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Exposure to light-at-night (LAN) has been reported to impair blood glucose regulation. The liver modulates blood glucose through mechanisms influenced by several factors that include peroxisome proliferator-activated receptor gamma coactivator-1alpha (PGC-1α) and glucose-6-phosphatase (G6Pase). This study investigated the effect of intermittent exposure to green and white LAN on some hepatic glucose regulatory factors in male Wistar rats. Animals were divided into three equal groups. Group I (control) was exposed to normal housing conditions. Groups II and III were each daily exposed to either green or white LAN for 2 h (7–9 pm) for 14 days. Body weight and blood glucose was monitored on days 0, 7, and 14. Thereafter, retro-orbital sinus blood was obtained after light thiopental anaesthesia and serum insulin was determined. Liver samples were also obtained and evaluated for glycogen, PGC-1α, and G6Pase activity. Insulin resistance was estimated using the HOMA-IR equation. Body weight and blood glucose on days 7 and 14 increased in groups II and III compared to control. Hepatic PGC-1α and G6Pase increased in group II (2.33 ± 0.31; 2.07 ± 0.22) and III (2.31 ± 0.20; 0.98 ± 0.23) compared to control (1.73 ± 0.21; 0.47 ± 0.11). Hepatic glycogen was 71.8 and 82.4% reduced in groups II and III compared to control. Insulin in group II increased (63.6%) whiles group III values reduced (27.3%) compared to control. Insulin resistance increased in group II (0.29 ± 0.09) compared to control (0.12 ± 0.03) and group III (0.11 ± 0.03), respectively. Exposure to 2 h green and white LAN in the early dark phase increases hepatic glycogenolysis and gluconeogenetic activities resulting in increased blood glucose. In male Wistar rats, exposure to green but not white LAN may predispose to insulin resistance. [ABSTRACT FROM AUTHOR]

Electric light has been widely adopted in numerous applications, including signage, display, and illumination. Enhancing its efficiency and quality has been the focal point until now. Long exposure to intensive blue-light-enriched white light is, however, likely to cause health concerns, such as retina damage and melatonin suppression. A good light should hence be redefined as, at least, human-friendly, besides energy-saving and high-quality. Here, we demonstrate a novel design approach toward a good light based on the state-of-the-art solid-state lighting technologies. Taking the typical phosphor converted white-light-emitting diode (LED) for lighting, for example, a 2000 K orange-white emission with a black-body-radiation chromaticity can be 5 times safer than the 5000 K pure-white counterpart from a retina-protection perspective and 3.9 times safer from an MLT-secretion perspective. Further tuning its chromaticity from black-body-radiation- to sunlight-style, the 2000 K LED can be made 303% safer in terms of maximum retina permissible exposure limit or 100% better in terms of melatonin suppression sensitivity. Moreover, its corresponding efficacy limit can be increased from 270 to 285 lm/W, while keeping light quality constant at 91, in terms of natural light spectrum resemblance index. The same approach can be extended to organic LED as well as the design of a good light for display, wherein pure-white emission with a color temperature around 6000 K is suggested to replace the bluish-white backlight to safeguard human health. [ABSTRACT FROM AUTHOR]

Abstract 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.

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. [ABSTRACT FROM AUTHOR]

A better understanding of the spatial sensitivity of the human circadian system to photic stimulation can provide practical solutions for optimized circadian light exposures. Two psychophysical experiments, involving 25 adult participants in Experiment 1 (mean age = 34.0 years [SD 15.5]; 13 females) and 15 adult participants in Experiment 2 (mean age = 43.0 years [SD 12.6]; 12 females), were designed to investigate whether varying only the spatial distribution of luminous stimuli in the environment while maintaining a constant spectrally weighted irradiance at the eye could influence nocturnal melatonin suppression. Two spatial distributions were employed, one where the luminous stimulus was presented On-axis (along the line of sight) and one where two luminous stimuli were both presented Off-axis (laterally displaced at center by 14°). Two narrowband LED light sources, blue (λmax = 451 nm) for first experiment and green (λmax = 522 nm) for second experiment, were used in both the On-axis and the Off-axis spatial distributions. The blue luminous stimulus targeting the fovea and parafovea (On-axis) was about three times more effective for suppressing melatonin than the photometrically and spectrally matched stimulus targeting the more peripheral retina (Off-axis). The green luminous stimulus targeting the fovea and parafovea (On-axis) was about two times more effective for suppressing melatonin than the photometrically and spectrally matched stimulus targeting the more peripheral retina (Off-axis).

