Effects of artificial light at night on human health: A literature review of observational and experimental studies applied to exposure assessment

A photometric mapping of the night sky brightness of the Maltese islands

Over the years, the Maltese Islands have seen a marked rise in the prevalence of artificial lighting at night. The most evident type of light pollution arising from this evolution in anthropogenic night-time lighting is artificial skyglow via partial back-scattering in the atmosphere, leading to an increase in the Night Sky Brightness (NSB). The importance of understanding and quantifying the geographical distribution of the NSB is underscored by the adverse impact of light pollution on various spheres, from astronomical observation to ecology and human health. For the first time, we present a detailed map of the NSB over the Maltese archipelago carried out with Unihedron Sky Quality Meters. We show that the vast majority of the area of the Maltese Islands is heavily light polluted, with 87% of the area registering a NSB < 20.39mag_SQM/arcsec² (Bortle Class 5 or higher) and 37.3% < 19.09mag_SQM/arcsec² (Bortle Class 6 or higher), with the Milky Way being visible for only 12.8% of the area (adopting a visibility threshold > 20.4 - 21.29mag_SQM/arcsec²; Bortle Class 4). Coastal Dark Sky Heritage Areas on the island of Gozo retain generally darker skies than the rest of the islands, but light pollution originating further inland is encroaching upon and adversely affecting these sites. The methodology presented in this study can be adopted for continued future studies in Malta as well as for other regions.

How Much Lighting is Required to Feel Safe When Walking Through the Streets at Night?

Public space lighting (PSL) is indispensable after the natural dark. However, little is known about how much PSL people actually need to feel sufficiently safe in different real-world urban settings. The present study attempts to answer this question by employing a novel real-time interactive approach, according to which, observers use a specially-designed mobile phone application to assess and report the perceived attributes of street lighting and the feeling of safety (FoS) it generates. To validate the proposed approach, a systematic survey was conducted in three cities in Israel—Tel Aviv-Yafo and Haifa, which lie on the Mediterranean coast, and Be’er Sheba, which lies inland. Additionally, instrumental PSL measurements were performed at the same locations. As the study reveals, the necessary level of illumination required by urban residents to feel safe differs by city and is significantly higher in Be’er Sheba, other factors held equal, in compare to Haifa and Tel Aviv-Yafo. This difference may be attributed to stronger daylight that the residents of the desert city of Be’er Sheba are accustomed to, and, therefore, may prefer stronger nighttime illumination. The difference could also be related to the relatively low socio-economic status and somewhat higher crime rates in the latter city. Findings also show a significant and positive association between FoS and instrumentally measured PSL levels, although this association exhibits diminishing returns. To the best of our knowledge, the present study is the first to use an interactive location- and time-based mobile phone technology, which can potentially provide more accurate and reliable assessments, compared to traditional “pen and paper” survey techniques.

The Association of Ambient Air Pollution with Sleep Apnea: The Multi-Ethnic Study of Atherosclerosis

RATIONALE

Air pollution may influence sleep through airway inflammation or autonomic nervous system pathway alterations. Epidemiological studies may provide evidence of relationships between chronic air pollution exposure and sleep apnea.

OBJECTIVES

To determine whether ambient-derived pollution exposure is associated with obstructive sleep apnea and objective sleep disruption.

METHODS

We analyzed data from a sample of participants in MESA (Multi-Ethnic Study of Atherosclerosis) who participated in both the Sleep and Air studies. Mean annual and 5-year exposure levels to nitrogen dioxide (NO₂) and particulate matter ≤ 2.5 μm in aerodynamic diameter (PM_2.5) were estimated at participants' homes using spatiotemporal models based on cohort-specific monitoring. Participants completed in-home full polysomnography and 7 days of wrist actigraphy. We used multivariate models, adjusted for demographics, comorbidities, socioeconomic factors, and site, to assess whether air pollution was associated with sleep apnea (apnea-hypopnea index ≥ 15) and actigraphy-measured sleep efficiency.

RESULTS

The participants (n = 1,974) were an average age of 68 (±9) years, 46% male, 36% white, 24% Hispanic, 28% black, and 12% Asian; 48% had sleep apnea and 25% had a sleep efficiency of ≤88%. A 10 ppb annual increase in NO₂ exposure was associated with 39% greater adjusted odds of sleep apnea (95% confidence interval [CI], 1.03-1.87). A 5 μg/m³ greater annual PM_2.5 exposure was also associated with 60% greater odds of sleep apnea (95% CI, 0.98-2.62). Sleep efficiency was not associated with air pollution levels in fully adjusted models.

CONCLUSIONS

Individuals with higher annual NO₂ and PM_2.5 exposure levels had a greater odds of sleep apnea. These data suggest that in addition to individual risk factors, environmental factors also contribute to the variation of sleep disorders across groups, possibly contributing to health disparities.

Sleep Health: An Opportunity for Public Health to Address Health Equity

The concept of sleep health provides a positive holistic framing of multiple sleep characteristics, including sleep duration, continuity, timing, alertness, and satisfaction. Sleep health promotion is an underrecognized public health opportunity with implications for a wide range of critical health outcomes, including cardiovascular disease, obesity, mental health, and neurodegenerative disease. Using a socioecological framework, we describe interacting domains of individual, social, and contextual influences on sleep health. To the extent that these determinants of sleep health are modifiable, sleep and public health researchers may benefit from taking a multilevel approach for addressing disparities in sleep health. For example, in addition to providing individual-level sleep behavioral recommendations, health promotion interventions need to occur at multiple contextual levels (e.g., family, schools, workplaces, media, and policy). Because sleep health, a key indicator of overall health, is unevenly distributed across the population, we consider improving sleep health a necessary step toward achieving health equity.

Adherence and acceptability of light therapies to improve sleep in intrinsic circadian rhythm sleep disorders and neuropsychiatric illness: a systematic review

Sleep problems and circadian misalignment affect health and well-being and are highly prevalent in those with co-morbid neuropsychiatric disorders. Interventions altering light exposure patterns of affected individuals are a promising non-pharmacological treatment option, shown by previous meta-analyses to improve sleep, and often described as minimally invasive. To best translate laboratory-based mechanistic research into effective treatments, acceptability and barriers to adherence should be understood, but these have not yet been systematically evaluated. Here, we examined evidence regarding adherence and acceptability in studies of light or dark interventions using various delivery devices and protocols to improve sleep in intrinsic circadian rhythm sleep-wake disorders and neuropsychiatric illness. Attrition during intervention was low, and reported experiences were largely positive, but measurement and reporting of self-reported experiences, expectations, and adverse effects were poor. Approaches to management and measurement of adherence were varied, and available light monitoring technology appeared under-exploited, as did mobile technology to prompt or track adherence. Based on these findings we suggest recommended reporting items on acceptability and adherence for future investigations. Few studies assessed baseline light exposure patterns, and few personalised interventions. Overall, many applied studies exhibited an approach to light schedule interventions still reminiscent of laboratory protocols; this is unlikely to maximise acceptability and clinical effectiveness. For the next phase of translational research, user acceptability and adherence should receive increased attention during intervention design and study design. We suggest framing light therapies as complex interventions, and emphasise the occupationally embedded (daily activity routine embedded) context in which they occur.

