Outdoor light at night and postmenopausal breast cancer risk in the NIH-AARP diet and health study

Exposure to Light at Night and Risk of Cancer: A Systematic Review, Meta-Analysis, and Data Synthesis

BACKGROUND

Emerging interest surrounds the role of environmental factors, notably exposure to light at night (LAN), as a potential cause of cancer. The aim of this study was to conduct a systematic review and, if possible, meta-analysis of observational studies on LAN and cancer risk of multiple types.

METHODS

A systematic literature search in PubMed, Web of Science, and Embase, spanning from inception to May 2023, was conducted. Studies focusing on the association between LAN exposure and cancer risk in adult populations were included. We used random effects models to calculate pooled risk estimates (RR) and 95% confidence intervals (CI). We assessed study quality using the Risk of Bias in Non-randomized Studies of Interventions.

RESULTS

Among 8492 initially identified studies, 26 met the inclusion criteria (13 were case-control and 13 were cohort studies). These studies were published from 2001 to 2023 and assessed diverse cancer types in North America, Asia, Europe, and Australia. Except for breast cancer, there was a paucity of site-specific cancer studies. In the meta-analysis of 19 breast cancer studies, higher exposure to indoor (summary RR, 1.08; 95% CI 1.01-1.15) and outdoor (summary RR, 1.10; 95% CI, 1.04-1.15) LAN were associated with increased risk. After excluding one low-quality study, the results were unchanged.

CONCLUSIONS

We found a positive association between LAN exposure and breast cancer risk in women. However, data are lacking for other cancer types, and further studies are required to better understand the role of LAN on cancer.

Mobility-oriented measurements of people's exposure to outdoor artificial light at night (ALAN) and the uncertain geographic context problem (UGCoP)

Advanced nighttime light (NTL) remote sensing techniques enable the large-scope epidemiological investigations of people's exposure to outdoor artificial light at night (ALAN) and its health effects. However, multiple uncertainties remain in the measurements of people's exposure to outdoor ALAN, including the representations of outdoor ALAN, the contextual settings of exposure measurements, and measurement approaches. Non-exposed but included outdoor ALAN and causally irrelevant outdoor ALAN may manifest as contextual errors, and these uncertain contextual errors may lead to biased measurements and erroneous interpretations when modeling people's health outcomes. In this study, we systematically investigated outdoor ALAN exposure measurements in different geographic contexts using either residence-based or mobility-oriented measurements, different spatial scales, and multiple NTL data sources. Based on the GPS data collected from 208 participants in Hong Kong, outdoor ALAN exposures were measured from NTL imagery at 10 m, 130 m, and 500 m spatial resolutions using in-situ methods or 100 m, 300 m, and 500 m buffer zone averaging. Descriptive analysis, multiple t-tests, and logistic regression were employed to examine the differences between outdoor ALAN exposure measurements using various contextual settings and their effects on modeling people's overall health. Our results confirmed that different contextual settings may lead to significantly different outdoor ALAN exposure measurements. Our results also confirmed that contextual errors may lead to erroneous conclusions when using improper contextual settings to model people's overall health. Consequentially, we suggest measuring people's exposure to outdoor ALAN using the mobility-oriented approach, NTL representation with the high spatial resolution, and a very small buffer zone as a contextual unit to derive outdoor ALAN exposure. This study articulates essential methodological issues induced by uncertainties in outdoor ALAN exposure measurements and can provide essential implications and suggestions for a broad scope of studies that need accurate outdoor ALAN exposure measurements.

Molecular mechanisms of artificial light at night affecting circadian rhythm disturbance

Artificial light at night (ALAN) pollution has been regarded as a global environmental concern. More than 80% of the global population is exposed to light pollution. Exacerbating this issue, artificially lit outdoor areas are growing by 2.2% per year, while continuously lit areas have brightened by 2.2% each year due to rapid population growth and expanding urbanization. Furthermore, the increasing prevalence of night shift work and smart device usage contributes to the inescapable influence of ALAN. Studies have shown that ALAN can disrupt endogenous biological clocks, resulting in a disturbance of the circadian rhythm, which ultimately affects various physiological functions. Up until now, scholars have studied various disease mechanisms caused by ALAN that may be related to the response of the circadian system to light. This review outlines the molecular mechanisms by which ALAN causes circadian rhythm abnormalities in sleep disorders, endocrine diseases, cardiovascular disease, cancer, immune impairment, depression, anxiety and cognitive impairments.

