Nocturnal Melatonin Suppression Research Articles

Numerical correlation between non-visual metrics and brightness metrics—implications for the evaluation of indoor white lighting systems in the photopic range

From the beginning of the 21textrm{st} century until today, the demand for lighting systems includes not only visual parameters (brightness, contrast perception, color quality), but also non-visual parameters. It is necessary to define the new non-visual parameters for the realization of the new concept of Human Centric Lighting (HCL) or Integrative Lighting. As a contribution to this approach, many international research groups have tried to quantify the non-visual parameters such as Circadian Stimulus by Rea et. al. in USA (CS_{2018}, CS_{2021}), Melanopic Equivalent Daylight (D_{65}) illuminance, mEDI of the CIE S 026/E:2018 or the latest formula by Giménez et al., for the nocturnal melatonin suppression. Therefore, it is necessary to analyze the correlation between these non-visual metrics and brightness metrics such as the equivalent luminance of Fotios et al., or the latest brightness model of TU Darmstadt so that scientists, lighting engineers and lighting system users can correctly apply them in their work. In this context, this paper attempts to investigate and analyze these correlations between the three metric groups based on the database of 884 light sources of different light source technologies and daylight spectra. The obtained results show that the latest Circadian Stimulus model of Rea et. al. CS_{2021} with the improvement of Circadian Light CL_{A,2021} (CL_{A,2.0}) has solved the disadvantage of CS_{2018}, especially for the interrupted point between warm and cold white (about 3710,K) or the junction between negative and positive signal of the opponent channel (B -(L+M)). Moreover, these three metrics of the three research groups contain a high correlation coefficient, so that one metric can be transformed by linear functions to the other two parameters.

Towards intelligent illumination systems: from the basics of light science to its application

The development and design of lighting systems is closely linked to the physiology of the human visual system. Whereas with the first generation of light sources, the visual appearance of objects in an illuminated environment was only possible by adjusting the level of illuminance. In contrast, with modern semiconductor light-emitting diode (LED) systems, the emitted spectrum can be flexibly varied. This new degree of freedom has led to an interdisciplinary field of research, aiming to explore the effect of light on humans in terms of physiological, psychological and cognitive parameters and to model their mechanisms or make them quantifiable via mathematical metrics. Today’s quality assessment of light spectra is composed of metrics that combine colour perception, contrast sensitivity, visual sensation, non-visual responses and cognitive preference. A lighting system that takes these aspects into account is commonly referred to as an integrative lighting solution or Human Centric Lighting. This article describes the current knowledge about the human eye’s visual and non-visual processing system, the development of colour rendering metrics, and the light-induced effect on nocturnal melatonin suppression. Then, the basic concept of an intelligent and individually adaptable lighting system will be discussed.Practical Relevance: This article deals with the basics of light science and covers the fundamental aspects of intelligent lighting systems, which with the help of multi-channel LED luminaires, could address the visual properties of light and the human circadian system separately via metameric spectra.

Effects of different light incident angles via a head-mounted device on the magnitude of nocturnal melatonin suppression in healthy young subjects

Bright light is a primary zeitgeber (synchronizer) for the central circadian pacemaker in humans. Recently, head-mounted devices for light therapy have been developed to treat patients suffering from circadian rhythm sleep disorders. In this study, to evaluate the influence of the light incident angle of head-mounted devices on the human circadian pacemaker, we examined the effects of bright light (ca.10000 lx) from two different angles (55° vs. 28°) on the suppression of melatonin secretion at night. Twenty-nine subjects (25.1 ± 6.3 SD years) participated in the present study. The subjects were kept under dim light conditions (< 5 lx) from 4 h before their habitual bedtime, followed by exposure to 1 h of bright light at two different angles during their habitual bedtime. Saliva samples were collected every hour under dim light conditions and then collected every 30 min during the bright light exposure. To assess the effect of the light incident angle on ipRGCs mediating light-evoked pupillary constriction, pupil size was measured in before and after exposure to bright light. Melatonin suppression in the group exposed to light at 28° was significantly higher than that in the group with light at 55° (p < 0.001). The pupillary constriction was significantly greater in the group exposed to light at 28° than that in the group with light at 55° (p < 0.001). The present findings suggest that the light incident angle is an important factor for bright light therapy and should be considered to effectively use head-mounted devices in home and clinical settings.