OBJECTIVES: Shift workers’ increased risk of various adverse health outcomes has been linked to light-at-night (LAN) exposure, but few studies have measured LAN exposure in workplaces. To inform future research methods, this study aimed to (i) measure shift workers’ exposures to LAN across industries, occupations, and work environments and (ii) assess components of variance across different exposure groupings and metrics. METHODS: Between October 2015 and March 2016, 152 personal full-shift measurements were collected from 102 night shift workers in emergency health services (paramedics, dispatchers) and healthcare industries (nurses, care aides, security guards, unit clerks, and laboratory, pharmacy, and respiratory therapy staff) in the province of British Columbia, Canada. Descriptive and variance component analyses were conducted for the 23:00–05:00 period to characterize exposures using multiple metrics of potential biological relevance (median lux, 90^th percentile lux, sum of minutes ≥30 lux, and sum of minutes ≥100 lux). RESULTS: Average exposure levels were highest in the healthcare industry. By occupation, laboratory workers and care aides displayed the highest and emergency dispatch officers displayed the lowest levels for all LAN exposure metrics. Between-group variance was large relative to within-group variance for all exposure groupings and metrics, and increased as grouping specificity increased (moving from industry to occupation). CONCLUSIONS: Results from this study suggest that high-level grouping schemes may provide a simple yet effective way of characterizing individual LAN exposures in epidemiological studies of shift work. Ongoing measurement of LAN exposures and assessment of exposure variability is needed in future studies of shift workers as a means to increase sampling efficiency, reduce measurement error, and maximize researchers’ ability to detect relationships where they exist.

Background: Night-shift work, exposure to artificial light-at-night (ALAN) and particularly blue light spectrum, and the consequent circadian disruption may increase the risk of breast and prostate cancer. Colorectal cancer risk may also be increased among night-shift workers. We investigated the association between exposure to ALAN according to light spectrum and colorectal cancer among subjects who had never worked at night in a general population case-control study in Spain.Methods: We examined information on 661 incident histologically verified colorectal cancer cases and 1,322 controls from Barcelona and Madrid, 2007-2013. Outdoor ALAN exposure was based on images from the International Space Station (ISS) including data on remotely sensed upward light intensity. We derived adjusted odds ratio (OR) estimates and confidence intervals (CI) for visual light, blue light, and spectral sensitivities of the five human photopigments assigned to participant's geocoded longest residence.Results: Exposure to blue light spectrum was positively associated with colorectal cancer (OR = 1.6; 95% CI: 1.2-2.2; highest vs. lowest tertile). ORs were similar (OR = 1.7; 95% CI: 1.3-2.3) when further adjusting for area socioeconomic status, diet patterns, smoking, sleep, and family history. We observed no association for outdoor visual light (full spectrum) (OR = 1.0; 95% CI, 0.7-1.2; highest vs. lowest tertile). Analysis of the five photopigments gave similar results with increased risks for shorter wavelengths overlapping with the blue spectrum and no association for longer wavelengths.Conclusions: Outdoor blue light spectrum exposure that is increasingly prevalent in recent years may be associated with colorectal cancer risk. See video abstract: http://links.lww.com/EDE/B708. [ABSTRACT FROM AUTHOR]

Abstract Background In this review, we examine the continually expanding and increasingly compelling data linking radiation and various chemicals in our environment to the current high incidence of breast cancer. Abstract Singly and in combination, these toxicants may have contributed significantly to the increasing rates of breast cancer observed over the past several decades. Exposures early in development from gestation through adolescence and early adulthood are particularly of concern as they re-shape the program of genetic, epigenetic and physiological processes in the developing mammary system, leading to an increased risk for developing breast cancer. In the 8 years since we last published a comprehensive review of the relevant literature, hundreds of new papers have appeared supporting this link, and in this update, the evidence on this topic is more extensive and of better quality than that previously available. Conclusion Increasing evidence from epidemiological studies, as well as a better understanding of mechanisms linking toxicants with development of breast cancer, all reinforce the conclusion that exposures to these substances – many of which are found in common, everyday products and byproducts – may lead to increased risk of developing breast cancer. Moving forward, attention to methodological limitations, especially in relevant epidemiological and animal models, will need to be addressed to allow clearer and more direct connections to be evaluated.

Exposing chicks to one hour of light during the night disrupts the release of a hormone that is needed by cells in the developing brain to survive.

The molecular mechanisms by which environmental light conditions affect cerebellar development are incompletely understood. We showed that circadian disruption by light-at-night induced Purkinje cell death through pineal allopregnanolone (ALLO) activity during early life in chicks. Light-at-night caused the loss of diurnal variation of pineal ALLO synthesis during early life and led to cerebellar Purkinje cell death, which was suppressed by a daily injection of ALLO. The loss of diurnal variation of pineal ALLO synthesis induced not only reduction in pituitary adenylate cyclase-activating polypeptide (PACAP), a neuroprotective hormone, but also transcriptional repression of the cerebellar Adcyap1 gene that produces PACAP, with subsequent Purkinje cell death. Taken together, pineal ALLO mediated the effect of light on early cerebellar development in chicks.