Ambient fine particulate matter and breast cancer incidence in a large prospective US cohort

BACKGROUND

Fine particulate matter (PM2.5) has been inconsistently associated with breast cancer incidence, however, few studies have considered historic exposure when levels were higher.

METHODS

Outdoor residential PM2.5 concentrations were estimated using a nationwide spatiotemporal model for women in the National Institutes of Health-AARP Diet and Health Study, a prospective cohort located in 6 states (California, Florida, Louisiana, New Jersey, North Carolina, and Pennsylvania) and 2 metropolitan areas (Atlanta, GA, and Detroit, MI) and enrolled in 1995-1996 (n = 196 905). Annual average PM2.5 concentrations were estimated for a 5-year historical period 10 years prior to enrollment (1980-1984). We used Cox regression to estimate adjusted hazard ratios (HRs) and 95% confidence intervals (CIs) for the association between a 10 µg/m3 increase in PM2.5 and breast cancer incidence overall and by estrogen receptor status and catchment area.

RESULTS

With follow-up of participants through 2017, a total of 15 870 breast cancer cases were identified. A 10 ug/m3 increase in PM2.5 was statistically significantly associated with overall breast cancer incidence (HR = 1.08, 95% CI = 1.02 to 1.13). The association was evident for estrogen receptor-positive (HR = 1.10, 95% CI = 1.04 to 1.17) but not estrogen receptor-negative tumors (HR = 0.97, 95% CI = 0.84 to 1.13; Pheterogeneity = .3). Overall breast cancer hazard ratios were more than 1 across the catchment areas, ranging from a hazard ratio of 1.26 (95% CI = 0.96 to 1.64) for North Carolina to a hazard ratio of 1.04 (95% CI = 0.68 to 1.57) for Louisiana (Pheterogeneity = .9).

CONCLUSIONS

In this large US cohort with historical air pollutant exposure estimates, PM2.5 was associated with risk of estrogen receptor-positive breast cancer. State-specific estimates were imprecise but suggest that future work should consider region-specific associations and the potential contribution of PM2.5 chemical constituency in modifying the observed association.

Understanding the role of environmental and socioeconomic factors in the geographic variation of breast cancer risk in the US-wide Sister Study

OBJECTIVE

To describe the geographic pattern of breast cancer incidence in a nationwide prospective cohort and investigate whether environmental exposures and/or neighborhood socioeconomic status explain observed geographic disparities.

METHODS

Using accelerated failure time models with a spatial random effect term, we mapped the health region-level association between residential location and breast cancer incidence for 44,707 participants in the Sister Study after controlling for established individual-level breast cancer risk factors. We performed a variable selection process to select environmental exposures [i.e., ambient nitrogen dioxide (NO2) and fine particulate matter (PM2.5), PM2.5 chemical composition, outdoor light at night (LAN), ambient noise, ultraviolet radiation, and greenspace] and neighborhood-level factors [i.e., population density and area deprivation index (ADI)] that predicted breast cancer incidence and quantified the spatial variation explained by the selected factors. We also considered whether the geographic pattern and predictors were similar when restricting to estrogen receptor-positive (ER+) tumors.

RESULTS

We observed a spatial patterning in the incidence of overall breast cancer (Moran's I = 16.7, p < 0.05) and ER+ breast cancer (Moran's I = 13.2, p < 0.05), with a lower risk observed in the South and Southeast and a greater risk in the Northwest and certain areas of the Midwest and Northeast. NO2, LAN, and ADI explained 21.4% of the spatial variation in overall breast cancer incidence whereas NO2, PM2.5 chemical composition, LAN, greenspace, and ADI together explained 63.3% of the spatial variation in ER+ breast cancer incidence.

CONCLUSIONS

Our findings provide additional evidence for a role of environmental exposures in breast cancer incidence and suggest that geographic-based risk factors may vary according to breast cancer subtype. Our findings support the need for additional research to quantify the relative contributions of geographic-based risk factors for breast cancer.

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.

