychological distress positively correlated with negative coping style ( r = 0.266, P < 0.01) and sleep quality (PSQIT) ( r = 0.532, P < 0.01). A significant positive correlation was found between psychological distress and all dimensions of sleep quality ( r = 0.158–0.456, P < 0.05). Professional title, positive coping style, negative coping style, sleep quality (PSQIT), subjective sleep quality, sleep disorder and daytime dysfunction predicted psychological distress in psychiatric nurses ( R ² = 0.363, F = 65.343, P < 0.01). The relationship between negative coping style and psychological distress was partially mediated by sleep quality, with the mediating effect accounting for 37.97% of the total effect.
Conclusions
Psychiatric nurses have a high rate of psychological distress, which is closely related to coping styles, and sleep quality has a certain regulatory effect.
... As a consequence, they reported feeling more positive, less stressed, and not as 'mentally exhausted', the latter being a pervasive experience of the pandemic (Marsh 2021). Exposure to light in natural environments has a positive impact on sleep quality and quantity (Dumont and Beaulieu 2007;Düzgün and Durmaz Akyol 2017;Corley et al. 2021) and camping, even for a short period, can be beneficial to human circadian timing and sleep patterns (Stothard et al. 2017). Frequently, studies take place in remote areas away from artificial light, but our research suggests that camping in a domestic garden may have similar benefits with participants documenting their reconnection with the natural light-dark cycle and its beneficial cognitive effects, e.g. ...
The restrictions imposed by COVID-19 lockdown(s) left many feeling trapped at home. One leisure activity that saw a surge in popularity during lockdown was ‘home’ camping. Camping has long been associated with positive health and well-being outcomes and during lockdown camping at home was documented across social media platforms as people shared experiences of their micro-adventures. This paper will draw on social media (Instagram) and survey (> 260 responses) data gathered from ‘regular’ campers and those who had never previously camped during the UK lockdowns. Specifically, we explore: (i) what motivated home camping; (ii) the impact of camping activity on physical and mental well-being; (iii) the role it played in fostering and/or nurturing social relationships in isolating circumstances (iv) how digital practices were incorporated into camping as an activity. As such, the paper will provide a valuable contribution to understand the transformative potentials of restricted leisure practices in the pandemic. © 2022 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group.
... It may not be surprising that the seasonal daylight differences impact human behaviours and affect, 18 however, it was not until recent decades that people started to ...
Objectives
It is believed that inadequate environmental light, especially in facilities such as care homes, contribute to the diurnal changes of behavioural and psychological symptoms of dementia (BPSD) historically referred to as “sundowning syndrome”. Conceptual models of sundowning phenomena have shifted emphasis from the role of light in vision (image forming) to its role in circadian rhythm modulation. However, the grounds for this change are unclear and the evidence on which it is based has not been examined comprehensively.
Methods
We have searched literature on sundowning syndrome and its association with light and studies evaluating BPSD, behavioural rhythm and environmental light in care homes in four databases (PubMed, Web of Science, Embase and Cochrane Library) from inception to 31 January 2021.
Results
Of the nine studies investigating light, behavioural rhythm and BPSD in care homes identified, we found evidence that insufficient natural light exposure was associated with worsening of BPSD and disrupted activity rhythm but it was not clear whether this related to image forming or disrupted circadian rhythm. There was a paucity of evidence in relation to the role of low levels of light for image forming in the context of a specific BPSD symptom: visual hallucinations. We also found literature on the possible role of light outside the visible spectrum influencing cognition. Based on the evidence, we proposed a new model integrating different components of light in BPSD and sundowning syndrome that combines its image forming and circadian roles.
Conclusions
Inadequate light may be a risk factor for BPSD and sundowning syndrome for dementia patients through a range of different mechanisms. It is recommended that multiple neuro‐endocrinological and socio‐environmental factors relevant to light such as adjusting the environmental setting, increasing light exposure, and scheduling activities should be considered when treating dementia patients with BPSD.
... More recent work in Antarctica suggests that a month-long period of daylight deprivation increases retinal sensitivity to bright, short wavelength light (generated by narrow bandwidth LEDs, Kawasaki et al. 2018). Another study of indoor and outdoor dayworkers only found the expected correlation between evening light exposure and later circadian timing of the melatonin rhythm when they considered the ratio between daytime and evening light, rather than daytime or evening light exposure alone (Dumont and Beaulieu 2007). Finally, similar to findings on phase shifting and melatonin suppression, effects of light on alertness also seem to depend on prior light history (Chang et al. 2013). ...
Architectural lighting has potent biological effects but applied lighting practices that capitalize on this potential have been limited. In this review, we endeavor to consolidate and synthesize key references that will be useful for lighting professionals, with the goal of supporting knowledge translation into pragmatic lighting strategies. Specifically, we explain relevant terminology, outline basic concepts, identify key references, provide a balanced overview of the current state of knowledge, and highlight important remaining questions. We summarize the physiological effects of light on human health and well-being, including a description of the processes underlying the photic regulation of circadian, neuroendocrine, and neurobehavioral functions. We review seminal work elucidating the elements mediating the potency of light for these physiological responses, with specific attention to factors critical for interpreting those findings. In parallel, we explain and endorse melanopic Equivalent Daylight Illuminance (Ev,melD65) as the preferred measure to quantify the biological potency of light. Ultimately, while future studies are necessary to further facilitate the translation of laboratory knowledge to domestic and workplace settings, the immediate potential for applied lighting to better support human health is clear. Aiming for integrative lighting solutions that have biologically high potency light during the day and low potency during the night is perhaps the most immediate improvement to be made in order to better support applications for humans.
... Exposure to natural light. Another potential factor is that surfing typically involves exposure to bright natural light, which can help regulate circadian rhythm and facilitate adequate quality and quantity of sleep through increasing the amplitude of the nighttime melatonin secretion peak (Dumont & Beaulieu, 2007;Emens & Burgess, 2015). Disruptions in circadian rhythm have been linked to the development and maintenance of many psychological disorders, including depression, bipolar disorder, anxiety disorders and attention deficit hyperactivity disorder (ADHD; Baird, Coogan, Siddiqui, Donev, & Thome, 2012;Dueck, Thome, & Haessler, 2012;Germain & Kupfer, 2008;Melo, Abreu, Neto, de Bruin, & de Bruin, 2017). ...
There is growing interest in surfing as a recreational activity that may facilitate skill development and improved mental health. However, there remains uncertainty regarding the causal processes through which surfing may improve psychological well-being. With the aim to guide future research, we review potential mechanisms that may underpin the psychotherapeutic effects of surfing. A range of plausible factors are identified, including exercise, water immersion, exposure to sunlight, transcendent experiences, reductions in rumination and the satisfaction of basic psychological needs. Further research is needed to clarify the effectiveness of surfing-based therapies and to establish the relative contributions of the causal mechanisms at play.
... However, the natural environment can also increase sleep quality for some individuals due to the light pollution and the physical activity (melatonin regulation). Light pollution and lack of exposition to natural light can impact sleep circadian rhythm [68]. The natural environment exposure can influence sleep quality positively by regulating melatonin secretion, reducing artificial light exposure, promoting exercise and reduce some city noises [69]. ...
Outdoor activity can help to promote an active lifestyle; however, it is often
associated with risks from its surrounding environment. Understanding physiological responses to several outdoor activities and how to use simple monitoring
tips to reduce risks will provide real-life applications in the preparation of outdoor
recreation. The purpose of this chapter focuses on common stressful conditions:
thermoregulation, energy demand, musculoskeletal injuries risks, sleep and
recovery. These are some constraints that can be encountered in any outdoor
context. The physiological responses and recommendations based on up-to-date
research will provide useful methods for risk assessment and how to manage
them. Finally, the health benefits from outdoor activity in different populations
will complete this chapter in order to help specialists structured and adapted their
intervention planning.
... Currently, there is very limited data on light levels in real shift work conditions, e.g. 38 . The 90 lx can result in ~ 50% of the maximum phase shifting capacity and melatonin suppression, and the 450 lx can cause near-maximum phase shifting capacity and melatonin suppression 39 . ...