Blue light emitting from the white light for displays and lighting imposes threat to eyes and physiology. We will present here an action spectrum of melatonin generation suppression and the function of photoretinitis, and the methods of quantifying the blue hazards. Orange light of around 610nm is recommended as the basic lighting component for both applications. [ABSTRACT FROM AUTHOR]

Circadian rhythms are recurring patterns in a range of behavioural, physiological and molecular parameters that display periods of near 24 h, and are underpinned by an endogenous biological timekeeping system. Circadian clocks are increasingly recognised as being key for health. Environmental light is the key stimulus that synchronises the internal circadian system with the external time cues. There are emergent health concerns regarding increasing worldwide prevalence of electric lighting, especially man-made light-at-night, and light's impact on the circadian system may be central to these effects. A number of previous studies have demonstrated increased depression-like behaviour in various rodent experimental models exposed to dim light-at-night. In this study we set out to study the impact of dim light-at-night on circadian and affective behaviours in C57Bl/6 mice. We set out specifically to examine the impact of sex on light at night's effects, as well as the impact of housing conditions. We report minimal impact of light-at-night on circadian and affective behaviours, as measured by the tail suspension test, the forced swim test, the sucrose preference test and the elevated plus maze. Light-at-night was also not associated with an increase in body weight, but was associated with a decrease in the cell proliferation marker Ki-67 in the dentate gyrus. In summary, we conclude that experimental contextual factors, such as model species or strain, may be considerable importance in the investigation of the impact of light at night on mood-related parameters. [ABSTRACT FROM AUTHOR]

The objective of this article is to review the basis supporting the usefulness of melatonin as an adjuvant therapy for breast cancer (BC) prevention in several groups of individuals at high risk for this disease. Melatonin, as a result of its antiestrogenic and antioxidant properties, as well as its ability to improve the efficacy and reduce the side effects of conventional antiestrogens, could safely be associated with the antiestrogenic drugs presently in use. In individuals at risk of BC due to night shift work, the light-induced inhibition of melatonin secretion, with the consequent loss of its antiestrogenic effects, would be countered by administering this neurohormone. BC risk from exposure to metalloestrogens, such as cadmium, could be treated with melatonin supplements to individuals at risk of BC due to exposure to this xenoestrogen. The BC risk related to obesity may be reduced by melatonin which decrease body fat mass, inhibits the enhanced aromatase expression in obese women, increases adiponectin secretion, counteracts the oncogenic effects of elevated concentrations of leptin; and decreases blood glucose levels and insulin resistance. Despite compelling experimental evidence of melatonin’s oncostatic actions being susceptible to lowering BC risk, there is still a paucity of clinical trials focused on this subject. [ABSTRACT FROM AUTHOR]

Background: In this review, we examine the continually expanding and increasingly compelling data linking radiation and various chemicals in our environment to the current high incidence of breast cancer. Singly and in combination, these toxicants may have contributed significantly to the increasing rates of breast cancer observed over the past several decades. Exposures early in development from gestation through adolescence and early adulthood are particularly of concern as they re-shape the program of genetic, epigenetic and physiological processes in the developing mammary system, leading to an increased risk for developing breast cancer. In the 8 years since we last published a comprehensive review of the relevant literature, hundreds of new papers have appeared supporting this link, and in this update, the evidence on this topic is more extensive and of better quality than that previously available.Conclusion: Increasing evidence from epidemiological studies, as well as a better understanding of mechanisms linking toxicants with development of breast cancer, all reinforce the conclusion that exposures to these substances - many of which are found in common, everyday products and byproducts - may lead to increased risk of developing breast cancer. Moving forward, attention to methodological limitations, especially in relevant epidemiological and animal models, will need to be addressed to allow clearer and more direct connections to be evaluated. [ABSTRACT FROM AUTHOR]

Light pollution is increasing worldwide, affecting human health and ecosystem quality. The adverse effect of this novel pollution, mediated in mammals by suppression of the pineal neuro-hormone melatonin production and secretion, particularly by short wavelength (SWL) illumination. Currently, this problem is not challenged sufficiently, even ignored by decision-makers at local and national levels, as well as other related organizations. Therefore, we assume that the correct way to deal with it will be by treating the dark night as an ecosystem-service for temporal organization of humans as other organisms. Therefore, chasing darkness away and mainly by SWL illumination is as giving up the natural light/dark cycles offered as an ecosystem-service. So far, we have no environmental economic tools for assessing the real coast of the health damages or reduction in pollination caused by light pollution. Using Artificial Light at Night (ALAN) as a loss of ecosystem-services will enable us to give it a realistic economic value thus an opportunity to re-evaluate the environmental cost of SWL efficient illumination. This will also help decision-makers to move to the next stage of illumination preferring sustainable illumination. [ABSTRACT FROM AUTHOR]

