Light Exposure during Days with Night, Outdoor, and Indoor Work

Multimodal in-vehicle lighting system increases daytime light exposure and alertness in truck drivers under Arctic winter conditions

Drowsiness while driving negatively impacts road safety, especially in truck drivers. The present study investigated the feasibility and alerting effects of a daylight-supplementing in-truck lighting system (DS) providing short-wavelength enriched light before, during, and after driving. In a within-participants design, eight truck drivers drove a fully-loaded truck under wintry Scandinavian conditions (low daylight levels) with a DS or placebo system for five days. Subjective and objective measures of alertness were recorded several times daily, and evening melatonin levels were recorded three times per study condition. DS significantly increased daytime light exposure without causing negative side effects while driving. In addition, no negative carry-over effects were observed on evening melatonin and sleepiness levels or on nighttime sleep quality. Moreover, objective alertness (i.e., psychomotor vigilance) before and after driving was significantly improved by bright light exposure. This effect was accompanied by improved subjective alertness in the morning. This field study demonstrated that DS was able to increase daytime light exposure in low-daylight conditions and to improve alertness in truck drivers before and after driving (e.g., during driving rest periods). Further studies are warranted to investigate the effects of daylight-supplementing in-cabin lighting on driving performance and road safety measures.

Guanxin V alleviates ventricular remodeling after acute myocardial infarction with circadian disruption by regulating mitochondrial dynamics

PURPOSE

Circadian disruption has been a common issue due to modern lifestyles. Ventricular remodeling (VR) is a pivotal progressive pathologic change after acute myocardial infarction (AMI) and circadian disruption may have a negative influence on VR according to the latest research. Whether or not Guanxin V (GXV) has a positive effect on VR after AMI with circadian disruption drew our interest.

METHODS

Rats were randomly divided into a sham group, an AMI group, an AMI with circadian disruption group, and an AMI with circadian disruption treated with the GXV group according to a random number table. RNA sequencing (RNA-Seq) was utilized to confirm the different expressed genes regulated by circadian disruption. Cardiac function, inflammation factors, pathological evaluation, and mitochondrial dynamics after the intervention were conducted to reveal the mechanism by which GXV regulated VR after AMI with circadian disruption.

RESULTS

RNA-Seq demonstrated that NF-κB was up-regulated by circadian disruption in rats with AMI. Functional and pathological evaluation indicated that compared with the AMI group, circadian disruption was associcataed with deteriorated cardiac function, expanded infarcted size, and exacerbated fibrosis and cardiomyocyte apoptosis. Further investigation demonstrated that mitochondrial dynamics imbalance was induced by circadian disruption. GXV intervention reversed the inflammatory status including down-regulation of NF-κB. Reserved cardiac function, limited infarct size, and ameliorated fibrosis and apoptosis were also observed in the GXV treated group. GXV maintained mitochondrial fission/fusion imbalance through suppressed expression of mitochondrial fission-associated proteins.

CONCLUSION

The study findings suggest that identified mitochondrial dysfunctions may underlie the link between circadian disruption and VR. GXV may exert cardioprotection after AMI with circadian disruption through regulating mitochondrial dynamics.

Novel insights into indoor air purification capability of microalgae: characterization using multiple air quality parameters and comparison with common methods

Indoor air purification received more attention recently. In this study, the effects of six common indoor ornamental plants (Epripremnum aureum, Chlorphytum comosum, Aloe vera, Sedum sediforme, Cereus cv. Fairy Castle, and Sedum adolphii) and three kinds of microalgae (Chlorella sp. HQ, Scenedesmus sp. LX1, and C. vulgaris) on the removal of four types of air pollutants (particulate matters less than 2.5 (PM_2.5) and 10 μm (PM₁₀) in size, formaldehyde (HCHO) and total volatile organic compounds (VOC_S)) in test chamber compared with common physical purification methods (high efficiency particulate air filter and nano activated carbon absorption) were investigated. Their effects on oxygen, carbon dioxide, and relative humidity were also evaluated. The results showed that microalgae, especially C. vulgaris, was more suitable for removing PM_2.5 and PM₁₀, and the removal rates were 55.42 ± 25.77% and 45.76 ± 5.32%, respectively. The removal rates of HCHO and VOCs by all three kings of microalgae could reach 100%. Part of ornamental plants took a longer time to achieve 100% removal of HCHO and VOCs. Physical methods were weaker than ornamental plants and microalgae in terms of increased relative humidity and O₂ content. In general, microalgae, especially C. vulgaris could purify indoor air pollutants more efficiently. The above studies provided data and theoretical support for the purification of indoor air pollutants by microalgae.