Night shift work can associate with an increased risk for depression. As night workers experience a 'misalignment' between their circadian system and daily sleep-wake behaviors, with negative health consequences, we investigated whether exposure to circadian misalignment underpins mood vulnerability in simulated shift work. We performed randomized within-subject crossover laboratory studies in non-shift workers and shift workers. Simulated night shifts were used to induce a misalignment between the endogenous circadian pacemaker and sleep/wake cycles (circadian misalignment), while environmental conditions and food intake were controlled. Circadian misalignment adversely impacted emotional state, such that mood and well-being levels were significantly decreased throughout 4 days of continuous exposure to circadian misalignment in non-shift workers, as compared to when they were under circadian alignment (interaction of "circadian alignment condition" vs. "day", mood: p < 0.001; well-being: p < 0.001; adjusted p-values). Similarly, in shift workers, mood and well-being levels were significantly reduced throughout days of misalignment, as compared to circadian alignment (interaction of "circadian alignment condition" vs. "day", mood: p = 0.002; well-being: p = 0.002; adjusted p-values). Our findings indicate that circadian misalignment is an important biological component for mood vulnerability, and that individuals who engage in shift work are susceptible to its deleterious mood effects.
... This may be particularly applicable for athletes sleeping in unfamiliar environments (e.g., hotel rooms) or athletes sleeping in residential dorms (e.g., collegiate athletes). Exposure to light after dark infl uences circadian rhythms, and subsequent can adversely affect sleep ( Dumont & Beaulieu, 2007 ), and it follows that the bedroom environment should be dark. Practically, darkening curtains may be useful in blocking external sources of artifi cial light (e.g., street lights), while sleep masks should also be considered. ...
Finally, the authoritative resource that serious cyclists have been waiting for has arrived. The perfect blend of science and application, Cycling Science takes you inside the sport, into the training room and research lab, and onto the course.
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Contributions from 43 top cycling scientists and coaches from around the world
The latest thinking on the rider-machine interface, including topics such as bike fit, aerodynamics, biomechanics, and pedaling technique
Information about environmental stressors, including heat, altitude, and air pollution
A look at health issues such as on-bike and off-bike nutrition, common injuries, fatigue, overtraining, and recovery
Help in planning training programs, including using a power meter, managing cycling data, off-the-bike training, cycling specific stretching, and mental training
The latest coaching and racing techniques, including pacing theories, and strategies for road, track, MTB, BMX, and ultra-distance events
In this book, editors and cycling scientists Stephen Cheung, PhD, and Mikel Zabala, PhD, have assembled the latest information for serious cyclists.
... The mechanism underlying the association between LAN exposure and manic symptoms in BD remains unknown, but it may be related to circadian rhythm dysfunction and sleep disturbance. Light exposure has a primary role in the regulation of circadian rhythms in humans (Dumont and Beaulieu 2007), and LAN exposure causes disruption of the biological clock and suppression of melatonin secretion (Lunn et al. 2017;Reiter et al. 2007;Smolensky et al. 2016Smolensky et al. , 2015. Furthermore, BD has been suggested to associate with the abnormality of circadian rhythm, including evening preference, light hypersensitivity, and the abnormal of melatonin and cortisol secretions (Bellivier et al. 2015;Geoffroy 2018). ...
Previous studies have found that keeping the room dark at night was associated with a decrease in manic symptoms for patients with bipolar disorder (BD). However, the association between light at night of real-life conditions and manic symptoms is unclear. We investigated the association between bedroom light exposure at night and manic symptoms in BD patients. One-hundred and eighty-four outpatients with BD participated in this cross-sectional study. The average light intensity at night during sleep was evaluated using a portable photometer for seven consecutive nights. Manic symptoms were assessed using the Young Mania Rating Scale (YMRS), and scores ≥5 were treated as a “hypomanic state.” The median (interquartile range) YMRS score was 2.0 (0–5.0), and 52 (28.2%) participants were in a hypomanic state. The prevalence of a hypomanic state was significantly higher in the participants with an average light intensity at night exposure of ≥3 lux than in those with <3 lux (36.7% versus 21.9%; P = .02). In multivariable logistic regression analysis adjusted for BD type, depressive symptoms, sleep duration, and daytime physical activity, the odds ratio (OR) for a hypomanic state was significantly higher for the participants with an average light intensity at night exposure of ≥3 lux than for those with <3 lux (OR: 2.15, 95% confidence interval: 1.09–4.22, P = .02). This association remained significant at the cutoff value of YMRS score ≥6 (OR: 2.51, 95% confidence interval: 1.15–5.46; P = .02). The findings of this study indicate bedroom light exposure at night is significantly associated with manic symptoms in BD patients. Although the results of this cross-sectional investigation do not necessarily imply causality, they may serve to inform beneficial nonpharmacological intervention and personalized treatment of BD patients.
... Man is a "day animal" with a biological clock that synchronizes the biological functions so that functions associated with activity occur during the daytime and resting functions occur at night [42,43]. The 2017 Nobel Prize in Physiology or Medicine was awarded for the discoveries of molecular mechanisms controlling the circadian rhythm. ...
This chapter covers the following issues: air quality, thermal conditions and ventilation. It comprises ventilation, human and other sources of pollution and energy load, cooling and humidification, microbial and organic pollutions. Open shelves, fleecy surfaces, carpets and office machines can add to pollutions. An addendum is included with Norwegian ventilation requirements in non-industrial buildings.
... This may be particularly applicable for athletes sleeping in unfamiliar environments (e.g., hotel rooms) or athletes sleeping in residential dorms (e.g., collegiate athletes). Exposure to light after dark infl uences circadian rhythms, and subsequent can adversely affect sleep ( Dumont & Beaulieu, 2007 ), and it follows that the bedroom environment should be dark. Practically, darkening curtains may be useful in blocking external sources of artifi cial light (e.g., street lights), while sleep masks should also be considered. ...
... People visualize using natural light, which controls the body's neurochemicals, hormones, and natural rhythm. Much research (Dumont and Beaulieu 2007;Kaida et al. 2006;Eastman 1990;Lewy and Sack 1996) has been conducted on the effects of inadequate natural light on humans. There is a direct correlation between insufficient natural light and mental issues such as impatience, fatigue, illness, insomnia, depression, alcoholism, and suicide. ...
The elderly suffer from discomfort in social life owing to the decline of their physical, psychological, and social functions. The elderly who spend a lot of time indoors require an intelligent system to extend their time to live independently in a residential environment. Recently, the Ambient Assisted Living (AAL) concept was introduced to commercialize various technologies and apply them to urban and architectural environments. However, AAL’s connection to architectural elements is insufficient. This study intends to build a residential environment platform that integrates Internet of Things (IoT) technology and architectural elements to support the independence of the elderly based on the AAL concept. The proposed platform is designed to be applied to various scenarios and services. A responsive façade system was designed to verify the platform, and the usefulness of the system was evaluated through the interaction of the designed façade and an acting manager.
... Light is considered as the main factor or Zeitgeber (time giver) when it comes for synchronization of the human circadian clock with 24-h dark-night cycle derived from the constant external solar clock [7]. In normal conditions, this circadian rhythm entrainment is essential for regulating physiological and biological functions of humans including body temperature, heart rate, gene expression as well as sleep characteristics [8,9]. ...
We aimed to assess the association of sunlight exposure with sleep duration and sleep onset time in children. Data were obtained from the fifth survey of a national school-based surveillance program in Iran. Sunlight exposure time, sleep duration, sleep onset time, physical activity time, mental health status and frequency of consuming coffee and tea were recorded. Overall, 14 274 students aged 7-18 years were recruited. Sleep duration was associated positively with sex, age, body mass index and physical activity, as well as with sunlight exposure and negatively with the consumption of coffee and tea. Higher physical activity, exposure to sunlight and mental status score in children exposed to sunlight via their face, hands, arms and feet, reduced the likelihood of sleep onset time after midnight (odds ratio (OR) = 0.909, 0.741 and 0.554 respectively). Daily exposure to sunlight may increase sleep duration and advance the sleep onset time in children and adolescents.
... The symptoms of shift work are similar to jet lag, but the overall impact on health is more severe because shift workers are typically unable to synchronize with their new LD cycle due to frequent work schedule changes and shifted sleep-wake patterns on non-work days (Rajaratnam and Arendt, 2001). Shift workers report poor mood and exhibit an increased risk for development of MDD (Angerer et al., 2017;Asaoka et al., 2013;Dumont and Beaulieu, 2007;Scott et al., 1997). Furthermore, duration of shift work history is positively correlated with severity of depressive symptoms (Lee et al., 2017). ...