The objective of this article is to review the basis supporting the usefulness of melatonin as an adjuvant therapy for breast cancer (BC) prevention in several groups of individuals at high risk for this disease. Melatonin, as a result of its antiestrogenic and antioxidant properties, as well as its ability to improve the efficacy and reduce the side effects of conventional antiestrogens, could safely be associated with the antiestrogenic drugs presently in use. In individuals at risk of BC due to night shift work, the light-induced inhibition of melatonin secretion, with the consequent loss of its antiestrogenic effects, would be countered by administering this neurohormone. BC risk from exposure to metalloestrogens, such as cadmium, could be treated with melatonin supplements to individuals at risk of BC due to exposure to this xenoestrogen. The BC risk related to obesity may be reduced by melatonin which decrease body fat mass, inhibits the enhanced aromatase expression in obese women, increases adiponectin secretion, counteracts the oncogenic effects of elevated concentrations of leptin; and decreases blood glucose levels and insulin resistance. Despite compelling experimental evidence of melatonin’s oncostatic actions being susceptible to lowering BC risk, there is still a paucity of clinical trials focused on this subject.

Enterprises organized in clusters are often efficient in stimulating urban development, productivity and profit outflows. Identifying the clusters of economic activities thus becomes an important step in devising regional development policies, aimed at the formation of clusters of economic activities in geographic areas in which this objective is desirable. However, a major problem with the identification of such clusters stems from limited reporting by individual countries and administrative entities on the regional distribution of specific economic activities, especially for small regional subdivisions. In this study, we test a possibility that missing data on geographic concentrations of economic activities in the European NUTS3 regions can be reconstructed using light-at-night satellite measurements, and that such reconstructed data can then be used for cluster identification. The matter is that light-at-night, captured by satellite sensors, is characterized by different intensity, depending on its source-production facilities, services, etc. As a result, light-at-night can become a marker of different types of economic activities, a hypothesis that the present study confirms. In particular, as the present analysis indicates, average light-at-night intensities emitted from NUTS3 regions help to explain up to 94 % variance in the areal density of several types of economic activities, performing especially well for professional, scientific and technical services $$({R}^{2}=0.742{-}0.939)$$ , public administration $$({R}^{2}=0.642{-}0.934)$$ , as well as for arts, entertainment and recreation $$(\hbox {R}^{2}=0.718{-}0.934)$$ . As a result, clusters of these economic activities can be identified using light-at-night data, thus helping to supplement missing information and assist regional analysis. [ABSTRACT FROM AUTHOR]

Decreased melatonin production, due to nighttime exposure to light, has been proposed as one of the physiological mechanisms increasing cancer risk in night workers. However, few studies measured melatonin production in night workers, and most of these studies did not measure melatonin over 24 h. One study compared total melatonin production between day and night shifts in rotating night workers and did not find significant differences. However, without baseline measures, it was not possible to exclude that melatonin production was reduced during both day and night work. Here, we used data collected in a simulation study of night work to determine the effect of night work on both nighttime and 24-h melatonin production, during three consecutive days of simulated night work. Thirty-eight healthy subjects (15 men, 23 women; 26.6 ± 4.2 years) participated in a 6-d laboratory study. Circadian phase assessments were made with salivary dim light melatonin onset (DLMO) on the first and last days. Simulated day work (09:00-17:00 h) occurred on the second day, followed by three consecutive days of simulated night work (00:00-08:00 h). Light intensity at eye level was set at 50 lux during both simulated day and night work. The subjects were divided into three matched groups exposed to specific daytime light profiles that produced various degrees of circadian phase delays and phase advances. Melatonin production was estimated with the excretion of urinary 6-sulfatoxymelatonin (aMT6s). For the entire protocol, urine was collected every 2 h, except for the sleep episodes when the interval was 8 h. The aMT6s concentration in each sample was multiplied by the urine volume and then added to obtain total aMT6s excretion during nighttime (00:00-08:00 h) and during each 24-h day (00:00-00:00 h). The results showed that melatonin production progressively decreased over consecutive days of simulated night work, both during nighttime and over the 24 h. This decrease was larger in women using oral contraceptives. There was no difference between the three groups, and the magnitude of the decrease in melatonin production for nighttime and for the 24 h was not associated with the magnitude of the absolute circadian phase shift. As light intensity was relatively low and because the decrease in melatonin production was progressive, direct suppression by nighttime light exposure was probably not a significant factor. However, according to previous experimental observations, the decrease in melatonin production most likely reflects the circadian disruption associated with the process of re-entrainment. It remains to be determined whether reduced melatonin production can be harmful by itself, but long-term and repeated circadian disruption most probably is. [ABSTRACT FROM AUTHOR]