County-level artificial light at night (ALAN) in the contiguous US (2012-2019): spatial variations, temporal trends, and environmental justice analyses

Artificial light at night (ALAN) is a growing environmental hazard with economic, ecological, and public health implications. Previous studies suggested a higher burden of light pollution and related adverse effects in disadvantaged communities. It is critical to characterize the geographic distribution and temporal trend of ALAN and identify associated demographic and socioeconomic factors at the population level to lay the foundation for environmental and public health monitoring and policy-making. We used satellite data from the Black Marble suite to characterize ALAN in all counties in contiguous US and reported considerable variations in ALAN spatiotemporal patterns between 2012 and 2019. As expected, ALAN levels were generally higher in metropolitan and coastal areas; however, several rural counties in Texas experienced remarkable increase in ALAN since 2012, while population-level ALAN burden also increased substantially in many metropolitan areas. Importantly, we found that during this period, although the overall ALAN levels in the USA declined modestly, the temporal trend of ALAN varied across areas with different racial/ethnic compositions: counties with a higher percentage of racial/ethnic minority groups, particularly Hispanic populations, exhibited significantly less decline. As a result, the differences in ALAN levels, as measured by the Black Marble product, across racial/ethnic groups became larger between 2012 and 2019. In conclusion, our study documented variations in ALAN spatiotemporal patterns across America and identified multiple population correlates of ALAN patterns that warrant further investigations. Future studies should identify underlying factors (e.g., economic development and decline, urban planning, and transition to newer lighting technologies such as light emitting diodes) that may have contributed to ALAN disparities in the USA.

Circadian pattern subtyping unveiling distinct immune landscapes in breast cancer patients for better immunotherapy

BACKGROUND

While epidemiological studies have established a firm link between circadian disruption and tumorigenesis, the role and mechanism are not fully understood, complicating the design of therapeutic targets related to circadian rhythms (CR). Here, we aimed to explore the intertumoral heterogeneity of CR and elucidate its impact on the tumor microenvironment (TME), drug sensitivity, and immunotherapy.

METHODS

Based on unsupervised clustering of 28 CR genes, two distinct CR subtypes (cluster-A and cluster-B) were identified in the TCGA cohort. We further constructed a circadian rhythm signature (CRS) based on the CR genes primarily responsible for clustering to quantify CR activity and to distinguish CR subtypes of individual patients from external datasets. CR subtypes were evaluated by TME characteristics, functional annotation, clinical features, and therapeutic response.

RESULTS

The cluster-B (low-CRS) group was characterized by highly enriched immune-related pathways, high immune cell infiltration, and high anti-tumor immunity, while the cluster-A (high-CRS) group was associated with immunosuppression, synaptic transmission pathways, EMT activation, poor prognosis, and drug resistance. Immunohistochemistry (IHC) results demonstrated that high CD8+ T cell infiltration was associated with low-CR-protein expression. Importantly, patients with low CRS were more likely to benefit from immune checkpoint blockade (ICB) treatment, possibly due to their higher tumor mutation burden (TMB), increased immune checkpoint expression, and higher proportion of "hot" immunophenotype.

CONCLUSION

In a nutshell, the cross talk in CR could reflect the TME immunoreactivity in breast cancer. Besides providing the first comprehensive pathway-level analysis of CR in breast cancer, this work highlights the potential clinical utility of CR for immunotherapy.

Artificial light at night and social vulnerability: An environmental justice analysis in the U.S. 2012-2019

BACKGROUND

Artificial Light at Night (ALAN) is an emerging health risk factor that has been linked to a wide range of adverse health effects. Recent study suggested that disadvantaged neighborhoods may be exposed to higher levels of ALAN. Understanding how social disadvantage correlates with ALAN levels is essential for identifying the vulnerable populations and for informing lighting policy.

METHODS

We used satellite data from the National Aeronautics and Space Administration's (NASA) Black Marble data product to quantify annual ALAN levels (2012-2019), and the Center for Disease Control and Prevention's (CDC) Social Vulnerability Index (SVI) to quantify social disadvantage, both at the US census tract level. We examined the relationship between the ALAN and SVI (overall and domain-specific) in over 70,000 tracts in the Contiguous U.S., and investigated the heterogeneities in this relationship by the rural-urban status and US regions (i.e., Northeast, Midwest, South, West).

RESULTS

We found a significant positive relationship between SVI and ALAN levels. On average, the ALAN level in the top 20% most vulnerable communities was 2.46-fold higher than that in the 20% least vulnerable communities (beta coefficient (95% confidence interval) for log-transformed ALAN, 0.90 (0.88, 0.92)). Of the four SVI domains, minority and language status emerged as strong predictors of ALAN levels. Our stratified analysis showed considerable and complex heterogeneities across different rural-urban categories, with the association between greater vulnerability and higher ALAN primarily observed in urban cores and rural areas. We also found regional differences in the association between ALAN and both overall SVI and SVI domains.

CONCLUSIONS

Our study suggested ALAN as an environmental justice issue that may carry important public health implications. Funding National Aeronautics and Space Administration.

