Exposure to light at night and risk of depression in the elderly

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

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

The association between outdoor artificial light at night exposure and antenatal depression and anxiety symptoms: A retrospective cohort study in China

BACKGROUND

Outdoor artificial light at night (ALAN) has emerged as a significant source of environmental pollution, however its association with antenatal depression and anxiety symptoms has been rarely explored before.

METHODS

This study was based on a cohort study conducted at the Maternal and Child Health Care Center in Ma'anshan City, Anhui Province, China, which ultimately included 1047 pregnant women. Depression and anxiety symptoms were evaluated utilizing the self-administered Patient Health Questionnaire (PHQ-9) and the 7-item Generalized Anxiety Scale (GAD-7), respectively. Exposure levels to outdoor ALAN were calculated utilizing satellite data and the participants' usual addresses. Logistic regression and restricted cubic spline were used to assess the association between exposure to outdoor ALAN and depression and anxiety symptoms in pregnant women.

RESULTS

After adjusting for confounding factors, high ALAN exposure during the pre-pregnancy period (ORdepression = 3.16, 95% CI: 1.14-8.75; ORanxiety = 3.09, 95% CI: 1.51-6.28) and first trimester (ORdepression = 2.90, 95% CI: 1.13-7.45; ORanxiety = 3.11, 95% CI: 1.55-6.25) were associated with increased risks of antenatal depression and anxiety symptoms. Restricted cubic spline analyses showed the above associations were not nonlinear.

CONCLUSION

Our study is the first to propose that exposure to high levels of outdoor ALAN three months before pregnancy and during the first trimester of pregnancy is a risk factor for antenatal depression and anxiety symptoms.

Lactic acid contributes to the emergence of depression-like behaviors triggered by blue light exposure during sleep

The threat posed by light pollution to human health is increasing remarkably. As demand for high-efficiency and bright lighting increases, so does the blue light content from artificial sources. Although animal studies suggested blue light induced depression-like behaviors, human evidence remained limited, and the mechanisms by which blue light affects depression remained elusive. This study aimed to investigate the association between blue light exposure and depression in humans, and explored the underlying mechanisms that driving depression-like behaviors induced by blue light. Our population findings showed that the high-blue-light exposure at night was positively associated with depressive symptoms. Lactic acid was relevant to depression with Mendelian randomization analysis. Moreover, animal studies demonstrated that exposure to blue light during sleep (BLS) induced depression-like behaviors in the animals. Metabolomics and colorimetric analyses revealed elevated levels of lactic acid in the cerebrospinal fluid and lateral habenula (LHb) of rats with depression-like behaviors induced by BLS. The administration of a lactate inhibitor (Oxamate) alleviated these behaviors, along with changes in neuronal excitability, synaptic function, and morphology in the LHb. Overall, our study suggests that excessive exposure to high blue light-content artificial light at night links to increased depressive symptoms, revealing possible molecular mechanisms and prevention strategies, which are crucial for addressing environmentally related mental health issues.

Stress and the domestic cat: have humans accidentally created an animal mimic of neurodegeneration?

Many neurodegenerative diseases (NDD) appear to share commonality of origin, chronic ER stress. The endoplasmic reticulum (ER) is a dynamic organelle, functioning as a major site of protein synthesis and protein posttranslational modifications, required for proper folding. ER stress can occur because of external stimuli, such as oxidative stress or neuroinflammatory cytokines, creating the ER luminal environment permissive for the accumulation of aggregated and misfolded proteins. Unresolvable ER stress upregulates a highly conserved pathway, the unfolded protein response (UPR). Maladaptive chronic activation of UPR components leads to apoptotic neuronal death. In addition to other factors, physiological responses to stressors are emerging as a significant risk factor in the etiology and pathogenesis of NDD. Owned cats share a common environment with people, being exposed to many of the same stressors as people and additional pressures due to their "quasi" domesticated status. Feline Cognitive Dysfunction Syndrome (fCDS) presents many of the same disease hallmarks as human NDD. The prevalence of fCDS is rapidly increasing as more people welcome cats as companions. Barely recognized 20 years ago, veterinarians and scientists are in infancy stages in understanding what is a very complex disease. This review will describe how cats may represent an unexplored animal mimetic phenotype for human NDD with stressors as potential triggering mechanisms. We will consider how multiple variations of stressful events over the short-life span of a cat could affect neuronal loss or glial dysfunction and ultimately tip the balance towards dementia.

Lights at night mediate depression-like behavioral and molecular phenotypes in a glucocorticoid-dependent manner in male rats

Nocturnal light pollution, an underappreciated mood manipulator, disturbs the circadian rhythms of individuals in modern society. Preclinical and clinical studies have suggested that exposure to lights at night (LANs) results in depression-like phenotypes. However, the mechanism underlying the action of LANs remains unclear. Therefore, this study explored the potential influence of LANs on depression-related brain regions by testing brain-derived neurotrophic factor (BDNF), synaptic transmission, and plasticity in male Sprague-Dawley rats. Depression-related behavioral tests, enzyme-linked immunosorbent assays, and intracellular and extracellular electrophysiological recordings were performed. Resultantly, rats exposed to either white or blue LAN for 5 or 21 days exhibited depression-like behaviors. Both white and blue LANs reduced BDNF expression in the medial prefrontal cortex (mPFC) and ventrolateral periaqueductal gray (vlPAG). Moreover, both lights at night (LANs) elevated the plasma corticosterone levels. Pharmacologically, the activation of glucocorticoid receptors mimics the LAN-mediated effects on depression-like behaviors and reduces BDNF levels, whereas the inhibition of glucocorticoid receptors blocks LAN-mediated behavioral and molecular actions. Electrophysiologically, both LANs attenuated the stimulation-response curve, increased the paired-pulse ratio, and decreased the frequency and amplitude of miniature excitatory postsynaptic currents in the vlPAG. In the mPFC, LANs attenuate long-term potentiation and long-term depression. Collectively, these results suggested that white and blue LANs disturbed BDNF expression, synaptic transmission, and plasticity in the vlPAG and mPFC in a glucocorticoid-dependent manner. The results of the present study provide a theoretical basis for understanding the effects of nocturnal light exposure on depression-like phenotypes.

Subjective evaluation of home environment and levels of self-reported depression in middle to old age: Results from the HCHS study

OBJECTIVES

The immediate living environment might, like other lifestyle factors, be significantly related to mental well-being. The current study addresses the question whether five relevant subjective home environment variables (i.e., protection from disturbing nightlight, daylight entering the home, safety at home, quality of window views, and noise disturbance) are associated with levels of self-reported depression over and above well-known sociodemographic and common lifestyle variables.

METHODS

Data from the Hamburg City Health Study (HCHS) were analyzed. In N = 8757 with available PHQ-9 depression data, multiple linear regression models were computed, with demographic data, lifestyle variables, and variables describing the subjective evaluation of the home environment.

RESULTS

The model explained 15% of variance in depression levels, with ratings for the subjective evaluation of home environment accounting for 6%. Better protection from disturbing light at night, more daylight entering the home, feeling safer, and perceived quality of the window views, were all significantly associated with lower, while more annoyance by noise was associated with higher levels of self-reported depression. Results did not differ if examining a sample of the youngest (middle-aged participants: 46-50 years) versus oldest (70-78 years) participants within HCHS.

CONCLUSION

Beyond studying the role of lifestyle factors related to self-reported depression, people's homes may be important for subclinical levels of depression in middle and older age, albeit the direction of effects or causality cannot be inferred from the present study. The development of a consensus and tools for a standardized home environment assessment is needed.