Megacities, migration and an evolutionary approach to bipolar disorder: a study of Sardinian immigrants in Latin America

Objective:

To determine whether people with a Sardinian genetic background who live in the megacities of South America have a higher frequency of hypomania than residents of Sardinia.

Methods:

A community survey of Sardinian immigrants was carried out in four Brazilian metropoles (n=218) and Buenos Aires (n=306). The results were compared with those of a study involving a similar methodology (Mood Disorder Questionnaire [MDQ] as a screening tool) conducted in seven Italian regions, including a sub-sample from Sardinia.

Results:

There was a higher prevalence of lifetime hypomania among Sardinians living in the Brazilian metropoles than among those living in Sardinia. This result was also consistent with Sardinian immigrants in Buenos Aires. After stratification by sex and age, the lifetime prevalence of MDQ scores ≥ 8 among Sardinians in South-American megacities and Sardinia was 8.6% vs. 2.9%, respectively (p < 0.0001).

Conclusions:

The higher frequency of hypomania in migrant populations appears to favor an evolutionary view in which mood disorders may be a maladaptive aspect of a genetic background with adaptive characteristics.

A novel low-cost method for assessing intra-urban variation in night time light and applications to public health

Night time lighting (NTL) pollution is a public health concern given its known impact on a range of health outcomes. The daily cycle of the hue of natural ambient light shifting from relatively blue-white light at noon to relatively yellow-red light at sunset is important for human functioning. Disruptions of the circadian clock can result in melatonin suppression, sleep and mood disorders, and increased risks of cancer in adults. Current measures of intra-urban variation in NTL are based on costly in-person or coarse satellite image-based assessments. The central objective of the current study is to validate a novel low-cost measure of intra-urban NTL variation. Estimates of red, green and blue NTL intensity were derived from a cloud-free night time image of the city of Montreal, Canada, taken from the International Space Station (ISS). The new measures are shown to converge with in-person assessed NTL and to predict known child health-related outcomes. Specifically, the results suggest that ISS-assessed blue NTL is associated with feelings of safety and self-reported health. In conclusion, ISS-based measures of NTL, particularly of blue NTL, are valid indicators of intra-urban variation in NTL for applications in public health. Limitations of, and future directions for, the method are discussed.

Sleep Quality of Hospitalized Patients, Contributing Factors, and Prevalence of Associated Disorders

Background

Data in the literature has shown poor sleep quality to be frequently observed in hospitalized patients and known to be associated with poor treatment outcome. Many factors may impact poor sleep quality, and there is currently limited available data. We aim to determine the prevalence of poor sleep quality and associated factors in patients admitted to internal medicine wards as well as the change of sleep quality over time after admission.

Methods

An analytic observational study was conducted at the internal medicine wards at the King Chulalongkorn Memorial Hospital, Bangkok, Thailand. Patients were personally interviewed to evaluate the history of sleep quality at home, sleep quality after the first and the third days of admission, and potential associated factors. The Pittsburgh Sleep Quality Index and screening questionnaires for the common diseases associated with poor sleep quality were also utilized. The logistic regression analysis was used to determine the independent factors which led to poor sleep quality.

Results

Data were collected from 96 patients during the period of June 2015 to February 2016. The mean age of the patients was 50.8 ± 16.7 years, and 51% were male. Infectious disease was the most common principal diagnosis accounted for 29.2%. The results show high prevalence of poor sleep quality after the first night of admission compared to baseline sleep quality at home (50% vs. 18.8%; p < 0.001). After 3 days of admission, the prevalence of poor sleep quality was reduced to the level close to baseline sleep quality at home (28.1% vs. 18.8%; p = 0.13). Multivariate analysis demonstrated that light exposure and pain were the main independent factors for poor sleep quality on the first day (odds ratio 6.68; 95% CI 2.25-19.84) and on the third day (odds ratio 3.47; 95% CI 1.24-9.71), respectively.

Conclusions

This is the first study conducted on the sleep quality of hospitalized patients that included the follow-up period during hospital admission. Our study demonstrated high prevalence of poor sleep quality in hospitalized patients on the first day. Interestingly, the sleep quality was partly improved during hospitalization. Light exposure and pain were demonstrated to be the factors associated with poor sleep quality.

Environmental open-source data sets and sleep-wake rhythms of populations: an overview

OBJECTIVE/BACKGROUND

In recent decades, the epidemiology of sleep disorders has mainly consisted of interviewing subjects through validated questionnaires; more recently, this has been done by assessing total sleep time (TST) per 24 h via sleep logs or connected devices. Thus, a vast amount of data has helped demonstrate the decline of TST in most countries. Nonetheless, we believe from a societal and environmental point of view that sleep researchers have largely overlooked a wide-open field of data that may help us to better understand and describe global sleep wake rhythms (SWR), eg, data regarding the sleep environment.

METHODS

Based on recent literature, we identified several environmental and societal fields that may have an effect on SWR. With the help of an expert panel, we selected the five most pertinent fields with multiple open-source data sets that may have an impact on human SWR. Then, we performed web-based research and proposed open-field data sets for each field, all of which are open to researchers and possibly scientifically associated with SWR.

RESULTS

The open fields relevant to the environment that we selected were noise, light pollution, and radio frequencies. The two societal fields were transportation and internet use. The evolution of most of these fields in recent decades may explain (even partially) the decline in TST. Importantly, the open data sets in each field are widely available to sleep researchers.

CONCLUSIONS

SWR must be assessed not only by patient accounts, but also in terms of the evolution of environmental cues.

Perception of Sleep Disturbances due to Bedtime Use of Blue Light-Emitting Devices and Its Impact on Habits and Sleep Quality among Young Medical Students

Introduction

The use of blue light-emitting devices (smartphones, tablets, and laptops) at bedtime has negative effects on sleep due to light stimulation and/or problematic excessive use. We aimed to evaluate, among young medical students, if the perception of sleep disturbances due to bedtime use of these devices is consistent with healthier habits and a better sleep quality.

Materials and methods

294 medical students in medicine and pharmacy from the Faculty of Medicine and Pharmacy of Rabat, Morocco, took part in this anonymous and voluntary cross-sectional study and answered an electronic questionnaire. Student and Mann–Whitney U tests were used to compare variables between 2 groups based on their perception of sleep disturbances. The level of significance was p ≤ 0.05.

Results

286 students (97.3%) used a blue light-emitting smart device at bedtime before sleep, and sleep quality was poor (Pittsburgh Sleep Quality Index, PSQI > 5) in 101 students (35.3%). The perception of sleep disturbances due to this night usage was reported by 188 of them (65.7%). In this group, 154 (81.9%) used their device with all the lights turned off in the room (p=0.02), 34 (18.1%) put devices under pillows (p=0.04), 114 (60.6%) interrupted sleep to check messages (p < 0.001), and the mean duration use of these technologies at bedtime was 2 h ± 23 min per night (p=0.02). Also, the mean sleep duration was 6.3 hours ± 1.25 (p=0.04), 119 (63.3%) presented fatigue on waking more than one time per week (p=0.04), and 76 (40.4%) presented poor sleep quality (75.2% of the students with PSQI > 5) (p=0.005).

Conclusions

Despite the perception of sleep disturbances due to bedtime use of blue light-emitting devices, unhealthy sleep habits tend to be frequent in young medical students and worrying because it is associated to significant poor sleep quality.