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.

Circadian rhythm disrupting behaviours and cancer outcomes in breast cancer survivors: a systematic review

PURPOSE

Circadian rhythm disruptors (e.g., night-shift work) are risk factors for breast cancer, however studies on their association with prognosis is limited. A small but growing body of research suggests that altered sleep patterns and eating behaviours are potential mechanistic links between circadian rhythm disruptors and breast cancer. We therefore systematically summarised literature examining the influence of circadian rhythm disrupting behaviours on cancer outcomes in women with breast cancer.

METHODS

A systematic search of five databases from inception to January 2021 was conducted. Original research published in English, assessing the relationship between post-diagnosis sleep patters and eating behaviours, and breast cancer outcomes were considered. Risk of bias was assessed using the Newcastle-Ottawa Assessment Scale for Cohort Studies.

RESULTS

Eight studies published original evidence addressing sleep duration and/or quality (k = 7) and, eating time and frequency (k = 1). Longer sleep duration (≥ 9 h versus [referent range] 6-8 h) was consistently associated with increased risk of all outcomes of interest (HR range: 1.37-2.33). There was limited evidence to suggest that measures of better sleep quality are associated with lower risk of all-cause mortality (HR range: 0.29-0.97). Shorter nightly fasting duration (< 13 h versus ≥ 13 h) was associated with higher risk of all breast cancer outcomes (HR range: 1.21-1.36).

CONCLUSION

Our review suggests that circadian rhythm disrupting behaviours may influence cancer outcomes in women with breast cancer. While causality remains unclear, to further understand these associations future research directions have been identified. Additional well-designed studies, examining other exposures (e.g., light exposure, temporal eating patterns), biomarkers, and patient-reported outcomes, in diverse populations (e.g., breast cancer subtype-specific, socio-demographic diversity) are warranted.

Light at night and cause-specific mortality risk in Mainland China: a nationwide observational study

BACKGROUND

While epidemiological studies have found correlations between light at night (LAN) and health effects, none has so far investigated the impacts of LAN on population mortality yet. We aimed to estimate the relative risk for mortality from exposure to LAN in Mainland China.

METHODS

This time-stratified case-crossover nationwide study used NPP-VIIRS to obtain daily LAN data of Mainland China between 2015 and 2019. The daily mortality data were obtained from the Disease Surveillance Point System in China. Conditional Poisson regression models were applied to examine the relative risk (RR) for mortality along daily LAN in each county, then meta-analysis was performed to combine the county-specific estimates at the national or regional level.

RESULTS

A total of 579 counties with an average daily LAN of 4.39 (range: 1.02-35.46) were included in the main analysis. The overall RRs per 100 nW/cm²/sr increases in daily LAN were 1.08 (95%CI: 1.05-1.11) for all-cause mortality and 1.08 (95%CI: 1.05-1.11) for natural-cause mortality. A positive association between LAN and all natural cause-specific mortality was observed, of which the strongest effect was observed on mortality caused by neuron system disease (RR = 1.32, 95%CI: 1.14-1.52). The results were robust in both younger and old, as well as in males and females. The more pronounced effect of LAN was observed in median LAN-level regions. Combined with an exposure-response curve, our study suggests a non-linear association between LAN and mortality in China.

CONCLUSIONS

Our study shows LAN is associated with mortality in China, particularly for neuron system disease-related mortality. These findings have important implications for public health policy establishment to minimize the health consequences of light pollution.

Outdoor light at night and risk of endometrial cancer in the NIH-AARP diet and health study

PURPOSE

Outdoor light at night (LAN) can result in circadian disruption and hormone dysregulation and is a suspected risk factor for some cancers. Our study is the first to evaluate the association between LAN and risk of endometrial cancer, a malignancy with known relationship to circulating estrogen levels.

METHODS

We linked enrollment addresses (1996) for 97,677 postmenopausal women in the prospective NIH-AARP cohort to satellite imagery of nighttime radiance to estimate LAN exposure. Multivariable Cox models estimated hazard ratios (HR) and 95% confidence intervals (95% CI) for LAN quintiles and incident endometrial cancer overall (1,669 cases) and endometrioid adenocarcinomas (991 cases) through follow-up (2011). We tested for interaction with established endometrial cancer risk factors.