Light at night and lung cancer risk: A worldwide interdisciplinary and time-series study

Background

Light at night (LAN) has become a concern in interdisciplinary research in recent years. This global interdisciplinary study aimed to explore the exposure-lag-response association between LAN exposure and lung cancer incidence.

Methods

LAN data were obtained from the Defense Meteorological Satellite Program's Operational Linescan System. Data of lung cancer incidence, socio-demographic index, and smoking prevalence of populations in 201 countries/territories from 1992 to 2018 were collected from the Global Burden of Disease Study. Spearman correlation tests and population-weighted linear regression analysis were used to evaluate the correlation between LAN exposure and lung cancer incidence. A distributed lag nonlinear model (DLNM) was used to assess the exposure-lag effects of LAN exposure on lung cancer incidence.

Results

The Spearman correlation coefficients were 0.286-0.355 and the population-weighted linear regression correlation coefficients were 0.361-0.527. After adjustment for socio-demographic index and smoking prevalence, the Spearman correlation coefficients were 0.264-0.357 and the population-weighted linear regression correlation coefficients were 0.346-0.497. In the DLNM, the maximum relative risk was 1.04 (1.02-1.06) at LAN exposure of 8.6 with a 2.6-year lag time. After adjustment for socio-demographic index and smoking prevalence, the maximum relative risk was 1.05 (1.02-1.07) at LAN exposure of 8.6 with a 2.4-year lag time.

Conclusion

High LAN exposure was associated with increased lung cancer incidence, and this effect had a specific lag period. Compared with traditional individual-level studies, this group-level study provides a novel paradigm of effective, efficient, and scalable screening for risk factors.

Blue light at night produces stress-evoked heightened aggression by enhancing brain-derived neurotrophic factor in the basolateral amygdala

Light is an underappreciated mood manipulator. People are often exposed to electronic equipment, which results in nocturnal blue light exposure in modern society. Light pollution drastically shortens the night phase of the circadian rhythm. Preclinical and clinical studies have reported that nocturnal light exposure can influence mood, such as depressive-like phenotypes. However, the effects of blue light at night (BLAN) on other moods and how it alters mood remain unclear. Here, we explored the impact of BLAN on stress-provoked aggression in male Sprague‒Dawley rats, focusing on its influence on basolateral amygdala (BLA) activity. Resident-intruder tests, extracellular electrophysiological recordings, and enzyme-linked immunosorbent assays were performed. The results indicated that BLAN produces stress-induced heightened aggressive and anxiety-like phenotypes. Moreover, BLAN not only potentiates long-term potentiation and long-term depression in the BLA but also results in stress-induced elevation of brain-derived neurotrophic factor (BDNF), mature BDNF, and phosphorylation of tyrosine receptor kinase B expression in the BLA. Intra-BLA microinfusion of BDNF RNAi, BDNF neutralizing antibody, K252a, and rapamycin blocked stress-induced heightened aggressive behavior in BLAN rats. In addition, intra-BLA application of BDNF and 7,8-DHF caused stress-induced heightened aggressive behavior in naïve rats. Collectively, these results suggest that BLAN results in stress-evoked heightened aggressive phenotypes, which may work by enhancing BLA BDNF signaling and synaptic plasticity. This study reveals that nocturnal blue light exposure may have an impact on stress-provoked aggression. Moreover, this study provides novel insights into the BLA BDNF-dependent mechanism underlying the impact of the BLAN on mood.

Artificial light at night, MRI-based measures of brain iron deposition and incidence of multiple mental disorders

BACKGROUND

Epidemiologic evidence on whether iron accumulation in brain modified the association between artificial light at night (ALAN) and incident mental disorders is lacking. The authors aims to investigate modification of brain iron deposition on the associations of ALAN with multiple mental disorders in the middle-aged and older adults.

METHODS

This prospective study used data from the UK Biobank. ALAN was drawn from satellite datasets. Susceptibility-weighted magnetic resonance imaging was used to ascertain iron content of each brain region. T2* signal loss was used as indices of iron deposition. The main outcomes are impacts of ALAN exposure on onset of wide spectrum of physician-diagnosed mental disorders, which was estimated by time-varying Cox proportional hazard model. The authors further conducted stratified analyses by levels of iron brain deposition to examine the potential modifying effects.

RESULTS

Among 298,283 participants followed for a median of 10.91 years, higher ALAN exposure was associated with increased risk of mental disorders. An IQR (11.37 nW/cm2/sr) increase in annual levels of ALAN was associated with an HR of 1.050 (95 % CI: 1.034,1.066) for any mental disorder, 1.076 (95 % CI: 1.053,1.099) for substance use disorder, and 1.036 (95 % CI: 1.004,1.069) for depression disorder in fully adjusted models. The exposure-response curves showed steeper trends at lower ALAN levels and a plateau at higher exposures. The associations were stronger in participants with high iron deposition in left hippocampus, left accumbens and left pallidum.

CONCLUSIONS

ALAN was associated with multiple mental disorders in the middle-aged and older adults, and the findings indicated stricter standards of ALAN is needed and targeted preventive measures are warranted, especially with high brain iron deposition.

Sleep, light exposure at night, and psychological wellbeing during pregnancy

BACKGROUND

Psychological wellbeing during pregnancy is imperative for optimal maternal outcomes. The present study aimed to determine the association between sleep quality, light exposure at night, and psychological wellbeing in the 2nd and 3rd trimesters of pregnancy.

METHODS

This prospective study was conducted in 9 randomly selected government maternity clinics in Kuala Lumpur, Malaysia. Healthy women aged 20-48 years old with single pregnancy were recruited using convenience sampling (n = 169). Sleep quality, light exposure at night, and psychological wellbeing were self-reported using the Pittsburgh Sleep Quality Index (PSQI), Harvard Light Exposure Assessment (H-LEA), and Depression, Anxiety, and Stress Scale (DASS-21) in the 2nd trimester and followed-up at the 3rd trimester.

RESULTS

During the 2nd and 3rd trimesters of pregnancy, mild to severe symptoms of stress (10.7 and 11.3%), anxiety (42 and 44.3%), and depression (9.6 and 16.6%) were observed among the participants. Adjusted multiple linear regression revealed that poor sleep quality and higher light exposure at night were attributed to greater stress and depression symptoms in the 3rd trimester. Higher lux level exposed from 10 pm to < 1 am was associated with increased stress (β = 0.212, p = 0.037) and depression (β = 0.228, p = 0.024). Only poor sleep quality was observed to adversely affect anxiety (β = 0.243, p = 0.002) and depression levels (β = 0.259, p = 0.001) in the 2nd trimester.

CONCLUSIONS

Present study provided preliminary findings on the association between sleep quality, light at night, and psychological wellbeing of pregnant women. As a recommendation, future research could investigate whether public health interventions aimed at decreasing artificial light at night can benefit sleep quality and the psychological health of pregnant women.

The association between long-term exposure to outdoor artificial light at night and poor sleep quality among Chinese veterans: A multi-city study

BACKGROUND

A handful of previous studies have reported the association between exposure to outdoor artificial light at night (ALAN) and sleep problems. However, evidence for such association is limited in low- and middle-income countries. This study aimed to examine the association between outdoor ALAN exposure and sleep quality in veterans across different regions of China.

METHODS

Within the network of the Chinese Veteran Clinical Research Platform, we selected 7258 participants from 277 veteran communities in 18 cities across China during December 2009 and December 2011, using a multi-stage stratified cluster sampling strategy. Face-to-face interviews with the participants were conducted by trained investigators. We used the Pittsburgh Sleep Quality Index (PSQI) to assess participants' sleep quality. We defined poor sleep quality as a PSQI global score >7. The 3-year average exposure to outdoor ALAN prior to the baseline interview was calculated using satellite imagery data, according to participants' geolocation information. The association of ALAN exposure with sleep quality was examined using the mixed-effects logistic regression models with natural cubic splines.

