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

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 mediating role of systemic inflammation in the association between bedroom light at night and new-onset depressive symptoms among Chinese young adults: A prospective cohort study

BACKGROUND

The detrimental effects of exposure to light at night (LAN) have received increasing attention. However, the effects of LAN exposure on depressive symptoms and underlying mechanism are less explored.

OBJECTIVES

To investigate the association between LAN exposure with new-onset and trajectories of depressive symptoms, and the potential mediating role of systemic inflammation.

METHODS

Baseline bedroom LAN exposure was monitored every minute for 2 consecutive nights using a portable illuminance meter. Fasting blood samples were collected at the 1-year follow-up to determine high sensitivity C-reactive protein (hs-CRP). Depressive symptoms were assessed at baseline, 1- and 2-year follow-up using the Mood and Feelings Questionnaire (MFQ).

RESULTS

At baseline, the mean age of the 347 participants was 18.7 ± 0.8 years, and 35.2 % were men. At 2-year follow-up, the new-onset depressive symptoms were 14.7 %. Compared with low-LANavg (average light intensity from bedtime to rising time) intensity group (LANavg < 3 lx), those with high-LANavg intensity (LANavg ≥ 3 lx) were associated with an 125 % increase in risk for depressive symptoms (HR = 2.25; 95 % CI: 1.27, 4.00); Compared with short-LAN5 (duration of nighttime light intensity ≥5 lx) duration group (LAN5 < 45 min), those with long-LAN5 duration (LAN5 ≥ 45 min) were associated with an 119 % increase in risk for depressive symptoms (HR = 2.19; 95 % CI: 1.18, 4.06). Participants were classified into 3 trajectory groups: consistently low, slow or rapid increase depressive symptoms; both intensity and duration of LAN exposure were associated with higher likelihood of slow or rapid increase depressive symptoms. Additionally, hs-CRP partially mediated the relationship between intensity (mediation proportion: 7.1 %) and duration (mediation proportion: 10.6 %) of LAN exposure with depressive symptoms.

CONCLUSION

Excessive bedroom LAN exposure is associated with increased risk of depressive symptoms among young adults, and systemic inflammation may be a partial mediator in the LAN-depressive symptoms association.

Incidence of depression among community-dwelling older adults: A systematic review

We aimed to synthesise information related to the incidence of depression and depressive symptoms (DDS) in a community-dwelling older adult population at a global level. In this systematic review, we included articles with a cohort study design that evaluated the incidence of depression or depressive symptoms in older adults aged 60 years or more in a community-dwelling environment. Six databases were used: Web of Science, PubMed, Scopus, LILACS, SciELO, and Cochrane, and the entire selection process was independently performed by peers. We divided the included articles into subgroups according to the DDS assessment instrument: (i) Geriatric Depression Scale; (ii) Center for Epidemiologic Studies Depression Scale; (iii) miscellaneous scales; and (iv) diagnostic interviews. Each cumulative incidence value obtained per item was adjusted for a 1-year follow-up period, which generated an annual cumulative incidence (AcI). From 46 articles, 42 used scales to evaluate the depressive variable, with an AcI estimate of around 4.5%. The articles that assessed depression categorically observed a variation in AcI between 0.2% and 7.0%. Among all the materials included, the group that used the Geriatric Depression Scale observed the lowest and the highest AcI, 1.3% and 26.6% respectively. Most of the productions were from countries in the Asian continent (52.2%), followed by Europe (30.4%), the Americas (13%), and Oceania (4.4%). Despite the variation of AcI, we found a frequent occurrence of DDS in older adults in the community-dwelling environment, which highlights the need for preventive actions and better-targeted early care, especially in terms of primary health care.

Outdoor light at night and depressive symptoms in male veterans: a multicenter cross-sectional study in China

Previous studies have indicated depression was associated with environmental exposures, but evidence is limited for the association between outdoor light at night (LAN) and depression. This study aims to examine the association between long-term outdoor LAN exposure and depressive symptoms using data from the Chinese Veteran Clinical Research platform. A total of 6445 male veterans were selected from 277 veteran communities in 18 cities of China during 2009‒2011. Depressive symptoms were evaluated using the Chinese version of the Center for Epidemiological Studies Depression scale. Outdoor LAN was estimated using the Global Radiance Calibrated Nighttime Lights data. The odds ratio and 95% confidence intervals of depressive symptoms at the high level of outdoor LAN exposure against the low level during the 1 years before the investigation was 1.49 (1.15, 1.92) with p-value for trend < 0.01, and those associated with per interquartile range increase in LAN exposure was 1.22 (1.06, 1.40).

