Glucose tolerance in mice exposed to light-dark stimulus patterns mirroring dayshift and rotating shift schedules

Link between circadian rhythm and benign prostatic hyperplasia (BPH)/lower urinary tract symptoms (LUTS)

BACKGROUND

Benign prostatic hyperplasia (BPH) is the most common urologic disease in aging males, affecting 50% of men over 50 and up to 80% of men over 80 years old. Its negative impact on health-related quality of life implores further investigation into its risk factors and strategies for effective management. Although the exact molecular mechanisms underlying pathophysiological onset of BPH are poorly defined, the current hypothesized contributors to BPH and lower urinary tract symptoms (LUTS) include aging, inflammation, metabolic syndrome, and hormonal changes. These processes are indirectly influenced by circadian rhythm disruption. In this article, we review the recent evidence on the potential association of light changes/circadian rhythm disruption and the onset of BPH and impact on treatment.

METHODS

A narrative literature review was conducted using PubMed and Google Scholar to identify supporting evidence. The articles referenced ranged from 1975 to 2023.

RESULTS

A clear relationship between BPH/LUTS and circadian rhythm disruption is yet to be established. However, common mediators influence both diseases, including proinflammatory states, metabolic syndrome, and hormonal regulation that can be asserted to circadian disruption. Some studies have identified a possible relationship between general LUTS and sleep disturbance, but little research has been done on the medical management of these diseases and how circadian rhythm disruption further affects treatment outcomes.

CONCLUSIONS

There is evidence to implicate a relationship between BPH/LUTS and circadian rhythm disruptions. However, there is scarce literature on potential specific link in medical management of the disease and treatment outcomes with circadian rhythm disruption. Further study is warranted to provide BPH patients with insights into circadian rhythm directed appropriate interventions.

Chronic blue light-emitting diode exposure harvests gut dysbiosis related to cholesterol dysregulation

Night shift workers have been associated with circadian dysregulation and metabolic disorders, which are tightly coevolved with gut microbiota. The chronic impacts of light-emitting diode (LED) lighting at night on gut microbiota and serum lipids were investigated. Male C57BL/6 mice were exposed to blue or white LED lighting at Zeitgeber time 13.5-14 (ZT; ZT0 is the onset of "lights on" and ZT12 is the "lights off" onset under 12-hour light, 12-hour dark schedule). After 33 weeks, only the high irradiance (7.2 J/cm2) of blue LED light reduced the alpha diversity of gut microbiota. The high irradiance of white LED light and the low irradiance (3.6 J/cm2) of both lights did not change microbial alpha diversity. However, the low irradiance, but not the high one, of both blue and white LED illuminations significantly increased serum total cholesterol (TCHO), but not triglyceride (TG). There was no significant difference of microbial abundance between two lights. The ratio of beneficial to harmful bacteria decreased at a low irradiance but increased at a high irradiance of blue light. Notably, this ratio was negatively correlated with serum TCHO but positively correlated with bile acid biosynthesis pathway. Therefore, chronic blue LED lighting at a high irradiance may harvest gut dysbiosis in association with decreased alpha diversity and the ratio of beneficial to harmful bacteria to specifically dysregulates TCHO metabolism in mice. Night shift workers are recommended to be avoid of blue LED lighting for a long and lasting time.

Alignment Between 24-h Light-Dark and Activity-Rest Rhythms Is Associated With Diabetes and Glucose Metabolism in a Nationally Representative Sample of American Adults

OBJECTIVE

The alignment between environmental stimuli (e.g., dark, light) and behavior cycles (e.g., rest, activity) is an essential feature of the circadian timing system, a key contributor to metabolic health. However, no previous studies have investigated light-activity alignment in relation to glycemic control in human populations.

RESEARCH DESIGN AND METHODS

The analysis included ∼7,000 adults (aged 20-80 years) from the National Health and Nutrition Examination Survey (NHANES) (2011-2014) with actigraphy-measured, multiday, 24-h activity and light data. We used phasor analysis to derive phasor magnitude and phasor angle, which measures coupling strength and phase difference between the activity-rest and light-dark cycles, respectively. We used multinomial logistic regression and multiple linear regression to study phasor magnitude and phasor angle in relation to diabetes (primary outcome) and multiple secondary biomarkers of glycemic control.