Artificial light decreases the amplitude of daily rhythms in human lifestyle principally by permitting activity and food intake to occur during hours of darkness, and allowing day-time activity to occur in dim light, indoors. Endogenous circadian timing mechanisms that oscillate with a period of 24 h have evolved to ensure physiology is synchronized with the daily variations in light, food, and social cues of the environment. Artificial light affects the synchronization between these oscillators, and metabolic disruption may be one consequence of this. By dampening the amplitude of environmental timing cues and disrupting circadian rhythmicity, artificial lighting might initiate metabolic disruption and contribute to the association between global urbanization and obesity. The aim of this review is to explore the historical, physiological, and epidemiological relationships between artificial light and circadian and metabolic dysfunction. [ABSTRACT FROM AUTHOR]

Introduction: Artificial light-at-night is known to affect a broad array of behaviours and physiological processes. In urbanized bird species, light-at-night advances important biological rhythms such as daily cycles of activity/rest and timing of reproduction, but our knowledge of the underlying physiological mechanisms is limited. Given its role as chronobiological signal, melatonin is a strong candidate for mediating the effects of light-at-night. Results: We exposed urban and rural European blackbirds (Turdus merula) to two light treatments equal in photoperiod but with different light intensities at night. The control group was exposed to 0.0001 lux (almost darkness), while the experimental group was exposed to 0.3 lux at night, simulating conditions recorded previously on free-living urban blackbirds. We obtained diel profiles of plasma melatonin for all birds in summer (July) and winter (January), while simultaneously recording locomotor activity. Daily patterns of melatonin concentrations were clearly affected by light-at-night in both seasons. In winter, melatonin concentrations of light-at-night birds were lower in the early and late night than in those of birds kept in darkness. In summer, melatonin concentrations of the light-at-night birds were lower through all night compared to birds kept in darkness. Locomotor activity in light-at-night birds was overall higher than in control individuals, both during the day and at night, and it increased sharply before dawn. In winter, the amount of activity before dawn in the light-at-night group correlated with changes in melatonin from midnight to late night: the greater the decrease in melatonin, the greater the amount of pre-dawn activity. Urban and rural birds responded similarly to light-at-night with respect to melatonin, but differed in their behaviour, with rural birds showing more locomotor activity than urban counterparts. Conclusions: This study points to reduced melatonin release at night as a potential physiological mechanism underlying the advanced onset of morning activity of urbanized birds. Based on the pattern of melatonin secretion, we suggest that birds responded to light-at-night as if they were exposed to a longer day than birds kept under dark nights. [ABSTRACT FROM AUTHOR]

Effect of light regimens (standard 12:12 light/dark, constant light, natural lightning of the north-west of Russia) and that of melatonin on the development of metabolic syndrome during aging of rats was studied. It was found out that during the process of aging of rats kept in the conditions of the broken rhythm of day and night, different disturbances of metabolism in the form of abdominal obesity, hyperinsulinemia, hypercholesterolemia, hyperglycemia, hyperbetalipoproteinemia and glycosuria occurred. These disturbances can be considered to be metabolic syndrome or the syndrome of insulin resistance. The use of melatonin at night time starting in the rats of 4 month old allowed to decrease the age metabolism disorders in the rats. This fact indirectly proves the insufficiency of this hormone in human in the conditions of natural lighting of the north-west of Russia. [ABSTRACT FROM AUTHOR]

The influence of different light regimes (constant light, LL; constant darkness, DD; standard light regime, LD, 12 hours light/12 hours darkness; and natural lighting of the northwest of Russia (NL) on non-tumor pathology revealed in the post-mortem examination of female rats has been studied. It was found that keeping 25-days-old animals under LL and NL conditions led to an increase in the number of infectious diseases and the substantially faster development of spontaneous tumors (2.9 and 3.3 diseases per one rat, respectively), variety of nontumor pathology found in dead rats, compared with the animals in standard (standard light) regime (1.72 diseases per one rat). Light deprivation (DD) led to a substantial reduction in the development of new growth, as well as nontumor and infectious diseases (1.06 diseases per one rat), compared to the same parameters in a standard light regime. [ABSTRACT FROM AUTHOR]