Synchronizing circadian (24 h) rhythms in physiology and behavior with the environmental light-dark cycle is critical for maintaining optimal health. Dysregulation of the circadian system increases susceptibility to numerous pathological conditions including major depressive disorder. Stress is a common etiological factor in the development of depression and the circadian system is highly interconnected to stress-sensitive neurotransmitter systems such as the serotonin (5-hydroxytryptamine, 5-HT) system. Thus, here we propose that stress-induced perturbation of the 5-HT system disrupts circadian processes and increases susceptibility to depression. In this review, we first provide an overview of the basic components of the circadian system. Next, we discuss evidence that circadian dysfunction is associated with changes in mood in humans and rodent models. Finally, we provide evidence that 5-HT is a critical factor linking dysregulation of the circadian system and mood. Determining how these two systems interact may provide novel therapeutic targets for depression.
... Specifically, light is the main environmental regulator of circadian rhythm. As the human brain tends to wake when the environment transitions from darkness to light [38], night workers find it difficult to sleep during the day. ...
Abstract Background Previous studies have reported that an irregular work schedule, particularly nighttime work, is associated with an altered lipid profile. Additionally, a mismatch in circadian rhythm can affect sleeping and eating habits, leading to poor health. This study aimed to examine the association between night work and dyslipidemia among South Korean adults aged ≥30 years. Methods For this study, the data of 5813 participants in the 2013–2016 Korea National Health and Nutrition Examination Survey were analyzed. Diagnoses of dyslipidemia were based on blood sampling tests of total cholesterol, high-density lipoprotein (HDL), low-density lipoprotein (LDL) cholesterol, and triglyceride levels. Night work was defined as that conducted during evening (6 P.M.–12 A.M.) and overnight hours (12 A.M.–8 A.M.). The association between night work hours and dyslipidemia in South Korean men and women was investigated using a logistic regression analysis. Results After adjusting for sociodemographic, economic, health-related, and nutritional factors, an association of night work with dyslipidemia was observed in male participants (odds ratio = 1.53, 95% confidence interval: 1.05–2.24). In subset analyses of male participants, night workers who skipped meals were more likely to have dyslipidemia than their day-working counterparts. Among men who slept
In early childhood, consolidation of sleep from a biphasic to a monophasic sleep-wake pattern, that is, the transition from sleeping during an afternoon nap and at night to sleeping only during the night, represents a major developmental milestone. Reduced napping behavior is associated with an advance in the timing of the circadian system; however, it is unknown if this advance represents a standard response of the circadian clock to altered patterns of light exposure or if it additionally reflects features of the developing circadian system. Using a mathematical model of the human circadian pacemaker, we investigated the impact of napping and non-napping patterns of light exposure on entrained circadian phases. Simulated light schedules were based on published data from 20 children (34.2 ± 2.0 months) with habitual napping or non-napping sleep patterns (15 nappers). We found the model predicted different circadian phases for napping and non-napping light patterns: both the decrease in afternoon light during the nap and the increase in evening light associated with napping toddlers' later bedtimes contributed to the observed circadian phase difference produced between napping and non-napping light schedules. We systematically quantified the effects on phase shifting of nap duration, timing, and light intensity, finding larger phase delays occurred for longer and earlier naps. In addition, we simulated phase response curves to a 1-h light pulse and 1-h dark pulse to predict phase and intensity dependence of these changes in light exposure. We found the light pulse produced larger shifts compared with the dark pulse, and we analyzed the model dynamics to identify the features contributing to this asymmetry. These findings suggest that napping status affects circadian timing due to altered patterns of light exposure, with the dynamics of the circadian clock and light processing mediating the effects of the dark pulse associated with a daytime nap.
40 Hz light flicker can activate multiple brain regions of wild-type mice. However, there are no systematic studies on the behavioral effects of 40 Hz light flicker on wild-type mice. Adult wild-type C57BL/6J mice were treated with 40 Hz light flicker (200 lux, 40 Hz, 1 h/day for 3 weeks) to evaluate its effects on several behaviors, including mood, locomotor activity, memory, social interaction, mechanical pain, and sense of smell. In the open field test, the elevated zero-maze test, forced swimming test, and tail suspension test, 40 Hz mice showed no anxiety and depression-like behaviors. In the rotarod test, no differences were found between the anti-fatigue ability and motor coordination ability. In memory-related tests, 40 Hz mice showed the short-term cognitive enhancement in the novel object recognition test. Interestingly, 40 Hz mice showed no enhanced the long-term memory performance in the contextual fear conditioning test, and tone-cued fear conditioning test. Besides, 40 Hz mice increased their exploration of social cues that were unfamiliar to them and differed significantly from their own experiences. In terms of sensory abilities, 40 Hz mice had unchanged pain sensitivity in the von Frey fiber test and significant enhancement in the olfactory ability in the food-seeking test. In conclusion, this 40 Hz light stimulation paradigm has high safety and can improve the specific behavioral ability, which provides a theoretical basis for the future use of 40 Hz light flicker as a disease prevention or treatment method.
Light helps mankind synchronize the circadian rhythm, necessitating the need to create a luminous environment in a bedroom. Many studies have focused on the effect of bedroom lighting regulation on sleep. However, there was a lack of research on how psychology responses are connected to sleep in residential bedroom. Thus, this chamber-based study explored mood differences among three correlated color temperatures (CCT; 2700 K, 4100 K, 5500 K). Additionally, the study analyzed the correlation of pre- and post-sleep psychological states with sleep quality. The results showed that suitable artificial lights (CCT at 2700K) in a bedroom before and after sleep under different conditions would provide the relaxation for subjects. Moreover, SOL, SWS, and SE were significantly different across different CCTs. According to the correlation and regression analysis, there were four groups of Pearson significantly correlated variables with coefficients of determination ranging from 0.34 to 0.70. Among them, 67% of the variation in SOL could be explained by the degree of pre sleep relaxation and pleasure. Furthermore, abundant and healthy sleep might perpetuate the mood generated by artificial lights. Finally, the roles of psychological states and sleep physiological responses should be considered while creating comfortable lighting conditions in bedrooms.
Exposure to light fundamentally influences human physiology and behaviour by synchronising our biological clock to the external light-dark cycle and controlling melatonin production. In addition to well-controlled laboratory studies, more naturalistic approaches to examining these "non-visual" effects of light have been developed in recent years. As naturalistic light exposure is quite unlike well-controlled stimulus conditions in the laboratory, it is critical to measure light exposure in a person-referenced way, the "spectral diet". To this end, light loggers have been developed to capture personalised light exposure. As an alternative to light sensors integrated into wrist-worn actimeters, pendants or brooch-based light loggers, a recently developed wearable light logger laterally attached to spectacle frames enables the measurement of biologically relevant quantities in the corneal plane. Here, we examine the usability and acceptability of using the light logger in an undergraduate student sample (n=18, mean+1SD: 20.1+1.7 yrs; 9 female; Oxford, UK) in real-world conditions during a 24-hour measurement period. We probed the acceptability of the light logger using rating questionnaires and open-ended questions. Our quantitative results show a modest acceptability of the light logger. A thematic analysis of the open-ended questions reveals that the form factor of the device, in particular, size, weight and stability, and reactions from other people to the wearer of the light logger, were commonly mentioned aspects. In sum, the results indicate the miniaturisation of light loggers and "invisible" integration into extant everyday objects as key areas for future technological development, facilitating the availability of light exposure data for developing personalised intervention strategies in both research, clinical and consumer contexts.
The effect of light, main zeitgeber of the circadian system, depends on the time of day it is received. A brief trip to the Antarctic summer (ANT) allowed us to explore the impact of a sudden and synchronized increase in light exposure on activity-rest rhythms and sleep patterns of 11 Uruguayan university students, and to assess the significance of light history in determining individual circadian phase shift. Measurements collected in the peri-equinox in Montevideo, Uruguay (baseline situation, MVD) and in ANT, included sleep logs, actigraphy, and salivary melatonin to determine dim-light melatonin onset (DLMO), the most reliable marker of circadian phase. The increase in light exposure in ANT with respect to MVD (affecting both light-sensitive windows with opposite effects on the circadian phase) resulted in no net change in DLMO among participants as some participants advanced their DLMO and some others delayed it. The ultimate cause of each participant's distinctive circadian phase shift relied on the unique change in light exposure each individual was subjected to between their MVD and ANT. This is the first study to show a clear physiological effect of light either advancing or delaying the circadian phase dependent on individual light history in an ecological study.