RESULTS

We observed no association for endometrial cancer overall (HR_Q1vsQ5 0.92; 95% CI 0.78-1.08; p trend = 0.67) or endometrioid adenocarcinoma (HR_Q1vsQ5 1.01; 95% CI 0.82-1.24; p trend = 0.36). Although body mass index and menopause hormone therapy were both associated with risk, there was no evidence of interaction with LAN (p interactions = 0.52 and 0.50, respectively).

CONCLUSION

Our study did not find an association between outdoor LAN and endometrial cancer risk, but was limited by the inability to account for individual-level exposure determinants. Future studies should consider approaches to improve characterization of personal exposures to light.

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.

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.

Light at night and the risk of breast cancer: Findings from the Sister study

BACKGROUND

Light at night (LAN) may alter estrogen regulation through circadian disruption. High levels of outdoor LAN may increase breast cancer risk, but studies have largely not considered possible residual confounding from correlated environmental exposures. We evaluated the association between indoor and outdoor LAN and incident breast cancer.

METHODS

In 47,145 participants in the prospective Sister Study cohort living in the contiguous U.S., exposure to outdoor LAN was determined using satellite-measured residential data and indoor LAN was self-reported (light/TV on, light from outside the room, nightlight, no light). We used Cox proportional hazards models to calculate hazard ratios (HRs) and 95% confidence intervals (CIs) for the associations between outdoor and indoor LAN and breast cancer risk. Models were adjusted for age, race/ethnicity, educational attainment, annual household income, neighborhood disadvantage, latitude, and population density as a proxy for urbanicity. To evaluate the potential for residual confounding of the outdoor LAN and breast cancer relationship by factors associated with urbanicity, we considered further adjustment for exposures correlated with outdoor LAN including NO2 [Spearman correlation coefficient, rho (ρ) = 0.78], PM2.5 (ρ = 0.36), green space (ρ =  - 0.41), and noise (ρ = 0.81).

RESULTS

During 11 years of follow-up, 3,734 breast cancer cases were identified. Outdoor LAN was modestly, but non-monotonically, associated with a higher risk of breast cancer (Quintile 4 vs 1: HR = 1.10, 95% CI: 0.99-1.22; Quintile 5 vs 1: HR = 1.04, 95% CI: 0.93-1.16); however, no association was evident after adjustment for correlated ambient exposures (Quintile 4 vs 1: HR = 0.99, 95% CI: 0.86-1.14; Quintile 5 vs 1: HR = 0.89, 95% CI: 0.74-1.06). Compared to those with no indoor LAN exposure, sleeping with a light or TV on was associated with a HR = 1.09 (95% CI: 0.97-1.23) in the adjusted model.

CONCLUSIONS

Outdoor LAN does not appear to increase the risk of breast cancer after adjustment for correlated environmental exposures.

Integrating Multiscale Geospatial Environmental Data into Large Population Health Studies: Challenges and Opportunities

Quantifying the exposome is key to understanding how the environment impacts human health and disease. However, accurately, and cost-effectively quantifying exposure in large population health studies remains a major challenge. Geospatial technologies offer one mechanism to integrate high-dimensional environmental data into epidemiology studies, but can present several challenges. In June 2021, the National Institute of Environmental Health Sciences (NIEHS) held a workshop bringing together experts in exposure science, geospatial technologies, data science and population health to address the need for integrating multiscale geospatial environmental data into large population health studies. The primary objectives of the workshop were to highlight recent applications of geospatial technologies to examine the relationships between environmental exposures and health outcomes; identify research gaps and discuss future directions for exposure modeling, data integration and data analysis strategies; and facilitate communications and collaborations across geospatial and population health experts. This commentary provides a high-level overview of the scientific topics covered by the workshop and themes that emerged as areas for future work, including reducing measurement errors and uncertainty in exposure estimates, and improving data accessibility, data interoperability, and computational approaches for more effective multiscale and multi-source data integration, along with potential solutions.

Outdoor light at night and risk of liver cancer in the NIH-AARP diet and health study

PURPOSE

Accumulating evidence suggests that light at night (LAN) disrupts circadian rhythms and may increase risk of liver cancer. However, there is no population-based study that examined LAN and liver cancer risk. Therefore, we aimed to investigate the association between outdoor LAN and liver cancer risk in a prospective cohort.

METHODS

Residential outdoor LAN level was measured from satellite imagery in the NIH-AARP Diet and Health Study, a prospective cohort of 451,945 men and women, 50-71 years old. Relative risks (RR) and 95% confidence intervals (CIs) were estimated using Cox proportional hazard models that adjusted for known risk factors for liver cancer and neighborhood characteristics.