Decreased melatonin production, due to acute suppression of pineal melatonin secretion by light exposure during night work, has been suggested to underlie higher cancer risks associated with prolonged experience of night work. However, the association between light exposure and melatonin production has never been measured in the field. In this study, 24-h melatonin production and ambulatory light exposure were assessed during both night-shift and day//evening-shift periods in 13 full-time rotating shiftworkers. Melatonin production was estimated with the excretion of urinary 6-sulfatoxymelatonin (aMT6s), and light exposure was measured with an ambulatory photometer. There was no difference in total 24-h aMT6s excretion between the two work periods. The night-shift period was characterized by a desynchrony between melatonin and sleep-wake rhythms, as shown by higher melatonin production during work and lower melatonin production during sleep when working night shifts than when working day//evening shifts. Light exposure during night work showed no correlation with aMT6s excreted during the night of work ( p > .5), or with the difference in 24-h aMT6s excretion between the two work periods ( p > .1). However, light exposure during night work was negatively correlated with total 24-h aMT6s excretion over the entire night-shift period ( p < .01). In conclusion, there was no evidence of direct melatonin suppression during night work in this population. However, higher levels of light exposure during night work may have decreased total melatonin production, possibly by initiating re-entrainment and causing internal desynchrony. This interpretation is consistent with the proposition that circadian disruption, of which decreased melatonin production is only one of the adverse consequences, could be the mediator between night shiftwork and cancer risks. (Author correspondence: ) [ABSTRACT FROM AUTHOR]

Due to its disruptive effects on circadian rhythms and sleep deprivation at night, shiftworking is currently recognized as a risk factor for breast cancer (BC). As revealed by the present analysis based on a comparative case-control study of 1679 women, exposure to light-at-night (LAN) in the “sleeping habitat” is significantly associated with BC risk (odds ratio [OR] = 1.220, 95% confidence interval [CI] = 1.118–1.311; p < .001), controlling for education, ethnicity, fertility, and alcohol consumption. The novelty of the present research is that, to the best of the authors’ knowledge, it is the first study to have identified an unequivocal positive association between bedroom-light intensity and BC risk. Thus, according to the results of the present study, not only should artificial light exposure in the working environment be considered as a potential risk factor for BC, but also LAN in the “sleeping habitat.” [ABSTRACT FROM AUTHOR]

In 2007, the IARC (WHO) has classified “shift-work that involves circadian disruption” as potentially carcinogenic. Ample evidence leaves no doubt that shift-work is detrimental for health, but the mechanisms behind this effect are not well understood. The hormone melatonin is often considered to be a causal link between night shift and tumor development. The underlying “light-at-night” (LAN) hypothesis is based on the following chain of arguments: melatonin is a hormone produced under the control of the circadian clock at night, and its synthesis can be suppressed by light; as an indolamine, it potentially acts as a scavenger of oxygen radicals, which in turn can damage DNA, which in turn can cause cancer. Although there is no experimental evidence that LAN is at the basis of increased cancer rates in shiftworkers, the scenario “light at night can cause cancer” influences research, medicine, the lighting industry and (via the media) also the general public, well beyond shiftwork. It is even suggested that baby-lights, TVs, computers, streetlights, moonlight, emergency lights, or any so-called “light pollution” by urban developments cause cancer via the mechanisms proposed by the LAN hypothesis. Our commentary addresses the growing concern surrounding light pollution. We revisit the arguments of the LAN theory and put them into perspective regarding circadian physiology, physical likelihood (e.g., what intensities reach the retina), and potential risks, specifically in non-shiftworkers. [ABSTRACT FROM AUTHOR]

Background: Breast cancer incidence is increasing globally for largely unknown reasons. The possibility that a portion of the breast cancer burden might be explained by the introduction and increasing use of electricity to light the night was suggested >20 years ago.Methods: The theory is based on nocturnal light-induced disruption of circadian rhythms, notably reduction of melatonin synthesis. It has formed the basis for a series of predictions including that non-day shift work would increase risk, blind women would be at lower risk, long sleep duration would lower risk and community nighttime light level would co-distribute with breast cancer incidence on the population level.Results: Accumulation of epidemiological evidence has accelerated in recent years, reflected in an International Agency for Research on Cancer (IARC) classification of shift work as a probable human carcinogen (2A). There is also a strong rodent model in support of the light-at-night (LAN) idea.Conclusion: If a consensus eventually emerges that LAN does increase risk, then the mechanisms for the effect are important to elucidate for intervention and mitigation. The basic understanding of phototransduction for the circadian system, and of the molecular genetics of circadian rhythm generation are both advancing rapidly, and will provide for the development of lighting technologies at home and at work that minimize circadian disruption, while maintaining visual efficiency and aesthetics. In the interim, there are strategies now available to reduce the potential for circadian disruption, which include extending the daily dark period, appreciate nocturnal awakening in the dark, using dim red light for nighttime necessities, and unless recommended by a physician, not taking melatonin tablets. [ABSTRACT FROM AUTHOR]

