Association between exposure to light at night (LAN) and sleep problems: A systematic review and meta-analysis of observational studies

Sleep Capital: Linking Brain Health to Wellbeing and Economic Productivity Across the Lifespan

INTRODUCTION AND FRAMEWORK

Sleep capital contributes to individual and societal wellbeing, productivity, and economic outcomes and involves a novel aspect of brain capital. It encompasses the quality and quantity of sleep as integral components that influence cognitive abilities, mental and brain health, and physical health, affecting workplace productivity, learning, decision-making, and overall economic performance. Here, we bring a framework to understand the complex relationship between sleep quality, health, wellbeing, and economic productivity. Then we outline the multilevel impact of sleep on cognitive abilities, mental/brain health, and economic indicators, providing evidence for the substantial returns on investment in sleep health initiatives. Moreover, sleep capital is a key factor when considering brain health across the lifespan, especially for the aging population.

DISCUSSION

We propose specific elements and main variables to develop specific indexes of sleep capital to address its impacts on health, wellbeing and productivity.

CONCLUSION

Finally, we suggest policy recommendations, workplace interventions, and individual strategies to promote sleep health and brain capital. Investing in sleep capital is essential for fostering a healthier, happier, fairer and more productive society.

Sleep problems mediate the association between outdoor nighttime light and symptoms of depression and anxiety: A cross-sectional, multi-city study in Bulgaria

BACKGROUND

Nighttime light is a growing anthropogenic health threat, particularly in urban areas. Limited evidence suggests that exposure to outdoor artificial light at night (ALAN) may be associated with people's mental health by disrupting sleep-wake cycles.

AIMS

We assessed 1) the association between ALAN exposure and adults' symptoms of depression and anxiety, 2) whether the association was modified by sex, age, and income, and 3) the mediating role of sleep problems.

METHODS

We obtained cross-sectional data from 4,068 adults from the five largest Bulgarian cities. Depression and anxiety symptoms were measured using the 4-item Patient Health Questionnaire (PHQ-4). Sleep problems were self-reported based on three items. Outdoor ALAN at residential addresses was assessed using annual radiance levels obtained from satellite imagery. Regression models were adjusted for person-level characteristics, green space, and nitrogen dioxide (NO2). We also assessed effect modification by sex, age, and income. Using mediation analyses, we tested sleep problems as a mediator of the ALAN-PHQ-4 association.

RESULTS

Greater ALAN exposure in the fully adjusted model was marginally associated with higher PHQ-4 scores. We observed no effect modification. The mediator, sleep problems, was also positively associated with ALAN. The mediation of sleep problems was significantly positive. While the direct association was null, the total ALAN association was marginally and positively associated with PHQ-4 scores.

CONCLUSIONS

Our findings suggest a positive association between outdoor nighttime light pollution and mental health. Poor sleep quality is a possible pathway relating ALAN exposure to mental health. Considering the increasing ubiquity and intensity of urban nighttime illumination, light pollution-reducing policies may provide significant health benefits for urban populations.

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.

Associations of light exposure patterns with sleep among Dutch children: The ABCD cohort study

Light exposure affects the circadian system and consequently can affect sleep quality. Only few studies examined this relationship in children. We evaluated associations between light exposure patterns and sleep metrics in children. We measured the sleep parameters of 247 Dutch children, aged between 11 and 13 years and recruited from the ABCD cohort, using actigraphy and sleep records for 7 consecutive nights. Personal light exposures were measured with a light meter during the whole day and night. We applied generalized mixed-effects regression models, adjusted for possible confounders, to evaluate the associations of light exposure patterns on sleep duration, sleep efficiency and sleep-onset delay. In the models mutually adjusted for potential confounders, we found the amount of hours between the first time of bright light in the morning and going to sleep and the duration of bright light to be significantly associated with decreased sleep duration (in min; β: -2.02 [95% confidence interval: -3.84, -0.25], β: -8.39 [95% confidence interval: -16.70, -0.07], respectively) and with shorter sleep-onset delay (odds ratio: 0.88 [95% confidence interval: 0.80, 0.97], odds ratio: 0.40 [95% confidence interval: 0.19, 0.87], respectively). Increased light intensities at night were associated with decreased sleep duration (T2 β: -8.54 [95% confidence interval: -16.88, -0.20], T3 β: -14.83 [95% confidence interval: -28.04, -1.62]), while increased light intensities before going to bed were associated with prolonged sleep onset (odds ratio: 4.02 [95% confidence interval: 2.09, 7.73]). These findings further suggest that children may be able to influence their sleep quality by influencing the light exposure patterns during day and night.