RESULTS

During an average 12.2 years of follow-up, 897 liver cancers, 603 of which were hepatocellular carcinomas (HCC), were diagnosed. Residential outdoor LAN was not associated with risk of liver cancer (RR_{Q5 vs Q1} = 0.96, 95% CI: 0.77-1.20, p trend = 0.771) or HCC (RR_{Q5 vs Q1} = 0.82, 95% CI: 0.62-1.07, p trend = 0.425).

CONCLUSION

No association between outdoor LAN and risk of liver cancer or HCC may in part be due to limitations in LAN assessment. More studies on the relationship between light intensity, duration, timing, and wavelength and liver cancer are warranted.

Light at night and risk of breast cancer: a systematic review and dose-response meta-analysis

Breast cancer is the most common malignancy in women and the second leading cause of cancer death overall. Besides genetic, reproductive, and hormonal factors involved in disease onset and progression, greater attention has focused recently on the etiologic role of environmental factors, including exposure to artificial lighting such as light-at-night (LAN). We investigated the extent to which LAN, including outdoor and indoor exposure, affects breast cancer risk. We performed a systematic review of epidemiological evidence on the association between LAN exposure and breast cancer risk, using a dose–response meta-analysis to examine the shape of the relation. We retrieved 17 eligible studies through September 13, 2021, including ten cohort and seven case–control studies. In the analysis comparing highest versus lowest LAN exposure, we found a positive association between exposure and disease risk (risk ratio [RR] 1.11, 95% confidence interval-CI 1.07–1.15), with comparable associations in case–control studies (RR 1.14, 95% CI 0.98–1.34) and cohort studies (RR 1.10, 95% CI 1.06–1.15). In stratified analyses, risk was similar for outdoor and indoor LAN exposure, while slightly stronger risks were observed for premenopausal women (premenopausal: RR 1.16, 95% CI 1.04–1.28; postmenopausal: 1.07, 95% CI 1.02–1.13) and for women with estrogen receptor (ER) positive breast cancer (ER + : RR 1.09, 95% CI 1.02–1.17; ER–: RR 1.07, 95% CI 0.92–1.23). The dose–response meta-analysis, performed only in studies investigating outdoor LAN using comparable exposure assessment, showed a linear relation up to 40 nW/cm²/sr after which the curve flattened, especially among premenopausal women. This first assessment of the dose–response relation between LAN and breast cancer supports a positive association in selected subgroups, particularly in premenopausal women.

Acute mild dim light at night slightly modifies sleep but does not affect glucose homeostasis in healthy men

OBJECTIVE

We evaluated the effect of acute mild light exposure at night on sleep architecture and glucose homeostasis.

PATIENTS/METHODS

Twenty healthy normal-weight men took part in two conditions of a randomized, controlled, balanced cross-over experimental study: i) two-consecutive nights with 8-h of sleep under dLAN (<5 lux) or ii) total darkness (CON). Sleep was evaluated by polysomnography. In the morning following 'night2', glucose homeostasis was assessed by an intravenous glucose tolerance test (ivGTT) with consecutive measures of glucose, insulin, and c-peptide. Plasma cortisol was measured at night before sleep, after morning awakening, and during mid-afternoon hours.

RESULTS

There was no significant difference in total sleep time, sleep efficiency, and sleep latency between conditions (all p > 0.66). However, NREM sleep stage N3 latency was prolonged after dLAN (p = 0.02) and NREM sleep stage 2 was decreased after two nights with dLAN (p = 0.04). During the first sleep hour, power in slow-oscillations, slow-waves, and delta bands diminished after dLAN (all p < 0.04). Glucose, insulin, and c-peptide were not altered by dLAN (all p > 0.14). Cortisol was reduced in the afternoon after 'night1' and in the morning after 'night2' (both p < 0.03).

CONCLUSIONS

dLAN slightly disturbed sleep architecture and quality without impairment of glucose homeostasis. Longer exposure to chronic dLAN might be needed to unmask its hypothesized metabolic consequences.

Outdoor artificial light at night: A forgotten factor in green space and health research

Exposure to green space has been associated with a range of human health benefits, largely in spatial epidemiological studies. Green space and artificial light at night are both associated with breast and prostate cancer, depressive symptoms, obesity, and sleep problems, and are both influenced by the built environment and urbanisation. We identified a negative correlation between green space diversity and outdoor artificial light at night for Australian major cities. Outdoor artificial light at night is therefore a potential, but overlooked, confounder in spatial epidemiological studies of green space exposure and human health, and should be incorporated into future models.