RESULTS

Lower alignment strength (i.e., a shorter phasor magnitude) and more delayed activity relative to the light cycle (i.e., a larger phasor angle) were both associated with diabetes. Specifically, compared with individuals in the quintiles indicating the most proper alignment (Q5 for phasor magnitude and Q1 for phasor angle), those in the quintiles with the most impaired alignment had a >70% increase in the odds of diabetes for phasor magnitude (odds ratio 1.76 [95% CI 1.39, 2.24]) and for phasor angle (1.73 [1.34, 2.25]). Similar associations were observed for biomarkers for glucose metabolism. The results were generally consistent across diverse sociodemographic and obesity groups.

CONCLUSIONS

The alignment pattern between 24-h activity-rest and light-dark cycles may be a critical factor in metabolic health.

The impact of shift-work light conditions on tissue-specific circadian rhythms of canonical clock genes: insights from a mouse model study

Background: The natural day-night cycle synchronizes our circadian rhythms, but modern work practices like night shifts disrupt this pattern, leading to increased exposure to nighttime light. This exposure is linked to various health issues. While some studies have explored the effects of night shifts on human circadian rhythms, there is limited research on the consequences of long-term exposure to shift-work light conditions. Rodents can provide valuable insights into these effects. This study aimed to examine how short- or long-term exposure to rotating shifts and chronic jetlag affects the core circadian oscillators in the liver and skin of mammals. Methods: C57BL/6J male mice were subjected to simulated shift-work light conditions, including short-term or long-term rotating shifts and chronic jet-lag conditions. Liver and skin samples were collected every four hours over a 24-hour period on the second day of constant darkness. RNA was extracted and qRT-PCR analysis was conducted to measure the circadian gene expression in liver and skin tissues. Circadian rhythm analysis using CircaCompare compared the control group to mice exposed to shift-work light conditions. Results: The liver's circadian clock is significantly altered in mice under long-term rotating shift conditions, with a lesser but still noticeable impact in mice experiencing chronic jetlag. However, short-term rotating shift conditions do not significantly affect the liver's circadian clock. Conversely, all three simulated shift conditions affect the skin's circadian clock, indicating that the skin clock is more sensitive to shift-work light conditions than the liver clock. Compared to the liver, the skin's circadian clock is greatly affected by long-term rotating shift conditions. Conclusions: The study findings indicate more pronounced disturbances in the canonical clock genes of the skin compared to the liver under simulated shift-work light conditions. These results suggest that the skin clock is more vulnerable to the effects of shift-work.

Circadian Rhythms Disrupted by Light at Night and Mistimed Food Intake Alter Hormonal Rhythms and Metabolism

Availability of artificial light and light-emitting devices have altered human temporal life, allowing 24-hour healthcare, commerce and production, and expanding social life around the clock. However, physiology and behavior that evolved in the context of 24 h solar days are frequently perturbed by exposure to artificial light at night. This is particularly salient in the context of circadian rhythms, the result of endogenous biological clocks with a rhythm of ~24 h. Circadian rhythms govern the temporal features of physiology and behavior, and are set to precisely 24 h primarily by exposure to light during the solar day, though other factors, such as the timing of meals, can also affect circadian rhythms. Circadian rhythms are significantly affected by night shift work because of exposure to nocturnal light, electronic devices, and shifts in the timing of meals. Night shift workers are at increased risk for metabolic disorder, as well as several types of cancer. Others who are exposed to artificial light at night or late mealtimes also show disrupted circadian rhythms and increased metabolic and cardiac disorders. It is imperative to understand how disrupted circadian rhythms alter metabolic function to develop strategies to mitigate their negative effects. In this review, we provide an introduction to circadian rhythms, physiological regulation of homeostasis by the suprachiasmatic nucleus (SCN), and SCN-mediated hormones that display circadian rhythms, including melatonin and glucocorticoids. Next, we discuss circadian-gated physiological processes including sleep and food intake, followed by types of disrupted circadian rhythms and how modern lighting disrupts molecular clock rhythms. Lastly, we identify how disruptions to hormones and metabolism can increase susceptibility to metabolic syndrome and risk for cardiovascular diseases, and discuss various strategies to mitigate the harmful consequences associated with disrupted circadian rhythms on human health.