Artificial light at night and risk of depression: a systematic review and meta-analysis

BACKGROUND

Artificial light at night (ALAN) has been increasingly recognized as a potential environmental risk factor for mental health issues. However, no meta-analyses have been conducted to summarize the findings. This study aimed to evaluate the pooled associations between outdoor and indoor ALAN exposures and the risk of depression.

METHODS

Adhering to the PRISMA guideline, we conducted systematic searches across PubMed, Web of Science, EMBASE, Cochrane, and Ovid databases for studies published before May 1st, 2024.

RESULTS

A total of 7 studies (5 for outdoor ALAN and 2 for indoor ALAN) with a combined total of 560,219 participants were included in the meta-analysis. Specifically, a 1 nW/cm2/sr increase in outdoor ALAN was associated with a 0.43% (95% CI: 0.21%, 0.65%) increase in depression risk. Meanwhile, a 1 lux increase in indoor ALAN was associated with a 3.29% (95% CI: 0.85%, 5.79%) increase in depression risk. No potential heterogeneity was observed for outdoor ALAN exposure and indoor ALAN exposure. Subgroup analyses for outdoor ALAN indicated that development level, sample size, age group, sex, study design, modality of depression assessment, or adjustment of sleep-related variables in models may not be potential sources of heterogeneity. Sensitivity analyses confirmed the robustness of the findings, while evidence of publication bias was observed for studies on outdoor ALAN.

CONCLUSIONS

Our findings suggest that both outdoor and indoor ALAN exposures are associated with increased risk of depression. These results underscore the importance of considering outdoor and indoor ALAN in public health strategies aimed at reducing depression risk. Nevertheless, further studies with prospective design are still warranted considering the limited study numbers.

Lower regional urbanicity and socioeconomic status attenuate associations of green spaces with hypertension and diabetes mellitus: a national representative cross-sectional study in China

BACKGROUND

High blood pressure (HBP) and diabetes mellitus (DM) are two of the most prevalent cardiometabolic disorders globally, especially among individuals with lower socio-economic status (SES). Studies have linked residential greenness to decreased risks of HBP and DM. However, there has been limited evidence on whether SES may modify the associations of residential greenness with HBP and DM.

METHODS

Based on a national representative cross-sectional study among 44,876 adults, we generated the normalized difference vegetation index (NDVI) at 1 km spatial resolution to characterize individuals' residential greenness level. Administrative classification (urban/rural), nighttime light index (NLI), individual income, and educational levels were used to characterize regional urbanicity and individual SES levels.

RESULTS

We observed weaker inverse associations of NDVI with HBP and DM in rural regions compared to urban regions. For instance, along with per interquartile range (IQR, 0.26) increment in residential NDVI at 0∼5 year moving averages, the ORs of HBP were 1.04 (95%CI: 0.94, 1.15) in rural regions and 0.85 (95%CI: 0.79, 0.93) in urban regions (P = 0.003). Along with the decrease in NLI levels, there were continuously decreasing inverse associations of NDVI with DM prevalence (P for interaction <0.001). In addition, weaker inverse associations of residential NDVI with HBP and DM prevalence were found among individuals with lower income and lower education levels compared to their counterparts.

CONCLUSIONS

Lower regional urbanicity and individual SES could attenuate the associations of residential greenness with odds of HBP and DM prevalence.

The importance of residential dusk and dawn light exposure for sleep quality, health, and well-being

Light exposure during twilight plays a critical role in the entrainment of the human circadian system. People are most often at home during dusk and dawn, and light exposure at home - either natural or from electric light - may therefore contribute substantially to sleep and well-being. However, very little research has focused on the effects of home lighting on sleep and well-being, and even less research has investigated the effects of light exposure during twilight. Therefore, a literature study was performed to collect studies on light exposure at home during dusk and dawn. Studies looking at light exposure during dusk and dawn have focused on either electric light intervention (i.e., dusk and dawn simulation) at home or in the laboratory or daylight exposure in the bedroom (i.e., the presence and type of curtains in the bedroom). Most research has focused on dawn simulation during the darker months of the year, often using sunrise alarms. In general, study results pointed to the importance of twilight light exposure at home for sleep and well-being. These results may depend on the characteristics of the user, such as age or chronotype.