Associations of long-term exposure to environmental noise and outdoor light at night with age at natural menopause in a US women cohort

Previous studies have suggested noise, especially at night time, and light at night (LAN) could cause neuroendocrine disturbance and circadian disruption, which may lead to ovarian follicle atresia and earlier onset of menopause. However, no study to date has directly investigated the associations of exposure to these factors and menopausal age.

Methods

Premenopausal women from the Nurses' Health Study II (NHS II) were followed from age 40 through 2015. Median daytime and nighttime anthropogenic noise and outdoor LAN exposure were measured from a geospatial prediction model and satellite images, respectively, at residential addresses throughout the follow-up. Time-varying Cox proportional hazard models were used to calculate the hazard ratios and 95% confidence intervals, adjusting for individual lifestyle, reproductive history, and neighborhood socioeconomic factors. Possible effect modification by region, smoking status, body mass index, race/ethnicity, history of rotating shift work, and census tract population density and median income was examined.

Results

A total of 63,380 of 105,326 women self-reported natural menopause during 1,043,298 person-years of follow-up. No associations were found for noise (both daytime and nighttime) and outdoor LAN exposure with age at natural menopause (hazard ratios = 0.99-1.00) in the fully adjusted models. Sensitivity analyses showed similar null associations. No meaningful effect modification was found for region, smoking status, body mass index, race/ethnicity, history of rotating shift work, and census tract socioeconomic measures in stratified analyses.

Conclusion

No associations were found between environmental noise and outdoor LAN exposure in mid-adulthood and menopausal age in this cohort of US women.

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.

Light at Night and Risk of Pancreatic Cancer in the NIH-AARP Diet and Health Study

Circadian disruption may play a role in carcinogenesis. Recent research suggests that light at night (LAN), a circadian disruptor, may be a risk factor for cancer. Moreover, LAN has been linked to obesity and diabetes, two risk factors for pancreatic ductal adenocarcinoma (PDAC). Here we examine the relationship between LAN and PDAC in an epidemiologic study of 464,371 participants from the NIH-AARP Diet and Health Study. LAN was estimated from satellite imagery at baseline (1996), and incident primary PDAC cases were ascertained from state cancer registries. Cox proportional hazards models were used to estimate HRs and two-sided 95% confidence intervals (CI) for the association between quintiles of LAN and PDAC in the overall population stratified by sex. Over up to 16.2 years of follow-up, a total of 2,502 incident PDAC were identified in the cohort. Higher estimated LAN exposure was associated with an elevated PDAC risk. Compared with those living in areas in the lowest LAN quintile, those in areas in the highest quintile had a 27% increase PDAC risk [HR (95% CI), 1.24 (1.03-1.49)], with similar risk for men [1.21 (0.96-1.53)] and women [1.28 (0.94-1.75)]. In addition, stronger associations were observed in normal and overweight groups compared with the obese group (P interaction = 0.03). Our results support the hypothesis that LAN and circadian disruption may be risk factors for PDAC. SIGNIFICANCE: Our study suggests that higher LAN is a risk factor for pancreatic cancer, contributing to the growing literature that demonstrates the potentially adverse health effects of light pollution.

Outdoor light at night and breast cancer incidence in the Danish Nurse Cohort

BACKGROUND

Knowledge of the role of melatonin, xenograft experiments, and epidemiological studies suggests that exposure to light at night (LAN) may disturb circadian rhythms, possibly increasing the risk of developing breast cancer.

OBJECTIVES

We examined the association between residential outdoor LAN and the incidence of breast cancer: overall and subtypes classified by estrogen (ER) and progesterone (PR) receptor status.

METHODS

We used data on 16,941 nurses from the Danish Nurse Cohort who were followed-up from the cohort baseline in 1993 or 1999 through 2012 in the Danish Cancer Registry for breast cancer incidence and the Danish Breast Cancer Cooperative Group for breast cancer ER and PR status. LAN exposure data were obtained from the U.S. Defense Meteorological Satellite Program (DMSP) available for 1996, 1999, 2000, 2003, 2004, 2006, and 2010 in nW/cm²/sr unit, and assigned to the study participants' residence addresses during the follow-up. Time-varying Cox regression models were used to calculate the hazard ratios (HRs) and 95% confidence intervals (CIs) for the association between LAN and breast cancer, adjusting for individual characteristics, road traffic noise, and air pollution.