Physical and Social Environment Relationship With Sleep Health and Disorders

Sleep health is a multidimensional construct that includes adequate duration, quality, and appropriately timed sleep that may be influenced by environmental factors. In this review, we focus on how an individual's living and sleeping environment, both the surrounding neighborhood physical and social features and the atmosphere around them, may impact their sleep health. We explore the associations of the physical environment (urban density, recreational facilities, green space, mixed land use, and healthy food stores), neighborhood deprivation (disadvantage and disorder), and the social environment (social cohesion, safety, and stigma) with sleep in both adult and pediatric populations. We investigate how physical and social environmental features may lead to alterations in the timing, duration, and quality of sleep and contribute to the most prevalent sleep disorders: insomnia, sleep apnea, and circadian rhythm disorders. We also review how ambient factors such as artificial light, environmental noise, and air pollution may contribute to sleep pathology. We have included key studies and recent emerging data regarding how the differential distribution of environmental factors that may affect sleep health may contribute to sleep health disparities.

Light Pollution, Circadian Photoreception, and Melatonin in Vertebrates

Artificial light at night (ALAN) is increasing exponentially worldwide, accelerated by the transition to new efficient lighting technologies. However, ALAN and resulting light pollution can cause unintended physiological consequences. In vertebrates, production of melatonin—the “hormone of darkness” and a key player in circadian regulation—can be suppressed by ALAN. In this paper, we provide an overview of research on melatonin and ALAN in vertebrates. We discuss how ALAN disrupts natural photic environments, its effect on melatonin and circadian rhythms, and different photoreceptor systems across vertebrate taxa. We then present the results of a systematic review in which we identified studies on melatonin under typical light-polluted conditions in fishes, amphibians, reptiles, birds, and mammals, including humans. Melatonin is suppressed by extremely low light intensities in many vertebrates, ranging from 0.01–0.03 lx for fishes and rodents to 6 lx for sensitive humans. Even lower, wavelength-dependent intensities are implied by some studies and require rigorous testing in ecological contexts. In many studies, melatonin suppression occurs at the minimum light levels tested, and, in better-studied groups, melatonin suppression is reported to occur at lower light levels. We identify major research gaps and conclude that, for most groups, crucial information is lacking. No studies were identified for amphibians and reptiles and long-term impacts of low-level ALAN exposure are unknown. Given the high sensitivity of vertebrate melatonin production to ALAN and the paucity of available information, it is crucial to research impacts of ALAN further in order to inform effective mitigation strategies for human health and the wellbeing and fitness of vertebrates in natural ecosystems.

The Sleep of Shelter Dogs Was Not Disrupted by Overnight Light Rather than Darkness in a Crossover Trial

Simple Summary

Dogs are often left unattended overnight in shelters. This has led shelter mangers to worry that the dogs were suffering from separation anxiety and, therefore, exhibiting stereotypic or repetitive behaviors such as pacing, barking or digging at exits. Mangers also worried that dogs exposed to light at night were not able to sleep or slept less because some areas of the shelter were lit for security reasons. The ten dogs in this study were walked twice daily and provided with many enrichment devices and music during the day. They were housed in individual rooms each with a window allowing visualization of the dog by the public and vice versa. The dogs slept 10.8 h/night when in darkness and 10.5 h/night when their pens were lightened; there was no significant difference. They exhibited no stereotypic behaviors. They slept in bouts of slightly less than an hour, arising after each bout to stand up and then lie down again. Apparently, these well-stimulated shelter dogs slept soundly in the absence of people.

Abstract

Dogs in shelters may be unattended at night. The purpose of this study is to describe the night-time behavior of dogs in a shelter and to determine if artificial light affected their sleeping patterns. Ten dogs were video-recorded under both light and dark conditions and their behavior recorded using focal animal sampling. The dogs were lying down 649 ± 40 min (mean ± SD) in the light condition and 629 ± 58 min in the dark condition each night. They awoke, stood up, turned around and then lay down again every 48 to 50 min. There was no significant difference in time spent lying between the two conditions (p > 0.05). Light did not seem to affect their behavior. The conclusion is that dogs in shelters may sleep in the absence of people and that light does not disrupt their sleep patterns.

Light exposure at night and sleep quality in bipolar disorder: The APPLE cohort study

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.

Diurnal rodents as pertinent animal models of human retinal physiology and pathology

This presentation will survey the retinal architecture, advantages, and limitations of several lesser-known rodent species that provide a useful diurnal complement to rats and mice. These diurnal rodents also possess unusually cone-rich photoreceptor mosaics that facilitate the study of cone cells and pathways. Species to be presented include principally the Sudanian Unstriped Grass Rat and Nile Rat (Arvicanthis spp.), the Fat Sand Rat (Psammomys obesus), the degu (Octodon degus) and the 13-lined ground squirrel (Ictidomys tridecemlineatus). The retina and optic nerve in several of these species demonstrate unusual resilience in the face of neuronal injury, itself an interesting phenomenon with potential translational value.

Day length predicts investment in human immune function: Shorter days yield greater investment

Winter is characterized by stressful conditions which compromise health and render animals more vulnerable to infection and illness than during other times of the year. Organisms are hypothesized to adapt to these seasonal stressors by increasing investment in immune function in response to diminished photoperiod duration. Here, we examined this hypothesis in a sample of healthy human participants. Using several functional immune assays in vitro, as well as by utilizing measures of in vivo proinflammatory cytokine levels, we predicted that shorter day length would be associated with greater investment in immunological function. Results revealed that shorter days predicted significant upregulation of several facets of immune function, including natural killer cell cytotoxicity, peripheral blood mononuclear cell proliferation (in response to, and in the absence of stimulation), and plasma levels of interleukin-6, as well as lower rates of Staphylococcus aureus growth in serum ex vivo. Further, consistent with the hypothesis that these trade-offs would be offset by decreased investment in mating effort, shorter day length also predicted lower levels of total testosterone in men. These results suggest that ambient photoperiod may be a powerful regulator of human immunological activity, providing some of the first evidence of seasonal changes in multiple facets of human immune function.

Chronic exposure to green light aggravates high-fat diet-induced obesity and metabolic disorders in male mice

Light is involved in many critical physiological or biochemical processes of human beings, such as visual sensing and the production of vitamin D. Recent studies have showed that the lights of different wavelengths have a profound influence in life activities. For example, blue light promotes alertness, whereas green light (GL) induces sleep in mice. On the other hand, metabolic homeostasis is regulated by a variety of factors, including dietary habits and light exposure. Our study aims to study whether certain wavelength of light would affect metabolic status of mice. Mice were divided into normal diet-fed group and high-fat diet (HFD)-fed group, and then exposed to various colors of the light. Physiological parameters, such as body weight, food intake and water drinking were regularly measured. Glucose tolerance test and pyruvate tolerance test were simultaneously performed. After mice were humanely sacrificed, liver histology and serologic analysis were performed for detecting lipid levels. We found that GL group showed obvious glucose intolerance and increased levels of serum and liver lipid contents compared to white light group. Meanwhile, the expression levels of lipid metabolism-related genes were almost down-regulated in liver. Furthermore, melatonin receptor-1b and thyroid hormone receptor-β expression levels were significantly lowered in liver of GL-treated obese mice, suggesting that these hormone pathways may mediate the changes of lipid metabolism. Our data indicate that GL has a detrimental effect on the energy metabolism and aggravates HFD-induced obesity in mice. In addition to malnutrition, the colors of the lights also have a profound influence in the metabolic homeostasis and should be taken into consideration in the therapy of metabolic disorders.