The relationship between everyday light exposure and sleep was studied for office workers. The study was conducted during the upswing of the COVID-19 pandemic, enabling a comparison between Office and Home Workdays. Fifteen full-time office employees were monitored for a period of 4–6 weeks. They wore a light-tracking device on their clothes and had a sleep tracker at home. Compared to an Office Workday, light exposure was lower in the afternoon and total sleep time was almost 5 minutes longer on a Home Workday. Sleep efficiency was the same on both workday types. A higher median illuminance level in the afternoon was significantly related to later sleep onset on an Office Workday. Higher median illuminance levels in the morning were related to earlier awakening. Counter to expectations, higher light levels in the evening were also related to earlier awakening. Everyday light exposure matters for sleep quality but may affect circadian functioning differently than the often more extreme light interventions employed in laboratory experiments. Moreover, differences in outcomes between Office and Home Workdays signal the need for further investigation to provide supportive light levels during workhours.
Insulin-like growth factor (IGF) family plays important roles in regulating the development of various organ systems through stimulating cell proliferation and differentiation. Photoperiod is an important factor affecting growth and development in the chicken, yet the effect of constant light exposure in early life on IGF1 and IGF2 expression in the chicken remains unclear. In this study, one-day-old chickens were kept in either constant light (24L:0D, LL) or natural photoperiod (12L:12D, LD) for the first week of life and then maintained in constant light from 8 d to 21 d of age. Constant light exposure in early life reduced mRNA expression of IGF gene family, including mRNA expression of IGF1, IGF2 and IGF2 binding proteins (IGF2BPs), in the hippocampus, hypothalamus and liver of chickens at both 7 d and 21 d of age. Moreover, constant light exposure increased mRNA expression of genes involved in RNA methylation N6-methyladenosine (m 6A) in a tissue-specific manner. Interestingly, higher m 6A on 3’UTR of IGF2 mRNA coincides with lower IGF2 mRNA, indicating a possible role of m 6A in the post-transcriptional regulation of IGF2 expression in the hippocampus, hypothalamus, and liver of chickens. These findings suggest a m 6A-mediated gene regulation of IGF gene family in different organs of chicken and expand our knowledge on mechanism of gene regulation in response to early life experience.
Objective:
A previous cross-sectional study reported that nighttime light is associated with increased occurrence of manic symptoms in bipolar disorder; however, the longitudinal association between nighttime light and subsequent mood episode relapses remains unclear. We determined whether bedroom nighttime light was associated with mood episode relapses in patients with bipolar disorder.
Methods:
This prospective cohort study included 172 outpatients with bipolar disorder who participated in an Association between the Pathology of Bipolar Disorder and Light Exposure in Daily Life (APPLE) cohort study. A portable photometer was used to measure illuminance in the bedroom from bedtime to rising time during 7 consecutive nights for baseline assessment. Then, the participants were assessed at a 2-year follow-up for mood episode relapses.
Results:
Of the 172 participants, 157 (91%) completed the 2-year follow-up, and 39 (22%) experienced manic or hypomanic episodes (with or without mixed features), during that time. In the Cox proportional-hazards model, the hazard ratio (HR) for manic/hypomanic episode relapses was significantly higher when the average nighttime illuminance was ≥3 lux (n = 71) than when it was <3 lux (n = 101; HR, 2.54; 95% confidence interval (CI), 1.33-4.84). In the multivariable model adjusted for a propensity score in relation to nighttime light, the relationship remained significant (HR, 2.17; 95% CI, 1.04-4.52). The association between nighttime light and depressive episode relapses was not significantly different.
Conclusions:
Keeping the bedroom dark at night may prevent hypomanic and manic episodes.
Study objectives:
Cognitive behavioral treatment for insomnia is performed under the premise that feedback provided by evaluation of sleep diaries written by patients will result in good sleep. The sleep diary is essential for behavior therapy and sleep hygiene education. However, limitations include subjectivity and laborious input. We aimed to develop an artificial intelligence sleep prediction model and to find factors associated with good sleep using a wrist-worn actigraphy device.
Methods:
We enrolled 109 participants who reported having no sleep disturbances. We developed a sleep prediction model using 733 days of actigraphy data of physical activity and light exposure. Twenty-four sleep prediction models were developed based on different data sources (actigraphy alone, sleep diary alone, or combined data), different durations of data (1 or 2 days), and different analysis methods (extreme gradient boosting, convolutional neural network, long short-term memory, logistic regression analysis). The outcome measure of "good sleep" was defined as ≥90% sleep efficiency.
Results:
Actigraphy model performance was comparable to sleep diary model performance. Two-day models generally performed better than 1-day models. Among all models, the 2-day, combined (actigraphy and sleep diary), extreme gradient boosting model had the best performance for predicting good sleep (accuracy=0.69, area under the curve=0.70).
Conclusions:
The findings suggested that it is possible to develop automated sleep models with good predictive performance. Further research including patients with insomnia is needed for clinical application.
Intellectual disability is a neurodevelopment disorder that affects the intellectual and adaptive functioning. The individual fails to meet standards of personal independence and social responsibility in one or more aspects of daily life, including communication, social participation, academic or occupational functioning, and personal independence at home or in community settings. There is an immense need to understand and be aware of the signs and symptoms of the disorder. This chapter focuses on the process of the assessment which is necessary to identify intellectual deficiency and also the issues that should be taken care of during the process. The various principles and tools of assessment, which can be used to measure IQ, are mentioned. It also focuses on the various challenging behaviors and functional analysis. It also focuses on recent and efficient management strategies that can be used to help the affected person cope and acquire new skills.
Light pollution has become a potential health risk factor worldwide. Chronic exposure to constant light (CCL) leads to depressive-like behavior, yet the mechanism remains unclear. In this study, mice exposed to CCL for 3 weeks exhibited depression-like behaviors, with decreased melatonin in plasma and increased oxidative stress in hippocampus. Meanwhile, CCL-exposed mice showed elevated plasma corticosterone (CORT) levels and diminished glucocorticoid receptor (GR) phosphorylation in hippocampus. Concurrently, glycogen synthase kinase 3 beta (GSK3β) was inactivated with increased phosphorylation at Ser9. The interrelationship of GSK3β and GR was clarified in mouse hippocampal neuron (HT-22) cells. GSK3β inhibitor CHIR-99021 induced GR inhibition with diminished phosphorylation, while GR inhibitor RU486 did not affect GSK3β expression or phosphorylation. Furthermore, GSK3β-mediated GR inhibition was reproduced in vitro in HT-22 cells treated with melatonin receptor antagonist luzindole and H2O2 in combination. Finally, melatonin reversed GSK3β-mediated GR inhibition in hippocampus and improved CCL-induced depression-like behavior in mice. These results indicate that CCL induces melatonin deficiency and oxidative stress in hippocampus, which in turn leads to GSK3β-mediated GR inhibition and depression-like behavior in mice.
Background:
Sunlight exposure is a major risk factor for eye disorders. Most outdoor workers cannot avoid sunlight exposure. This study aimed to analyze the relationship between outdoor sunlight exposure and eye disorders in an economically active population.
Methods:
This study analyzed the 2008-2012 Korea National Health and Nutritional Examination Survey data. Sunlight exposure was categorized as < 5 hours and > 5 hours. We also analyzed the dose-dependent relationship between exposure to sunlight and eye disorders (cataracts, pterygium, and age-related macular degeneration [AMD]) using data from 2010 to 2012 by subdividing the exposure groups into < 2 hours, 2-5 hours, and ≥ 5 hours. Eye disorders were diagnosed by an ophthalmologist. The study participants were stratified by sex, and the results were analyzed using the χ2 test and multiple logistic regression analysis.