RESULTS

The exposure-response curve for sleep quality associated with ALAN exposure was nonlinear, with a threshold value of 49.20 nW/cm2/sr for the 3-year average exposure to outdoor ALAN prior to the baseline interview. Higher ALAN exposure above the threshold was associated with increased risk of poor sleep quality. After adjusting for potential confounders, the odds ratios (and 95%CI, 95% confidence intervals) were 1.15 (0.97, 1.36) and 1.45 (1.17, 1.78) at the 75th and 95th percentiles of ALAN against the threshold. The association of ALAN exposure with poor sleep quality was more pronounced in veterans with depression than those without. Higher OR of poor sleep quality at the 75th percentile of ALAN against the threshold was observed in veterans with depression than those without [2.09 (1.16, 3.76) vs. 1.09 (0.92, 1.30)].

CONCLUSIONS

Long-term exposure to outdoor ALAN was associated with higher risk of poor sleep quality in Chinese veterans. Effective outdoor ALAN management may help to reduce the burden of sleep disorders in Chinese veterans.

Long-term Pu-erh tea consumption improves blue light-induced depression-like behaviors

Blue light emitted by smartphones and tablets at night increases the risk of depression. Pu-erh tea has been reported to reduce the risk of depression by regulating tryptophan metabolism, but its underlying protective mechanism on depression induced by blue light at night (BLAN) remains unclear. In this work, two groups of C57BL6/J mice were given water or 0.25% (w/v) Pu-erh tea for 120 days, followed by a 45-day BLAN treatment (400 lux blue light between 21:00 and 23:00) to simulate blue light emitted from electronic equipment. Our results indicated that BLAN induced depression-like behaviors and gut microbiota disorders in healthy mice. Pu-erh tea intake significantly reshaped the gut microbiome (especially Bifidobacterium) and regulated the metabolism of short-chain fatty acids (SCFAs) which protected the integrity of the intestinal barrier. This improvement further reduced blood-brain barrier (BBB) damage and alleviated neuroinflammation by inhibiting MyD88/NF-κB pathways which finally regulated neurotransmitters such as brain-derived neurotrophic factor (BDNF) and serotonin (5-hydroxytryptamine, 5-HT). Collectively, 0.25% (w/v) Pu-erh tea has the potential to prevent BLAN-induced depression-like behaviors by reshaping the gut microbiota and increasing the generation of SCFAs via the gut-brain axis.

The circadian system and mood related behavior in mice

Most organisms on earth have evolved an internal clock in order to predict daily recurring events. This clock called circadian clock has a period of about 24 h and allows organisms to organize biochemical and physiological processes over one day. Changes in lighting conditions as they occur naturally over seasons, or man made by jet lag or shift work, advance or delay clock phase in order to synchronize an organism's physiology to the environment. A misalignment of the clock to its environment results in sleep disturbances and mood disorders. Although there are strong associations between the circadian clock and mood disorders such as depression, the underlying molecular mechanisms are not well understood. This review describes the currently known molecular links between circadian clock components and mood related behaviors in mice, which will help to understand the causal links between the clock and mood in humans in the future.

Outdoor artificial light at night and human health: A review of epidemiological studies

We conducted a non-systematic review of epidemiological studies on a potential link between exposure to outdoor artificial light at night (O-ALAN) and disease occurrence in humans published since 2009. In recent years, a number of presses have been published on this issue, but the conclusions have been mixed. We therefore decided to critically analyze the available epidemiological evidence of such a correlation. After a careful search, 51 studies were identified and included in the review. They addressed the potential link between O-ALAN exposure and the incidence of breast cancer, other cancers, sleep and circadian rhythm disorders, obesity and cardiovascular diseases, mental disorders, infectious diseases, and complications during pregnancy and childbirth. The vast majority of papers revealed the existence of such a link. However, the amount of epidemiological evidence supporting the correlation across groups of disorders varied widely. In addition, we found that all papers contained at least one of the following omissions: lack of the temporal and spatial resolution in light at night measurements, measuring only light intensity without considering its wavelength, and not accounting for many important confounding factors in their statistical analyses. Therefore, we believe that the link between O-ALAN exposure and the occurrence of the disorders in question suggested by the authors of the reviewed papers may be in some cases at least to some extent, a coincidence. Further epidemiological studies, free of significant omissions highlighted in this paper, are needed.

Circadian rhythms as modulators of brain health during development and throughout aging

The circadian clock plays a prominent role in neurons during development and throughout aging. This review covers topics pertinent to the role of 24-h rhythms in neuronal development and function, and their tendency to decline with aging. Pharmacological or behavioral modification that augment the function of our internal clock may be central to decline of cognitive disease and to future chronotherapy for aging-related diseases of the central nervous system.

Long-term exposure to outdoor light at night and mild cognitive impairment: A nationwide study in Chinese veterans

BACKGROUND

Evidence is limited for the association between outdoor light at night (LAN) and mild cognitive impairment (MCI), a transitional stage between normal aging and dementia and Alzheimer's disease in the elderly. In this study, the association between outdoor LAN and MCI was examined based on a multi-city study among veterans in China.

METHODS

A total of 5496 participants from 18 cities across China were investigated during 2009-2011, selected using a multi-stage random sampling method. Participants' cognitive function was firstly assessed using the Mini Mental State Examination and the Montreal Cognitive Assessment in the Chinese version, and then was further confirmed by clinical examination. Participants' exposure to outdoor LAN was estimated using the Global Radiance Calibrated Nighttime Lights Product at a spatial resolution of around 1 km. The mixed-effects logistic regression model was used to examine the association between outdoor LAN and MCI.

RESULTS

After controlling for covariates, odds ratio (OR) and 95 % confidence intervals (95%CI) of MCI was 1.44 (95%CI: 1.36, 1.52) associated with per interquartile range (IQR = 21.17 nW/cm²/sr) increase in exposure to outdoor LAN during the 3 years before the investigation, and for categorical variable of LAN, the highest OR was observed for the highest against the lowest quartile of LAN with a monotonically increasing trend (p values for trend <0.001). Furthermore, higher ORs were observed for females, veterans who had less educational attainment, and had no regular social activities.

CONCLUSIONS

Our study revealed that exposure to excessive outdoor LAN was associated with higher risk of MCI. Effective measures should be taken to reduce LAN exposure, which may help to prevent MCI.

Association of outdoor artificial light at night with mental health among China adults: a prospective ecology study

Multiple environmental changes are related to mental disorders. However, research on the association between artificial light at night (ALAN) and mental health in China is limited, particularly at the national level. We used a "difference-in-differences" design and logistic regression to explore the relationship between ALAN changes and scores on self-assessed mental health. Participants were drawn from the China Family Panel Studies of adults in 2012 and 2018. The final analysis was based on 21,036 adults from 25 provinces throughout China. The brighter the ALAN, the worse was the mental health, and this connection was unaffected by particulate matter 2.5 (PM_2.5) or temperature. ALAN sensitivity may differ among populations. Our findings suggest that exposure to brighter ALAN is associated significantly with worse mental health among Chinese adults. Environmental policies that reduce ALAN could improve the mental health of the Chinese public.

Artificial light at night and risk of mental disorders: A systematic review

BACKGROUND

Emerging evidence suggests a possible association between artificial light at night (LAN) exposure and physiological and behavioral changes, with implications on mood and mental health. Due to the increased amount of individuals' LAN exposure, concerns have been raised regarding harmful impact of light pollution on mental health at the population level.