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.

Reducing nighttime light exposure in the urban environment to benefit human health and society

Nocturnal light pollution can have profound effects on humans and other organisms. Recent research indicates that nighttime outdoor lighting is increasing rapidly. Evidence from controlled laboratory studies demonstrates that nocturnal light exposure can strain the visual system, disrupt circadian physiology, suppress melatonin secretion, and impair sleep. There is a growing body of work pointing to adverse effects of outdoor lighting on human health, including the risk of chronic diseases, but this knowledge is in a more nascent stage. In this Review, we synthesize recent research on the context-specific factors and physiology relevant to nocturnal light exposure in relation to human health and society, identify critical areas for future research, and highlight recent policy steps and recommendations for mitigating light pollution in the urban environment.

Understanding light pollution: Recent advances on its health threats and regulations

The prevalence of artificial lights not only improves the lighting conditions for modern society, but also poses kinds of health threats to human health. Although there are regulations and standards concerning light pollution, few of them are based on the potential contribution of improper lighting to diseases. Therefore, a better understanding of the health threats induced by light pollution may promote risk assessment and better regulation of artificial lights, thereby a healthy lighting environment. This review is based on a careful collection of the latest papers from 2018 to 2022 about the health threats of light pollution, both epidemiologically and experimentally. In addition to summing up the novel associations of light pollution with obesity, mental disorders, cancer, etc., we highlight the toxicological mechanism of light pollution via circadian disruption, since light pollution directly interferes with the natural light-dark cycles, and damages the circadian photoentrainment of organisms. And by reviewing the alternations of clock genes and disturbance of melatonin homeostasis induced by artificial lights, we aim to excavate the profound impacts of light pollution based on accumulating studies, thus providing perspectives for future research and guiding relevant regulations and standards.

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.

Associations between indoor light pollution and unhealthy outcomes in 2,947 adults: Cross-sectional analysis in the HEIJO-KYO cohort

Nighttime use of artificial light is usual and essential in these modern times. Although light exposure at night (LAN) is reportedly a risk factor of several diseases, epidemiological studies on indoor LAN levels are still limited. Hence, the present study aimed to measure bedroom LAN levels by using light meters in a larger sample than in previous studies, and to evaluate the associations with comprehensive health outcomes. Out of 3012 participants, 2947 (mean age, 69.3 years; female, 60.6%) completed the bedroom LAN intensity measurement. The median bedroom LAN intensity was 1.0 lux (interquartile range, 0.2-4.0 lux). In a multivariable analysis adjusted for potential confounding factors, the highest quartile group of bedroom LAN intensity had significantly higher body weight, body mass index, abdominal circumference, and low-density lipoprotein cholesterol than the lowest quartile group. The group with a median LAN intensity ≥10 lux had significantly higher white blood cell counts and had significantly lower high-density lipoprotein cholesterol levels than the group with a median LAN intensity <10 lux. In addition, the groups with median LAN intensities ≥3 and ≥10 lux had significantly higher odds ratios for sleep disturbances and depressive symptoms than the group with <3 and <10 lux, respectively. Therefore, the present study provided real-world data on bedroom LAN levels as a marker for indoor light pollution in a large sample and suggested that higher bedroom LAN levels are significantly associated with parameters of obesity, dyslipidemia, systemic inflammation, sleep disturbances, and depressive symptoms.

Multidimensional Environmental Factors and Sleep Health for Aging Adults: A Focused Narrative Review

The timing, amount, and quality of sleep are critical for an individual's health and quality of life. This paper provides a focused narrative review of the existing literature around multidimensional environments and sleep health for aging adults. Five electronic databases, Scopus, Web of Science, PubMed/Medline; EBSCOhost, PsycINFO (ProQuest), and Google Scholar yielded 54,502 total records. After removing duplicates, non-peer reviewed academic articles, and nonrelevant articles, 70 were included for review. We were able to categorize environmental factors into housing security, home environment, and neighborhood environment, and, within each environmental category, specific elements/aspects are discussed. This paper provides a comprehensive map connecting identified levels of influence (individual, home/house, and neighborhood-level) in which subfactors are listed under each level of influence/category with the related literature list. Our review highlights that multidimensional environmental factors can affect aging adults' sleep health and eventually their physical, mental, and cognitive health and that sleep disparities exist in racial minorities in socioeconomically disadvantaged communities in which cumulative environmental stressors coexist. Based on this focused narrative review on the multidimensional sleep environments for aging adults, knowledge gaps are identified, and future research directions are suggested.