Results:
In the female group, the odds ratio of pterygium in the high-level sunlight exposure group was 1.47 (95% confidence interval [CI]: 1.15-1.89). Regarding AMD, the odds ratios were 1.42 (95% CI: 1.16-1.73), 1.33 (95% CI: 1.03-1.73), and 1.58 (95% CI: 1.15-2.16) in the total, male, and female groups, respectively. Analysis of the dose-response relationship revealed that the odds ratios of pterygium in the high-level sunlight exposure subgroups of the total and female groups were 1.62 (95% CI: 1.25-2.08) and 2.00 (95% CI: 1.39-2.88), respectively.
Conclusions:
This study demonstrated a relationship between sunlight exposure and eye disorders in an economically active population. Women were found to be especially vulnerable to pterygium. However, additional prospective studies to clarify the pathophysiology of pterygium are needed.
Objective
Light therapy has been suggested to have a curative effect on bipolar depression; however, preventive effects of light exposure on depressive episodes remain unclear. This study evaluated whether daytime light exposure in real‐life situations was associated with a preventive effect on relapse into depressive episodes in patients with bipolar disorder.
Methods
This prospective, naturalistic, observational study was conducted in Japan between August 2017 and June 2020. Outpatients with bipolar disorder were objectively evaluated for daytime light exposure over 7 consecutive days using an actigraph that could measure ambient light at baseline assessment and then assessed at 12‐month follow‐up for relapse into mood episodes.
Results
Of 202 participants, 198 (98%) completed follow‐up at 12 months and 78 (38%) experienced relapse into depressive episodes during follow‐up. In a Cox proportional hazards model adjusting for potential confounders, a longer time above 1000 lux at daytime was significantly associated with decrease in relapse into depressive episodes (per log min; hazard ratio, 0.66; 95% confidence interval, 0.50–0.91). In addition, a higher average illuminance and longer time above 1000 lux in the morning exhibited a significant decrease in relapse into depressive episodes (per log lux and per log min; hazard ratio, 0.65 and 0.61; 95% confidence interval, 0.49–0.86 and 0.47–0.78, respectively). The association between daytime light exposure and relapse into manic/hypomanic/mixed episodes was not significantly different.
Conclusion
A significant association was observed between increased daytime light exposure, mainly in the morning, and decreased relapse into depressive episodes.
While most individuals spend a substantial amount of time sleeping, Japan is among the developed countries whose residents register the fewest number of hours of sleep. I thus examine the causal effects of sleep on labor productivity, utilizing panel datasets for Japanese men. The potential endogeneity of deciding how many hours to sleep is addressed by using fixed effects panel data models with an instrumental variable estimation technique. Exploiting the annual variation in the average sunshine duration between cities as an instrument, I then show that a one-hour increase in the weekly number of hours of sleep increases the wage rate by up to 6–8% on average. These results suggest that sleep duration could enhance labor productivity.
Obesity and overweight are highly prevalent in individuals with bipolar disorder and are associated with a risk of developing not only physical but also mental problems. The current study aimed to determine the association between bedroom light exposure at night and obesity in individuals with bipolar disorder. This cross-sectional study enrolled 200 outpatients with bipolar disorder. The light intensity in the bedroom between bedtime and rising time was measured for seven consecutive nights using a portable photometer. Body mass index (BMI) was determined using self-reported height and weight, and obesity was defined as a BMI ≥ 25 kg/m2. The overall prevalence of obesity was 44%. In the multivariable logistic regression analysis adjusted for age, gender, use of psychiatric medications, sleep parameters, and physical activity, the odds ratio (OR) for obesity was significantly higher in the group exposed to an average light intensity ≥ 3 lux (n = 112) than in the group exposed to an average light intensity < 3 lux (n = 88) (OR, 2.13; 95% confidence interval, 1.19-4.21; P = 0.01). Furthermore, individuals exposed to an average light intensity ≥ 3 lux were significantly higher body weight (adjusted mean, 68.7 vs. 64.4 kg; P = 0.03) and BMI (adjusted mean, 25.6 vs. 24.2 kg/m2; P = 0.04) than those exposed to an average light intensity < 3 lux. A significant association was observed between bedroom light exposure at night and obesity in patients with bipolar disorder. Further longitudinal investigations are necessary to clarify this association.
Objectives
Recent studies have suggested that evening blue light exposure is associated with sleep and circadian rhythm abnormalities. This study examined the effect of blue‐blocking (BB) glasses on sleep and circadian rhythm in patients with bipolar disorder (BD).
Methods
We used a randomized placebo‐controlled double‐blinded design. Outpatients with BD and also with insomnia were randomly assigned to wear either orange glasses (BB) or clear ones (placebo) and were instructed to use these from 20:00 hours until bedtime for 2 weeks. The primary outcome metric was the difference in change from baseline to after intervention in sleep quality, as measured by the visual analog scale (VAS).
Results
Forty‐three patients were included in this study (BB group, 21; placebo group, 22). The change in sleep quality as per the VAS metric was not significantly different between the two groups (95% confidence interval [CI], −3.34 to 24.72; P = 0.13). However, the Morningness–Eveningness Questionnaire score had shifted to an advanced rhythm in the BB group and to a delayed rhythm in the placebo group, and the difference in these changes was statistically significant (95% CI, 1.69 to 7.45; P = 0.003). The change in the actigraphy sleep parameters and mood symptoms were not significantly different between the two groups.
Conclusion
Although concurrent medications may have influenced, our results suggest that BB glasses may be useful as an adjunctive treatment for circadian rhythm issues in patients with BD.
Intellectual disability is a neurodevelopment disorder that affects the intellectual and adaptive functioning. The individual fails to meet standards of personal independence and social responsibility in one or more aspects of daily life, including communication, social participation, academic or occupational functioning, and personal independence at home or in community settings. There is an immense need to understand and be aware of the signs and symptoms of the disorder. This chapter focuses on the process of the assessment which is necessary to identify intellectual deficiency and also the issues that should be taken care of during the process. The various principles and tools of assessment, which can be used to measure IQ, are mentioned. It also focuses on the various challenging behaviors and functional analysis. It also focuses on recent and efficient management strategies that can be used to help the affected person cope and acquire new skills.
The relevance of altered rest-activity rhythm (RAR) and light exposure rhythm (LER) in insomnia patients under natural conditions remains unclear. The aim of this study was to compare the parametric and nonparametric circadian variables of RAR and those of LER under natural conditions between insomnia patients and normal controls (NC) in a community-dwelling setting. The relationship of the nonparametric variables with sleep quality was also explored in both groups. Participants above 18 years old were recruited from three Public Health Centers in a rural area of Korea. Actigraphy (Actiwatch 2; Philips Respironics, Murrysville PA, USA) recording was conducted for 7 days. Subjects were eligible for our study if they had an insomnia disorder (ID) for at least 1 month. Actigraphy data of 78 normal control (NC) subjects (Age, 55.95 ± 13.22 years) and 104 patients with insomnia disorder (ID) (Age, 62.14 ± 12.34 years) were included for the analysis. Acrophases and amplitudes of RAR and LER were estimated using cosinor analysis. Interdaily stability (IS), intradaily variability (IV), and relative amplitude (RA) of these rhythms were determined using nonparametric methods. Parametric cosinor and nonparametric variables of RAR and LER were compared between the NC and ID groups. Generalized linear models (GLMs) were applied to evaluate the main effects of group and each nonparametric variable as well as a group by each variable interaction on the sleep onset latency (SOL), sleep efficiency (SE), and wake after sleep onset (WASO) reflecting sleep quality. Among sleep parameters, the ID group showed significantly lower SE and greater WASO than the NC group. There were no significant differences in the acrophase and amplitude of RAR and LER between the two groups. There were no significant differences in IV, IS, and RA of RAR and LER between the two groups either. GLMs for RAR revealed a significant interaction between the group and IS on the SOL (β = −46.39, p < 0.01), indicating a negative relationship of the IS with SOL in ID unlike its positive relationship in NC. There were no significant main effects of IV on the SOL, SE, and WASO, but significant main effects of RA on the SE and WASO (β = 63.65 and β = −221.43, respectively, p < 0.01). GLMs for LER revealed no significant main effects of IS, IV or RA on the SOL, SE, and WASO, but significant interactions between group and RA on the SE and WASO (β = 56.17 and β = −171.93, respectively, p < 0.05), indicating a stronger positive relationship of the RA with SE in ID compared to NC, and a negative relationship of the RA with WASO in ID, unlike its positive relationship in NC. Although our study did not reveal group differences in circadian variables of RAR and LER, it suggested that the regularity of RAR could be positively associated with sleep initiation, while the robustness of LER could be positively associated with sleep maintenance in insomnia patients.