Applications of Satellite Remote Sensing of Nighttime Light Observations: Advances, Challenges, and Perspectives

Nighttime light observations from remote sensing provide us with a timely and spatially explicit measure of human activities, and therefore enable a host of applications such as tracking urbanization and socioeconomic dynamics, evaluating armed conflicts and disasters, investigating fisheries, assessing greenhouse gas emissions and energy use, and analyzing light pollution and health effects. The new and improved sensors, algorithms, and products for nighttime lights, in association with other Earth observations and ancillary data (e.g., geo-located big data), together offer great potential for a deep understanding of human activities and related environmental consequences in a changing world. This paper reviews the advances of nighttime light sensors and products and examines the contributions of nighttime light remote sensing to perceiving the changing world from two aspects (i.e., human activities and environmental changes). Based on the historical review of the advances in nighttime light remote sensing, we summarize the challenges in current nighttime light remote sensing research and propose four strategic directions, including: Improving nighttime light data; developing a long time series of consistent nighttime light data; integrating nighttime light observations with other data and knowledge; and promoting multidisciplinary and interdisciplinary analyses of nighttime light observations.

Sleep architecture is related to birth season in 1-month-old infants

Individual variation in sleep quality, quantity, and architecture is pronounced in small infants. Reasons for this remain largely unclear, even though environmental and genetic factors have been suggested to play a role. In order to study the effect of birth seasons on infant sleep architecture, 85 healthy 1-month-old infants underwent an overnight polysomnography (PSG). The PSGs were conducted in 2011-2013. The cohort was divided into four subgroups according to the amount of seasonal light at the time of birth, with each group covering a period of approximately three months. The groups were labeled IL (increasing light), L (light), ID (increasing darkness), and D (dark), corresponding to spring, summer, autumn, and winter, respectively. We found the amount of stage R sleep (precursor of REM sleep, formerly active sleep) to be the highest in infants born in summer, whereas infants born in winter presented the smallest amount of stage R sleep. Infants born in summer presented the smallest amount of stage T sleep (transitional sleep), while stage T sleep was most abundant in infants born in winter. In addition, infants born in summer showed the shortest total sleep time (TST) and the smallest number of awakenings during the study night. This was the first PSG study to find out that birth season modifies the sleep architecture of infants.

The preference and costs of sleeping under light at night in forest and urban great tits

Artificial light at night (ALAN) is an increasing phenomenon associated with worldwide urbanization. In birds, broad-spectrum white ALAN can have disruptive effects on activity patterns, metabolism, stress response and immune function. There has been growing research on whether the use of alternative light spectra can reduce these negative effects, but surprisingly, there has been no study to determine which light spectrum birds prefer. To test such a preference, we gave urban and forest great tits (Parus major) the choice where to roost using pairwise combinations of darkness, white light or green dim light at night (1.5 lux). Birds preferred to sleep under artificial light instead of darkness, and green was preferred over white light. In a subsequent experiment, we investigated the consequence of sleeping under a particular light condition, and measured birds' daily activity levels, daily energy expenditure (DEE), oxalic acid as a biomarker for sleep debt and cognitive abilities. White light affected activity patterns more than green light. Moreover, there was an origin-dependent response to spectral composition: in urban birds, the total daily activity and night activity did not differ between white and green light, while forest birds were more active under white than green light. We also found that individuals who slept under white and green light had higher DEE. However, there were no differences in oxalic acid levels or cognitive abilities between light treatments. Thus, we argue that in naive birds that had never encountered light at night, white light might disrupt circadian rhythms more than green light. However, it is possible that the negative effects of ALAN on sleep and cognition might be observed only under intensities higher than 1.5 lux. These results suggest that reducing the intensity of light pollution as well as tuning the spectrum towards long wavelengths may considerably reduce its impact.

Analysing the evolutional and functional differentiation of four types of Daphnia magna cryptochrome in Drosophila circadian clock

Cryptochrome (CRY) plays an important role in the input of circadian clocks in various species, but gene copies in each species are evolutionarily divergent. Type I CRYs function as a photoreceptor molecule in the central clock, whereas type II CRYs directly regulate the transcriptional activity of clock proteins. Functions of other types of animal CRYs in the molecular clock remain unknown. The water flea Daphnia magna contains four Cry genes. However, it is still difficult to analyse these four genes. In this study, we took advantage of powerful genetic resources available from Drosophila to investigate evolutionary and functional differentiation of CRY proteins between the two species. We report differences in subcellular localisation of each D. magna CRY protein when expressed in the Drosophila clock neuron. Circadian rhythm behavioural experiments revealed that D. magna CRYs are not functionally conserved in the Drosophila molecular clock. These findings provide a new perspective on the evolutionary conservation of CRY, as functions of the four D. magna CRY proteins have diverse subcellular localisation levels. Furthermore, molecular clocks of D. magna have been evolutionarily differentiated from those of Drosophila. This study highlights the extensive functional diversity existing among species in their complement of Cry genes.

Altered ocular parameters from circadian clock gene disruptions

The pathophysiology of refractive errors is poorly understood. Myopia (nearsightedness) in particular both blurs vision and predisposes the eye to many blinding diseases during adulthood. Based on past findings of diurnal variations in the dimensions of the eyes of humans and other vertebrates, altered diurnal rhythms of these ocular dimensions with experimentally induced myopia, and evolving evidence that ambient light exposures influence refractive development, we assessed whether disturbances in circadian signals might alter the refractive development of the eye. In mice, retinal-specific knockout of the clock gene Bmal1 induces myopia and elongates the vitreous chamber, the optical compartment separating the lens and the retina. These alterations simulate common ocular findings in clinical myopia. In Drosophila melanogaster, knockouts of the clock genes cycle or period lengthen the pseudocone, the optical component of the ommatidium that separates the facet lens from the photoreceptors. Disrupting circadian signaling thus alters optical development of the eye in widely separated species. We propose that mechanisms of myopia include circadian dysregulation, a frequent occurrence in modern societies where myopia also is both highly prevalent and increasing at alarming rates. Addressing circadian dysregulation may improve understanding of the pathogenesis of refractive errors and introduce novel therapeutic approaches to ameliorate myopia development in children.

Shedding Some Light in the Dark-A Comparison of Personal Measurements with Satellite-Based Estimates of Exposure to Light at Night among Children in the Netherlands

BACKGROUND

Exposure to light at night (LAN) can perturb the biological clock and affect sleep and health. Previous epidemiological studies have evaluated LAN levels measured by satellites, but the validity of this measure as a proxy for personal LAN exposure is unclear. In addition, outdoor satellite-measured LAN levels are higher in urban environments, which means that this measure could potentially represent a proxy for other, likely urban, environmental exposures.

OBJECTIVES

We evaluated correlations of satellite-assessed LAN with measured bedroom light levels and explored correlations with other environmental exposures, in particular, air pollution, green space, and area-level socioeconomic position (SEP).