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 perceptions of artificial light-at-night, light-emitting device usage and environmental noise appraisal with psychological distress, sleep quality and chronotype: A cross sectional study

Exposure to artificial light-at-night (ALAN) is increasing globally, and there are concerns around how ALAN may impact sleep, psychological and physical health. However, there is a lack of evidence in the literature on how individuals perceive ALAN relative to their sleeping environment and habits, and how such perceptions correspond to objectively assessed night-time illuminance at the level of the residence. This cross-sectional study examined how such perceptions associate with sleep quality, sleep timing, psychological distress and cognitive failures. Further we examined the association between illuminance levels calculated as the biologically-relevant melatonin-suppression index (MSI) and the self-report of perception of ALAN. Five hundred and fifty two adult participants completed a survey addressing perception of ALAN in sleep environment along with the Pittsburgh Sleep Quality Index, Munich Chronotype Questionnaire, Cognitive Failure Questionnaire and the General Health Questionnaire. We report that perception of external ALAN in the sleeping environment was associated with poorer sleep quality, more cognitive failures and greater psychological distress, when controlling for age, sex, house location and MSI. No associations were found between the perception of external ALAN and MSI scores, and MSI scores were not associated with scores on any of the self-report measures. Internal lighting passing into the sleeping environment was associated with poorer sleep quality but not with psychological wellbeing. Habitual use of light-emitting devices was associated with poorer psychological wellbeing but not with sleep quality and sleep timing. Perception of environmental noise annoyance at night was associated with higher psychological distress and poorer quality sleep, and the perception of noise annoyance was associated with perception of ALAN. These results may suggest heightened attentional bias towards ALAN associated with poor sleep quality and higher levels of psychological distress, and highlight the need for more granular approaches in the study of ALAN and sleep and psychological health in terms of levels individual ALAN exposure, and an interpretation that seeks to integrate biological and psychological perspectives.

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.

Effect of nighttime bedroom light exposure on mood episode relapses in bipolar disorder

OBJECTIVE

A previous cross-sectional study reported that nighttime light is associated with increased occurrence of manic symptoms in bipolar disorder; however, the longitudinal association between nighttime light and subsequent mood episode relapses remains unclear. We determined whether bedroom nighttime light was associated with mood episode relapses in patients with bipolar disorder.

METHODS

This prospective cohort study included 172 outpatients with bipolar disorder who participated in an Association between the Pathology of Bipolar Disorder and Light Exposure in Daily Life (APPLE) cohort study. A portable photometer was used to measure illuminance in the bedroom from bedtime to rising time during 7 consecutive nights for baseline assessment. Then, the participants were assessed at a 2-year follow-up for mood episode relapses.

RESULTS

Of the 172 participants, 157 (91%) completed the 2-year follow-up, and 39 (22%) experienced manic or hypomanic episodes (with or without mixed features), during that time. In the Cox proportional-hazards model, the hazard ratio (HR) for manic/hypomanic episode relapses was significantly higher when the average nighttime illuminance was ≥3 lux (n = 71) than when it was <3 lux (n = 101; HR, 2.54; 95% confidence interval (CI), 1.33-4.84). In the multivariable model adjusted for a propensity score in relation to nighttime light, the relationship remained significant (HR, 2.17; 95% CI, 1.04-4.52). The association between nighttime light and depressive episode relapses was not significantly different.

CONCLUSIONS

Keeping the bedroom dark at night may prevent hypomanic and manic episodes.