To elucidate the reward effects of light, two experimental approaches have been adopted. An experiment for the study of the effects of exposure to a winter-like photoperiod on the diurnal rodent Arvicanthis ansorgei indicated that shortened day length with reduced light intensity induces a phase change in locomotor activity, alterations in the dopamine content in reward system structures, and alterations in the Per2 clock gene expression in the suprachiasmatic nucleus. These measures were improved by daily exposure to a one-hour pulse of light at late in the day. In a human model, subjective wellbeing, measured by experience sampling, was correlated with ambient luminosity measurements in participants with insomnia and healthy controls. Results indicated that subjective wellbeing increases with increasing light intensity in healthy young volunteers, in contrast to an overall deficit in reward evaluation in insomniacs. Light exposure should be taken into account as an important factor in determining the quality of life of insomniacs and in depression. Further studies should be conducted to elucidate the effect of ambient light signals on reward circuits.
BACKGROUND:
Sleep disturbance in bipolar disorder (BD) is common and is associated with a risk for mood episode recurrence. Thus, it is important to identify factors that are related to sleep disturbance in BD. This cross-sectional study investigated the association between exposure to light at night (LAN) and sleep parameters in patients with BD.
METHODS:
The sleep parameters of 175 outpatients with BD were recorded using actigraphy at their homes for seven consecutive nights and were evaluated using the Insomnia Severity Index (ISI). The average LAN intensity in the bedroom during bedtime and rising time was measured using a portable photometer, and the participants were divided into two groups: "Light" (≥5 lx) and "Dark" (<5 lx). The association between LAN and sleep parameters was tested with multivariable analysis by adjusting for potential confounder such as age, gender, current smoker, mood state, day length, daytime light exposure, and sedative medications.
RESULTS:
After adjusting for potential confounder, the actigraphy sleep parameters showed significantly lower sleep efficiency (mean, 80.1%vs. 83.4%; p = 0.01), longer log-transformed sleep onset latency (2.9 vs. 2.6 min; p = 0.01), and greater wake after sleep onset (51.4 vs. 41.6 min; p = 0.02) in the Light group than in the Dark group. Whereas, there were no significant differences in the ISI scores between the groups.
LIMITATIONS:
This was a cross-sectional study; therefore, the results do not necessarily imply that LAN causes sleep disturbance.
CONCLUSIONS:
Reducing LAN exposure may contribute to improved sleep quality in patients with BD.
Extensive evidence in rats indicates that variations in the daily lighting environment lead to gradual changes in retinal structure and function and that these changes represent an adaptive process, termed photostasis, whereby the sensitivity of the retina is slowly altered to ensure the absorption of a constant number of photons per day—a process that may have evolved to allow adaptation to seasonal variations in daytime light intensity and duration.
These clinical guidelines were developed by the Standards of Practice Committee and reviewed and approved by the Board of Directors of the American Academy of Sleep Medicine. The guidelines provide recommendations for the practice of sleep medicine in North America regarding the use of light therapy for treatment of various sleep disorders. This paper is based on a series of articles in the Journal of Biological Rhythms and also includes evidence tables from an updated Medline review covering the period January 1994 to December 1997. Evidence is presented by grade and level. Recommendations are identified as standards, guidelines, or options. Recommendations are provided for delayed sleep phase syndrome (DSPS), advanced sleep phase syndrome (ASPS), non-24-hour sleep-wake syndrome, jet lag, shift work, dementia, and sleep complaints in the healthy elderly. Light therapy appears generally safe if used within recommended intensity and time limits. Light therapy can be useful in treatment of DSPS and ASPS. Benefits of light therapy are less dear and treatment is an option in jet lag, shift work, and non-24-hour sleep-wake syndrome in some blind patients.
Full-spectrum light, of sufficiently high intensity, will suppress the secretion of melatonin at night in humans. Individual sensitivity to such suppression is variable, and the factors determining such sensitivity are largely unknown. By analogy with animal work previous short or long-term exposure to different light intensities may be an important determinant. We exploited the Antarctic environment to investigate these possibilities. Groups of healthy men, living on the British Antarctic Survey Base at Halley (75 degrees South) were exposed to dim (range 290-310 lux) and bright (range 2100-2300 lux) light either from 01.00-02.00 h or 05.00-0.600 h, both in winter and in summer. Plasma melatonin concentrations were determined by radioimmunoassay in serial blood samples taken before, during and after light treatment, and in control (darkness) conditions. Light suppression of melatonin was more effective in the latter part of the night in winter and this was particularly well-differentiated for dim light.
Using 'classical' experimental protocols, a human phase-response curve (PRC) to a single 3-h bright light pulse has been established. When the light pulse was centred slightly before the time of body temperature minimum, the circadian system delayed, whilst a pulse slightly after the minimum advanced it. Maximum phase shifts were about 2 h. When light pulses over 3 successive cycles were used, larger shifts (4-7 h) were produced. It is concluded that the human PRC does not differ in principle from that found in other species, except with respect to the light intensity required.
This study tested the capacity of different irradiances of monochromatic light to reduce plasma melatonin in normal humans. Six healthy male volunteers, 24-34 years old, were exposed to 0.01, 0.3, 1.6, 5, or 13 microW/cm2 of 509 nm monochromatic light for 1 h during the night on separate occasions. Light irradiance depressed plasma melatonin in a dose-response pattern. The data indicate that the mean threshold irradiance for suppressing melatonin is between 1.6 and 5 microW/cm2. Individual variations in threshold responses to monochromatic light were observed among the volunteers.
Previous studies have shown that bright light (2500 lux) suppresses nocturnal secretion of melatonin, while dim light (500 lux) has little or no effect. We have studied the effect of varying intensities of light on 5 normal male volunteers (age 18-28). The experiment was divided into 3 parts which took place at weekly intervals. Subjects remained under artificial light (fluorescent strip 150-250 lux) between 2000 h-2300 h, they then retired to bed in darkness. On each occasion, between 0030 h and 0100 h, the subjects were required to get up and were treated with light of different intensities; (a) less than 1 lux, (b) 300 lux and (c) 2500 lux respectively. Subjects returned to bed in darkness until 0700 h. Blood was sampled hourly from 2000 h-1000 h with additional samples at 2330 h, 0015 h, 0030 h, 0045 h, 0115 h and 0130 h. Plasma melatonin and 6-sulphatoxymelatonin (aMT6s), the major melatonin metabolite, were measured by radioimmunoassay. Dim (300 lux) and bright (2500 lux) light, both significantly suppressed melatonin levels compared to less than 1 lux (P less than 0.05 and P less than 0.01 respectively) at the following time points 0100 h, 0115 h and 0130 h. One subject did not show suppression with 300 lux. There was also a significant suppression of aMT6s levels, compared to less than 1 lux, after both 300 lux and 2500 lux at 0115 h (P less than 0.05, P less than 0.01), 0130 h (P less than 0.01, P less than 0.01) and 0200 h (P less than 0.01, P less than 0.001) respectively.(ABSTRACT TRUNCATED AT 250 WORDS)
Bright light can suppress nighttime melatonin production in humans, but ordinary indoor light does not have this effect. This
finding suggested that bright light may have other chronobiologic effects in humans as well. Eight patients who regularly
became depressed in the winter (as day length shortens) significantly improved after 1 week of exposure to bright light in
the morning (but not after 1 week of bright light in the evening). The antidepressant response to morning light was accompanied
by an advance (shift to an earlier time) in the onset of nighttime melatonin production. These results suggest that timing
may be critical for the antidepressant effects of bright light.
Seasonal affective disorder (SAD) is a syndrome characterized by recurrent depressions that occur annually at the same time each year. We describe 29 patients with SAD; most of them had a bipolar affective disorder, especially bipolar II, and their depressions were generally characterized by hypersomnia, overeating, and carbohydrate craving and seemed to respond to changes in climate and latitude. Sleep recordings in nine depressed patients confirmed the presence of hypersomnia and showed increased sleep latency and reduced slow-wave (delta) sleep. Preliminary studies in 11 patients suggest that extending the photoperiod with bright artificial light has an antidepressant effect.