METHODS

We compared satellite measurements with evening and nighttime bedroom measurements of illuminance (in units of lux) for 256 children, and we evaluated correlations between satellite-based measures and other urban exposures such as air pollution, area-level SEP, and surrounding green space for 3,021 children.

RESULTS

Satellite-measured LAN levels (nanowatts per centimeter squared per steradian) were not correlated with measured evening or nighttime lux levels [Spearman correlation coefficients ([Formula: see text]) [Formula: see text] to 0.04]. There was a weak correlation with measurements during the darkest time period if parents and their children reported that outdoor light sometimes or usually influenced indoor light levels ([Formula: see text], [Formula: see text]). In contrast, satellite-measured LAN levels were correlated with air pollution ([Formula: see text] with [Formula: see text], [Formula: see text] with [Formula: see text]), and surrounding green space ([Formula: see text] for green space within [Formula: see text] of the home). A weak correlation with area-level SEP was also observed ([Formula: see text]).

CONCLUSIONS

Outdoor satellite-assessed outdoor LAN exposure levels were correlated with urban environmental exposures, but they were not a good proxy for indoor evening or nighttime personal exposure as measured in our study population of 12-y-old children. Studies planning to evaluate potential risks from LAN should consider such modifying factors as curtains and indoor lighting and the use of electronic devices and should include performing indoor or personal measurements to validate any exposure proxies. The moderate-to-strong correlation of outdoor LAN with other environmental exposures should be accounted for in epidemiological investigations. https://doi.org/10.1289/EHP3431.

Exposure to artificial light at night increases innate immune activity during development in a precocial bird

Humans have greatly altered Earth's night-time photic environment via the production of artificial light at night (ALAN; e.g. street lights, car traffic, billboards, lit buildings). ALAN is a problem of growing importance because it may significantly disrupt the seasonal and daily physiological rhythms and behaviors of animals. There has been considerable interest in the impacts of ALAN on health of humans and other animals, but most of this work has centered on adults and we know comparatively little about effects on young animals. We exposed 3-week-old king quail (Excalfactoria chinensis) to a constant overnight blue-light regime for 6 weeks and assessed weekly bactericidal activity of plasma against Escherichia coli - a commonly employed metric of innate immunity in animals. We found that chronic ALAN exposure significantly increased bactericidal activity and that this elevation in immune performance manifested at different developmental time points in males and females. Whether this short-term increase in immune activity can be extended to wild animals, and whether ALAN-mediated increases in immune activity have positive or negative fitness effects, are unknown and will provide interesting avenues for future studies.

Artificial Light at Night of Different Spectral Compositions Differentially Affects Tumor Growth in Mice: Interaction With Melatonin and Epigenetic Pathways

Lighting technology is rapidly advancing toward shorter wavelength illuminations that offer energy-efficient properties. Along with this advantage, the increased use of such illuminations also poses some health challenges, particularly breast cancer progression. Here, we evaluated the effects of artificial light at night (ALAN) of 4 different spectral compositions (500-595 nm) at 350 Lux on melatonin suppression by measuring its urine metabolite 6-sulfatoxymelatonin, global DNA methylation, tumor growth, metastases formation, and urinary corticosterone levels in 4T1 breast cancer cell-inoculated female BALB/c mice. The results revealed an inverse dose-dependent relationship between wavelength and melatonin suppression. Short wavelength increased tumor growth, promoted lung metastases formation, and advanced DNA hypomethylation, while long wavelength lessened these effects. Melatonin treatment counteracted these effects and resulted in reduced cancer burden. The wavelength suppression threshold for melatonin-induced tumor growth was 500 nm. These results suggest that short wavelength increases cancer burden by inducing aberrant DNA methylation mediated by the suppression of melatonin. Additionally, melatonin suppression and global DNA methylation are suggested as promising biomarkers for early diagnosis and therapy of breast cancer. Finally, ALAN may manifest other physiological responses such as stress responses that may challenge the survival fitness of the animal under natural environments.

Working Time Society consensus statements: Evidence based interventions using light to improve circadian adaptation to working hours

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.

Sex and estrous cycle dependent changes in locomotor activity, anxiety and memory performance in aged mice after exposure of light at night

Light-at-night (LAN) can affect mammalian behaviour. But, the effects of LAN on aged rodents remain undefined yet. In the present investigation, aged Swiss Albino mice, habituated in regular light-dark cycle, were exposed to bright-light-pulse (1-h) at night on the day of study followed by experimentations for assessment of locomotor activities in the open field, anxiety in the elevated plus maze and short-term memory for novel object recognition (NOR) in the habituated field. Under without-bright-light exposure, (a) aged proestrous females showed greater locomotor activities and less anxiety than in aged diestrous females, (b) aged males showed locomotor activities and anxiety level similar to aged diestrous females and aged proestrous females respectively and (c) all animals failed to retain in object discrimination memory. LAN exposure exhibited the continual failure of such retention of memory while animals showed free and spontaneous exploration with thigmotactic behaviour having no object bias and/or phobia, but time stay in objects by animals altered variably among sexes and stages of estrous cycle. Overall, the LAN caused (a) diminution in locomotor activities, rise in anxiety and failure of memory for recognition of both familiar and novel objects in aged proestrous females, (b) hyperlocomotor activities and reduction in anxiety in both males and diestrous females with the failure of memory for recognition of novel objects only in aged males while diestrous females showed enhanced exploration time to both objects during NOR. Thus, nocturnal behaviour of aged mice varies with sex and estrous cycle and light acts differentially on them.

Using all-sky differential photometry to investigate how nocturnal clouds darken the night sky in rural areas

Artificial light at night has affected most of the natural nocturnal landscapes worldwide and the subsequent light pollution has diverse effects on flora, fauna and human well-being. To evaluate the environmental impacts of light pollution, it is crucial to understand both the natural and artificial components of light at night under all weather conditions. The night sky brightness for clear skies is relatively well understood and a reference point for a lower limit is defined. However, no such reference point exists for cloudy skies. While some studies have examined the brightening of the night sky by clouds in urban areas, the published data on the (natural) darkening by clouds is very sparse. Knowledge of reference points for the illumination of natural nocturnal environments however, is essential for experimental design and ecological modeling to assess the impacts of light pollution. Here we use differential all-sky photometry with a commercial digital camera to investigate how clouds darken sky brightness at two rural sites. The spatially resolved data enables us to identify and study the nearly unpolluted parts of the sky and to set an upper limit on ground illumination for overcast nights at sites without light pollution.

Observing the Impact of WWF Earth Hour on Urban Light Pollution: A Case Study in Berlin 2018 Using Differential Photometry

Earth Hour is one of the most successful coordinated mass efforts worldwide to raise awareness of environmental issues, with excessive energy consumption being one driver of climate change. The campaign, first organized by the World Wildlife Fund in Australia in 2007, has grown across borders and cultures and was celebrated in 188 countries in 2018. It calls for voluntarily reduction of electricity consumption for a single hour of one day each year. Switching off non-essential electric lights is a central theme and resulted in 17,900 landmarks going dark in 2018. This switch-off of lights during Earth Hour also leads to reduction of light pollution for this specific period. In principle, Earth Hour allows the study of light pollution and the linkage to electricity consumption of lighting. However, quantitative analysis of the impact of Earth Hour on light pollution (and electricity consumption) are sparse, with only a few studies published showing no clear impact or the reverse, suffering from residual twilight and unstable weather conditions. In this work, light pollution measurements during Earth Hour 2018 in an urban park (Tiergarten) in Berlin, Germany, are reported. A novel light measurement method using differential photometry with calibrated digital cameras enables tracking of the switching off and switching back on of the lights of Berlin’s iconic Brandenburg Gate and the buildings of Potsdamer Platz adjacent to the park. Light pollution reduction during the event was measurable, despite the presence of moonlight. Strategies for future work on light pollution using such events are discussed.