A review of the current state of research on artificial blue light safety as it applies to digital devices

Light is necessary for human health and well-being. As we spend more time indoors, we are being increasingly exposed to artificial light. The development of artificial lighting has allowed us to control the brightness, colour, and timing of our light exposure. Yet, the widespread use of artificial light has raised concerns about the impact of altering our light environment on our health. The widespread adoption of personal digital devices over the past decade has exposed us to yet another source of artificial light. We spend a significant amount of time using digital devices with light-emitting screens, including smartphones and tablets, at close range. The light emitted from these devices, while appearing white, has an emission spectrum with a peak in the blue range. Blue light is often characterised as hazardous as its photon energy is higher than that of other wavelengths of visible light. Under certain conditions, visible blue light can cause harm to the retina and other ocular structures. Blue light can also influence the circadian rhythm and processes mediated by melanopsin-expressing intrinsically photosensitive retinal ganglion cells. While the blue component of sunlight is necessary for various physiological processes, whether the low-illuminance artificial blue light emitted from digital devices presents a risk to our health remains an ongoing area of debate. As technological advancements continue, it is relevant to understand how new devices may influence our well-being. This review examines the existing research on artificial blue light safety and the eye, visual performance, and circadian functions.

The influence of bright and dim light on substrate metabolism, energy expenditure and thermoregulation in insulin-resistant individuals depends on time of day

AIMS/HYPOTHESIS

In our modern society, artificial light is available around the clock and most people expose themselves to electrical light and light-emissive screens during the dark period of the natural light/dark cycle. Such suboptimal lighting conditions have been associated with adverse metabolic effects, and redesigning indoor lighting conditions to mimic the natural light/dark cycle more closely holds promise to improve metabolic health. Our objective was to compare metabolic responses to lighting conditions that resemble the natural light/dark cycle in contrast to suboptimal lighting in individuals at risk of developing metabolic diseases.

METHODS

Therefore, we here performed a non-blinded, randomised, controlled, crossover trial in which overweight insulin-resistant volunteers (n = 14) were exposed to two 40 h laboratory sessions with different 24 h lighting protocols while staying in a metabolic chamber under real-life conditions. In the Bright day-Dim evening condition, volunteers were exposed to electric bright light (~1250 lx) during the daytime (08:00-18:00 h) and to dim light (~5 lx) during the evening (18:00-23:00 h). Vice versa, in the Dim day-Bright evening condition, volunteers were exposed to dim light during the daytime and bright light during the evening. Randomisation and allocation to light conditions were carried out by sequential numbering. During both lighting protocols, we performed 24 h indirect calorimetry, and continuous core body and skin temperature measurements, and took frequent blood samples. The primary outcome was plasma glucose focusing on the pre- and postprandial periods of the intervention.

RESULTS

Spending the day in bright light resulted in a greater increase in postprandial triacylglycerol levels following breakfast, but lower glucose levels preceding the dinner meal at 18:00 h, compared with dim light (5.0 ± 0.2 vs 5.2 ± 0.2 mmol/l, n = 13, p=0.02). Dim day-Bright evening reduced the increase in postprandial glucose after dinner compared with Bright day-Dim evening (incremental AUC: 307 ± 55 vs 394 ± 66 mmol/l × min, n = 13, p=0.009). After the Bright day-Dim evening condition the sleeping metabolic rate was identical compared with the baseline night, whereas it dropped after Dim day-Bright evening. Melatonin secretion in the evening was strongly suppressed for Dim day-Bright evening but not for Bright day-Dim evening. Distal skin temperature for Bright day-Dim evening was lower at 18:00 h (28.8 ± 0.3°C vs 29.9 ± 0.4°C, n = 13, p=0.039) and higher at 23:00 h compared with Dim day-Bright evening (30.1 ± 0.3°C vs 28.8 ± 0.3°C, n = 13, p=0.006). Fasting and postprandial plasma insulin levels and the respiratory exchange ratio were not different between the two lighting protocols at any time.

CONCLUSIONS/INTERPRETATION

Together, these findings suggest that the indoor light environment modulates postprandial substrate handling, energy expenditure and thermoregulation of insulin-resistant volunteers in a time-of-day-dependent manner.

TRIAL REGISTRATION

ClinicalTrials.gov NCT03829982.

FUNDING

We acknowledge the financial support from the Netherlands Cardiovascular Research Initiative: an initiative with support from the Dutch Heart Foundation (CVON2014-02 ENERGISE).