AIM

To perform a systematic review of observational studies to investigate if light at night, assessed both indoor and outdoor, may be associated with an increased risk of mental diseases in humans.

METHODS

We reviewed the epidemiological evidence on the association between LAN exposure, assessed either via satellite photometry or via measurements of bedroom brightness, and mental disorders. We systematically searched the PubMed, Embase and Web of Science databases up to April 1, 2022. Studies were included if they assessed the link between indoor or outdoor artificial light at night and one or more mental disorders in human populations.

RESULTS

Nine eligible studies were included in this review: six studies had a cross-sectional design, two had a longitudinal design with a median follow-up of 24 months, and one was a case-cohort study. Overall, we found moderate evidence of a positive association between LAN exposure and depressive symptoms and to a lesser extent other mental disorders, though the number of studies was limited and potential residual confounding such as socioeconomic factors, noise, or air pollution may have influenced the results.

CONCLUSIONS

Although more robust evidence is needed, the epidemiological evidence produced so far seems to support an association between LAN and risk of depressive disorders.

The Role of the Urban Exposome in the Increasing Global Rates of Pediatric Inflammatory Bowel Disease

Pediatric inflammatory bowel disease (IBD) is becoming increasingly common around the world, rapidly accelerating in regions undergoing rapid economic development. IBD is more common among those living in cities, and the association between the urban environment and IBD incidence is strongest in children. The "urban exposome" is defined as the totality of environmental exposures associated with urban living: air pollution, water contamination, green and blue space, nighttime light, noise, and availability of pre-processed and packaged foods. Investigation of the role of the urban exposome and IBD is in its infancy. Existing research has reached heterogeneous conclusions, and most studies have focused specifically on adult-onset disease and environmental exposures in isolation rather than the interaction between exposures. By better understanding the impact of the urban exposome on pediatric IBD, we can work to minimize these exposures and decrease the future burden of IBD in children.

On the relation between a green and bright window view and length of hospital stay in affective disorders

Background

The salutary effect of window views on greenery for inpatients in hospitals on length of stay and recovery rate has been repeatedly shown, however, not for psychiatric inpatients. The study assessed the association between a window view on green trees or man-made objects and brightness of the room on length of stay in a sample of psychiatric inpatients from one clinic.

Methods

Data records of 244 psychiatric inpatients (mean age in years 41.8; SD = 11.8; 59.8% female, length of stay varying between 7 and 100 days) that were admitted between May 2013 and October 2018 with affective disorders were examined. Window view was assessed with images taken from each room and classified into showing man-made objects or green trees. The percentage of green within each image was also calculated as greenness of the view. Brightness was assessed with a luxmeter.

Results

Although no effect was found for the dichotomous measures (man-made objects vs. green trees), a suppression effect emerged for percentage of green and brightness. The results indicate that both greenness of the window view as well as brightness significantly reduce length of stay in psychiatric inpatients with affective disorders.

Conclusions

The suppression effect likely results from the characteristics of the windows; the greenest rooms also being the darkest. Due to the infrastructure of the ward, greenness and brightness came at the expense of each other. The results generally support the importance of a view into greenery and natural sunlight for recovery.

Association of exposure to artificial light at night with atopic diseases: A cross-sectional study in college students

The impact of artificial light at night (ALAN) exposure on health has become increasingly prominent. However, little is known about the effect of ALAN exposure on atopic diseases. In this study, a cross-sectional analysis of incoming students was conducted in 5 geographically disperse universities which locate in Changsha (south), Wuhan (central), Xiamen (east), Urumchi (west), and Hohhot (north), respectively. All incoming students who consented to participate were recruited, followed by a health examination and a questionnaire survey. Prevalent atopic diseases were diagnosed by clinicians. Mean ALAN (nanoWatts/cm²/sr) during their adolescence was obtained from the remote sensing observed nighttime light data matching with their residence information, which was obtained from survey. Mixed generalized linear models (log-binomial) were used to estimate the associations, in terms of prevalence ratio (PR) with 95% confidence interval (CI). A total of 20106 participants were included in the analysis. Based on previous work, we chose factors including socioeconomic status, behavioural factors, major air pollutants, and air climatic parameters for adjustment. After full adjustment, the PR for atopic diseases was 1.35 (95% CI: 1.27-1.42; P < 0.001). The effect size of ALAN was the largest for asthma (PR = 1.80; 95% CI: 1.48-2.19; P < 0.001), followed by atopic rhinitis (PR = 1.42; 95% CI: 1.33-1.51; P < 0.001), and atopic dermatitis (PR = 1.20; 95% CI: 1.06-1.35; P = 0.003). Subgroup analyses by covariates showed consistent results. This study revealed that exposure to ALAN during adolescence may contribute to a higher risk of atopic diseases in young adulthood.

[Positive effect of bright light therapy on mood and sleep quality in institutionalized older people]

INTRODUCTION

Bright light exposure during the day has a positive effect on health and its deficit can cause multiple physiological and cognitive disorders, including depression. The aim of this study was to evaluate the effect of bright light therapy (BLT) on the quality of sleep and mood emotional state; cognitive status, global deterioration and quality of life in institutionalized elderly.

MATERIAL AND METHODS

This is a study with repeated measures design. Thirty-seven older people admitted to a nursing home. The study lasted 3 weeks. The first week, the reference values were established with the Oviedo Sleep Questionnaire, Yesavage Depression Scale, Mini-Mental, Global Scale of Impairment and European Quality of Life Questionnaire. During the second week, they were exposed to BLT (7,000-10,000lx at eye level) between 9:30 a.m. and 11:00 a.m. During the third week, all the data were re-evaluated.

RESULTS

All variables improved significantly after the application of light therapy. Sleep (COS) pre-test 4.1±1.49, post-test 4.9±1.46, p: 0.01), mood (pre-test 3.65±2.78, post-test 2.65±2.9, p: 0.01), cognitive state (pre-test 22.72±6.53, post-test 24±5.92, p: 0.001), state of global deterioration (pre-test 3.10±1.26, post-test 2.72±5.92, p: 0.001) and health-related quality of life (pre-test 6.93±1.86, post-test 7.82±1.62, p: 0.001).

CONCLUSIONS

Sleep quality, mood, cognitive status, global deterioration status and quality of life significantly improved after the application of light bright therapy.

Nighttime Light Hurts Mammalian Physiology: What Diurnal Rodent Models Are Telling Us

Natural sunlight permits organisms to synchronize their physiology to the external world. However, in current times, natural sunlight has been replaced by artificial light in both day and nighttime. While in the daytime, indoor artificial light is of lower intensity than natural sunlight, leading to a weak entrainment signal for our internal biological clock, at night the exposure to artificial light perturbs the body clock and sleep. Although electric light at night allows us "to live in darkness", our current lifestyle facilitates nighttime exposure to light by the use, or abuse, of electronic devices (e.g., smartphones). The chronic exposure to light at nighttime has been correlated to mood alterations, metabolic dysfunctions, and poor cognition. To decipher the brain mechanisms underlying these alterations, fundamental research has been conducted using animal models, principally of nocturnal nature (e.g., mice). Nevertheless, because of the diurnal nature of human physiology, it is also important to find and propose diurnal animal models for the study of the light effects in circadian biology. The present review provides an overview of the effects of light at nighttime on physiology and behavior in diurnal mammals, including humans. Knowing how the brain reacts to artificial light exposure, using diurnal rodent models, is fundamental for the development of new strategies in human health based in circadian biology.