Melatonin, circadian rhythms and glaucoma: current perspective.

Melatonin, circadian rhythms and glaucoma: current perspective.

Spatial sensitivity of human circadian response: Melatonin suppression from on-axis and off-axis light exposures

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).

Relative light sensitivities of four retinal hemi-fields for suppressing the synthesis of melatonin at night

The magnitude of the stimulus to the biological clock will depend upon the distribution of circadian phototransduction circuits across the retinae and the spatial distribution of luminous stimuli in the environment. The present study compared nocturnal melatonin suppression for light exposures to the superior, inferior, nasal, and temporal retina in one eye independent of shading from the brow and the nose. The stimulus was a 40° diameter luminous disc, half of which was blue light (LED, λpeak = 470 nm) and the other amber light (LED, λpeak = 590 nm). Experimentally, the orientation of the bipartite disc was rotated to each of the four cardinal points of the visual field. A full, 40° blue disc was also employed by replacing the amber half-disc with another blue half-disc. The blue full- and half-discs always produced 100 photopic lx at the cornea. As hypothesized, nocturnal melatonin suppression was statistically greatest when the blue half-disc was delivered to the nasal hemi-field (35%); the other three hemi-fields were equally affected by the blue half-disc (≈20%). Melatonin suppression for the full-disc was 24%, which was not statistically different than the average suppression for the four hemi-fields of 27%.

Intrinsically Photosensitive Retinal Ganglion Cells of the Human Retina.

Light profoundly affects our mental and physical health. In particular, light, when not delivered at the appropriate time, may have detrimental effects. In mammals, light is perceived not only by rods and cones but also by a subset of retinal ganglion cells that express the photopigment melanopsin that renders them intrinsically photosensitive (ipRGCs). ipRGCs participate in contrast detection and play critical roles in non-image-forming vision, a set of light responses that include circadian entrainment, pupillary light reflex (PLR), and the modulation of sleep/alertness, and mood. ipRGCs are also found in the human retina, and their response to light has been characterized indirectly through the suppression of nocturnal melatonin and PLR. However, until recently, human ipRGCs had rarely been investigated directly. This gap is progressively being filled as, over the last years, an increasing number of studies provided descriptions of their morphology, responses to light, and gene expression. Here, I review the progress in our knowledge of human ipRGCs, in particular, the different morphological and functional subtypes described so far and how they match the murine subtypes. I also highlight questions that remain to be addressed. Investigating ipRGCs is critical as these few cells play a major role in our well-being. Additionally, as ipRGCs display increased vulnerability or resilience to certain disorders compared to conventional RGCs, a deeper knowledge of their function could help identify therapeutic approaches or develop diagnostic tools. Overall, a better understanding of how light is perceived by the human eye will help deliver precise light usage recommendations and implement light-based therapeutic interventions to improve cognitive performance, mood, and life quality.

Modeling Circadian Phototransduction: Retinal Neurophysiology and Neuroanatomy.

The retina is a complex, but well-organized neural structure that converts optical radiation into neural signals that convey photic information to a wide variety of brain structures. The present paper is concerned with the neural circuits underlying phototransduction for the central pacemaker of the human circadian system. The proposed neural framework adheres to orthodox retinal neuroanatomy and neurophysiology. Several postulated mechanisms are also offered to account for the high threshold and for the subadditive response to polychromatic light exhibited by the human circadian phototransduction circuit. A companion paper, modeling circadian phototransduction: Quantitative predictions of psychophysical data, provides a computational model for predicting psychophysical data associated with nocturnal melatonin suppression while staying within the constraints of the neurophysiology and neuroanatomy offered here.