Abstract: Night is no longer dark in the modern world, and the Milky Way has disappeared. Electric light has benefits but there are also a few detriments. These are (1) loss of the night sky, (2) wasted energy, (3) harm to animal and plant life, (4) and perhaps increases in some severe human maladies such as cancers of breast and prostate. The science on phototransduction for the circadian system and on clock gene function is evolving rapidly, and it provides a rationale for the idea that circadian disruption from light at night could cause disease. Direct evidence from humans and rodent models has also accumulated to the point where the idea is no longer fanciful. Although it may seem logical now, the journey on the path from electric light to breast cancer has been a tortuous one, at least for me. [Copyright &y& Elsevier]

Abstract: The kernel density (KD) function estimates the intensity of events across a surface by calculating the overall number of cases situated within a given search radius from a target point. To form a continuous surface from individual observations, the KD technique does not require the presence of a parameter’s value in a given location (e.g., the incidence rate of a disease). This feature of KD smoothing is especially beneficial for empirical studies in which individual observations are represented by geographic coordinates only and have no other attributes, required by more commonly used smoothing techniques, such as spline and kriging. In the present study, we illustrate the use of KD technique for a study of association between the geographical distributions of breast cancer cases and exposure to artificial illumination during nighttime (light-at-night or LAN) in the city of Haifa, Israel. [Copyright &y& Elsevier]

The role of the modulation of the pineal gland function in development of breast cancer is discussed in this review. An inhibition of the pineal function with pinealectomy or with the exposure to the constant light regimen stimulates mammary carcinogenesis, whereas the light deprivation inhibits the carcinogenesis. Epidemiological observations on increased risk of breast cancer in night shift workers, flight attendants, radio and telegraph operators and on decreased risk in blind women are in accordance with the results of experiments in rodents. Treatment with pineal indole hormone melatonin inhibits mammary carcinogenesis in pinealectomized rats, in animals kept at the standard light/dark regimen (LD) or at the constant illumination (LL) regimen. Pineal peptide preparation Epithalamin and synthetic tetrapeptide Epitalon (Ala–Glu–Asp–Gly) are potent inhibitors of mammary carcinogenesis in rodents and might be useful in the prevention of breast cancer in women at risk. [Copyright &y& Elsevier]

A better understanding of the spatial sensitivity of the human circadian system to photic stimulation can provide practical solutions for optimized circadian light exposures. Two psychophysical experiments, involving 25 adult participants in Experiment 1 (mean age = 34.0 years [SD 15.5]; 13 females) and 15 adult participants in Experiment 2 (mean age = 43.0 years [SD 12.6]; 12 females), were designed to investigate whether varying only the spatial distribution of luminous stimuli in the environment while maintaining a constant spectrally weighted irradiance at the eye could influence nocturnal melatonin suppression. Two spatial distributions were employed, one where the luminous stimulus was presented On-axis (along the line of sight) and one where two luminous stimuli were both presented Off-axis (laterally displaced at center by 14°). Two narrowband LED light sources, blue ( λ max  = 451 nm) for first experiment and green ( λ max  = 522 nm) for second experiment, were used in both the On-axis and the Off-axis spatial distributions. The blue luminous stimulus targeting the fovea and parafovea (On-axis) was about three times more effective for suppressing melatonin than the photometrically and spectrally matched stimulus targeting the more peripheral retina (Off-axis). The green luminous stimulus targeting the fovea and parafovea (On-axis) was about two times more effective for suppressing melatonin than the photometrically and spectrally matched stimulus targeting the more peripheral retina (Off-axis)., (© 2021 The Authors.)

Objectives: Exposure to light-at-night (LAN) has been reported to impair blood glucose regulation. The liver modulates blood glucose through mechanisms influenced by several factors that include peroxisome proliferator-activated receptor gamma coactivator-1alpha (PGC-1α) and glucose-6-phosphatase (G6Pase). This study investigated the effect of intermittent exposure to green and white LAN on some hepatic glucose regulatory factors in male Wistar rats., Methods: Animals were divided into three equal groups. Group I (control) was exposed to normal housing conditions. Groups II and III were each daily exposed to either green or white LAN for 2 h (7-9 pm) for 14 days. Body weight and blood glucose was monitored on days 0, 7, and 14. Thereafter, retro-orbital sinus blood was obtained after light thiopental anaesthesia and serum insulin was determined. Liver samples were also obtained and evaluated for glycogen, PGC-1α, and G6Pase activity. Insulin resistance was estimated using the HOMA-IR equation., Results: Body weight and blood glucose on days 7 and 14 increased in groups II and III compared to control. Hepatic PGC-1α and G6Pase increased in group II (2.33 ± 0.31; 2.07 ± 0.22) and III (2.31 ± 0.20; 0.98 ± 0.23) compared to control (1.73 ± 0.21; 0.47 ± 0.11). Hepatic glycogen was 71.8 and 82.4% reduced in groups II and III compared to control. Insulin in group II increased (63.6%) whiles group III values reduced (27.3%) compared to control. Insulin resistance increased in group II (0.29 ± 0.09) compared to control (0.12 ± 0.03) and group III (0.11 ± 0.03), respectively., Conclusions: Exposure to 2 h green and white LAN in the early dark phase increases hepatic glycogenolysis and gluconeogenetic activities resulting in increased blood glucose. In male Wistar rats, exposure to green but not white LAN may predispose to insulin resistance., (© 2021 Walter de Gruyter GmbH, Berlin/Boston.)