Lighting in the Home and Health: A Systematic Review

Poor housing is an important determinant of poor health. One key aspect of housing quality is lighting. Light is important for visual performance and safety, and also plays a vital role in regulating human physiological functions. This review aims to synthesise existing evidence on the relationship between lighting in the home and health and recommends areas for future research. Three databases were searched for relevant literature using pre-defined inclusion criteria. Study quality was assessed using the Newcastle Ottawa Scale. Extracted data were qualitatively synthesised according to type of lighting (natural light, artificial light and light at night) and stratified by broad health domains (physical, mental and sleep health). Of the 4043 records retrieved, 28 studies met the inclusion criteria. There was considerable heterogeneity in light exposure metrics used and specific health outcome assessed by the studies. Lighting in the home can negatively affect health but the current evidence base is limited to a small number of studies in different domains of light and health. Further research surrounding specific health outcomes is required to better inform housing quality assessments and lighting practises in the home.

Circadian Strain, Light Exposure, and Depressive Symptoms in Rural Communities of Southern Brazil

Irregular light-dark cycles and circadian/sleep disturbances have been suggested as risk or co-occurring factors in depression. Among a set of metrics developed to quantify strain on the circadian system, social jetlag (SJL) has been put forward as a measure of the discrepancy between biological and social clocks. Here, we approached the question on whether light exposure and SJL would also be associated with depressive symptoms in Quilombola communities in Southern Brazil. These rural communities are void of potential confounders of modern lifestyles and show low levels of SJL. 210 Quilombolas (age range 16-92; 56% women) were asked about their sleep times and light exposure using the Munich ChronoType Questionnaire (MCTQ). The Beck Depression Inventory (BDI) was used to assess depressive symptoms. Additionally, we analyzed 7-day actimetry recordings in 124 subjects. BDI scores higher than 10 (having clinically significant depressive symptoms; controlled for age and sex in the multivariate analysis) were positively associated with SJL >1 h and negatively associated with median light exposure during the day, especially in the morning from 8:00 to 10:00. Our results suggest that low light exposure during the day, and higher levels of SJL are associated with depressive symptoms; longitudinal and experimental studies are needed to understand the underlying mechanisms. Nevertheless, we highlight the potential of treatment strategies aimed at decreasing circadian strain and insufficient light exposure, which are suggested as areas of further research in Psychiatry.

Association of Outdoor Artificial Light at Night With Mental Disorders and Sleep Patterns Among US Adolescents

IMPORTANCE

Indoor nighttime light exposure influences sleep and circadian rhythms and is known to affect mood-associated brain circuits in animals. However, little is known about the association between levels of nighttime outdoor light and sleep and mental health in the population, especially among adolescents.

OBJECTIVE

To estimate associations of outdoor artificial light at night (ALAN) with sleep patterns and past-year mental disorder among US adolescents.

DESIGN, SETTING, AND PARTICIPANTS

This population-based, cross-sectional study of US adolescents used the National Comorbidity Survey-Adolescent Supplement, a nationally representative cross-sectional survey conducted from February 2001 through January 2004. A probability sample of adolescents aged 13 to 18 years was included. Analyses were conducted between February 2019 and April 2020.

EXPOSURES

Levels of outdoor ALAN, measured by satellite, with means calculated within census block groups. ALAN values were transformed into units of radiance (nW/cm2/sr).

MAIN OUTCOMES AND MEASURES

Self-reported habitual sleep patterns (weeknight bedtime, weeknight sleep duration, weekend bedtime delay, and weekend oversleep) and past-year mood, anxiety, behavior, and substance use disorders, measured via an in-person structured diagnostic interview. Parent-reported information was included in behavior disorder diagnoses.

RESULTS

Among 10 123 adolescents (4953 boys [51.3%]; mean [SE] age, 15.2 [0.06] years [weighted]; 6483 for behavior disorder outcomes), ALAN was positively associated with indicators of social disadvantage, such as racial/ethnic minority status (median [IQR] ALAN: white adolescents, 12.96 [30.51] nW/cm2/sr; Hispanic adolescents: 38.54 [47.84] nW/cm2/sr; non-Hispanic black adolescents: 37.39 [51.88] nW/cm2/sr; adolescents of other races/ethnicities: 30.94 [49.93] nW/cm2/sr; P < .001) and lower family income (median [IQR] ALAN by family income-to-poverty ratio ≤1.5: 26.76 [52.48] nW/cm2/sr; >6: 21.46 [34.38] nW/cm2/sr; P = .005). After adjustment for several sociodemographic characteristics, as well as area-level population density and socioeconomic status, this study found that higher ALAN levels were associated with later weeknight bedtime, and those in the lowest quartile of ALAN reported the longest weeknight sleep duration. Those in the highest quartile of ALAN went to bed 29 (95% CI, 15-43) minutes later and reported 11 (95% CI, 19-2) fewer minutes of sleep than those in the lowest quartile. ALAN was also positively associated with prevalence of past-year mood and anxiety disorder: each median absolute deviation increase in ALAN was associated with 1.07 (95% CI, 1.00-1.14) times the odds of mood disorder and 1.10 (95% CI, 1.05-1.16) times the odds of anxiety disorder. Further analyses revealed associations with bipolar disorder (odds ratio [OR], 1.19 [95% CI, 1.05-1.35]), specific phobias (OR, 1.18 [95% CI, 1.11-1.26]), and major depressive disorder or dysthymia (OR, 1.07 [95% CI, 1.00-1.15]). Among adolescent girls, differences in weeknight bedtime by ALAN (third and fourth quartiles vs first quartile) were greater with increasing years since menarche (F3, 8.15; P < .001).

CONCLUSIONS AND RELEVANCE

In this study, area-level outdoor ALAN was associated with less favorable sleep patterns and mood and anxiety disorder in adolescents. Future studies should elucidate whether interventions to reduce exposure to ALAN may positively affect mental and sleep health.

Outdoor light at night, air pollution and depressive symptoms: A cross-sectional study in the Netherlands

BACKGROUND

Artificial light at night (ALAN) may be an anthropogenic stressor for mental health disturbing humans' natural day-night cycle. However, the few existing studies used satellite-based measures of radiances for outdoor ALAN exposure assessments, which were possibly confounded by traffic-related air pollutants.

OBJECTIVES

To assess 1) whether living in areas with increased exposure to outdoor ALAN is associated with depressive symptoms; and 2) to assess the potential confounding effects of air pollution.

METHODS

We used cross-sectional data from people (N = 10,482) aged 18-65 years in the Netherlands. Depressive symptoms were assessed with the Patient Health Questionnaire (PHQ-9). Satellite-measured annual ALAN were taken from the Visible Infrared Imaging Radiometer Suite. ALAN exposures were assessed at people's home address within 100 and 600 m buffers. We used generalized (geo)additive models to quantify associations between PHQ-9 scores and quintiles of ALAN adjusting for several potential confounders including PM_2.5 and NO₂.

RESULTS

Unadjusted estimates for the 100 m buffers showed that people in the 2^nd to 5^th ALAN quintile showed significantly higher PHQ-9 scores than those in the lowest ALAN quintile (β_Q2 = 0.503 [95% confidence intervals (CI): 0.207-0.798], β_Q3 = 0.587 [95% CI: 0.291-0.884], β_Q4 = 0.921 [95% CI: 0.623-1.218], β_Q5 = 1.322 [95% CI: 1.023-1.620]). ALAN risk estimates adjusted for individual and area-level confounders (i.e., PM_2.5, urbanicity, noise, land-use diversity, greenness, deprivation, and social fragmentation) were attenuated but remained significant for the 100 m buffer (β_Q2 = 0.420 [95% CI: 0.125-0.715], β_Q3 = 0.383 [95% CI: 0.071-0.696], β_Q4 = 0.513 [95% CI: 0.177-0.850], β_Q5 = 0.541 [95% CI: 0.141-0.941]). When adjusting for NO₂ per 100 m buffers, the air pollutant was associated with PHQ-9 scores, but ALAN did not display an exposure-response relationship. ALAN associations were insignificant for 600 m buffers.