Predictions of melatonin suppression during the early biological night and their implications for residential light exposures prior to sleeping

The magnitude of nocturnal melatonin suppression depends upon the spectrum, amount, and duration of light exposure. The functional relationship between melatonin suppression and the light spectrum and amount have been previously described. Only one duration-dependent parameter was needed to extend this functional relationship to predict nocturnal melatonin suppression during the early biological night from a variety of published studies. Those predictions suggest that ambient lighting commonly found in North American homes will not suppress melatonin for durations up to 3 h, whereas extended use of self-luminous displays in the home prior to sleep can.

Non-visual effects of diurnal exposure to an artificial skylight, including nocturnal melatonin suppression

BackgroundRecently, more consideration is being given to the beneficial effects of lighting on the maintenance and promotion of the health and well-being of office occupants in built environments. A new lighting technology using Rayleigh scattering has made it possible to simulate a blue sky. However, to date, no studies have examined the possible beneficial effects of such artificial skylights. The aims of this study were to examine the non-visual effects of artificial skylights and conventional fluorescent lights in a simulated office environment and to clarify the feature effects of the artificial skylights.MethodsParticipants were 10 healthy male adults. Non-visual effects were evaluated based on brain arousal levels (α-wave ratio and contingent negative variation [CNV]), autonomic nervous activity (heart rate variability [HRV]), work performance, and subjective responses during daytime exposure to either an artificial skylight or fluorescent lights, as well as nocturnal melatonin secretion.ResultsSubjective evaluations of both room lighting-related “natural” and “attractive” items and the “connected to nature” item were significantly higher with the skylight than with the fluorescent lights. Cortical arousal levels obtained from the early component of the CNV amplitude were significantly lower with the skylight than with the fluorescent lights, whereas α-wave ratio and work performance were similar between the two light sources. The HRV evaluation showed that sympathetic nerve tone was lower and parasympathetic nerve tone was higher, both significantly, for the skylight than for the fluorescent lights during daytime. Nocturnal melatonin secretion was significantly greater before and during light exposure at night under the daytime skylight than under the fluorescent lights.ConclusionsOur results suggest that artificial skylights have some advantages over conventional fluorescent lights in maintaining ordinary work performance during daytime with less psychological and physiological stress. The findings also suggest that the artificial skylights would enable built environments to maintain long-term comfort and productivity.

Epigenetic inhibition of the tumor suppressor ARHI by light at night-induced circadian melatonin disruption mediates STAT3-driven paclitaxel resistance in breast cancer.

Disruption of circadian time structure and suppression of circadian nocturnal melatonin (MLT) production by exposure to dim light at night (dLAN), as occurs with night shift work and/or disturbed sleep-wake cycles, is associated with a significantly increased risk of breast cancer and resistance to tamoxifen and doxorubicin. Melatonin inhibition of human breast cancer chemoresistance involves mechanisms including suppression of tumor metabolism and inhibition of kinases and transcription factors which are often activated in drug-resistant breast cancer. Signal transducer and activator of transcription 3 (STAT3), frequently overexpressed and activated in paclitaxel (PTX)-resistant breast cancer, promotes the expression of DNA methyltransferase one (DNMT1) to epigenetically suppress the transcription of tumor suppressor Aplasia Ras homolog one (ARHI) which can sequester STAT3 in the cytoplasm to block PTX resistance. We demonstrate that breast tumor xenografts in rats exposed to dLAN and circadian MLT disrupted express elevated levels of phosphorylated and acetylated STAT3, increased DNMT1, but reduced sirtuin 1 (SIRT1) and ARHI. Furthermore, MLT and/or SIRT1 administration blocked/reversed interleukin 6 (IL-6)-induced acetylation of STAT3 and its methylation of ARH1 to increase ARH1 mRNA expression in MCF-7 breast cancer cells. Finally, analyses of the I-SPY 1 trial demonstrate that elevated MT1 receptor expression is significantly correlated with pathologic complete response following neo-adjuvant therapy in breast cancer patients. This is the first study to demonstrate circadian disruption of MLT by dLAN driving intrinsic resistance to PTX via epigenetic mechanisms increasing STAT3 expression and that MLT administration can reestablish sensitivity of breast tumors to PTX and drive tumor regression.