Sociodemographic inequalities in residential nighttime light pollution in urban Bulgaria: An environmental justice analysis

INTRODUCTION

Outdoor nighttime light (NTL) is a potential anthropogenic stressor in urban settings. While ecological studies have identified outdoor NTL exposure disparities, uncertainties remain about disparities in individual exposure levels, particularly in Europe.

AIM

To assess whether some populations are disproportionately affected by outdoor NTL at their residences in urban Bulgaria.

METHODS

We analyzed 2023 data from a representative cross-sectional survey of 4,270 adults from the five largest Bulgarian cities. Respondents' annual exposures to outdoor artificial nighttime luminance were measured using satellite imagery and assigned at their places of residence. We calculated the Gini coefficient as a descriptive NTL inequality measure. Associations between respondents' NTL exposure levels and sociodemographic characteristics were assessed by estimating quantile mixed regression models. Stratified regressions were fitted by gender and for each city.

RESULTS

We found moderate distributive NTL inequalities, as indicated by a Gini coefficient of 0.214. Regression analyses showed associations between greater NTL exposure and higher educational attainment. Respondents with incomes perceived as moderate experienced less NTL exposure at the 0.5 and 0.8 quantiles, while unemployed respondents experienced lower exposure at the 0.2 and 0.5 quantiles. We observed null associations for the elderly and non-Bulgarian ethnicities. Regardless of the quantile, greater population density was associated with higher NTL levels. Stratification by sex did not yield substantial differences in the associations. We observed notable city-specific heterogeneities in the associations, with differences in the magnitudes and directions of the associations and the NTL quantiles.

CONCLUSIONS

NTL exposures appeared to embody an environmental injustice dimension in Bulgaria. Our findings suggest that some sociodemographic populations experience higher exposure levels to NTL; however, those are not necessarily the underprivileged or marginalized. Identifying populations with high exposure levels is critical to influencing lighting policies to ease related health implications.

Ambient chemical and physical approaches for the modulation of sleep and wakefulness

Humans spend a third of their lives asleep. While the sleep-wake behaviors are primarily modulated by homeostasis and circadian rhythm, several ambient chemical and physical factors, including light, sound, odor, vibration, temperature, electromagnetic radiation, and ultrasound, also affect sleep and wakefulness. Light at different wavelengths has different effects on sleep and wakefulness. Sound not only promotes but also suppresses sleep; this effect is mediated by certain nuclei, including the pedunculopontine nucleus and inferior colliculus. Certain sleep-promoting odorants regulate sleep through the involvement of the olfactory bulb and olfactory tubercle. In addition, vibrations may induce sleep through the vestibular system. A modest increase in ambient temperature leads to an increase in sleep duration through the involvement of the preoptic area. Electromagnetic radiation has a dual effect on sleep-wake behaviors. The stimulation produced by the ambient chemical and physical factors activates the peripheral sensory system, which converts the chemical and physical stimuli into nerve impulses. This signal is then transmitted to the central nervous system, including several nuclei associated with the modulation of sleep-wake behaviors. This review summarizes the effects of ambient chemical and physical factors on the regulation of sleep and wakefulness, as well as the underlying neurobiological mechanisms.

Interactive correlations between artificial light at night, health risk behaviors, and cardiovascular health among patients with diabetes: A cross-sectional study

BACKGROUND

Artificial light at night (ALAN) is a common phenomenon and contributes to the severe light pollution suffered by more than 80% of the world's population. This study aimed to evaluate the relationship between outdoor ALAN exposure and cardiovascular health (CVH) in patients with diabetes and the influence of various modifiable factors.

METHODS

A survey method based on the China Diabetes and Risk Factor Monitoring System was adopted. Study data were extracted for 1765 individuals with diabetes in Anhui Province. Outdoor ALAN exposure (nW/cm2/sr) within 1000 m of each participant's residential address was obtained from satellite imagery data, with a resolution of ~1000 m. Health risk behaviors (HRBs) were measured via a standardized questionnaire. A linear regression model was employed to estimate the relationship between outdoor ALAN, HRBs, and CVH.