Exposure to bedroom light pollution and cardiometabolic risk: A cohort study from Chinese young adults

Indoor light environment has altered dramatically and exposure to light at night (LAN) potential leads to the progression of cardiometabolic conditions. However, few studies have investigated the effect of bedroom LAN exposure on cardiometabolic risk. To estimate the associations between multi-period bedroom LAN exposure with cardiometabolic risk among Chinese young adults. We objectively measured multi-period bedroom LAN intensity using portable illuminance meter in an ongoing prospective cohort (n = 484). At one-year follow-up, 230 young adults provided fasting blood samples for quantification of cardiometabolic parameters. Cardiometabolic (CM)-risk score was derived as the sum of standardized sex-specific z-scores for waist circumference (WC), mean arterial pressure (MAP), high-density lipoprotein cholesterol (HDL-C), triglyceride (TG) and homeostasis model assessment for insulin resistance (HOMA-IR), with HDL-C multiplied by - 1. Multivariate and univariable linear regression models were used to examine associations of multi-period bedroom LAN exposure with cardiometabolic risk. Exposure to higher bedroom LAN intensity is associated with 1.47-unit increase in CM-risk score (95% CI: 0.69-2.25; P < 0.001). Besides, post-bedtime light exposure was associated with elevated fasting insulin (PBL-1h: β = 0.06, 95% CI: 0.01-0.10; PBL-4h: β = 0.33, 95% CI: 0.19-0.47) and HOMA-IR (PBL-1h: β = 0.013, 95% CI: 0-0.03; PBL-4h: β = 0.07, 95% CI: 0.04-0.11) while pre-awake light exposure was associated with elevated total cholesterol (PAL-1h: β = 0.03, 95% CI: 0.02-0.04; PAL-2h: β = 0.02, 95% CI: 0.01-0.03), triglyceride (PAL-1h: β = 0.015, 95% CI: 0.01-0.02; PAL-2h: β = 0.01, 95% CI: 0-0.02) and low-density lipoprotein cholesterol (PAL-1h: β = 0.02, 95% CI: 0.01-0.03; PAL-2h: β = 0.02, 95% CI: 0.01-0.03). Among young adults, bedroom LAN exposure was significantly associated with higher cardiometabolic risk. Furthermore, different periods of bedroom light exposure have time-dependent effect on cardiometabolic risk. Further research is needed to confirm our findings and to elucidate potential mechanisms.

Verification, analytical validation and clinical validation (V3) of wearable dosimeters and light loggers

Background

Light exposure is an important driver and modulator of human physiology, behavior and overall health, including the biological clock, sleep-wake cycles, mood and alertness. Light can also be used as a directed intervention, e.g., in the form of light therapy in seasonal affective disorder (SAD), jetlag prevention and treatment, or to treat circadian disorders. Recently, a system of quantities and units related to the physiological effects of light was standardized by the International Commission on Illumination (CIE S 026/E:2018). At the same time, biometric monitoring technologies (BioMeTs) to capture personalized light exposure were developed. However, because there are currently no standard approaches to evaluate the digital dosimeters, the need to provide a firm framework for the characterization, calibration, and reporting for these digital sensors is urgent.

Objective

This article provides such a framework by applying the principles of verification, analytic validation and clinical validation (V3) as a state-of-the-art approach for tools and standards in digital medicine to light dosimetry.

Results

This article describes opportunities for the use of digital dosimeters for basic research, for monitoring light exposure, and for measuring adherence in both clinical and non-clinical populations to light-based interventions in clinical trials.

Sex-specific association of exposure to bedroom light at night with general and abdominal adiposity in young adults

Experimental animal studies and limited epidemiologic evidence among elder population suggest that exposure to light at night (LAN) may be obesogenic. Nevertheless, little is known about the possible impact of bedroom LAN exposure on subsequent adiposity and the distribution pattern of the accumulated fat, especially in younger population. Here, we estimated longitudinal associations of objectively assessed bedroom LAN exposure with general and abdominal adiposity among young adults. We measured 2-night bedroom LAN exposure using a portable illuminometer in a cohort of young adults (n = 482). Body composition using multifrequency bioelectrical impedance analysis was evaluated at baseline and 1-year follow-up visit. Significant increases in fat mass (2.4 kg, P = 0.015 in male; 1.9 kg, P < 0.001 in female), visceral fat area (10.7 cm², P < 0.001 in male; 5.0 cm², P = 0.01 in female), waist circumference (3.8 cm, P = 0.039 in male; 2.5 cm, P = 0.047 in female) and percentage of body fat (3.6%, P = 0.002 in male; 3.0%, P = 0.001 in female) were observed among individuals with bedroom LAN higher than 5 lx. Compared to the lowest quartile group of bedroom LAN exposure, the highest quartile group was associated with an increase of 0.64 kg/m² in BMI (95% CI: 0.18-1.09 kg/m²; P = 0.006) and 1.22 kg increase in fat mass (95% CI: 0.10-2.34 kg; P = 0.025) among female participants, and 10.58 cm² in visceral fat area (95% CI: 4.85-16.31 cm²; P = 0.001) and 2.59 cm in waist circumference (95% CI: 0.37-4.81 cm; P = 0.023) among male participants. In this cohort of Chinese young adults, significant associations were observed between bedroom LAN exposure and adiposity in a sex- and fat depot-specific fashion. Further intervention and longitudinal studies could help elucidate the actual effects and develop sex-specific strategies against lifetime obesity and related metabolic disorders.