The effect of evening light on circadian-related outcomes: A systematic review

Bright light exposure at night can help workers adapt to their shift schedules, but there has been relatively little research on evening light. We conducted a systematic review of studies that manipulated light exposure in the evening (broadly defined as 16:00-22:00) before real or simulated night shifts. Across the five eligible studies, evening light produced phase delays in melatonin, body temperature, and sleep propensity; it also improved sleep quality, sleep duration, memory, and work performance. There were mixed effects for mood, no changes in sleepiness, and no negative effects. The confidence in these results ranged from moderate for physiological markers of circadian phase delays to very low for mood. Future studies should compare the relative effectiveness and safety of evening versus night-time light exposure. Overall, the benefits of evening light for shift workers are tentative yet promising.

Circadian effects on UV-induced damage and mutations

Skin cancer is the most diagnosed type of cancer in the United States, and while most of these malignancies are highly treatable, treatment costs still exceed $8 billion annually. Over the last 50 years, the annual incidence of skin cancer has steadily grown; therefore, understanding the environmental factors driving these types of cancer is a prominent research-focus. A causality between ultraviolet radiation (UVR) exposure and skin cancer is well-established, but exposure to UVR alone is not necessarily sufficient to induce carcinogenesis. The emerging field of circadian biology intersects strongly with the physiological systems of the mammalian body and introduces a unique opportunity for analyzing mechanisms of homeostatic disruption. The circadian clock refers to the approximate 24-hour cycle, in which protein levels of specific clock-controlled genes (CCGs) fluctuate based on the time of day. Though these CCGs are tissue specific, the skin has been observed to have a robust circadian clock that plays a role in its response to UVR exposure. This in-depth review will detail the mechanisms of the circadian clock and its role in cellular homeostasis. Next, the skin's response to UVR exposure and its induction of DNA damage and mutations will be covered - with an additional focus placed on how the circadian clock influences this response through nucleotide excision repair. Lastly, this review will discuss current models for studying UVR-induced skin lesions and perturbations of the circadian clock, as well as the impact of these factors on human health.

Circadian rhythm disruption with high-fat diet impairs glycemic control and bone quality

Biological functions, including glycemic control and bone metabolism, are highly influenced by the body's internal clock. Circadian rhythms are biological rhythms that run with a period close to 24 hours and receive input from environmental stimuli, such as the light/dark cycle. We investigated the effects of circadian rhythm disruption (CRD), through alteration of the light/dark schedule, on glycemic control and bone quality of mice. Ten-week-old male mice (C57/BL6, n = 48) were given a low-fat diet (LFD) or a high-fat diet (HFD) and kept on a dayshift or altered schedule (RSS3) for 22 weeks. Mice were divided into four experimental groups (n = 12/group): Dayshift/LFD, Dayshift/HFD, RSS3/LFD, and RSS3/HFD. CRD in growing mice fed a HFD resulted in a diabetic state, with a 36.2% increase in fasting glucose levels compared to the Dayshift/LFD group. Micro-CT scans of femora revealed a reduction in inner and outer surface expansion for mice on a HFD and altered light schedule. Cancellous bone demonstrated deterioration of bone quality as trabecular number and thickness decreased while trabecular separation increased. While HFD increased cortical bone mineral density, its combination with CRD reduced this phenomenon. The growth of mineral crystals, determined by small angle X-ray scattering, showed HFD led to smaller crystals. Considering modifications of the organic matrix, regardless of diet, CRD exacerbated the accumulation of fluorescent advanced glycation end-products (fAGEs) in collagen. Strength testing of tibiae showed that CRD mitigated the higher strength in the HFD group and increased brittleness indicated by lower post-yield deflection and work-to-fracture. Consistent with accumulation of fAGEs, various measures of toughness were lowered with CRD, but combination of CRD with HFD protected against this decrease. Differences between strength and toughness results represent different contributions of structural and material properties of bone to energy dissipation. Collectively, these results demonstrate that combination of CRD with HFD impairs glycemic control and have complex effects on bone quality.