Bright artificial light suppressed nocturnal secretion of melatonin in six normal human subjects. Room light of less intensity,
which is sufficient to suppress melatonin secretion in other mammals, failed to do so in humans. In contrast to the results
of previous experiments in which ordinary room light was used, these findings establish that the human response to light is
qualitatively similar to that of other mammals.
The unhealthy symptoms and many deleterious consequences of shift work can be explained by a mismatch between the work-sleep schedule and the internal circadian rhythms. This mismatch occurs because the 24-h zeitgebers, such as the natural light-dark cycle, keep the circadian rhythms from phase shifting to align with the night-work, day-sleep schedule. This is a review of studies in which the sleep schedule is shifted several hours, as in shift work, and bright light is used to try to phase shift circadian rhythms. Phase shifts can be produced in laboratory studies, when subjects are kept indoors, and faster phase shifting occurs with appropriately timed bright light than with ordinary indoor (dim) light. Bright light field studies, in which subjects live at home, show that the use of artificial nocturnal bright light combined with enforced daytime dark (sleep) periods can phase shift circadian rhythms despite exposure to the conflicting 24-h zeitgebers. So far, the only studies on the use of bright light for real shift workers have been conducted at National Aeronautics and Space Administration (NASA). In general, the bright light studies support the idea that the control of light and dark can be used to overcome many of the problems of shift work. However, despite ongoing practical applications (such as at NASA), much basic research is still needed.
In a study of the quantitative relationship between ambient light and depression in winter seasonal affective disorder, 13 outpatients and 13 normal comparison subjects each wore a light monitor for 1 week. The patients and normal subjects showed similar light exposure profiles; among the patients, severity of depression was inversely related to photoperiod, and there was a trend toward a correlation between greater severity of depression and later time of onset of morning light exposure. These findings suggest that vulnerability to short photoperiods may be related to depression in winter seasonal affective disorder.
Light is a potent stimulus for regulating the pineal gland's production of melatonin and the broader circadian system in humans. It initially was thought that only very bright photic stimuli (> or = 2500 lux) could suppress nocturnal melatonin secretion and induce other circadian responses. It is now known that markedly lower illuminances (< or = 200 lux) can acutely suppress melatonin or entrain and phase shift melatonin rhythms when exposure conditions are optimized. The elements for physical/biological stimulus processing that regulate photic influences on melatonin secretion include the physics of the light source, gaze behavior relative to the light source, and the transduction of light energy through the pupil and ocular media. Elements for sensory/neural signal processing become involved as photons are absorbed by retinal photopigments and neural signals are generated in the retinohypothalamic tract. Aspects of this physiology include the ability of the circadian system to integrate photic stimuli spatially and temporally as well as the wavelength sensitivity of the operative photoreceptors. Acute, light-induced suppression of melatonin is proving to be a powerful tool for clarifying how these elements of ocular and neural physiology influence the interaction between light and the secretion of melatonin from the human pineal gland.
The circadian rhythms of night shift workers do not usually adjust to their unusual work and sleep schedules, reducing their quality of life and producing potentially dangerous health and safety problems. This paper reviews field studies of simulated night work in which shifted light-dark cycles were constructed with artificial bright or medium-intensity light to produce circadian adaptation, ie the shifting of circadian rhythms to align with night work and day sleep schedules. By using these studies we describe fundamental principles of human circadian rhythms relevant to producing circadian adaptation to night shift work at a level designed for the reader with only a basic knowledge of circadian rhythms. These principles should enable the reader to start designing work/sleep-light/dark schedules for producing circadian adaptation in night shift workers. One specific schedule is presented as an example. Finally, we discuss phase-response curves to light and clarify common misconceptions about the production of circadian rhythm phase shifts.
The annual decrease of daylight duration initiates a depressive phase in patients with seasonal affective disorder (SAD), and light therapy treats it. How much bright light exposure in winter and summer these patients actually receive may help understand the pathogenetic factors initiating SAD.
During a week in winter and summer, women with and without SAD kept daily logs of the time spent outdoors, subjective sleep, and self-ratings of mood and alertness.
Compared with the winter depressive state, mood, alertness, and sleep of SAD patients improved in summer to control values, but did not correlate with the amount of light exposure. In summer, patients with SAD spent more time outdoors than controls.
Light logs--in comparison with light monitor measurements--may overestimate light exposure outdoors.
Women with SAD do not spend less time outdoors in winter than controls, but spend more time outdoors in summer.
Patients with SAD show a high amplitude seasonal difference in outdoor light exposure. The susceptibility to winter depression may arise not from behaviourally-related lack of sufficient light exposure, but an increased vulnerability to the amount of light received. They may require more light than controls to remain euthymic (higher light exposure in summer, light therapy in winter).
The pineal hormone melatonin has some circadian regulatory effects and is assumed to have a close relation with sleep initiation and maintenance. Many previous reports have described age-related decreases in melatonin levels, especially in elderly insomniacs (EIs), which may act as causal or exacerbating factors in sleep disturbances in the elderly. Ten elderly residents with psychophysiological insomnia (mean age, 74.2 yr), 10 healthy residents of the same home [elderly control (EC) group; mean age, 72.7 yr], and 10 healthy young control subjects (mean age, 20.9 yr) living at home participated in this study. The elderly persons, especially the EIs, were exposed to significantly less environmental light and simultaneously suffered from significantly diminished nocturnal melatonin secretion. Supplementary exposure to 4 h (1000 to 1200 h, 1400 to 1600 h) of midday bright light in the EI group significantly increased melatonin secretion to levels similar to those in the young control group without circadian phase-shifting. There was a tendency for the magnitude of the increase in nocturnal melatonin secretion stimulated by bright light to parallel amelioration of sleep disturbances in these subjects. The present findings suggest that we need to pay attention to elderly individuals who suffer under conditions of poor environmental light resulting in disorganized circadian rhythms, including the sleep-wake cycle.
Several studies in the late seventies characterized insensitivity to light as a feature of human melatonin synthesis. Later it hàs shown that bright light does suppress human melatonin secretion (Lewy et al. 1980). More recently it has been reported that even lower illuminances decrease the nighttime melatonin levels in humans (e.g. Bojkowski et al. 1987, McIntyre et al. 1989a). Technical and experimental differences may serve as an explanation for the deviating results. It is also possible that interindividual differences of sensitivity obtained from small groups of subjects distort the results. In the present preliminary study we attempted to find such individual differences.
Studies examining levels of illumination in adult populations have demonstrated that the level and amount of light exposure are lower in the elderly compared with younger adults, particularly in institutionalized patients with dementia. Although insufficient light exposure has been implied as a cause of sleep fragmentation, evidence for such a relationship is scant. Sixty-six institutionalized elderly had their activity and light exposure monitored for a 3-day period. Mean and median light levels, minutes spent over 1000 and over 2000 lux, percent sleep and wake, and number of naps were computed for daytime intervals, defined as 07.00–18.59. Percentages of sleep and wake, number of awakenings and mean duration of wake periods were computed for night-time intervals, defined as 22.00–05.59. Mesor, amplitude and acrophase of activity and of light were determined by cosinor analysis. A mixed linear model was used to assess the effects of daytime Actillume measures on subsequent night-time measures, and vice versa. Spearman correlations were computed, and multiple regression analyses were carried out with light variables and dementia level as predictors and sleep–wake and activity measures as dependent variables. The median light level was 54 lux and a median of only 10.5 min were spent over 1000 lux. Higher light levels predicted fewer night-time awakenings, and severe dementia predicted more daytime sleep and lower mean activity. Increased bright light exposure predicted later activity acrophase. There was an association between the acrophases of light and of activity, with maximum illumination preceding peak activity. These results suggest that daytime light exposure has an impact on both night-time sleep consolidation and timing of peak activity level.
Oral temperature readings were taken from six groups of shift-workers (n = 133). The measurements covered a total of 387 days and included readings on a day off and on days of the 1st, 2nd, 4th,
5th and 7th nightshift. The shiftworkers were asked to record oral temperature every 2 h, at work and at leisure, using special
thermometers (1°C equals 4 cm). Some of them also interrupted their sleep for additional measurements.