SAT-460 Perceived Well-Being and Light-Reactive Hormones: An Exploratory Study

Light can impact psychobiological processes in a healthy or harmful way, challenging designers to better understand the resources they are manipulating. The present exploratory study compared two forms of office lighting which differed in correlated colour temperatures and light level. A holistic approach, comprising visual, emotional and biological dimensions, was used to assess the lighting conditions that could favour productivity and well-being by means of the identification of congruent relationships between objective and subjective measurements in response to light stimuli. The former included analyses of melatonin and cortisol, and the latter were psychological instruments for measuring transitory mood, somnolence, and visual comfort. Controlled experiments were run in a laboratory with a repeated measures design, which yielded fifty-six evaluations. Although no extreme ranges of correlated colour temperatures were used in this study, the spectral blue component present in the correlated colour temperature of approximately 4000 K, and also provided by the light-emitting diodes system at a higher light level, could have contributed to render most of the strong effects on the inter and intra correlations among the psychobiological responses. The mediator role of the psychological profile of the individuals was demonstrated by the significant predictive value of the perceived stress measures. References Brainard GC, Hanifin JP, Greeson JM, Byrne B, Glickman G, Gerner E, Rollag MD. Action spectrum for melatonin regulation in humans: Evidence for a novel circadian photoreceptor. Journal of Neuroscience 2001; 21: 6405–6412. Lucas RJ, Peirson SN, Berson DM, Brown TM, Cooper HM, Czeisler CA, Figueiro MG, Gamlin PD, Lockley SW, O’Hagan HB, Price LLA, Provencio I, Skene DJ, Brainard GC. Measuring and using light in the melanopsin age. Trends in Neurosciences 2014; 37: 1–9. Rea MS, Figueiro MG. A working threshold for acute nocturnal melatonin suppression from ‘white’ light sources used in architectural applications. Journal of Carcinogenesis and Mutagenesis 2013. DOI: 10.4172/2157-2518- 1000150. Rea MS, Figueiro MG. Light as a circadian stimulus for architectural lighting. Lighting Research and Technology First published 6 December 2016. DOI: 1477153516682368. Rea MS. The lumen seen in a new light: Making distinctions between light, lighting and neuroscience. Lighting Research and Technology 2015; 47: 259–280

Altered metabolic and hormonal responses in male rats exposed to acute bright light-at-night associated with global DNA hypo-methylation

The association between light pollution and disruption of daily rhythms, metabolic and hormonal disorders, as well as cancer progression is well-recognized. These adverse effects could be due to nocturnal melatonin suppression. The signaling pathway by which light pollution affects metabolism and endocrine responses is unclear. We studied the effects of artificial light at night (ALAN11Artificial light at night.) on body mass, food and water intake, daily rhythms of body temperature, serum glucose and insulin in male rats. Daily rhythms of urine production and urinary 6-sulfatoxymelatonin (6-SMT226-sulfatoxymelatonin.), as well as global DNA methylation in pancreas and liver tissues were also assessed. Mass gain was higher in ALAN rats compared with controls. Food intake, water consumption, glucose, insulin, and 6-SMT levels markedly lessened in response to ALAN. Conversely, urine production and body temperature were elevated in ALAN rats compared with controls. Significant 24-h rhythms were detected for all variables that were altered in mesor, amplitude, and acrophase occurrences under ALAN conditions. DNA hypo-methylation was detected in ALAN pancreatic tissue compared with controls, but not in hepatic tissue. Overall, ALAN affects metabolic and hormonal physiology in different levels in which flexible crosstalk between melatonin and both epigenetics and metabolic levels expressed as body temperature rhythm, is suggested to mediate the environmental exposure at the molecular level and subsequently physiology is altered. The flexibility of epigenetic modifications provides a potential therapeutic target for rectifying ALAN adverse effects by epigenetic markers such as melatonin and behavioral lifestyle interventions for confining ALAN exposures as much as possible.

Nocturnal Melatonin Suppression by Adolescents and Adults for Different Levels, Spectra, and Durations of Light Exposure.