Adverse effects of circadian desynchrony on the male reproductive system: an epidemiological and experimental study

STUDY QUESTION

Is circadian desynchrony a risk factor of male reproductive damage in semen parameters and/or reproductive hormones?

SUMMARY ANSWER

Circadian desynchrony correlates with decrease of sperm count, which was improved when circadian desynchrony was attenuated.

WHAT IS KNOWN ALREADY

Circadian desynchrony caused by work (shift work) and non-work-related reasons is prevalent worldwide and has been found to be associated with decreased female fertility, but whether it harms male reproductive health is unclear.

STUDY DESIGN, SIZE, DURATION

A hybrid research was conducted. (i) A cross-sectional study of 1346 Chinese men in 2007 was used to analyze the association between semen/hormone biomarkers and work-related circadian desynchrony, which was divided into rotating shift work and permanent shift work against non-shift work. (ii) A cohort of 796 Chinese undergraduates from 2013 to 2014 was used to analyzed the association between semen/hormone biomarkers and non-work-related circadian desynchrony (between school days and days off). (iii) The biomarker identified simultaneously in both populations was further validated in male C57BL/6J mice housed under conditions simulating circadian desynchrony.

PARTICIPANTS/MATERIALS, SETTING, METHODS

A total of 17 semen/hormone biomarkers were compared among rotating shift workers and permanent shift workers against non-shift workers in the 1346 reproductive-age Chinese men. A total of 14 semen/hormone biomarker was analyzed in the undergraduate cohort for correlation with non-work-related circadian desynchrony (measured by Munich Chronotype Questionnaire) in 2013 and 2014 and compared between the 2 years. Photoperiod-shifting method was used to establish the mouse model, in which the biomarker was examined and molecular mechanism was explored by apoptosis analysis, DNA content analysis, transcriptome sequencing, real-time PCR and western blotting.

MAIN RESULTS AND THE ROLE OF CHANCE

Among the semen/hormone biomarkers, sperm count was found to be lower in rotating shift workers, who had a higher risk of low sperm count defined by Chinese Ministry of Health (total sperm/ejaculate < 120 × 10⁶) than non-shift workers (odds ratio = 1.26, 95% CI 1.05–1.52). This biomarker was replicated in the undergraduate cohort, where each hour of circadian desynchrony was associated with 1.16 (95% CI 1.02–1.31) fold odds of low sperm count, and sperm count increased during 2014 in men who reduced circadian desynchrony after 2013. A decrease of sperm count with circadian desynchrony and its recovery after removal of circadian desynchrony was also observed in the mouse model. During asynchrony, increased apoptosis was found in seminiferous tubules and the marker genes of post-spermatocyte stage cells were down-regulated. The most enriched functional pathway was homologous recombination, which happened during meiosis.

LIMITATIONS, REASONS FOR CAUTION

The study of human beings was observational while the animal study has potential difference in circadian desynchrony exposure and species susceptibility. Further researches are needed to clarify the causal relationship in men.

WIDER IMPLICATIONS OF THE FINDINGS

These findings provide novel insight to the effect of circadian desynchrony on male reproductive health and a potential strategy for prevention of reproductive damage.

STUDY FUNDING/COMPETING INTEREST(S)

This study was supported by the National Key R&D Program of China [2017YFC1002001] and National Natural Science Foundation of China [81871208]. There are no conflicts of interest to declare.

TRIAL REGISTRATION NUMBER

NA.