CONCLUSION

Accounting for NO₂ exposure suggested that air pollution rather than outdoor ALAN correlated with depressive symptoms. Future evaluations of health effects from ALAN should consider potential confounding by traffic-related exposures (i.e., NO₂).

Association of the Built Environment With Childhood Psychosocial Stress

Importance

Emerging research suggests that factors associated with the built environment, including artificial light, air pollution, and noise, may adversely affect children's mental health, while living near green space may reduce stress. Little is known about the combined roles of these factors on children's stress.

Objective

To investigate associations between components of the built environment with personal and home characteristics in a large cohort of children who were assessed for perceived stress.

Design, Setting, and Participants

In this cohort study, a total of 2290 Southern California Children's Health Study participants residing in 8 densely populated urban communities responded to detailed questionnaires. Exposures of artificial light at night (ALAN) derived from satellite observations, near-roadway air pollution (NRP) determined from a dispersion model, noise estimated from the US Traffic Noise Model, and green space from satellite observations of the enhanced vegetation index were linked to each participant's geocoded residence.

Main Outcomes and Measures

Children's stress was assessed at ages 13 to 14 years and 15 to 16 years using the 4-item Perceived Stress Scale (PSS-4), scaled from 0 to 16, with higher scores indicating greater perceived stress. Measurements were conducted in 2010 and 2012, and data were analyzed from February 6 to August 24, 2019. Multivariate mixed-effects models were used to examine multiple exposures; modification and mediation analyses were also conducted.

Results

Among the 2290 children in this study, 1149 were girls (50%); mean (SD) age was 13.5 (0.6) years. Girls had significantly higher perceived stress measured by PSS-4 (mean [SD] score, 5.7 [3.4]) than boys (4.9 [3.2]). With increasing age (from 13.5 [0.6] to 15.3 [0.6] years), the mean PSS-4 score rose from 5.6 (3.3) to 6.0 (3.4) in girls but decreased for boys from 5.0 (3.2) to 4.7 (3.1). Multivariate mixed-effects models examining multiple exposures indicated that exposure to secondhand smoke in the home was associated with a 0.85 (95% CI, 0.46-1.24) increase in the PSS-4 score. Of the factors related to the physical environment, an interquartile range (IQR) increase in ALAN was associated with a 0.57 (95% CI, 0.05-1.09) unit increase in the PSS-4 score together with a 0.16 score increase per IQR increase of near-roadway air pollution (95% CI, 0.02-0.30) and a -0.24 score decrease per IQR increase of the enhanced vegetation index (95% CI, -0.45 to -0.04). Income modified the ALAN effect size estimate; participants in households earning less than $48 000 per year had significantly greater stress per IQR increase in ALAN. Sleep duration partially mediated the associations between stress and both enhanced vegetation index (17%) and ALAN (18%).

Conclusions and Relevance

In this cohort study, children's exposure to smoke at home in addition to residential exposure to ALAN and near-roadway air pollution were associated with increased perceived stress among young adolescent children. These associations appeared to be partially mitigated by more residential green space. The findings may support the promotion of increased residential green spaces to reduce pollution associated with the built environment, with possible mental health benefits for children.

A circadian rhythm-gated subcortical pathway for nighttime-light-induced depressive-like behaviors in mice

Besides generating vision, light modulates various physiological functions, including mood. While light therapy applied in the daytime is known to have anti-depressive properties, excessive light exposure at night has been reportedly associated with depressive symptoms. The neural mechanisms underlying this day-night difference in the effects of light are unknown. Using a light-at-night (LAN) paradigm in mice, we showed that LAN induced depressive-like behaviors without disturbing the circadian rhythm. This effect was mediated by a neural pathway from retinal melanopsin-expressing ganglion cells to the dorsal perihabenular nucleus (dpHb) to the nucleus accumbens (NAc). Importantly, the dpHb was gated by the circadian rhythm, being more excitable at night than during the day. This indicates that the ipRGC→dpHb→NAc pathway preferentially conducts light signals at night, thereby mediating LAN-induced depressive-like behaviors. These findings may be relevant when considering the mental health effects of the prevalent nighttime illumination in the industrial world.

Towards a Sustainable Indoor Lighting Design: Effects of Artificial Light on the Emotional State of Adolescents in the Classroom

In recent years, articles have been published on the non-visual effects of light, specifically the light emitted by the new luminaires with light emitting diodes (LEDs) and by the screens of televisions, computer equipment, and mobile phones. Professionals from the world of optometry have raised the possibility that the blue part of the visible light from sources that emit artificial light could have pernicious effects on the retina. The aim of this work is to analyze the articles published on this subject, and to use existing information to elucidate the spectral composition and irradiance of new LED luminaires for use in the home and in public spaces such as educational centers, as well as considering the consequences of the light emitted by laptops for teenagers. The results of this research show that the amount of blue light emitted by electronic equipment is lower than that emitted by modern luminaires and thousands of times less than solar irradiance. On the other hand, the latest research warns that these small amounts of light received at night can have pernicious non-visual effects on adolescents. The creation of new LED luminaires for interior lighting, including in educational centers, where the intensity of blue light can be increased without any specific legislation for its control, makes regulatory developments imperative due to the possible repercussions on adolescents with unknown and unpredictable consequences.

Dim Light at Night Exposure Induces Cold Hyperalgesia and Mechanical Allodynia in Male Mice

The growing presence of artificial lighting across the globe presents a number of challenges to human and ecological health despite its societal benefits. Exposure to artificial light at night, a seemingly innocuous aspect of modern life, disrupts behavior and physiological functions. Specifically, light at night induces neuroinflammation, which is implicated in neuropathic and nociceptive pain states, including hyperalgesia and allodynia. Because of its influence on neuroinflammation, we investigated the effects of dim light at night exposure on pain responsiveness in male mice. In this study, mice exposed to four days of dim (5 lux) light at night exhibited cold hyperalgesia. Further, after 28 days of exposure, mice exhibited both cold hyperalgesia and mechanical allodynia. No heat/hot hyperalgesia was observed in this experiment. Altered nociception in mice exposed to dim light at night was concurrent with upregulated interleukin-6 and nerve growth factor mRNA expression in the medulla and elevated μ-opioid receptor mRNA expression in the periaqueductal gray region of the brain. The current results support the relationship between disrupted circadian rhythms and altered pain sensitivity. In summary, we observed that dim light at night induces cold hyperalgesia and mechanical allodynia, potentially through elevated neuroinflammation and dysregulation of the endogenous opioid system.