RESULTS

Participants' mean age was 59.10 ± 10.0 years. An association was observed between ALAN and CVH in patients with diabetes (β = 0.205) and exercise (β = -1.557), moderated by HRBs, or metabolic metrics. There was an association between ALAN, ALAN, vegetable intake, and CVH.

CONCLUSIONS

Exploring the relationship between ALAN exposure and cardiovascular and metabolic health provides policy data for improving light pollution strategies and reducing the risk of cardiovascular and metabolic disease in patients with diabetes.

Artificial Light at Night and Type 2 Diabetes Mellitus

The widespread and pervasive use of artificial light at night (ALAN) in our modern 24-hour society has emerged as a substantial disruptor of natural circadian rhythms, potentially leading to a rise in unhealthy lifestyle-related behaviors (e.g., poor sleep; shift work). This phenomenon has been associated with an increased risk of type 2 diabetes mellitus (T2DM), which is a pressing global public health concern. However, to date, reviews summarizing associations between ALAN and T2DM have primarily focused on the limited characteristics of exposure (e.g., intensity) to ALAN. This literature review extends beyond prior reviews by consolidating recent studies from 2000 to 2024 regarding associations between both indoor and outdoor ALAN exposure and the incidence or prevalence of T2DM. We also described potential biological mechanisms through which ALAN modulates glucose metabolism. Furthermore, we outlined knowledge gaps and investigated how various ALAN characteristics beyond only light intensity (including light type, timing, duration, wavelength, and individual sensitivity) influence T2DM risk. Recognizing the detrimental impact of ALAN on sleep health and the behavioral correlates of physical activity and dietary patterns, we additionally summarized studies investigating the potential mediating role of each component in the relationship between ALAN and glucose metabolism. Lastly, we proposed implications of chronotherapies and chrononutrition for diabetes management in the context of ALAN exposure.

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

STUDY OBJECTIVES

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Commuting time, working time, and their link to insomnia symptoms among Korean employees: A cross-sectional study

OBJECTIVE

Although commuting time is an extension of working hours, few studies have examined the relationship between commuting time and insomnia symptoms in relation to working time. Thus, this study investigated the relationship between commuting time and working time and their link to sleep disturbance.

METHODS

This study included employees with ≥35 weekly working hours (n = 30,458) using data from the Sixth Korean Working Conditions Survey conducted in Korea between October 2020 and April 2021. The association between commuting time (≤60, 61-120, and >120 minutes) and insomnia symptoms based on working hours (35-40, 41-52, and >52 h/wk) or shift work was investigated using survey-weighted logistic regression analysis.

RESULTS

Long commuting time (>120 min/d) combined with >52 working hours/week (OR: 7.88, 95% CI: 2.51-24.71) or combined with 41-52 h/wk (OR: 3.64, 95% CI: 2.15-6.14) was associated with a higher risk of insomnia symptoms compared with the reference group (working hours: 35-40 h/wk; daily commuting time: ≤60 minutes), after controlling for sex, age, socioeconomic factors, and work-related factors. Among shift workers, those with daily commuting time ≤60 minutes (OR: 1.71, 95% CI: 1.39-2.09), 61-120 minutes (OR: 2.63, 95% CI: 1.21-5.74), and >120 minutes (OR: 5.16, 95% CI: 2.14-12.44) had higher odds of insomnia symptoms than nonshift workers with ≤60 minutes daily commuting time.

CONCLUSION

Long working hours and shift work are associated with greater risk of insomnia symptoms.

Real-ambient bedroom light at night increases systemic inflammation and disrupts circadian rhythm of inflammatory markers

BACKGROUND

Exposure to light at night (LAN) has been associated with multiple adverse health outcomes. However, evidence is limited regarding the impacts of LAN exposure on human inflammation.

OBJECTIVES

To examine the association between real-ambient bedroom LAN exposure with systemic inflammation and circadian rhythm of inflammatory markers.