Undenatured type II collagen prevents and treats osteoarthritis and motor function degradation in T2DM patients and db/db mice

Osteoarthritis (OA) has been scarcely researched among patients with diabetes mellitus. This study aims to confirm the preventive and therapeutic effects of undenatured type II collagen (UC II) on OA in aging db/db mice and in patients with T2DM. Firstly, aging db/db mice were randomly assigned to three groups: the UC II intervention (UC II) group, old model (OM) group and positive control group. Meanwhile db/m mice and young db/db mice were used as the normal control and young control groups, respectively. Secondly, fifty-five T2DM patients diagnosed with knee OA were randomly assigned to two groups: UC-II and placebo control groups. After a three-month intervention in both mice and T2DM patients, the subjects' gait and physical activities were assessed and the serum biomarkers including inflammatory cytokines, oxidative stress factors and matrix metalloproteinases (MMPs) were measured. Compared with the OM group mice, those in the UC II group showed a significantly greater superiority in terms of motor functions including the movement trajectories area (163.25 ± 20.3 vs. 78.52 ± 20.14 cm²), the tremor index (0.42 vs. 1.23), standing time (left hind: 0.089 ± 0.03 vs. 0.136 ± 0.04 s), swing (right front: 0.12 ± 0.02 vs. 0.216 ± 0.02 s), stride length (right hind: 7.2 ± 0.9 vs. 5.7 ± 1.1 cm), step cycle (right hind: 0.252 ± 0.05 vs. 0.478 ± 0.11 s) and cadence (14.12 ± 2.7 vs. 7.35 ± 4.4 steps per s). In addition, the levels of IL-4, IL-10, CTX- II and TGF-β in the UC II group were 1.74, 2.23, 1.67 and 1.84 times higher than those in the OM group, respectively, while the levels of MMP-3 and MMP-13 in the UC II group were half those in the OM group. Correspondingly, UC II intervention significantly decreased the scores of pain, stiffness and physical function (p < 0.05), whereas the 6 MWT and total MET distances in the UC II group increased remarkably (p < 0.05). After a three-month period of intervention, the varus angle significantly decreased from 4.6 ± 2.0° to 3.0 ± 1.4° and the knee flexion range obviously increased from 57.9 ± 14.0° to 66.9 ± 10.4°. Importantly, the declining trend in the levels of hs-CRP and MDA and the incremental trend in the SOD level were consistent in the db/db mice and OA patients following UC II administration.

Light-Dark Patterns Mirroring Shift Work Accelerate Atherosclerosis and Promote Vulnerable Lesion Phenotypes

Background

Despite compelling epidemiological evidence that circadian disruption inherent to long‐term shift work enhances atherosclerosis progression and vascular events, the underlying mechanisms remain poorly understood. A challenge to the use of mouse models for mechanistic and interventional studies involving light‐dark patterns is that the spectral and absolute sensitivities of the murine and human circadian systems are very different, and light stimuli in nocturnal mice should be scaled to represent the sensitivities of the human circadian system.

Methods and Results

We used calibrated devices to deliver to low‐density lipoprotein receptor knockout mice light‐dark patterns representative of that experienced by humans working day shifts or rotating shift schedules. Mice under day shifts were maintained under regular 12 hours of light and 12 hours of dark cycles. Mice under rotating shift schedules were subjected for 11 weeks to reversed light‐dark patterns 4 days in a row per week, followed by 3 days of regular light‐dark patterns. In both protocols the light phases consisted of monochromatic green light at an irradiance of 4 µW/cm². We found that the shift work paradigm disrupts the foam cell's molecular clock and increases endoplasmic reticulum stress and apoptosis. Lesions of mice under rotating shift schedules were larger and contained less prostabilizing fibrillar collagen and significantly increased areas of necrosis.

Conclusions

Low‐density lipoprotein receptor knockout mice under light‐dark patterns analogous to that experienced by rotating shift workers develop larger and more vulnerable plaques and may represent a valuable model for further mechanistic and/or interventional studies against the deleterious vascular effects of rotating shift work.

Time for Novel Strategies to Mitigate Cardiometabolic Risk in Shift Workers

Circadian disruption induced by shift work is robustly associated with obesity, diabetes, and cardiovascular disease in humans. Less well-known are the mechanisms underlying these associations, and the effectiveness of strategies to reduce cardiometabolic risk in the shift work population. In this review, the different ways in which shift work can deteriorate cardiometabolic health, and how to use this information to reflect on various risk-mitigating strategies, is discussed. While individual strategies appear promising in animal studies, the multifactorial disease risk in shift workers likely requires a multidisciplinary approach. Therefore, the need for individually-tailored combined lifestyle interventions, that could be essential in reducing cardiometabolic disorders in the large population of shift workers in our 24/7 society, is argued.