RESULTS

Of 16,941 nurses, 745 developed breast cancer in total during 320,289 person-years of follow-up. We found no association between exposure to LAN and overall breast cancer. In the fully adjusted models, HRs for the highest (65.8-446.4 nW/cm²/sr) and medium (22.0-65.7 nW/cm²/sr) LAN tertiles were 0.97 (95% CI: 0.77, 1.23) and 1.09 (95% CI: 0.90, 1.31), respectively, compared to the lowest tertile of LAN exposure (0-21.9 nW/cm²/sr). We found a suggestive association between LAN and ER-breast cancer.

CONCLUSION

This large cohort study of Danish female nurses suggests weak evidence of the association between LAN and breast cancer incidence.

Associations between artificial light at night and risk for thyroid cancer: A large US cohort study

BACKGROUND

Light at night (LAN) inhibits nighttime secretion of melatonin and may cause circadian disruption, which may be a risk factor for cancer. Recent studies have linked high LAN exposure with elevated breast cancer risk. Given that breast cancer may share a common hormone-dependent etiology with thyroid cancer and that circadian rhythms play a role in regulating thyroid function, the authors hypothesized that exposure to LAN is positively associated with thyroid cancer incidence.

METHODS

This study examined the association between LAN and thyroid cancer incidence in the National Institutes of Health-American Association of Retired Persons Diet and Health Study. LAN exposure was estimated from satellite data and was linked to residential addresses at the baseline. Incident thyroid cancer cases were ascertained via linkage to state cancer registries. Cox regression was used to determine the relationship between LAN and thyroid cancer risk, with adjustments made for sociodemographic, lifestyle, and other environmental factors.

RESULTS

Among 464,371 participants, a positive association was found between LAN and thyroid cancer risk. Specifically, in comparison with the lowest quintile of LAN, the highest quintile was associated with a 55% increase in risk (hazard ratio [HR], 1.55; 95% confidence interval [CI], 1.18-2.02). The association was primarily driven by papillary thyroid cancer and was stronger in women (HR, 1.81; 95% CI, 1.26-2.60) than men (HR, 1.29; 95% CI, 0.86-1.94). In women, the association was stronger for localized cancer, whereas in men, the association was stronger for a more advanced stage. Results were consistent across different tumor sizes.

CONCLUSIONS

LAN was positively associated with thyroid cancer risk. Future studies are needed to confirm this association and identify underlying biological mechanisms.

Exposure to artificial light at night and risk of cancer: where do we go from here?

Despite experimental and mechanistic data suggesting circadian disruption’s role in carcinogenesis, mixed findings from epidemiological investigations of artificial light at night and cancer risk in the general population are difficult to interpret due to exposure assessment limitations. It will be important for future studies to assess and validate individual-level exposures, ideally over the lifetime.

Exposure to outdoor light at night and risk of breast cancer: A systematic review and meta-analysis of observational studies

Recent epidemiological studies have explored effects of light at night (LAN) exposure on breast cancer, but reported inconsistent findings. We performed a systematic review and meta-analysis of available evidence regarding the association of LAN assessed by satellite data with breast cancer. We conducted a systematic PubMed, Web of Science, and EMBASE database literature search until August 2020. Random-effects meta-analysis was applied to synthesis risk estimates. Heterogeneity was measured using statistics of Cochran's Q, I², and Tau² (τ²). We assessed publication bias through funnel plot and Egger's test. Moreover, subgroup analyses according to study design and menopausal status were performed. Risk of bias (RoB) of each included study was assessed using a domain-based RoB assessment tool. The confidence in the body of evidence was appraised using the GRADE approach for level-of-evidence translation. A total of 1157 studies were identified referring to LAN and breast cancer, from which 6 were included for quantitative synthesis. We found a significantly higher odds of breast cancer in the highest versus the lowest category of LAN exposure (OR = 1.11, 95% CI: 1.06, 1.16; I² = 0.0%). In the subgroup analyses stratified by menopausal status and study design, significant association was found in postmenopausal women (OR = 1.07, 95% CI = 1.00, 1.13) and cohort studies (OR = 1.11, 95% CI = 1.05, 1.18), while the summary estimates of premenopausal women and case-control studies showed no significance. The level of evidence for the association of LAN exposure and breast cancer risk was graded as "moderate" with "probably low" RoB according to the NTP/OHAT framework. In conclusion, this study suggests a link of LAN exposure with risk of breast cancer. Further high-quality prospective studies, especially performed in low-to middle-income countries with improvement in the area of LAN exposure assessment are needed to advance this field.