Age-related and individual features of the HPA axis stress responsiveness under constant light in nonhuman primates

The hypothalamic-pituitary-adrenal (HPA) axis is a key adaptive neuroendocrine system, dysfunction of which plays an important role in the increasing incidence of stress-dependent age-related pathology. Among the environmental factors effecting increase age-related diseases, great importance is given to disturbances of the light-dark schedule, particularly with increased illumination at night. While disruption of the light-dark schedule has long been recognized as a powerful behavioral stressor, little is known regarding stress reactivity of the HPA under constant light (CL) conditions, especially with aging and depending on the features of stress behavior. The purpose of this investigation was to study the age-related and individual features of the HPA axis response to acute stress exposure (ASE) under chronic CL in nonhuman primates that are known to differ in behavioral responsiveness to stress. Young and old female rhesus monkeys (with control standard behavior or anxiety and depression-like behavior) were exposed to CL (24 h light/day, 330-400 lux for 4 to 8 weeks). Control young and old monkeys were exposed to standard lighting (SL) with natural light during the day and darkness at night. All animals were subjected to ASE (restriction of mobility for 2 hours), functional tests with corticotrophin-releasing hormone and arginine-vasopressin, and study of circadian rhythms of cortisol and pineal melatonin secretion. For the first time an inhibitory effect of CL on the reaction of the adrenal cortex to ASE was revealed in all individuals, regardless of age and preexisting behavior stress reactivity, the mechanisms of which were age-dependent: due to inhibition of the pituitary ACTH secretion in young animals and mainly not affecting the ACTH secretion in old individuals. There were no significant changes in melatonin secretion both in young and old animals. The observed CL inhibition of adrenal cortical reactivity to ASE may be useful to correct increased vulnerability to ASE observed in individuals with preexisting anxiety and depression-like stress behaviors. On the other hand, the CL induced decrease in adrenal stress reactivity of behaviorally normal animals suggests a potential risk of reducing the adaptive capacity of the organism under conditions of continuous light exposure.

Photo-Oxidation of Therapeutic Protein Formulations: From Radical Formation to Analytical Techniques

UV and ambient light-induced modifications and related degradation of therapeutic proteins are observed during manufacturing and storage. Therefore, to ensure product quality, protein formulations need to be analyzed with respect to photo-degradation processes and eventually protected from light exposure. This task usually demands the application and combination of various analytical methods. This review addresses analytical aspects of investigating photo-oxidation products and related mediators such as reactive oxygen species generated via UV and ambient light with well-established and novel techniques.

A longitudinal study of morning, evening, and night light intensities and nocturnal sleep quality in a working population

We aimed to investigate whether higher light intensity in the morning is associated with better nocturnal sleep quality and whether higher light intensities in the evening or night have the opposite effect. Light intensity was recorded for 7 consecutive days across the year among 317 indoor and outdoor daytime workers in Denmark (55-56° N) equipped with a personal light recorder. Participants reported sleep quality after each nocturnal sleep. Sleep quality was measured using three parameters; disturbed sleep index, awakening index, and sleep onset latency. Associations between increasing light intensities and sleep quality were analyzed using mixed effects models with participant identity as a random effect. Overall, neither white nor blue light intensities during morning, evening, or night were associated with sleep quality, awakening, or sleep onset latency of the subsequent nocturnal sleep. However, secondary analyses suggested that artificial light during the morning and day contrary to solar light may increase vulnerability to evening light exposure. Altogether, we were not able to confirm that higher morning light intensity significantly improves self-reported sleep quality or that higher evening or night light intensities impair self-reported sleep quality at exposure levels encountered during daily life in a working population in Denmark. This suggests that light intensities alone are not important for sleep quality to a degree that it is distinguishable from other important parameters in daily life settings.

Assessment of the Light Exposures of Shift-working Nurses in London and Dortmund in Relation to Recommendations for Sleep and Circadian Health

Shift work causes disruption to circadian physiological processes in the human body, and desynchronization from the natural day-and-night rhythm. Circadian disruption is thought to explain the associations between shift work and various long-term diseases; light is an unrivalled synchronizer (or Zeitgeber) of circadian processes and inappropriate light exposure plausibly plays a critical role in the development of health impairments. As published measurement data on the actual light environments encountered by shift workers are sparse, nurses working in two hospitals in London (UK) and Dortmund (Germany) wore light-logging dosimetry devices to measure personal light exposures continuously over a week in three different seasons. The study identifies and quantifies several of the characteristics of light exposure related to different working patterns in winter, spring, and summer, and quantifies interindividual variations. These data enable informed design of light exposure interventions or changes to shifts to reduce unwanted effects of disruptive light exposure profiles.