Evaluating the Effects of Different Sleep Supplement Modes in Attenuating Metabolic Consequences of Night Shift Work Using Rat Model

PURPOSE

To study the effects of chronic-simulated night shift work using the rat model and examines if a particular sleep supplement mode could be better in alleviating the effects.

METHODS

The male Wistar rats were randomly divided into the control (CTL: 8 rats) and night shift work (NW: 24 rats) groups of rats. Based on the sleep supplement strategy, the NW group was further segregated into three subgroups (8 rats each); late sleep supplement group (LSS), early sleep supplement group (ESS), and intermittent sleep supplement group (ISS). Sleep deprivation was achieved using the standard small-platform-over water method. Parameters such as animal body weight and food intake were measured daily. The intraperitoneal glucose tolerance test, fasting plasma insulin concentration, insulin resistance index and insulin sensitivity were measured twice, in the 4th and 8th weeks of the study. Plasma corticosterone concentration and pathological changes in islets (insulitis) were measured at the end of the 8th week.

RESULTS

In NW group, night work resulted in a gain of body weight and albeit lower than that of the CTL group. NW rats also had higher food intake, showed impaired glucose metabolism and higher plasma corticosterone concentration. The sleep supplement experiments suggested that compared to the other modes, intermittent sleep supplement had significantly low changes in the body weight, glucose metabolism and the islet cells.

CONCLUSION

Similar to previous studies, we also found that night shift work adversely impacts the body weight and glucose metabolism in rats. However, upon evaluating different sleep supplement strategies, we found the intermittent sleep supplement strategy to be most effective.

Melatonin alleviates circadian system disruption induced by chronic shifts of the light-dark cycle in Octodon degus

Modern 24-h society lifestyle is associated with experiencing frequent shifts in the lighting conditions which can negatively impact human health. Here, we use the degus, a species exhibiting diurnal and nocturnal chronotypes, to: (a) assess the impact of chronic shifts of the light:dark (LD) cycle in the animal's physiology and behaviour and (b) test the therapeutic potential of melatonin in enhancing rhythmicity under these conditions. Degus were subjected to a "5d + 2d" LD-shifting schedule for 19 weeks. This protocol aims to mimic lighting conditions experienced by humans during shift work: LD cycle was weekly delayed by 8h during 5 "working" days (Morning, Afternoon and Night schedule); during weekends (2 days), animals were kept under Morning schedule. After 9 weeks, melatonin was provided daily for 6h in the drinking water. The "5d + 2d" shifting LD schedule led to a disruption in wheel-running activity (WRA) and body temperature (Tb) rhythms which manifested up to three separate periods in the circadian range. This chronodisruption was more evident in nocturnal than in diurnal degus, particularly during the Afternoon schedule when a phase misalignment between WRA and Tb rhythms appeared. Melatonin treatment and, to a lesser extent, water restriction enhanced the 24-h component, suggesting a potential role in ameliorating the disruptive effects of shift work.

Circadian misalignment alters insulin sensitivity during the light phase and shifts glucose tolerance rhythms in female mice