The human circadian system is primarily regulated by the 24-h LD cycle incident on the retina, and nocturnal melatonin suppression is a primary outcome measure for characterizing the biological clock's response to those light exposures. A limited amount of data related to the combined effects of light level, spectrum, and exposure duration on nocturnal melatonin suppression has impeded the development of circadian-effective lighting recommendations and light-treatment methods. The study's primary goal was to measure nocturnal melatonin suppression for a wide range of light levels (40 to 1000 lux), 2 white light spectra (2700 K and 6500 K), and an extended range of nighttime light exposure durations (0.5 to 3.0 h). The study's second purpose was to examine whether differences existed between adolescents' and adults' circadian sensitivity to these lighting characteristics. The third purpose was to provide an estimate of the absolute threshold for the impact of light on acute melatonin suppression. Eighteen adolescents (age range, 13 to 18 years) and 23 adults (age range, 24 to 55 years) participated in the study. Results showed significant main effects of light level, spectrum, and exposure duration on melatonin suppression. Moreover, the data also showed that the relative suppressing effect of light on melatonin diminishes with increasing exposure duration for both age groups and both spectra. The present results do not corroborate our hypothesis that adolescents exhibit greater circadian sensitivity to short-wavelength radiation compared with adults. As for threshold, it takes longer to observe significant melatonin suppression at lower CS levels than at higher CS levels. Dose-response curves (amount and duration) for both white-light spectra and both age groups can guide lighting recommendations when considering circadian-effective light in applications such as offices, schools, residences, and healthcare facilities.

Melatonin production influenced by low frequency magnetic fields

In several residential and occupational studies, suppression of nocturnal melatonin in humans, which is induced by magnetic field, has been reported. The pineal gland produces melatonin and consider it as its major secretory product, which has a vital role in human well-being and health as it was suggested by the growing literature. Generally, exposure to the electric field has many biological effects, and the research on which has recently made this neurohormone, which is associated with the generation and classification of electric field, a focal point. To raise the risk of cancer through changing the pineal glands' regular functions and disrupting the melatonin's nocturnal increase in its release and synthesis, exposure to magnetic fields has been hypothesized. It is very essential to ascertain whether hormonal levers are changed during the exposure of humans to a magnetic field at night because the evidence for the "melatonin hypothesis" relies chiefly upon rodent data. The field-induced alterations were failed to be observed by all studies which have investigated the alterations in melatonin under controlled laboratory conditions when humans are exposed to a magnetic field. However, melatonin levels are altered through the exposure to low frequency magnetic fields, as it has been proposed by several observational studies in occupational and residential settings, which usually differ in terms of the presence of possible confounders, the individuals' health status and their general characteristics, the exposure conditions, and the attained measurement's precisions, durations and types. The associated differences in the duration of exposure may lead to this model of conflicting results. In the laboratory studies, only one night of exposure to a magnetic field was received by volunteers. In contrast, participants in the observational studies, usually for long periods on a daily basis, received chronic exposures to such fields. The consistent measurements of each melatonin over time is considered as another related possible explanation. It is unknown if the frequent magnetic field exposures suppress the inherent stability of each measurement of melatonin over time. In conclusion, the explanation of the contrasting results obtained in laboratory studies, and not in observational ones, could be helped by the evidence for improved suppression or increased variable measurements of melatonin attained in studies with longer controlled exposures.

Short-wavelength enrichment of polychromatic light enhances human melatonin suppression potency.

The basic goal of this research is to determine the best combination of light wavelengths for use as a lighting countermeasure for circadian and sleep disruption during space exploration, as well as for individuals living on Earth. Action spectra employing monochromatic light and selected monochromatic wavelength comparisons have shown that short-wavelength visible light in the blue-appearing portion of the spectrum is most potent for neuroendocrine, circadian, and neurobehavioral regulation. The studies presented here tested the hypothesis that broad spectrum, polychromatic fluorescent light enriched in the short-wavelength portion of the visible spectrum is more potent for pineal melatonin suppression in healthy men and women. A total of 24 subjects were tested across three separate experiments. Each experiment used a within-subjects study design that tested eight volunteers to establish the full-range fluence-response relationship between corneal light irradiance and nocturnal plasma melatonin suppression. Each experiment tested one of the three types of fluorescent lamps that differed in their relative emission of light in the short-wavelength end of the visible spectrum between 400 and 500 nm. A hazard analysis, based on national and international eye safety criteria, determined that all light exposures used in this study were safe. Each fluence-response curve demonstrated that increasing corneal irradiances of light evoked progressively increasing suppression of nocturnal melatonin. Comparison of these fluence-response curves supports the hypothesis that polychromatic fluorescent light is more potent for melatonin regulation when enriched in the short-wavelength spectrum.