METHODS

Using data from a prospective cohort study of Chinese young adults. At baseline, bedroom LAN exposure was measured with a portable illuminance meter; fasting blood sample for high-sensitivity C-reactive protein (hs-CRP) assay was collected. At 3-year follow-up, 20 healthy young adults (10 LANavg < 5 lx, 10 LANavg ≥ 5 lx) were recruited from the same cohort; time-series venous blood samples were sampled every 4 h over a 24 h-cycle for the detection of 8 inflammatory markers. Circadian rhythm of inflammatory markers was assessed using cosinor analysis.

RESULTS

At baseline, the average age of the 276 participants was 18.7 years, and 33.3 % were male. Higher levels of bedroom LAN exposure were significantly associated with increased hs-CRP levels. The association between bedroom LAN exposure and systemic inflammation was only significant in the inactive group (MVPA < 2 h/d) but not in the physically active group (MVPA ≥ 2 h/d). In addition, exposure to higher levels of nighttime light (LANavg ≥ 5 lx) disrupted circadian rhythms (including rhythmic expression, circadian amplitude and circadian phase) of some inflammatory cytokines and inflammatory balance indicators.

CONCLUSION

Exposure to bedroom nighttime light increases systemic inflammation and disrupts circadian rhythm of inflammatory markers. Keep bedroom darkness at night may represent important strategies for the prevention of chronic inflammation. Additionally, for people living a community with higher nighttime light pollution, regular physical activity may be a viable option to counteract the negative impacts of LAN exposure on chronic inflammation.

Exposure to light at night (LAN) and risk of overweight/obesity, hypertension, and diabetes: a systematic review and meta-analysis

Current studies have presented conflicting findings regarding the associations between light at night (LAN) exposure and the risk of overweight/obesity, hypertension, and diabetes. Our study systematically summarized the evidence of the association between LAN exposure and the risk of overweight/obesity, hypertension, and diabetes. We searched five databases (PubMed, Web of Science, Embase, Scopus, and Cochrane) for observational studies published up to 1 August 2023. The pooled odds ratio (ORs) and 95% confidence intervals (CIs) were estimated by random-effects models for the association. Eighteen studies were included in the meta-analysis. Compared with the group with the lowest level of LAN, the group with the highest level of LAN is associated with an increased risk of overweight/obesity (pooled OR = 1.19, 95%CI: 1.13-1.26), hypertension (pooled OR: 1.86, 95% CI:1.28-2.72), and diabetes (pooled OR = 1.21, 95%CI: 1.07-1.31). Our meta-analysis demonstrated LAN exposure is associated with increased risk of overweight/obesity, hypertension, and diabetes.

Exposure to real-ambient bedroom light at night delayed circadian rhythm in healthy Chinese young adults: A cross-sectional study

BACKGROUND

Light at night (LAN) have attracted increased research attention on account of its widespread health hazards. However, the underlying mechanism remains unknown. The objective of this study was to investigate the effects of real-ambient bedroom LAN exposure on circadian rhythm among young adults and potential sex differences.

METHODS

Bedroom LAN exposure was measured at 60-s intervals for 2 consecutive days using a portable illuminance meter. Circadian phase was determined by the dim light melatonin onset (DLMO) time in 7 time-series saliva samples.

RESULTS

The mean age of the 142 participants was 20.7 ± 0.8 years, and 59.9% were women. The average DLMO time was 21:00 ± 1:11 h, with men (21:19 ± 1:12 h) later than women (20:48 ± 1:07 h). Higher level of LAN intensity (LANavg ≥ 3lx vs. LANavg < 3lx) was associated with an 81.0-min later in DLMO time (95% CI: 0.99, 1.72), and longer duration of nighttime light intensity ≥ 5lx (LAN5; LAN5 ≥ 45 min vs. LAN5 < 45 min) was associated with a 51.6-min later in DLMO time (95% CI: 0.46, 1.26). In addition, the delayed effect of LAN exposure on circadian phase was more pronounced in men than in women (all P-values <0.05).

CONCLUSIONS

Overall, bedroom LAN exposure was significantly associated with delayed circadian rhythm. Additionally, the delayed effect is more significant in men. Keeping bedroom dark at night may be a practicable option to prevent circadian disruption and associated health implications. Future studies with more advanced light measurement instrument and consensus methodology for DLMO assessment are warranted.