On the first day of the night shift the normal circadian rhythm of body temperature was virtually unchanged in most of the
groups. However in two groups with a higher physical load during nightwork, an increased temperature was observed during the
night (“masking effect”). There were no significant differences between the temperature rhythms in experienced (≥ 15 years
of shiftwork) and inexperienced shiftworkers (≤ 1 year of shiftwork) within the first nightshift. During the period of consecutive
nightshifts no clear re-entrainment of body temperature was observed. Re-entrainment to nightwork appears to be slower in
field studies than in experimental shiftwork studies, which might be explained by the influence of unshifted social “Zeitgebers”
in real life.
Plasma melatonin levels were measured in male Japanese quail exposed to lighting schedules consisting of combinations of bright light (2000 or 1500 lx), darkness, or dim light (2 lx) or to constant dim light. Melatonin levels in dim light were dependent upon the relative intensity of accompanying phases, being significantly higher when dim light was subjective night than when it was subjective day. There was no significant melatonin rhythm in constant dim light, even on the first day of constant dim light exposure. Melatonin levels were intermediate when dim light was accompanied by both bright light and darkness. These results indicate that melatonin secretion in birds does not depend solely on light intensity. Furthermore, these results suggest that the avian circadian system may be more sensitive to environmental cues than its mammalian counterpart.
Twelve subjects with winter depression who lived in the Chicago area recorded their times of going outside during daylight hours for one week during the winter and one week during the summer. These records produced estimates of the duration of daily sunlight exposure and of perceived dawn, dusk and skeleton photoperiod. There was more than twice as much sunlight exposure in summer compared to winter (3.0 vs. 1.2 h/day). The perceived skeleton photoperiod was 4-5 h longer in summer than winter, with a later perceived dusk contributing more to the lengthening than an earlier perceived dawn. The duration of sunlight exposure and perceived skeleton photoperiod in both seasons was much less than what was possible given the available daylight. These results are discussed with reference to the modern urban life style, bright light treatment of winter seasonal affective disorder, and factors which affect the perceived intensity of sunlight.
The response of the human circadian pacemaker to light was measured in 45 resetting trials. Each trial consisted of an initial
endogenous circadian phase assessment, a three-cycle stimulus which included 5 hours of bright light per cycle, and a final
phase assessment. The stimulus induced strong (type 0) resetting, with responses highly dependent on the initial circadian
phase of light exposure. The magnitude and direction of the phase shifts were modulated by the timing of exposure to ordinary
room light, previously thought to be undetectable by the human pacemaker. The data indicate that the sensitivity of the human
circadian pacemaker to light is far greater than previously recognized and have important implications for the therapeutic
use of light in the management of disorders of circadian regulation.
Patterns of seasonal changes in mood and behavior in Montgomery County, Maryland, were evaluated in randomly selected household samples by lay interviewers using a telephone version of the Seasonal Pattern Assessment Questionnaire. The method for selecting the sample unit was random-digit dialing. We found that 92% of the survey subjects noticed seasonal changes of mood and behavior to varying degrees. For 27% of the sample seasonal changes were a problem and 4.3% to 10% of subjects, depending on the case-finding definition, rated a degree of seasonal impairment equivalent to that of patients with seasonal affective disorder. The seasonal pattern of "feeling worst" exhibited a bimodal distribution with a greater winter and a substantially lower summer peak (ratio, 4.5:1). Younger women who have a problem with seasonal changes and who feel worse on short days tended to exhibit the highest seasonality scores. It is apparent from our study that seasonal affective disorder represents the extreme end of the spectrum of seasonality that affects a large percentage of the general population. The influence of environmental factors on mood disorders and mood changes in the general population might provide valuable insight into pathogenesis, treatment, and prevention of affective illness.
Five intensities of artificial light were examined for the effect on nocturnal melatonin concentrations. Maximum suppression of melatonin following 1 hr of light at midnight was 71%, 67%, 44%, 38%, and 16% with intensities of 3,000, 1,000, 500, 350, and 200 lux (lx), respectively. In contrast to some previous reports, light of 1,000 lx intensity was sufficient to suppress melatonin to near daytime levels, and intensities down to 350 lx were shown to significantly suppress nocturnal melatonin levels below prelight values. On the basis of these data, it is suggested that when examining the melatonin sensitivity of patient groups (such as bipolar affective disorders) to artificial light, an appropriate light intensity should be established in each laboratory. Light of less intensity (e.g., 200-350 lx) may be more suitable to dichotomize patient groups from control subjects.
The results reviewed clearly demonstrate that shift work is associated with increased subjective, behavioral, and physiological sleepiness. Apparently, the effects are due to combined circadian and homeostatic (sleep loss) influences. Sleepiness is particularly pronounced during the night shift, and may terminate in actual incidents of falling asleep at work. In some occupations this clearly constitutes a hazard that may endanger human lives and have large economic consequences. These risks clearly involve a larger number of people and should be of great significance to society.
Exposure to light was recorded from 10 healthy elderly adults and 13 age-matched subjects with senile dementia of the Alzheimer's type (SDAT). Data were recorded in the home, for an average of 5 days, while subjects continued their normal daily activities. Subjects were exposed to remarkably small intervals of illumination exceeding 2000 lux. Subjects with SDAT were exposed to bright light significantly less than healthy controls (0.5 vs. 1.0 hr). Whether or not they had SDAT, males were exposed to illumination exceeding 2000 lux significantly more than were females. Healthy elderly received about two-thirds the duration of bright light received by healthy younger subjects. These findings suggest an association between decreased exposure to bright light and the declines in sleep quality which typically accompany normal and pathological aging.
Three experiments were conducted to determine whether dim light is interpreted by Japanese quail as subjective day or night, and whether this interpretation depends upon absolute light intensity. Birds were exposed to 24-h days consisting of either bright light (2500-3000 lx) with dim light (0.5-5 lx) or dim light with darkness. Locomotor activity was higher in the brighter photophase, whether it was bright light or dim light, indicating that the birds interpreted the brighter phase as daytime. Dim light produced daytime activity levels when paired with darkness, but it produced nighttime activity when paired with bright light, indicating that activity rhythms are determined by relative not absolute light intensity. Similarly, photostimulation, as measured by growth of the cloacal protrusion area (CPA), depended upon photic context, not absolute light intensity. CPA growth occurred when birds were exposed to 16 h of dim light with 8 h of darkness (16dm:8dk) but not when exposed to 10 h of bright light with 14 h of dim light (10bt:14dm). Constant dim light was stimulatory regardless of previous dim light context. Photostimulation appears to depend upon subjective interpretations of day and night rather than solely upon light intensity.
The hypothalamic suprachiasmatic nuclei (SCN) of mammals function as a pacemaker driving circadian rhythms. This pacemaker is entrained to the daily light-dark cycle in the environment via the retina and central retinal projections to the anterior hypothalamus. We carried out a comparative study of the visual properties of rat and hamster SCN neurons. Extracellular single cell activity was recorded in the SCN of urethane-anaesthetized animals. In both species, visual SCN neurons responded to retinal illumination with a sustained increase or a sustained decrease in electrical discharge. The majority (75%) of these cells were activated by light. In both the rat and the hamster SCN, visually responsive cells altered their discharge rate as a monotonic function of luminance. The intensity-response curve could be described by a Michaelis function with a small working range between threshold and saturation (2-3 log units) and a relatively high threshold. Intensity-response curves in both species were occasionally different for increasing as opposed to decreasing luminance. Thus, hysteresis effects of illumination may occur in the SCN. The spontaneous firing rates as well as the responsiveness of visual SCN cells were subject to marked variations between and within cells. The overall photic responsiveness of SCN neurons, however, indicated that they are specialized for luminance coding in the range of light intensities naturally occurring at dawn and dusk. This property makes these cells suitable to mediate photic entrainment of circadian rhythms as well as the measurement of photoperiod.
Bright light has a role in natural coordination of mammalian circadian and seasonal rhythms. In humans, the light intensity must probably exceed 2000 lux to be optimal. Natural light exposures of 10 healthy adults were measured over a 24-hour period, using forehead illumination transducers connected to a portable computer. The subjects varied markedly in duration and timing of exposures to light greater than 2000 lux. On average, the subjects experienced bright light for only 90 minutes per day, less than the 3-8 hours of bright light necessary to maximally synchronize human circadian rhythms. These results suggest that natural and artificial light exposure for many Americans may be suboptimal for circadian and seasonal synchronization.