Reappraisal of the historical myopia epidemic in native Arctic communities

PURPOSE

This study was developed to explain the extraordinary rise in myopia prevalence beginning after 1950 in Indigenous Arctic communities considering recent findings about the risk factors for school myopia development. Myopia prevalence changed drastically from a historical low of less than 3% to more than 50% in new generations of young adults following the Second World War. At that time, this increase was attributed to concurrent alterations in the environment and way of life which occurred in an aggressive programme of de-culturalization and re-acculturation through residential school programmes that introduced mental, emotional and physical stressors. However, the predominant idea that myopia was genetic in nature won the discussion of the day, and research in the area of environmental changes was dismissed. There may have also been an association between myopia progression and the introduction of extreme mental, emotional and physical stressors at the time.

RECENT FINDINGS

Since 1978, animal models of myopia have demonstrated that myopiagenesis has a strong environmental component. Furthermore, multiple studies in human populations have shown since 2005 how myopia could be produced by a combination of limited exposure to the outdoors and heavy emphasis on academic subjects associated with intense reading habits. This new knowledge was applied in the present study to unravel the causes of the historical myopia epidemics in Inuit communities.

SUMMARY

After reviewing the available published data on myopia prevalence in circumpolar Inuit populations in the 20th century, the most likely causes for the Inuit myopia epidemic were the combination of increased near work (from almost none to daily reading) and the move from a mostly outdoor to a much more indoor way of life, exacerbated by fewer hours of sunshine during waking hours, the lower illuminance in the Arctic and the extreme psychophysical stress due to the conditions in the Residential Schools.

The interindividual variability of sleep timing and circadian phase in humans is influenced by daytime and evening light conditions

Human cognitive functioning shows circadian variations throughout the day. However, individuals largely differ in their timing during the day of when they are more capable of performing specific tasks and when they prefer to sleep. These interindividual differences in preferred temporal organization of sleep and daytime activities define the chronotype. Since a late chronotype is associated with adverse mental and physical consequences, it is of vital importance to study how lighting environments affect chronotype. Here, we use a mathematical model of the human circadian pacemaker to understand how light in the built environment changes the chronotype distribution in the population. In line with experimental findings, we show that when individuals spend their days in relatively dim light conditions, this not only results in a later phase of their biological clock but also increases interindividual differences in circadian phase angle of entrainment and preferred sleep timing. Increasing daytime illuminance results in a more narrow distribution of sleep timing and circadian phase, and this effect is more pronounced for longer photoperiods. The model results demonstrate that modern lifestyle changes the chronotype distribution towards more eveningness and more extreme differences in eveningness. Such model-based predictions can be used to design guidelines for workplace lighting that help limiting circadian phase differences, and craft new lighting strategies that support human performance, health and wellbeing.

Healthy Behaviors through Behavioral Design-Obesity Prevention

Evidence for behavior modification for improved health outcomes was evaluated for nutrition, physical activity (PA), and indoor environmental quality (IEQ). The databases searched included LISTA, PubMed, and Web of Science, with articles rated using an a priori baseline score of 70/100 to establish inclusion. The initial search produced 52,847 articles, 63 of which were included in the qualitative synthesis. Thirteen articles met inclusion for nutrition: cafeteria interventions, single interventions, and vending interventions. Seventeen articles on physical activity were included: stair use, walking, and adjustable desks. For IEQ, 33 articles met inclusion: circadian disruption, view and natural light, and artificial light. A narrative synthesis was used to find meaningful connections across interventions with evidence contributing to health improvements. Commonalities throughout the nutrition studies included choice architecture, increasing the availability of healthy food items, and point-of-purchase food labeling. Interventions that promoted PA included stair use, sit/stand furniture, workplace exercise facilities and walking. Exposure to natural light and views of natural elements were found to increase PA and improve sleep quality. Overexposure to artificial light may cause circadian disruption, suppressing melatonin and increasing risks of cancers. Overall, design that encourages healthy behaviors may lower risks associated with chronic disease.