Association of light at night with cardiometabolic disease: A systematic review and meta-analysis

Light at night (LAN) is a significant but underappreciated risk factor contributing to cardiometabolic disease (CMD). We therefore conducted the review examining the relationship of LAN exposure with CMD in order to investigate the effects of LAN exposure on CMD. We searched PubMed, Web of Science, Embase, and Scopus for eligible studies published from database inception to August 17, 2023. The pooled effect size was calculated using random-effects models. Heterogeneity among the studies was quantified by Cochran's Q test and I2 statistic. A total of 1,019,739 participants from 14 studies (5 cohort studies and 9 cross-sectional) were included. Among the 14 eligible studies, 9 on obesity, 4 on diabetes, 2 on hypertension, 1 on dyslipidemia, and 1 on coronary heart disease. Exposure to higher levels of LAN were associated with 21% higher risk of CMD (Summary risk ratio, SRR: 1.21, 95% CI = 1.16-1.27), accompanied by substantial heterogeneity (I2 = 61%; tau2 = 0.004; Cochran's Q = 41.02). Specifically, individuals in the highest category of LAN exposure exhibited 23% higher risk of obesity (SRR: 1.23, 95% CI = 1.14-1.32), 46% higher risk of diabetes (SRR: 1.46, 95% CI = 1.05-2.03) and 21% higher risk of other CMDs (SRR: 1.21, 95% CI = 1.10-1.34). Subgroup analyses revealed that the pooled-effect size of LAN and CMD was higher for indoor LAN than outdoor LAN (indoor LAN: SRR = 1.36; outdoor LAN: SRR = 1.17, P = 0.03). The overall quality was rated as moderate using GRADE guideline. Our study strengthens the evidence on the increase in CMD risk due to LAN exposure. Findings from this study have important implications for identifying modifiable risk factor of CMD, future prevention strategy development, and resource allocation for high-risk group.

Outdoor artificial light at night and male sperm quality: A retrospective cohort study in China

Due to the worldwide increased rate of infertility among reproductive-age couples, there is a growing interest in the relationship between environmental stimuli and human sperm quality. While animal studies have demonstrated the detrimental effects of outdoor artificial light at night (ALAN) on sperm quality, investigations based on human data are lacking. Therefore, we conducted a retrospective cohort study involving 1991 sperm donor candidates and employed multivariate linear regression and restricted cubic spline models to quantify the association between outdoor ALAN and sperm quality. The aim was to determine whether there exists an association between exposure to outdoor ALAN and sperm quality. The study included 1991 sperm donor candidates with the following characteristics: mean [SD] age, 24.98 [4.78] years; mean [SD] BMI, 22.13 [2.60] kg/m2; mean [SD] sleep duration, 7.66 [1.07] hours/day. Outdoor ALAN exposure of study participants ranged from 0 to 100 nW/cm2/sr. Multiple regression analysis on chronic exposure (0-90 days before sperm donation) and human sperm quality revealed the following associations: for CASA primary motion parameters, every 100-unit (nW/cm2/sr) increase in chronic outdoor ALAN was associated with a change of -0.043 [95%CI: 0.073, -0.014] in Linearity (LIN), and -5.523 [95%CI: 9.100, -1.946] in Curvilinear velocity (VCL). For CASA secondary motion parameters, every 100-unit (nW/cm2/sr) increase in chronic outdoor ALAN was associated with a change of -3.873 [95%CI: 4.926, -2.748] in non-progressive motility rate (NP). Furthermore, the primary sperm quality parameter exhibited a decline of -4.740 [95%CI: 8.853, -0.628] in sperm motility rate per 100-unit (nW/cm2/sr) increase in chronic outdoor ALAN. Similar associations were also observed for acute exposure (0-9 days before sperm donation). This retrospective study suggests that poorer sperm quality is more prevalent among adult males residing in areas with higher levels of outdoor ALAN, with a particularly pronounced impact observed in males below the age of 25 years.