Sleep disturbances and their relationship with excessive exposure to light at night: the Korean genome and epidemiology study

Although excessive artificial light at night is known to cause circadian disruption or nocturnal melatonin suppression, there was no systemic study which examined the association of light at night (LAN) and sleep disturbance. The aim of this study was performed to investigate how exposure to LAN can affect sleep in a population level. We carried out a cross-sectional study using the data from the Korean Genome and Epidemiology Study, which began in 2001 as an ongoing population-based study of Korean adults aged 39–70 years in Ansan and Ansung, South Korea. Using NOAA (national oceanic and atmospheric administration) satellite images, levels of LAN (0–63 W/cm 2 steradian) were dichotomized (high vs. low intensity) in both regions. The relationships between LAN exposure and sleep disturbances such as insomnia, excessive daytime sleepiness (EDS), insufficiency of sleep, snoring, irregularity of sleep, restless legs syndrome (RLS), and nap were investigated using multiple logistic regression. We estimated odds ratio (OR) and 95% confidence interval (CI) of LAN exposure parameter in each sleep disturbance using multiple logistic regression models adjusting for various clinical variables. The sample consisted of 8531 participants (4015 men and 4516 women) with mean age of 52.9 ± 9.0 years. The participants complained of insomnia (9.6%), EDS (13.7%), insufficiency of sleep (34.2%), snoring (62.7%), irregularity of sleep (26.3%), RLS (12.5%), and nap (37.8%). High LAN exposure was positively associated with insomnia (OR = 1.73, 95% CI [1.40, 2.14]) and snoring (OR = 1.20, 95% CI [1.06, 1.37]), but was negatively associated with EDS (OR = 0.73, 95% CI [0.61, 0.88]) and irregularity of sleep (OR = 0.65, 95% CI [0.57, 0.75]). On the other hand, LAN exposure was not associated with RLS, nap, or insufficiency of sleep. We concluded that high LAN exposure contributed to sleep disturbance such as insomnia and snoring. This study was supported by the KEITI of the Ministry of Environment of Korea (RQ201205099). This study was provided with biospecimens and data from the Korean Genome Analysis Project (4845–301), the Korean Genome and Epidemiology Study (4851–302), and Korea Biobank Project (4851–307, KBP- 2013–05) that were supported by the Korea Center for Disease Control, Republic of Korea. The light at night data was provided by the National Oceanic and Atmospheric Administration.

A Working Threshold for Acute Nocturnal Melatonin Suppression from “White” Light Sources used in Architectural Applications

Retinal light exposures can decrease melatonin production at night. Since nocturnal melatonin suppression by light has been implicated as an endocrine disruptor and linked to certain diseases, such as diabetes, obesity and cancer, it is important to be able to estimate a threshold light level needed to reliably suppress melatonin. The present study was designed to develop a working threshold for melatonin suppression from “white” light that might be experienced by people in their living environments. Twenty-eight subjects participated in two studies. In addition to dark, control nights, subjects were exposed to 8, 22, and 60 lux at the cornea (study 1, n=14) and to 60, 200, and 720 lux (study 2, n=14) of a “warm white” light source (correlated color temperature of 2670 K). These corneal illuminance levels translate to modeled melatonin suppression levels of 1%, 2%, 6%, 19%, and 42%. In both studies, participants came to the laboratory for four nights, separated by one week. One blood sample was drawn in dim light at midnight and another blood sample was drawn after 60-minute exposure to each light condition (including dark). Using an orthodox statistical criterion for a Type I error of α?< 0.05, only the 200 lux and the 720 lux exposures produced significant suppression levels (19% and 37%, respectively). Based upon a criterion modeled suppression level of 5% for a “cool white” light (6500 K), a corneal light exposure of 30 lux for 30 minutes from “white” light sources used in most architectural lighting applications is proposed as a conservative hypothesized working threshold for nocturnal melatonin suppression.