Constant Light Exerted Detrimental Cardiovascular Effects Through Sympathetic Hyperactivity in Normal and Heart Failure Rats

It has been documented that constant light exposure exerts complicated cardiovascular effects. However, a mounting collection of conflicting results did not make it any easier for researchers and physicians to consider the role of light on cardiovascular function. This study was designed to investigate how constant light exposure (24 h light/day) influences the cardiac function in normal and heart-failure (HF) rats. In normal rats, two groups of SD rats were accustomed in 12 h light/12 h dark (LD) or 24 h light (constant light, CL) for 4 weeks. In HF rats which was induced by myocardial infarction (MI) was let recover in LD for 4 weeks. Interestingly, compared with rats in LD environment (ejection fraction, EF%: 93.64 ± 2.02 in LD, 14.62 ± 1.53 in HF-LD), constant light (2 weeks) weakened the cardiac function in normal and HF rats (EF%: 79.42 ± 2.91 in CL, 11.50 ± 1.08 in HF-CL). The levels of renal sympathetic nerve activity and c-fos expression in the rostral ventrolateral medulla (RVLM), a key region controlling sympathetic outflow, were significantly increased in normal and HF rats after constant light (RSNA, Max%: 8.64 ± 0.48 in LD, 20.02 ± 1.24 in CL, 20.10 ± 1.16 in HF-LD, 26.82 ± 1.69 in HF-CL). In conclusion, it is suggested that constant light exposure exerts detrimental cardiovascular effects, which may be associated with the RVLM-related sympathetic hyperactivity.

The Role of Daylight for Humans: Gaps in Current Knowledge

Daylight stems solely from direct, scattered and reflected sunlight, and undergoes dynamic changes in irradiance and spectral power composition due to latitude, time of day, time of year and the nature of the physical environment (reflections, buildings and vegetation). Humans and their ancestors evolved under these natural day/night cycles over millions of years. Electric light, a relatively recent invention, interacts and competes with the natural light-dark cycle to impact human biology. What are the consequences of living in industrialised urban areas with much less daylight and more use of electric light, throughout the day (and at night), on general health and quality of life? In this workshop report, we have classified key gaps of knowledge in daylight research into three main groups: (I) uncertainty as to daylight quantity and quality needed for "optimal" physiological and psychological functioning, (II) lack of consensus on practical measurement and assessment methods and tools for monitoring real (day) light exposure across multiple time scales, and (III) insufficient integration and exchange of daylight knowledge bases from different disciplines. Crucial short and long-term objectives to fill these gaps are proposed.

Shedding Light on the Association between Night Work and Breast Cancer

Shift work that involves circadian disruption has been classified as probably carcinogenic to humans by the International Agency for Research on Cancer, although more recent epidemiological evidence is not consistent. Several mechanisms have been postulated to explain an association between night work and female breast cancer, but the most likely is suppression of the hormone melatonin by light exposure at night. Three articles recently published in this journal describe aspects of exposure to light during night work. These articles and other evidence suggest that nighttime light levels may not always be sufficient to affect melatonin production, which could in part explain the inconsistencies in the epidemiological data. There is need to improve the specificity and reliability of exposure assessments in future epidemiological studies of night shift workers.

A Quantitative General Population Job Exposure Matrix for Occupational Daytime Light Exposure

High daytime light levels may reduce the risk of affective disorders. Outdoor workers are during daytime exposed to much higher light intensities than indoor workers. A way to study daytime light exposure and disease on a large scale is by use of a general population job exposure matrix (JEM) combined with national employment and health data. The objective of this study was to develop a JEM applicable for epidemiological studies of exposure response between daytime light exposure, affective disorders, and other health effects by combining expert scores and light measurements. We measured light intensity during daytime work hours 06:00–17:59 for 1–7 days with Philips Actiwatch Spectrum® light recorders (Actiwatch) among 695 workers representing 71 different jobs. Jobs were coded into DISCO-88, the Danish version of the International Standard Classification of Occupations 1988. Daytime light measurements were collected all year round in Denmark (55–56°N). Arithmetic mean white light intensity (lux) was calculated for each hour of observation (n = 15,272), natural log-transformed, and used as the dependent variable in mixed effects linear regression models. Three experts rated probability and duration of outdoor work for all 372 jobs within DISCO-88. Their ratings were used to construct an expert score that was included together with month of the year and hour of the day as fixed effects in the model. Job, industry nested within job, and worker were included as random effects. The model estimated daytime light intensity levels specific for hour of the day and month of the year for all jobs with a DISCO-88 code in Denmark. The fixed effects explained 37% of the total variance: 83% of the between-jobs variance, 57% of the between industries nested in jobs variance, 43% of the between-workers variance, and 15% of the within-worker variance. Modeled daytime light intensity showed a monotonic increase with increasing expert score and a 30-fold ratio between the highest and lowest exposed jobs. Building construction laborers were based on the JEM estimates among the highest and medical equipment operators among the lowest exposed. This is the first quantitative JEM of daytime light exposure and will be used in epidemiological studies of affective disorders and other health effects potentially associated with light exposure.