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.

The impact of image resolution on power, bias, and confounding: A simulation study of ambient light at night exposure

Studies of the impact of environmental pollutants on health outcomes can be compromised by mismeasured exposures or unmeasured confounding with other environmental exposures. Both problems can be exacerbated by measuring exposure from data sources with low spatial resolution. Artificial light at night, for example, is often estimated from low-resolution satellite images, which may result in substantial measurement error and increased correlation with air or noise pollution.

METHODS

Light at night exposure was considered in simulated epidemiologic studies in Vancouver, British Columbia. First, we assessed statistical power and bias for hypothetical studies that replaced true light exposure with estimates from sources with low resolution. Next, health status was simulated based on pollutants other than light exposure, and we assessed the frequency with which studies might incorrectly attribute negative health impacts to light exposure as a result of unmeasured confounding by the other environmental exposures.

RESULTS

When light was simulated to be the causal agent, studies relying on low-resolution data suffered from lower statistical power and biased estimates. Additionally, correlations between light and other pollutants increased as the spatial resolution of the light exposure map decreased, so studies estimating light exposure from images with lower spatial resolution were more prone to confounding.

CONCLUSIONS

Studies estimating exposure to pollutants from data with lower spatial resolution are prone to increased bias, increased confounding, and reduced power. Studies examining effects of light at night should avoid using exposure estimates based on low-resolution maps, and should consider potential confounding with other environmental pollutants.

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.

Disruptions of Circadian Rhythms and Thrombolytic Therapy During Ischemic Stroke Intervention

Several endogenous and exogenous factors interact to influence stroke occurrence, in turn contributing to discernable daily distribution patterns in the frequency and severity of cerebrovascular events. Specifically, strokes that occur during the morning tend to be more severe and are associated with elevated diastolic blood pressure, increased hospital stay, and worse outcomes, including mortality, compared to strokes that occur later in the day. Furthermore, disrupted circadian rhythms are linked to higher risk for stroke and play a role in stroke outcome. In this review, we discuss the interrelation among core clock genes and several factors contributing to ischemic outcomes, sources of disrupted circadian rhythms, the implications of disrupted circadian rhythms in foundational stroke scientific literature, followed by a review of clinical implications. In addition to highlighting the distinct daily pattern of onset, several aspects of physiology including immune response, endothelial/vascular and blood brain barrier function, and fibrinolysis are under circadian clock regulation; disrupted core clock gene expression patterns can adversely affect these physiological processes, leading to a prothrombotic state. Lastly, we discuss how the timing of ischemic onset increases morning resistance to thrombolytic therapy and the risk of hemorrhagic transformation.

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).

Development and validation of nutrient estimates based on a food-photographic record in Japan

Background

Previous studies have reported that estimates of portion size, energy, and macronutrients such as carbohydrates, proteins, and fat based on the food-photographic record closely correlate with directly weighed values. However, the correlation based on a large sample of the test meal with the evidence of many nutrients is yet to be determined. We conducted this study to assess the correlation and difference between the food-photographic record and weighed results for 44 nutrients based on a larger number of test meals than those in previous studies.

Methods

We assessed the nutrients of test meals using a food-photographic record and direct weighing and compared the results of the two methods. Twenty participants prepared a total of 1163 test meals. Each participant cooked 28–29 different kinds of dishes. Five participants cooked the same dish with their own recipes. For the most commonly consumed 41 dishes, 20 participants served a meal with their usual portion size. For the remaining 73 dishes, five participants served a meal with their usual portion size. An independent researcher weighed each ingredient and calculated the nutrients of the test meals. The participants took photographs of the test meals using a digital camera. Two independent, trained analysts measured the longitudinal and transverse diameters of the food area on the photographs of the test meals, compared the portion size with the reference photographs, and calculated the nutrients based on a database that contained reference photographs.