Shift work and jet lag, characterized by circadian misalignment, can disrupt several physiological activities, but whether they affect the rhythm of glucose uptake and insulin sensitivity remain unclear. In the present study, female C57BL/6J mice were maintained for four weeks under the condition of 8-hour phase advance and delay every 3–4 days to mimic shift work. Intraperitoneal glucose tolerance test (IPGTT) and intraperitoneal insulin tolerance test (IPITT) were performed repeatedly at Zeitgeber time (ZT) 0, ZT6, ZT12, and ZT18. Glucose-stimulated insulin secretion (GSIS) test was performed at ZT6. We found that the average level of daily glucose tolerance did not decrease but the phase of glucose tolerance advanced by 2.27 hours and the amplitude attenuated by 20.4% in shift work mice. At ZT6, IPITT showed blood glucose at 30 min after insulin injection decreased faster in shift work mice (−3.50±0.74mmol/L, −61.58±7.89%) than that in control mice (−2.11±1.10mmol/L, −33.72±17.24%), but IPGTT and GSIS test showed no significant difference between the two groups. Food intake monitor showed that the feeding time of shift work mice continued to advance. Restricting feed to a fixed 12-hour period alleviated the increase of insulin sensitivity induced by shift-work. We also observed that an increase of blood glucose and liver glycogen at ZT0, as well as a phase advance of liver clock genes and some glucose metabolism-related genes such as forkhead box O1 (Foxo1) and peroxisome proliferator activated receptor alpha (Pparα) in shift work mice. Our results showed that light change-simulated shift work altered insulin sensitivity during the light phase and shifted glucose tolerance rhythms in female mice, suggesting a causal association between long-term shift work and type 2 diabetes.

Time-Restricted Feeding Improves Glucose Tolerance in Rats, but Only When in Line With the Circadian Timing System

Epidemiological studies indicate that shift-workers have an increased risk of type 2 diabetes mellitus (T2DM). Glucose tolerance and insulin sensitivity both are dependent on the circadian timing system (i.e., the time-of-day) and fasting duration, in rodents as well as humans. Therefore, question is whether manipulation of the circadian timing system, for example by changing the timing of feeding and fasting, is a potential preventive treatment for T2DM. Time-restricted feeding (TRF) is well-known to have profound effects on various metabolic measures, including glucose metabolism. However, experiments that directly measure the effects of TRF on glucose tolerance and/or insulin sensitivity at different time points throughout the 24 h cycle are lacking. Here we show, in rats, that TRF in line with the circadian timing system (i.e., feeding during the active phase) improves glucose tolerance during intravenous glucose tolerance tests (ivGTT) in the active phase, as lower insulin levels were observed with similar levels of glucose clearance. However, this was not the case during the inactive phase in which more insulin was released but only a slightly faster glucose clearance was observed. Contrasting, TRF out of sync with the circadian timing system (i.e., feeding during the inactive phase) worsened glucose tolerance, although only marginally, likely because of adaptation to the 4 week TRF regimen. Our results show that TRF can improve glucose metabolism, but strict adherence to the time-restricted feeding period is necessary, as outside the regular eating hours glucose tolerance is worsened.

Non-visual effects of light: how to use light to promote circadian entrainment and elicit alertness

In addition to stimulating the visual system, light incident on the retina stimulates other biological functions, also referred to as non-visual responses. Among the most notable biological functions are human circadian rhythms, which are bodily rhythms that, in constant darkness, oscillate with a period close to, but typically slightly longer than 24 hours. Twenty-four-hour light-dark patterns incident on the retina are the major synchronizer of circadian rhythms to the local time on Earth. Entrainment of circadian rhythms has been implicated in health and well-being. Light can also elicit an acute alerting effect on people, similar to a "cup of coffee." This review summarizes the literature on how light affects entrainment and alertness and how it can be used to achieve these aims.

Light at night as an environmental endocrine disruptor

Environmental endocrine disruptors (EEDs) are often consequences of human activity; however, the effects of EEDs are not limited to humans. A primary focus over the past ∼30years has been on chemical EEDs, but the repercussions of non-chemical EEDs, such as artificial light at night (LAN), are of increasing interest. The sensitivity of the circadian system to light and the influence of circadian organization on overall physiology and behavior make the system a target for disruption with widespread effects. Indeed, there is increasing evidence for a role of LAN in human health, including disruption of circadian regulation and melatonin signaling, metabolic dysregulation, cancer risk, and disruption of other hormonally-driven systems. These effects are not limited to humans; domesticated animals as well as wildlife are also exposed to LAN, and at risk for disrupted circadian rhythms. Here, we review data that support the role of LAN as an endocrine disruptor in humans to be considered in treatments and lifestyle suggestions. We also present the effects of LAN in other animals, and discuss the potential for ecosystem-wide effects of artificial LAN. This can inform decisions in agricultural practices and urban lighting decisions to avoid unintended outcomes.