Use of Electroencephalography (EEG) for the Analysis of Emotional Perception and Fear to Nightscapes

As the necessity for safety and aesthetic of nightscape have arisen, the importance of nightscapes (i.e., nighttime landscape) planning has garnered the attention of mainstream consciousness. Therefore, this study was to suggest the guideline for nightscape planning using electroencephalography (EEG) technology and survey for recognizing the characteristics of a nightscape. Furthermore, we verified the electroencephalography (EEG) method as a tool for landscape evaluation. Therefore, this study analyzed the change of relative alpha wave and relative beta wave and perceived fear of participants depending on twelve nightscape settings (four types of settings: Built nightscape images group with an adult; Built nightscape images groups without an adult; Nature-dominant nightscape images with an adult; and Nature-dominant nightscape images without an adult). Our findings indicate that the most fearful nightscape setting was recorded in Built nightscape images groups without an adult figure in perceived fear result depending on four types of nightscape settings. In Nature-dominant nightscape images, on the other hand, the nightscape setting with an adult figure was more fearful than the setting without an adult. The interaction effect between landscape type (built and nature-dominant) and adult presence towards perceived fear was verified and it showed that the image with adult affects landscape type. For electroencephalography (EEG) results, several brain activities in the relative alpha and beta wave showed significant differences depending on nightscape settings, which situates electroencephalography (EEG) as an invaluable tool for evaluating landscapes. Based on our physiological electroencephalography (EEG) experiment, we provide a new analytic view of the nightscape. The approach we utilized enables a deeper understanding of emotional perception and fear among human subjects by identifying the physical environment which impacts how they experience nightscapes.

Fetal Programming of Renal Dysfunction and High Blood Pressure by Chronodisruption

Adverse prenatal conditions are known to impose significant trade-offs impinging on health and disease balance during adult life. Among several deleterious factors associated with complicated pregnancy, alteration of the gestational photoperiod remains largely unknown. Previously, we reported that prenatal manipulation of the photoperiod has adverse effects on the mother, fetus, and adult offspring; including cardiac hypertrophy. Here, we investigated whether chronic photoperiod shifting (CPS) during gestation may program adult renal function and blood pressure regulation. To this end, pregnant rats were subjected to CPS throughout pregnancy to evaluate the renal effects on the fetus and adult offspring. In the kidney at 18 days of gestation, both clock and clock-controlled gene expression did not display a daily pattern, although there were recurrent weaves of transcriptional activity along the 24 h in the control group. Using DNA microarray, significant differential expression was found for 1,703 transcripts in CPS relative to control fetal kidney (835 up-regulated and 868 down-regulated). Functional genomics assessment revealed alteration of diverse gene networks in the CPS fetal kidney, including regulation of transcription, aldosterone-regulated Na+ reabsorption and connective tissue differentiation. In adult offspring at 90 days of age, circulating proinflammatory cytokines IL-1β and IL-6 were increased under CPS conditions. In these individuals, CPS did not modify kidney clock gene expression but had effects on different genes with specific functions in the nephron. Next, we evaluated several renal markers and the response of blood pressure to 4%NaCl in the diet for 4 weeks (i.e., at 150 days of age). CPS animals displayed elevated systolic blood pressure in basal conditions that remained elevated in response to 4%NaCl, relative to control conditions. At this age, CPS modified the expression of Nhe3, Ncc, Atp1a1, Nr3c1 (glucocorticoid receptor), and Nr3c2 (mineralocorticoid receptor); while Nkcc, Col3A1, and Opn were modified in the CPS 4%+NaCl group. Furthermore, CPS decreased protein expression of Kallikrein and COX-2, both involved in sodium handling. In conclusion, gestational chronodisruption programs kidney dysfunction at different levels, conceivably underlying the prehypertensive phenotype observed in the adult CPS offspring.

Outdoor Artificial Nighttime Light and Use of Hypnotic Medications in Older Adults: A Population-Based Cohort Study

STUDY OBJECTIVES

Outdoor artificial nighttime light is increasingly recognized as a form of environmental pollution. Excessive nighttime light exposure, whether from indoor or outdoor sources, has been associated with a number of deleterious effects on human health. We performed a population-based cohort study in South Korea to assess the possible association between outdoor nocturnal lighting and insomnia in older adults, as measured by prescriptions for hypnotic drugs.

METHODS

This study used data from the 2002-2013 National Health Insurance Service-National Sample Cohort (NHIS-NSC), and a total of 52,027 adults who were age 60 years or older were included in the study. Light data were based on satellite mapping of artificial light. The usage data of two hypnotic drugs, zolpidem (N05CF02) and triazolam (N05CD05), were extracted from the NHIS-NSC records.

RESULTS

Of the 52,027 patients in this cohort, 11,738 (22%) had prescriptions for hypnotic drugs. Increasing outdoor artificial nighttime light exposure (stratified by quartile) was associated with an increased prevalence of hypnotic prescriptions and daily dose intake. Compared with individuals in the lowest quartile 1, the regression coefficients for prescription days and daily defined doses of all hypnotic drugs and certain hypotonic drugs were significantly higher among those living in areas with higher outdoor artificial nighttime light (quartiles 2 through 4).

CONCLUSIONS

Outdoor artificial nighttime light exposure was significantly associated with prescription of hypnotic drugs in older adults. These findings are consistent with the hypothesis that outdoor artificial nighttime light may cause sleep disturbances.

Cities and Mental Health

BACKGROUND

More than half of the global population currently lives in cities, with an increasing trend for further urbanization. Living in cities is associated with increased population density, traffic noise and pollution, but also with better access to health care and other commodities.

METHODS

This review is based on a selective literature search, providing an overview of the risk factors for mental illness in urban centers.

RESULTS

Studies have shown that the risk for serious mental illness is generally higher in cities compared to rural areas. Epidemiological studies have associated growing up and living in cities with a considerably higher risk for schizophrenia. However, correlation is not causation and living in poverty can both contribute to and result from impairments associated with poor mental health. Social isolation and discrimination as well as poverty in the neighborhood contribute to the mental health burden while little is known about specific interactions between such factors and the built environment.

CONCLUSION

Further insights on the interaction between spatial heterogeneity of neighborhood resources and socio-ecological factors is warranted and requires interdisciplinary research.