Results

Rank correlation coefficients between estimates from the food-photographic record of each test meal and weighed results were high for portion size (r = 0.93), energy (r = 0.93), protein (r = 0.90), fat (r = 0.92), and carbohydrate (r = 0.94), and those for the 44 nutrients ranged from 0.78 to 0.94. We found high reproducibility between the two analysts for all the nutrients (r > 0.90).

Conclusions

We found a high correlation and small difference between the food-photographic record method and weighed results of a large number of nutrients in many test meals.

Daily and Seasonal Variation in Light Exposure among the Old Order Amish

Exposure to artificial bright light in the late evening and early night, common in modern society, triggers phase delay of circadian rhythms, contributing to delayed sleep phase syndrome and seasonal affective disorder. Studying a unique population like the Old Order Amish (OOA), whose lifestyles resemble pre-industrial societies, may increase understanding of light’s relationship with health. Thirty-three participants (aged 25–74, mean age 53.5; without physical or psychiatric illnesses) from an OOA community in Lancaster, PA, were assessed with wrist-worn actimeters/light loggers for at least 2 consecutive days during winter/spring (15 January–16 April) and spring/summer (14 May–10 September). Daily activity, sleep–wake cycles, and their relationship with light exposure were analyzed. Overall activity levels and light exposure increased with longer photoperiod length. While seasonal variations in the amount and spectral content of light exposure were equivalent to those reported previously for non-Amish groups, the OOA experienced a substantially (~10-fold) higher amplitude of diurnal variation in light exposure (darker nights and brighter days) throughout the year than reported for the general population. This pattern may be contributing to lower rates of SAD, short sleep, delayed sleep phase, eveningness, and metabolic dysregulation, previously reported among the OOA population.

Population-Based Approaches to Mental Health: History, Strategies, and Evidence

There is growing recognition in the fields of public health and mental health services research that the provision of clinical services to individuals is not a viable approach to meeting the mental health needs of a population. Despite enthusiasm for the notion of population-based approaches to mental health, concrete guidance about what such approaches entail is lacking, and evidence of their effectiveness has not been integrated. Drawing from research and scholarship across multiple disciplines, this review provides a concrete definition of population-based approaches to mental health, situates these approaches within their historical context in the United States, and summarizes the nature of these approaches and their evidence. These approaches span three domains: (a) social, economic, and environmental policy interventions that can be implemented by legislators and public agency directors, (b) public health practice interventions that can be implemented by public health department officials, and (c) health care system interventions that can be implemented by hospital and health care system leaders.

Circadian disruption: What do we actually mean?

The circadian system regulates physiology and behavior. Acute challenges to the system, such as those experienced when traveling across time zones, will eventually result in re-synchronization to local environmental time cues, but this re-synchronization is oftentimes accompanied by adverse short-term consequences. When such challenges are experienced chronically, adaptation may not be achieved, as for example in the case of rotating night shift workers. The transient and chronic disturbance of the circadian system is most frequently referred to as "circadian disruption", but many other terms have been proposed and used to refer to similar situations. It is now beyond doubt that the circadian system contributes to health and disease, emphasizing the need for clear terminology when describing challenges to the circadian system and their consequences. The goal of this review is to provide an overview of the terms used to describe disruption of the circadian system, discuss proposed quantifications of disruption in experimental and observational settings with a focus on human research, and highlight limitations and challenges of currently available tools. For circadian research to advance as a translational science, clear, operationalizable, and scalable quantifications of circadian disruption are key, as they will enable improved assessment and reproducibility of results, ideally ranging from mechanistic settings, including animal research, to large-scale randomized clinical trials.

Circadian insights into the biology of depression: Symptoms, treatments and animal models

In depression, symptoms range from loss of motivation and energy to suicidal thoughts. Moreover, in depression alterations might be also observed in the sleep-wake cycle and in the daily rhythms of hormonal (e.g., cortisol, melatonin) secretion. Both, the sleep-wake cycle and hormonal rhythms, are regulated by the internal biological clock within the hypothalamic suprachiasmatic nucleus (SCN). Therefore, a dysregulation of the internal mechanism of the SCN might lead in the disturbance of temporal physiology and depression. Hence, circadian symptoms in mood disorders can be used as important biomarkers for the prevention and treatment of depression. Disruptions of daily rhythms in physiology and behavior are also observed in animal models of depression, giving thus an important tool of research for the understanding of the circadian mechanisms implicated in mood disorders. This review discusses the alterations of daily rhythms in depression, and how circadian perturbations might lead in mood changes and depressive-like behavior in humans and rodents respectively. The use of animal models with circadian disturbances and depressive-like behaviors will help to understand the central timing mechanisms underlying depression, and how treating the biological clock(s) it may be possible to improve mood.