Acute exposure to low-level light at night is sufficient to induce neurological changes and depressive-like behavior

The advent and wide-spread adoption of electric lighting over the past century has profoundly affected the circadian organization of physiology and behavior for many individuals in industrialized nations; electric lighting in homes, work environments, and public areas have extended daytime activities into the evening, thus, increasing night-time exposure to light. Although initially assumed to be innocuous, chronic exposure to light at night (LAN) is now associated with increased incidence of cancer, metabolic disorders, and affective problems in humans. However, little is known about potential acute effects of LAN. To determine whether acute exposure to low-level LAN alters brain function, adult male, and female mice were housed in either light days and dark nights (LD; 14 h of 150 lux:10 h of 0 lux) or light days and low level light at night (LAN; 14 h of 150 lux:10 h of 5 lux). Mice exposed to LAN on three consecutive nights increased depressive-like responses compared to mice housed in dark nights. In addition, female mice exposed to LAN increased central tendency in the open field. LAN was associated with reduced hippocampal vascular endothelial growth factor-A (VEGF-A) in both male and female mice, as well as increased VEGFR1 and interleukin-1β mRNA expression in females, and reduced brain derived neurotrophic factor mRNA in males. Further, LAN significantly altered circadian rhythms (activity and temperature) and circadian gene expression in female and male mice, respectively. Altogether, this study demonstrates that acute exposure to LAN alters brain physiology and can be detrimental to well-being in otherwise healthy individuals.

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.

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.

Sleep Environment and Insomnia in Elderly Persons Living at Home

The aim of this study was to draw a portrait of the sleep environment of elderly persons living in private households and to determine its relationship with the presence of insomnia. A sample of 599 individuals aged 70 years and older responded to questions about the comfort of their pillow and mattress and the noise level and brightness of their bedroom at night and in the morning. They were also asked whether or not they shared their bed or bedroom with a sleep partner. The Insomnia Severity Index was used to assess insomnia severity. Over 40% of the study participants were using a pillow that was not very comfortable, and almost 30% said that their bedroom was not completely quiet. Binomial logistic regression results revealed that two variables were significantly associated with insomnia symptoms: a pillow rated as moderately comfortable to very uncomfortable and a bedroom that was not completely quiet. No other sleep environment characteristics considered in this study were associated with the risk of insomnia. These results indicate that a nonnegligible proportion of the elderly population endures a suboptimal sleep environment. Although it is difficult to predict the real impact of changes to the sleep environment, this study supports the proposal that simple, minor changes to the bedroom can promote sleep in the elderly.

Effects of light at night on laboratory animals and research outcomes

Light has substantial influences on the physiology and behavior of most laboratory animals. As such, lighting conditions within animal rooms are potentially significant and often underappreciated variables within experiments. Disruption of the light/dark cycle, primarily by exposing animals to light at night (LAN), disturbs biological rhythms and has widespread physiological consequences because of mechanisms such as melatonin suppression, sympathetic stimulation, and altered circadian clock gene expression. Thus, attention to the lighting environment of laboratory animals and maintaining consistency of a light/dark cycle is imperative for study reproducibility. Light intensity, as well as wavelength, photoperiod, and timing, are all important variables. Although modern rodent facilities are designed to facilitate appropriate light cycling, there are simple ways to modify rooms to prevent extraneous light exposure during the dark period. Attention to lighting conditions of laboratory animals by both researchers and research care staff ensures best practices for maintaining animal welfare, as well as reproducibility of research results. (PsycINFO Database Record

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

Previous studies have indicated that minimal exposure to light at night (LAN) increases depression risk, even at 5 lux, in nocturnal and diurnal mammals. Although such low-level LAN may affect human circadian physiology, the association between exposure to LAN and depressive symptoms remains uncertain. In the present study, bedroom light intensity was measured objectively, and depressive symptoms were assessed, during 2010-2014 in Nara, Japan. Of 863 participants (mean age = 71.5 years) who did not have depressive symptoms at baseline, 73 participants reported development of depressive symptoms during follow-up (median, 24 months). Compared with the "dark" group (average of <5 lux; n = 710), the LAN group (average of ≥5 lux; n = 153) exhibited a significantly higher depression risk (hazard ratio = 1.89; 95% CI: 1.13, 3.14), according to a Cox proportional hazards model adjusting for age, sex, body mass index, and economic status. Further, the significance remained in a multivariable model adjusting for hypertension, diabetes, and sleep parameters (hazard ratio = 1.72; 95% CI: 1.03, 2.89). Sensitivity analyses using bedroom light data with a cutoff value of ≥10 lux suggested consistent results. In conclusion, these results indicated that exposure to LAN in home settings was independently associated with subsequent depression risk in an elderly general population.

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.

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.

Investigating the application of motion accelerometers as a sleep monitoring technique and the clinical burden of the intensive care environment on sleep quality: study protocol for a prospective observational study in Australia

INTRODUCTION

Sleep is a state of quiescence that facilitates the significant restorative processes that enhance individuals' physiological and psychological well-being. Patients admitted to the intensive care unit (ICU) experience substantial sleep disturbance. Despite the biological importance of sleep, sleep monitoring does not form part of standard clinical care for critically ill patients. There exists an unmet need to assess the feasibility and accuracy of a range of sleep assessment techniques that have the potential to allow widespread implementation of sleep monitoring in the ICU.

KEY MEASURES

The coprimary outcome measures of this study are to: determine the accuracy and feasibility of motion accelerometer monitoring (ie, actigraphy) and subjective assessments of sleep (nursing-based observations and patient self-reports) to the gold standard of sleep monitoring (ie, polysomnography) in evaluating sleep continuity and disturbance. The secondary outcome measures of the study will include: (1) the association between sleep disturbance and environmental factors (eg, noise, light and clinical interactions) and (2) to describe the sleep architecture of intensive care patients.

METHODS AND ANALYSIS

A prospective, single centre observational design with a within subjects' assessment of sleep monitoring techniques. The sample will comprise 80 adults (aged 18 years or more) inclusive of ventilated and non-ventilated patients, admitted to a tertiary ICU with a Richmond Agitation-Sedation Scale score between +2 (agitated) and -3 (moderate sedation) and an anticipated length of stay >24 hours. Patients' sleep quality, total sleep time and sleep fragmentations will be continuously monitored for 24 hours using polysomnography and actigraphy. Behavioural assessments (nursing observations) and patients' self-reports of sleep quality will be assessed during the 24-hour period using the Richards-Campbell Sleep Questionnaire, subjective sleepiness evaluated via the Karolinska Sleepiness Scale, along with a prehospital discharge survey regarding patients' perception of sleep quality and disturbing factors using the Little Sleep Questionnaire will be undertaken. Associations between sleep disturbance, noise and light levels, and the frequency of clinical interactions will also be investigated. Sound and luminance levels will be recorded at 1 s epochs via Extech SDL600 and SDL400 monitoring devices. Clinical interactions will be logged via the electronic patient record system Metavision which documents patient monitoring and clinical care.

ETHICS AND DISSEMINATION

The relevant institutions have approved the study protocol and consent procedures. The findings of the study will contribute to the understanding of sleep disturbance, and the ability to implement sleep monitoring methods within ICUs. Understanding the contribution of a clinical environment on sleep disturbance may provide insight into the need to address clinical environmental issues that may positively influence patient outcomes, and could dispel notions that the environment is a primary factor in sleep disturbance. The research findings will be disseminated via presentations at national and international conferences, proceedings and published articles in peer-reviewed journals.

TRIAL REGISTRATION NUMBER

ACTRN12615000945527; Pre-results.

Medical hypothesis: Light at night is a factor worth considering in critical care units

Exposure to light at night is not an innocuous consequence of modernization. There are compelling data linking long-term exposure to occupational and environmental light at night with serious health conditions, including heart disease, obesity, diabetes, and cancer. However, far less is known about the physiological and behavioral effects of acute exposure to light at night. Among healthy volunteers, acute night-time light exposure increases systolic blood pressure and inflammatory markers in the blood, and impairs glucose regulation. Whether critically ill patients in a hospital setting experience the same physiological shifts in response to evening light exposure is not known. This paper reviews the available data on light at night effects on health and wellbeing, and argues that the data are sufficiently compelling to warrant studies of how lighting in intensive care units may be influencing patient recovery.