Ecology of the cardiovascular system: Part II - A focus on non-air related pollutants

An integrated exposomic view of the relation between environment and cardiovascular health should consider the effects of both air and non-air related environmental stressors. Cardiovascular impacts of ambient air temperature, indoor and outdoor air pollution were recently reviewed. We aim, in this second part, to address the cardiovascular effects of noise, food pollutants, radiation, and some other emerging environmental factors. Road traffic noise exposure is associated with increased risk of premature arteriosclerosis, coronary artery disease, and stroke. Numerous studies report an increased prevalence of hypertension in people exposed to noise, especially while sleeping. Sleep disturbances generated by nocturnal noise are followed by a neuroendocrine stress response. Some oxidative and inflammatory endothelial reactions are observed during experimental session of noise exposure. Moreover, throughout the alimentation, the cardiovascular system is exposed to persistent organic pollutants (POPs) as dioxins or pesticides, and plastic associated chemicals (PACs), such as bisphenol A. Epidemiological studies show positive associations of exposures to POPs and PACs with diabetes, arteriosclerosis and cardiovascular disease incidence. POPs and PACS share some abilities to interact with nuclear receptors activating different pathways leading to oxidative stress, insulin resistance and angiotensin potentiation. Regarding radiation, survivors of nuclear explosion have an excess risk of cardiovascular disease. Dose-effect relationships remain debated, but an increased cardiovascular risk at low dose of radiation exposure may be of concern. Some emerging environmental factors like electromagnetic fields, greenspace and light exposure may also require further attention. Non-air related environmental stressors also play an important role in the burden of cardiovascular disease. Specific methodologies should be developed to assess the interactions between air and non-air related pollutants.

Effects of Dietary and Lighting Conditions on Diurnal Locomotor Activity and Body Temperature in Microminipigs

The effects of dietary and lighting conditions on diurnal rhythm of locomotor activity (LA) and body temperature (BT) using four adult male microminipigs were investigated. Different feeding times, diet and lighting conditions were applied sequentially for 3 weeks in each phase as follows: Phase I: Morning mealtime, normal diet, 12-h lights on; phase II: mealtime changed to afternoon; phase III: diet changed to high-fat diet; phase IV: lighting changed to 20-h on; and phase V: phase I repeated. LA was measured by an actigraph which was worn on the body of each pig. A BT recording module (Thermochron Type-SL) was implanted in the neck subcutaneously. Phase II increased BT compared with phase I. Phase III increased LA and BT compared with phase II. Phase IV increased LA compared with phase III. LA in phase V was higher compared with phase I. These results can be extrapolated to other diurnal animals such as humans. This study provides an example of the effects of diet and lighting on biological activities in microminipigs under low-invasive procedures measuring LA and BT, leading to low variations in these measures.

Impacts of artificial light at night on sleep: A review and prospectus

Natural cycles of light and darkness govern the timing of most aspects of animal behavior and physiology. Artificial light at night (ALAN)-a recent and pervasive form of pollution-can mask natural photoperiodic cues and interfere with biological rhythms. One such rhythm vulnerable to perturbation is the sleep-wake cycle. ALAN may greatly influence sleep in humans and wildlife, particularly in animals that sleep predominantly at night. There has been some recent evidence for impacts of ALAN on sleep, but critical questions remain. Some of these can be addressed by adopting approaches already entrenched in sleep research. In this paper, we review the current evidence for impacts of ALAN on sleep, highlight gaps in our understanding, and suggest opportunities for future research.

Environmental Determinants of Insufficient Sleep and Sleep Disorders: Implications for Population Health

PURPOSE OF REVIEW

Sleep is important for overall health and well-being. Insufficient sleep and sleep disorders are highly prevalent among adults and children and therefore a public health burden, particularly because poor sleep is associated with adverse health outcomes. Emerging evidence has demonstrated that environmental factors at the household- and neighborhood-level can alter healthy sleep. This paper will (1) review recent literature on the environmental determinants of sleep among adults as well as children and adolescents; and (2) discuss the opportunities and challenges for advancing research on the environment and sleep.

RECENT FINDINGS

Epidemiologic research has shown that social features of environments, family, social cohesion, safety, noise, and neighborhood disorder can shape and/or impact sleep patterns; and physical features such as light, noise, traffic, pollution, and walkability can also influence sleep and is related to sleep disorders among adults and children. Prior research has mainly measured one aspect of the environment, relied on self-reported sleep, which does not correlate well with objective measures, and investigated cross-sectional associations. Although most studies are conducted among non-Hispanic white populations, there is growing evidence that indicates that minority populations are particularly vulnerable to the effects of the environment on insufficient sleep and sleep disorders.

SUMMARY

There is clear evidence that environmental factors are associated with insufficient sleep and sleep disorders. However, more research is warranted to evaluate how and which environmental factors contribute to sleep health. Interventions that target changes in the environment to promote healthy sleep should be developed, tested, and evaluated as a possible pathway for ameliorating sleep health disparities and subsequently health disparities.

Circadian rhythms, refractive development, and myopia

PURPOSE

Despite extensive research, mechanisms regulating postnatal eye growth and those responsible for ametropias are poorly understood. With the marked recent increases in myopia prevalence, robust and biologically-based clinical therapies to normalize refractive development in childhood are needed. Here, we review classic and contemporary literature about how circadian biology might provide clues to develop a framework to improve the understanding of myopia etiology, and possibly lead to rational approaches to ameliorate refractive errors developing in children.

RECENT FINDINGS

Increasing evidence implicates diurnal and circadian rhythms in eye growth and refractive error development. In both humans and animals, ocular length and other anatomical and physiological features of the eye undergo diurnal oscillations. Systemically, such rhythms are primarily generated by the 'master clock' in the surpachiasmatic nucleus, which receives input from the intrinsically photosensitive retinal ganglion cells (ipRGCs) through the activation of the photopigment melanopsin. The retina also has an endogenous circadian clock. In laboratory animals developing experimental myopia, oscillations of ocular parameters are perturbed. Retinal signaling is now believed to influence refractive development; dopamine, an important neurotransmitter found in the retina, not only entrains intrinsic retinal rhythms to the light:dark cycle, but it also modulates refractive development. Circadian clocks comprise a transcription/translation feedback control mechanism utilizing so-called clock genes that have now been associated with experimental ametropias. Contemporary clinical research is also reviving ideas first proposed in the nineteenth century that light exposures might impact refraction in children. As a result, properties of ambient lighting are being investigated in refractive development. In other areas of medical science, circadian dysregulation is now thought to impact many non-ocular disorders, likely because the patterns of modern artificial lighting exert adverse physiological effects on circadian pacemakers. How, or if, such modern light exposures and circadian dysregulation contribute to refractive development is not known.

SUMMARY

The premise of this review is that circadian biology could be a productive area worthy of increased investigation, which might lead to the improved understanding of refractive development and improved therapeutic interventions.

Constant light during lactation programs circadian and metabolic systems

Exposure to light at night is a disruptive condition for the adult circadian system, leading to arrhythmicity in nocturnal rodents. Circadian disruption is a risk factor for developing physiological and behavioral alterations, including weight gain and metabolic disease. During early stages of development, the circadian system undergoes a critical period of adjustment, and it is especially vulnerable to altered lighting conditions that may program its function, leading to long-term effects. We hypothesized that during lactation a disrupted light-dark cycle due to light at night may disrupt the circadian system and in the long term induce metabolic disorders. Here we explored in pups, short- and long-term effects of constant light (LL) during lactation. In the short term, LL caused a loss of rhythmicity and a reduction in the immunopositive cells of VIP, AVP, and PER1 in the suprachiasmatic nucleus (SCN). In the short term, the affection on the circadian clock in the pups resulted in body weight gain, loss of daily rhythms in general activity, plasma glucose and triglycerides (TG). Importantly, the DD conditions during development also induced altered daily rhythms in general activity and in the SCN. Exposure to LD conditions after lactation did not restore rhythmicity in the SCN, and the number of immunopositve cells to VIP, AVP, and PER1 remained reduced. In the long term, daily rhythmicity in general activity was restored; however, daily rhythms in glucose and TG remained disrupted, and daily mean levels of TG were significantly increased. Present results point out the programming role played by the LD cycle during early development in the function of the circadian system and on metabolism. This study points out the risk represented by exposure to an altered light-dark cycle during early stages of development.