Light level and duration of exposure determine the impact of self-luminous tablets on melatonin suppression

Exposure to light from self-luminous displays may be linked to increased risk for sleep disorders because these devices emit optical radiation at short wavelengths, close to the peak sensitivity of melatonin suppression. Thirteen participants experienced three experimental conditions in a within-subjects design to investigate the impact of self-luminous tablet displays on nocturnal melatonin suppression: 1) tablets-only set to the highest brightness, 2) tablets viewed through clear-lens goggles equipped with blue light-emitting diodes that provided 40 lux of 470-nm light at the cornea, and 3) tablets viewed through orange-tinted glasses (dark control; optical radiation <525 nm ≈ 0). Melatonin suppressions after 1-h and 2-h exposures to tablets viewed with the blue light were significantly greater than zero. Suppression levels after 1-h exposure to the tablets-only were not statistically different than zero; however, this difference reached significance after 2 h. Based on these results, display manufacturers can determine how their products will affect melatonin levels and use model predictions to tune the spectral power distribution of self-luminous devices to increase or to decrease stimulation to the circadian system.

Associations of Circadian Disruption of Sleep and Nutritional Factors with Risk of Cancer

Background: Daily entrainment of the human circadian clock is important for good human health. In previous studies, shift work has been linked to higher risk of chronic diseases, including certain types of cancers. Exposure to light at night suppresses the physiologic production of melatonin, a hormone that has antiproliferative effects on intestinal cancers. In the present review, we examine the available evidence on sleep disruption, changes in nutrient intake and nutritional factors and risk of cancers. Methods: Internet search of PubMed and discussion with colleagues. Results: Recent studies indicate that night shift work appears to have independent influence on the function of the endocrine system, gastrointestinal tract and circadian brain function. Sleep disruption enhances cortisol secretion and ghrelin release from the stomach and decreases melatonin and leptin which interfere with functioning of beta cells of pancreas. Apart from biological dysfunctions, behavioral changes, increased intake of refined carbohydrates, w-6 fats and low w-3 fats, physical inactivity, excess of tobacco and alcoholism appear to be common among night shift workers. Leptin signals the brain to feel satiety whereas ghrelin, produced in the stomach, signals hunger. Recent studies also indicate that sleep-deprived individuals with hormonal changes have greater cravings for sweet and fatty foods. Apart from this, stress hormone cortisol, which increases with sleep deprivation also contribute to hunger. In addition to altered hormone levels, late night awakening provides greater opportunity to eat, smoke and drink alcohol and eating often includes high-caloric foods. Epidemiological studies indicate that sleep disruption may be associated with obesity and other chronic diseases including cancers. Since electric light at night has adverse effects among night shift workers compared to day shift workers, it has been proposed that a portion of the high and rising risk of breast and prostate cancer worldwide may be because of night shift work. The suppression of melatonin by exposure to light at night may be one reason for the higher rates of breast, prostate and colorectal cancers in the developed world. Suppression of nocturnal melatonin by exposure to light at night results in lack of protection by melatonin on cancer cell receptor sites which allows the uptake of linoleic acid (LA) which in turn enhances the growth of cancer cells. Melatonin is a protective, oncostatic hormone and strong antioxidant having evolved in all plants and animals over the millennia. It is possible that rotating night shift at least three nights per month for 15 or more years may increase the risk of colorectal cancer and other cancers. Conclusions: Experimental evidence and limited human evidence allowed the International Agency for Research on Cancer (IARC) to classify circadian disruption of sleep, as a probable human carcinogen, group 2A. Behavioral changes, intake of fast foods, physical inactivity, excess of tobacco and alcoholism are common among night shift workers which may also apart from deficiency of melatonin.