Chlordane exposure impairs the growth and behavior of Drosophila

Chlordane, a previously extensively utilized insecticidal pesticide, has since been prohibited, however, owing to its limited degradability, it continues to persist significantly in soil and water reservoirs, subsequently accumulating within plant and animal organisms, representing a substantial threat to human health. Despite extensive research conducted over the past few decades to investigate the toxic effects of chlordane, there remains a notable dearth of studies focusing on its impact on sleep activity. Therefore, in this study, the effects of short-term and long-term exposure to chlordane on the activity and sleep of Drosophila were investigated. When exposed to chlordane at a concentration of 1 μM, Drosophila lost body weight, decreased body size and resulted in lipid metabolism disorders. In addition, chlordane exposure altered the arousal and sleep behaviors of Drosophila. Short-term exposure to chlordane resulted in an increase in night-time sleep duration, while long-term exposure to chlordane resulted in an increase in activity and a decrease in sleep, as evidenced by a decrease in the duration of each sleep session and the appearance of sleep fragmentation. Under conditions of long-term chlordane exposure, reactive oxygen species levels were significantly up-regulated in Drosophila. Our results suggest that long-term chlordane exposure triggers oxidative stress damage in Drosophila, leading to sleep disruption. This study offers novel insights into the harmful impacts of environmental pollutants on human sleep patterns and proposes that mitigating the presence of chlordane in the environment could potentially contribute to the reduction of global sleep disorder prevalence.

Light at night exposure and risk of breast cancer: a meta-analysis of observational studies

Objective

The aim of this meta-analysis is to evaluate the impact of light at night (LAN) exposure on the risk of breast cancer across varying factors.

Method

We conducted a systematic search of literature up to July 15, 2023, including PubMed, Cochrane Library, and Embase databases, using keywords related to breast cancer and LAN exposure. Cohort study and case-control study literature on night light exposure and breast cancer risk were included. Statistical analyses were performed using Stata software version 17.0. To address heterogeneity among different studies, we employed a random-effects model for analysis and assessed publication bias using funnel plots and Egger's test.

Results

We included 13 case-control and 8 cohort studies with 734,372 participants worldwide. In the Newcastle-Ottawa Scale (NOS) assessments, the average score was 7.43 (ranging from 5 to 9). The overall meta-analysis demonstrated a significant association between exposure to LAN and risk of breast cancer (RR = 1.12; 95% CI: 1.06-1.17; I2 = 31.3%, p < 0.001). In the subgroup analysis, the results of the analysis for study types (case-control studies: RR = 1.16; 95% CI: 1.06-1.27; I2 = 40.4%, p = 0.001; cohort studies: RR = 1.08; 95% CI: 1.04-1.14; I2 = 0.0%, p < 0.001) and the results for light exposure types (outdoor LAN: RR = 1.07; 95% CI: 1.02-1.13; I2 = 30.9%, p = 0.004) are presented. In the analysis conducted for continents, the highest breast cancer risk was observed in the Asian population (Asian: RR = 1.24; 95% CI: 1.15-1.34; I2 = 0.0%, p < 0.001) and in the analysis of estrogen receptor status (ER+: RR = 1.10; 95% CI: 1.03-1.18; I2 = 17.0%, p = 0.005;). We also conducted an analysis on menopausal status and various lifestyles but did not find any statistically significant findings.

Conclusion

Our study demonstrates that LAN exposure is associated with an increased risk of breast cancer, particularly in the Asian population. Among the existing hypotheses, the idea that LAN exposure leads to a decrease in melatonin is widely accepted. However, until the mechanism of this effect is clearly elucidated, it is not recommended to take melatonin supplements for breast cancer prevention without medical advice. We hope to conduct more high-quality research, especially concerning the investigation of other environmental confounding factors, to further advance this field.

Outdoor artificial light at night and risk of early-onset dementia: A case-control study in the Modena population, Northern Italy

Background

Dementia is a neurological syndrome characterized by severe cognitive impairment with functional impact on everyday life. It can be classified as young onset dementia (EOD) in case of symptom onset before 65, and late onset dementia (LOD). The purpose of this study is to assess the risk of dementia due to light pollution, and specifically outdoor artificial light at night (LAN).

Methods

Using a case-control design, we enrolled dementia patients newly-diagnosed in the province of Modena in the period 2017-2019 and a referent population from their caregivers. We geo-referenced the address of residence on the date of recruitment, provided it was stable for the previous five years. We assessed LAN exposure through 2015 nighttime luminance satellite images from the Visible Infrared Imaging Radiometer Suite (VIIRS). Using a logistic regression model adjusted for age, sex, and education, we calculated the risk of dementia associated with increasing LAN exposure, namely using <10 nW/cm²/sr as reference and considering ≥10-<40 nW/cm²/sr intermediate and ≥40 nW/cm²/sr high exposure, respectively We also implemented non-linear assessment using a spline regression model.