Exposing chicks to one hour of light during the night disrupts the release of a hormone that is needed by cells in the developing brain to survive., Competing Interests: SL, RM, AW No competing interests declared, (© 2019, Leung et al.)

The molecular mechanisms by which environmental light conditions affect cerebellar development are incompletely understood. We showed that circadian disruption by light-at-night induced Purkinje cell death through pineal allopregnanolone (ALLO) activity during early life in chicks. Light-at-night caused the loss of diurnal variation of pineal ALLO synthesis during early life and led to cerebellar Purkinje cell death, which was suppressed by a daily injection of ALLO. The loss of diurnal variation of pineal ALLO synthesis induced not only reduction in pituitary adenylate cyclase-activating polypeptide (PACAP), a neuroprotective hormone, but also transcriptional repression of the cerebellar Adcyap1 gene that produces PACAP, with subsequent Purkinje cell death. Taken together, pineal ALLO mediated the effect of light on early cerebellar development in chicks., Competing Interests: SH, MK, TT, KT, MS, MN, MO, IS, GH, VC, XL, TM, JK, TN, KM, HO, TT, TT, AM, KT No competing interests declared, (© 2019, Haraguchi et al.)

Purpose of Review: Night work is increasingly common and a necessity in certain sectors of the modern 24-h society. The embedded exposure to light-at-night, which suppresses the nocturnal hormone melatonin with oncostatic properties and circadian disruption, i.e., misalignment between internal and external night and between cells and organs, are suggested as main mechanisms involved in carcinogenesis. In 2007, the International Agency for Research on Cancer (IARC) classified shift work that involves circadian disruption as probably carcinogenic to humans based on limited evidence from eight epidemiologic studies on breast cancer, in addition to sufficient evidence from animal experiments. The aim of this review is a critical update of the IARC evaluation, including subsequent and the most recent epidemiologic evidence on breast cancer risk after night work., Recent Findings: After 2007, in total nine new case-control studies, one case-cohort study, and eight cohort studies are published, which triples the number of studies. Further, two previous cohorts have been updated with extended follow-up. The assessment of night shift work is different in all of the 26 existing studies. There is some evidence that high number of consecutive night shifts has impact on the extent of circadian disruption, and thereby increased breast cancer risk, but this information is missing in almost all cohort studies. This in combination with short-term follow-up of aging cohorts may explain why some cohort studies may have null findings. The more recent case-control studies have contributed interesting results concerning breast cancer subtypes in relation to both menopausal status and different hormonal subtypes. The large differences in definitions of both exposure and outcome may contribute to the observed heterogeneity of results from studies of night work and breast cancer, which overall points in the direction of an increased breast cancer risk, in particular after over 20 years of night shifts. Overall, there is a tendency of increased risk of breast cancer either after over 20 years of night shift or after shorter periods with many consecutive shifts. More epidemiologic research using standardized definitions of night work metrics and breast cancer subtypes as well as other cancers is needed in order to improve the epidemiologic evidence in combination with animal models of night work. Also, evidence-based preventive interventions are needed.

We evaluated the effect of various light/dark regimens on the survival, life span and tumorigenesis in rats. Two hundred eight male and 203 females LIO rats were subdivided into 4 groups and kept at various light/dark regimens: standard 12:12 light/dark (LD); natural lighting of the North-West of Russia (NL); constant light (LL), and constant darkness (DD) since the age of 25 days until natural death. We found that exposure to NL and LL regimens accelerated development of metabolic syndrome and spontaneous tumorigenesis, shortened life span both in male and females rats as compared to the standard LD regimen. We conclude that circadian disruption induced by light-at-night accelerates aging and promotes tumorigenesis in rats. This observation supports the conclusion of the International Agency Research on Cancer that shift-work that involves circadian disruption is probably carcinogenic to humans.