The effect of dim light at night on cerebral hemodynamic oscillations during sleep: A near-infrared spectroscopy study

Recent studies have reported that dim light at night (dLAN) is associated with risks of cardiovascular complications, such as hypertension and carotid atherosclerosis; however, little is known about the underlying mechanism. Here, we evaluated the effect of dLAN on the cerebrovascular system by analyzing cerebral hemodynamic oscillations using near-infrared spectroscopy (NIRS). Fourteen healthy male subjects underwent polysomnography coupled with cerebral NIRS. The data collected during sleep with dim light (10 lux) were compared with those collected during sleep under the control dark conditions for the sleep structure, cerebral hemodynamic oscillations, heart rate variability (HRV), and their electroencephalographic (EEG) power spectrum. Power spectral analysis was applied to oxy-hemoglobin concentrations calculated from the NIRS signal. Spectral densities over endothelial very-low-frequency oscillations (VLFOs) (0.003-0.02 Hz), neurogenic VLFOs (0.02-0.04 Hz), myogenic low-frequency oscillations (LFOs) (0.04-0.15 Hz), and total LFOs (0.003-0.15 Hz) were obtained for each sleep stage. The polysomnographic data revealed an increase in the N2 stage under the dLAN conditions. The spectral analysis of cerebral hemodynamics showed that the total LFOs increased significantly during slow-wave sleep (SWS) and decreased during rapid eye movement (REM) sleep. Specifically, endothelial (median of normalized value, 0.46 vs. 0.72, p = 0.019) and neurogenic (median, 0.58 vs. 0.84, p = 0.019) VLFOs were enhanced during SWS, whereas endothelial VLFOs (median, 1.93 vs. 1.47, p = 0.030) were attenuated during REM sleep. HRV analysis exhibited altered spectral densities during SWS induced by dLAN, including an increase in very-low-frequency and decreases in low-frequency and high-frequency ranges. In the EEG power spectral analysis, no significant difference was detected between the control and dLAN conditions. In conclusion, dLAN can disturb cerebral hemodynamics via the endothelial and autonomic systems without cortical involvement, predominantly during SWS, which might represent an underlying mechanism of the increased cerebrovascular risk associated with light exposure during sleep.

Circadian and Metabolic Effects of Light: Implications in Weight Homeostasis and Health

Daily interactions between the hypothalamic circadian clock at the suprachiasmatic nucleus (SCN) and peripheral circadian oscillators regulate physiology and metabolism to set temporal variations in homeostatic regulation. Phase coherence of these circadian oscillators is achieved by the entrainment of the SCN to the environmental 24-h light:dark (LD) cycle, coupled through downstream neural, neuroendocrine, and autonomic outputs. The SCN coordinate activity and feeding rhythms, thus setting the timing of food intake, energy expenditure, thermogenesis, and active and basal metabolism. In this work, we will discuss evidences exploring the impact of different photic entrainment conditions on energy metabolism. The steady-state interaction between the LD cycle and the SCN is essential for health and wellbeing, as its chronic misalignment disrupts the circadian organization at different levels. For instance, in nocturnal rodents, non-24 h protocols (i.e., LD cycles of different durations, or chronic jet-lag simulations) might generate forced desynchronization of oscillators from the behavioral to the metabolic level. Even seemingly subtle photic manipulations, as the exposure to a “dim light” scotophase, might lead to similar alterations. The daily amount of light integrated by the clock (i.e., the photophase duration) strongly regulates energy metabolism in photoperiodic species. Removing LD cycles under either constant light or darkness, which are routine protocols in chronobiology, can also affect metabolism, and the same happens with disrupted LD cycles (like shiftwork of jetlag) and artificial light at night in humans. A profound knowledge of the photic and metabolic inputs to the clock, as well as its endocrine and autonomic outputs to peripheral oscillators driving energy metabolism, will help us to understand and alleviate circadian health alterations including cardiometabolic diseases, diabetes, and obesity.

Effects of a high level of illumination before sleep at night on chorioretinal thickness and ocular biometry

The choroid is affected by many factors. One of the factors, change in illumination has been suggested to influence choroidal thickness. However, the effects of bright light before sleep at night on the human eye are not well established. The purpose of this study was to investigate the effects of a high level of illumination in the evening on ocular measurements. Twenty-seven men with myopia spent seven consecutive nights in the sleep laboratory. During the first two nights, subjects were exposed to light at 150 lux between 20:00 and midnight. Then, for five consecutive nights, they were exposed to ambient light at 1000 lux between 20:00 and midnight. Ocular parameters and their diurnal variations were compared between the two periods and the effects of a high level of illumination were analyzed. After subjects were exposed to 1000 lux of illumination, axial length increased with borderline significance (p = 0.064). Macular volume and retinal thickness did not change. However, subfoveal choroidal thickness after exposure to 1000 lux of illumination (245.37 ± 52.84 μm) was significantly lower than that after 150 lux of illumination (268.00 ± 57.10 μm), (p < 0.001). Significant diurnal variations were found in mean keratometry (p = 0.039), intraocular pressure (IOP, p = 0.003), ocular perfusion pressure (OPP, p < 0.0001), macular volume (p = 0.019), and subfoveal choroidal thickness (p < 0.0001). A high level of illumination had significant effects on only IOP and OPP (p = 0.027 and 0.017, respectively). Bright light exposure before sleep at an intensity as high as 1000 lux reduced subfoveal choroidal thickness in healthy young men. In conclusion, diurnal variation in choroidal thickness can be affected by bright light exposure before sleep.

Resources of dark skies in German climatic health resorts

Illumination of nocturnal environments is increasing steadily worldwide. While there are some benefits for mankind, light at night affects animals, plants, and human health by blurring the natural distinction between day and night. International regulations exist to protect the environment for the maintenance of human health but nocturnal darkness is not considered. In Germany, cities and communities labeled as Climatic Health Resorts provide for high standards in air quality. However, their degree of nocturnal darkness is unexplored so far. In our study, we examined the degree of nocturnal darkness in German Climatic Health Resorts by two datasets based on georeferenced remote sensing data. The majority of Climatic Health Resorts (93.1 %) are able to offer a relative respite (≥ 20 mag/arcsec²) from a degraded nocturnal environment, while only 3.4 % are able to offer a dark, if by no means pristine, night environment (≥ 21 mag/arcsec²). Climatic Health Resorts emit less light as well as are less affected by night sky brightness compared to the average of non-classified communities. In combination with daytime requirements, the resorts provide conditions for a more distinct day-and-night-cycle than non-classified communities.

Timing of light exposure affects mood and brain circuits

Temporal organization of physiology is critical for human health. In the past, humans experienced predictable periods of daily light and dark driven by the solar day, which allowed for entrainment of intrinsic circadian rhythms to the environmental light-dark cycles. Since the adoption of electric light, however, pervasive exposure to nighttime lighting has blurred the boundaries of day and night, making it more difficult to synchronize biological processes. Many systems are under circadian control, including sleep-wake behavior, hormone secretion, cellular function and gene expression. Circadian disruption by nighttime light perturbs those processes and is associated with increasing incidence of certain cancers, metabolic dysfunction and mood disorders. This review focuses on the role of artificial light at night in mood regulation, including mechanisms through which aberrant light exposure affects the brain. Converging evidence suggests that circadian disruption alters the function of brain regions involved in emotion and mood regulation. This occurs through direct neural input from the clock or indirect effects, including altered neuroplasticity, neurotransmission and clock gene expression. Recently, the aberrant light exposure has been recognized for its health effects. This review summarizes the evidence linking aberrant light exposure to mood.