Light Modulation of Human Clocks, Wake, and Sleep

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

Pre-awake light exposure and sleep disturbances: findings from the HEIJO-KYO cohort

OBJECTIVES

To evaluate the associations between pre-awake light (PAL) exposure and subjective and objective measures of sleep quality.

METHODS

In this cross-sectional study of 1108 elderly participants (mean age, 71.9 years), we measured bedroom light intensity using a bedside light meter for two nights and sleep quality using actigraphy and a questionnaire. PAL was determined as the 2h-average light intensity before rise time, and sleep disturbance was defined as the Pittsburgh sleep quality index score ≥6.

RESULTS

Sleep disturbance prevalence increased with increased PAL exposure (P = 0.002). In multivariable models adjusted for potential confounders, the odds ratio (OR) for sleep disturbances was significantly higher in the highest quartile PAL group (Q4) than in the lowest quartile group (Q1) (OR, 1.65; 95% CI, 1.16-2.34). This association occurred independent of post-bedtime light exposure; and was stronger in the later chronotype group (n = 556) (OR, 1.80; 95% CI, 1.05-3.09) than in the earlier chronotype group (n = 552) (OR, 1.64; 95% CI, 1.01-2.64). Actigraphic sleep efficiency in the Q4 group was significantly lower by 2.6% (95% CI, 1.3-3.8) than that in the Q1 group. Moreover, longer wake after sleep onset by 7.5 min (95% CI, 2.8-12.2) and sleep onset latency by 0.2 log min (95% CI, 0.1-0.4) were observed in the Q4 group than the Q1 group.

CONCLUSIONS

Higher PAL exposure was significantly associated with a higher prevalence of sleep disturbances, independent of post-bedtime light exposure. Consistent results were observed in the actigraphy analysis.

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

Chronotype and Mental Health: Recent Advances

PURPOSE OF REVIEW

Evening chronotype is increasingly recognized as a correlate of, and perhaps a contributor to, mental illness. The current review evaluates recent evidence for the association between chronotype and mental illness and putative mechanisms underlying the association, while highlighting methodological advances and areas of research that are relatively under-examined in the literature.

RECENT FINDINGS

While evening chronotype is most consistently associated with severity of mood disorder symptoms, emerging evidence implicates evening chronotype as a transdiagnostic correlate of substance use severity, anxiety symptoms, attentional difficulties, and maladaptive behaviors such as aggression. Longitudinal studies point to the possibility that evening chronotype precedes problematic substance use, depression, and anxiety. Neural processes related to reward and affective regulation may underlie associations between evening chronotype and illness. The literature on chronotype and mental illness has evolved to (1) include associations with a broader range of psychiatric symptom profiles; (2) explore underlying mechanisms; and (3) expand on earlier research using objective measures and more sophisticated study designs. In addition to further mechanistic research, additional work is needed to examine the stability and key subcomponents of the chronotype construct, as well as more attention to pediatric and special populations. This research is needed to clarify the chronotype-mental health relationship, and to identify how, when, and what aspects of chronotype can be targeted via therapeutic interventions.

Circadian Health and Light: A Report on the National Heart, Lung, and Blood Institute's Workshop

Despite the omnipresence of artificial and natural light exposure, there exists little guidance in the United States and elsewhere on light exposure in terms of timing, intensity, spectrum, and other light characteristics known to affect human health, performance, and well-being; in parallel, there is little information regarding the quantity and characteristics of light exposure that people receive. To address this, the National Center on Sleep Disorders Research, in the Division of Lung Diseases, National Heart, Lung, and Blood Institute, held a workshop in August 2016 on circadian health and light. Workshop participants discussed scientific research advances on the effects of light on human physiology, identified remaining knowledge gaps in these research areas, and articulated opportunities to use appropriate lighting to protect and improve circadian-dependent health. Based on this workshop, participants put forth the following strategic intent, objectives, and strategies to guide discovery, measurement, education, and implementation of the appropriate use of light to achieve, promote, and maintain circadian health in modern society.

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.