Results

We recruited 58 EOD cases, 34 LOD cases and 54 controls. Average LAN exposure levels overlapped for EOD cases and controls, while LOD cases showed higher levels. Compared with the lowest exposure, the risk of EOD associated with LAN was higher in the intermediate exposure (OR = 1.36, 95% CI 0.54-3.39), but not in the high exposure category (OR = 1.04, 95% CI 0.32-3.34). In contrast, the risk of LOD was positively associated with LAN exposure, with ORs of 2.58 (95% CI 0.26-25.97) and 3.50 (95% CI 0.32-38.87) in the intermediate and high exposure categories, respectively. The spline regression analysis showed substantial lack of association between LAN and EOD, while almost linear although highly imprecise association emerged for LOD.

Conclusions

Although the precision of the estimates was affected by the limited sample size and the study design did not allow us to exclude the presence of residual confounding, these results suggest a possible role of LAN in the etiology of dementia, particularly of its late-onset form.

Time Spent Outdoors and Associations with Sleep, Optimism, Happiness and Health before and during the COVID-19 Pandemic in Austria

Social restriction measures (SRM) implemented during the COVID-19 pandemic led to a reduction in time spent outdoors (TSO). The aim of this study was to describe TSO and evaluate its association with sleep outcomes, optimism, happiness and health-status before and during SRM. Two online surveys were conducted in 2017 (N = 1004) and 2020, during SRM (N = 1010), in samples representative of the age, sex and region of the Austrian population. Information on the duration of TSO, sleep, optimism, happiness and health-status was collected. Multivariable-adjusted logistic regression models were used to study the association of TSO with chronic insomnia, short sleep, late chronotype, optimism, happiness and self-rated health-status. The mean TSO was 3.6 h (SD: 2.18) in 2017 and 2.6 h (SD: 1.87) during times of SRM. Men and participants who were older, married or in a partnership and lived in a rural area reported longer TSO. Participants who spent less time outdoors were more likely to report short sleep or a late chronotype in both surveys and, in 2020, also chronic insomnia. Less TSO was associated with lower happiness and optimism levels and poor health-status. Our findings suggest that TSO may be a protective factor for sleep, mood and health, particularly during stressful and uncertain times.

Outdoor light at night, genetic predisposition and type 2 diabetes mellitus: A prospective cohort study

BACKGROUND

According to animal and human epidemiologic studies, exposure to outdoor light at night (LAN) may cause circadian disruption, which may disturb sleep quality and lead to incident type 2 diabetes mellitus (T2DM).

METHODS

We followed 283,374 persons from 2006 through 2020. Outdoor LAN exposure was estimated using satellite data for individual address with 500 m² scale buffer during follow-up. Incidence of T2DM was confirmed by hospital inpatient records. We identified potential confounders by a directed acyclic graph, including demographic, genetic, individual and regional level socioeconomic status, and environmental risk factors, and calculated hazard ratios (HRs) and 95% confidence intervals (CIs) through time-varying Cox proportional hazard model. Furthermore, we examined the association of outdoor LAN with a defined health sleep scores and moderation of genetic predisposition and shift work on the relationship of outdoor LAN and incident T2DM.

RESULTS

We identified 7,775 incident T2DM cases over 3,027,505 person-years. Higher outdoor LAN exposures were significantly associated with higher risk of T2DM. The estimated HR for incident T2DM with an interquartile range (IQR: 11.22 nW/cm²/sr) increase in outdoor LAN was 1.05 (95%CI: 1.01, 1.09) in the fully adjusted model. Participants who lived in the highest quarter of outdoor LAN area were more likely to develop T2DM (HR: 1.14,95%CI: 1.02, 1.27). Besides, those who were exposed to higher levels of outdoor LAN had poorer sleep quality. No moderation role of PRS on outdoor LAN-induced T2DM observed both on the multiplicated and additive scale. The hazards of outdoor LAN were observed in those who never owned a night shift work.

CONCLUSION

Although further work is required to clarify potential mechanisms, our findings indicate that exposure to residential outdoor LAN may contribute to T2DM risk and low sleep quality.