ABBREVIATIONS

AVP: arginine vasopressin peptide; CRY: cryptochrome; DD: constant darkness; DM: dorsomedial; LD: light-dark cycle; LL: constant light; NICUs: neonatal intensive care units; P: postnatal days; PER: period; S.E.M.: standard error of the mean; SCN: suprachiasmatic nucleus; TG: triglycerides; VIP: vasointestinal peptide; VL: ventrolateral; ZT: zeitgeber time.

The Value of Darkness: A Moral Framework for Urban Nighttime Lighting

The adverse effects of artificial nighttime lighting, known as light pollution, are emerging as an important environmental issue. To address these effects, current scientific research focuses mainly on identifying what is bad or undesirable about certain types and uses of lighting at night. This paper adopts a value-sensitive approach, focusing instead on what is good about darkness at night. In doing so, it offers a first comprehensive analysis of the environmental value of darkness at night from within applied ethics. A design for values orientation is utilized to conceptualize, define, and categorize the ways in which value is derived from darkness. Nine values are identified and categorized via their type of good, temporal outlook, and spatial characteristics. Furthermore, these nine values are translated into prima facie moral obligations that should be incorporated into future design choices, policy-making, and innovations to nighttime lighting. Thus, the value of darkness is analyzed with the practical goal of informing future decision-making about urban nighttime lighting.

Invited Commentary: "Bedroom Light Exposure at Night and the Incidence of Depressive Symptoms: A Longitudinal Study of the HEIJO-KYO Cohort"

In modern society, we are increasingly disconnected from natural light/dark cycles and beset by round-the-clock exposure to artificial light. Light has powerful effects on physical and mental health, in part via the circadian system, and thus the timing of light exposure dictates whether it is helpful or harmful. In their compelling paper, Obayashi et al. (Am J Epidemiol. 2018;187(3):427-434.) offer evidence that light at night can prospectively predict an elevated incidence of depressive symptoms in older adults. Strengths of the study include the longitudinal design and direct, objective assessment of light levels, as well as accounting for multiple plausible confounders during analyses. Follow-up studies should address the study's limitations, including reliance on a global self-report of sleep quality and a 2-night assessment of light exposure that may not reliably represent typical light exposure. In addition, experimental studies including physiological circadian measures will be necessary to determine whether the light effects on depression are mediated through the circadian system or are so-called "direct" effects of light. In any case, these exciting findings could inform novel approaches to preventing depressive disorders in older adults.

Coping with the New Era: Noise and Light Pollution, Hperactivity and Steroid Hormones. Towards an Evolutionary View of Bipolar Disorders

Human population is increasing in immense cities with millions of inhabitants, in which life is expected to run 24 hours a day for seven days a week (24/7). Noise and light pollution are the most reported consequences, with a profound impact on sleep patterns and circadian biorhythms. Disruption of sleep and biorhythms has severe consequences on many metabolic pathways. Suppression of melatonin incretion at night and the subsequent effect on DNA methylation may increase the risk of prostate and breast cancer. A negative impact of light pollution on neurosteroids may also affect mood. People who carry the genetic risk of bipolar disorder may be at greater risk of full-blown bipolar disorder because of the impact of noise and light pollution on sleep patterns and circadian biorhythms. However, living in cities may also offers opportunities and might be selective for people with hyperthymic temperament, who may find themselves advantaged by increased energy prompted by increased stimulation produced by life in big cities. This might result in the spreading of the genetic risk of bipolar disorder in the coming decades. In this perspective the burden of poor quality of life, increased disability adjusted life years and premature mortality due to the increases of mood disorders is the negative side of a phenomenon that in its globality also shows adaptive aspects. The new lifestyle also influences those who adapt and show behaviors, reactions and responses that might resemble the disorder, but are on the adaptive side.

Outdoor light at night and the prevalence of depressive symptoms and suicidal behaviors: A cross-sectional study in a nationally representative sample of Korean adults

BACKGROUND

Outdoor light at night (LAN) is an increasingly prevalent type of environmental pollution. Studies have demonstrated that outdoor LAN can disrupt circadian rhythms, potentially contributing to insomnia, cancer, cardiovascular disease, and metabolic changes in humans. We investigated the association of outdoor LAN with depressive symptoms and suicidal behaviors in South Korean adults.

METHODS

This study used data from the 2009 Korean Community Health Survey, a representative sample dataset. Study population consisted of 113,119 participants for the assessment of depressive symptoms and 152,159 participants for the assessment of suicidal behavior. Depressive symptoms were measured using the Korean version of the Center for Epidemiologic Studies Depression Scale (depressive symptoms, score of > 16). Suicidal behaviors were defined as the experience of suicidal ideation or attempt. Outdoor LAN was estimated by satellite data from the National Centers for Environmental Information.

RESULTS

Participants with depressive symptoms or history of suicidal behaviors were more likely to have exposure to outdoor LAN than those without depressive symptoms or suicidal behaviors. Compared with adults living in areas exposed to the lowest outdoor LAN, those living in areas exposed to the highest levels had higher likelihood depressive symptoms (OR = 1.29; 95% CI: 1.15-1.46) or suicidal behaviors (OR = 1.27; 95% CI: 1.16-1.39). Significant dose-response relationships were observed between outdoor LAN and the odds of depressive symptoms and suicidal behaviors.

CONCLUSION

Outdoor LAN was found to be significantly associated with depressive symptoms and suicidal behaviors, suggesting that it may be an environmental contributor to mental health problems.

Influence of artificially induced light pollution on the hormone system of two common fish species, perch and roach, in a rural habitat

Almost all life on earth has adapted to natural cycles of light and dark by evolving circadian and circannual rhythms to synchronize behavioural and physiological processes with the environment. Artificial light at night (ALAN) is suspected to interfere with these rhythms. In this study we examined the influence of ALAN on nocturnal melatonin and sex steroid blood concentrations and mRNA expression of gonadotropins in the pituitary of European perch (Perca fluviatilis) and roach (Rutilus rutilus). In a rural experimental setting, fish were held in net cages in drainage channels experiencing either additional ALAN of ~15 lx at the water surface or natural light conditions at half-moon. No differences in melatonin concentrations between ALAN and natural conditions were detected. However, blood concentration of sex steroids (17β-estradiol; 11-ketotestosterone) as well as mRNA expression of gonadotropins (luteinizing hormone, follicle stimulating hormone) was reduced in both fish species. We conclude that ALAN can disturb biological rhythms in fish in urban waters. However, impacts on melatonin rhythm might have been blurred by individual differences, sampling methods and moonlight. The effect of ALAN on biomarkers of reproduction suggests a photo-labile period around the onset of gonadogenesis, including the experimental period (August). Light pollution therefore has a great potential to influence crucial life history traits with unpredictable outcome for fish population dynamics.