Differential regulation of circadian melatonin rhythm and sleep-wake cycle by bright lights and nonphotic time cues in humans

Morning physical activity may be more beneficial for blood lipids than afternoon physical activity in older adults: a cross-sectional study

BACKGROUND

The effect of differences in daily physical activity patterns on blood lipids has not been determined. This study examines the effects of the differences in free-living daily physical activity patterns (amount and intensity) on blood lipid levels in older adults.

METHODS

This cross-sectional study included 51 older participants (71.8 ± 0.6 years, men = 8, women = 43). A triaxial accelerometer was used to assess physical activity patterns. The time from awakening to bedtime for each participant was used for group classification based on the amount (number of steps) and intensity (moderate-to-vigorous physical activity, MVPA) of physical activity. The morning step group (M Step) was defined as those who took more steps in the morning, and the afternoon step group (A Step) was defined as those who took more steps in the afternoon. The same method was used for MVPA (morning MVPA: M MVPA; afternoon MVPA: A MVPA). Blood samples were collected at the start of the study to determine blood lipid levels.

RESULTS

Number of steps taken showed a trend toward lower low-density lipoprotein cholesterol (LDL-C) levels in the M Step group compared with the A Step group. The LDL/high-density lipoprotein (HDL) ratio was significantly lower in the M Step group than the A Step group (p < 0.05). The M MVPA group also had higher HDL-C levels and significantly lower LDL/HDL ratios than the A MVPA group (p < 0.05).

CONCLUSIONS

These results suggest that compared with afternoon physical activity, daily morning physical activity (amount and intensity) is more effective in improving blood lipid levels.

The Relationship between Circadian Rhythm and Cancer Disease

The circadian clock regulates biological cycles across species and is crucial for physiological activities and biochemical reactions, including cancer onset and development. The interplay between the circadian rhythm and cancer involves regulating cell division, DNA repair, immune function, hormonal balance, and the potential for chronotherapy. This highlights the importance of maintaining a healthy circadian rhythm for cancer prevention and treatment. This article investigates the complex relationship between the circadian rhythm and cancer, exploring how disruptions to the internal clock may contribute to tumorigenesis and influence cancer progression. Numerous databases are utilized to conduct searches for articles, such as NCBI, MEDLINE, and Scopus. The keywords used throughout the academic archives are "circadian rhythm", "cancer", and "circadian clock". Maintaining a healthy circadian cycle involves prioritizing healthy sleep habits and minimizing disruptions, such as consistent sleep schedules, reduced artificial light exposure, and meal timing adjustments. Dysregulation of the circadian clock gene and cell cycle can cause tumor growth, leading to the need to regulate the circadian cycle for better treatment outcomes. The circadian clock components significantly impact cellular responses to DNA damage, influencing cancer development. Understanding the circadian rhythm's role in tumor diseases and their therapeutic targets is essential for treating and preventing cancer. Disruptions to the circadian rhythm can promote abnormal cell development and tumor metastasis, potentially due to immune system imbalances and hormonal fluctuations.

Move the night way: how can physical activity facilitate adaptation to shift work?

Shift work, involving night work, leads to impaired sleep, cognition, health and wellbeing, and an increased risk of occupational incidents. Current countermeasures include circadian adaptation to phase shift circadian biomarkers. However, evidence of real-world circadian adaptation is found primarily in occupations where light exposure is readily controlled. Despite this, non-photic adaptation to shift work remains under researched. Other markers of shift work adaptation exist (e.g., improvements in cognition and wellbeing outcomes) but are relatively unexplored. Timeframes for shift work adaptation involve changes which occur over a block of shifts, or over a shift working career. We propose an additional shift work adaptation timeframe exists which encompasses acute within shift changes in markers of adaptation. We also propose that physical activity might be an accessible and cost-effective countermeasure that could influence multiple markers of adaptation across three timeframes (Within Shift, Within Block, Within Work-span). Finally, practical considerations for shift workers, shift work industries and future research are identified.

Circadian Rhythms, Chrononutrition, Physical Training, and Redox Homeostasis-Molecular Mechanisms in Human Health

A multitude of physiological processes, human behavioral patterns, and social interactions are intricately governed by the complex interplay between external circumstances and endogenous circadian rhythms. This multidimensional regulatory framework is susceptible to disruptions, and in contemporary society, there is a prevalent occurrence of misalignments between the circadian system and environmental cues, a phenomenon frequently associated with adverse health consequences. The onset of most prevalent current chronic diseases is intimately connected with alterations in human lifestyle practices under various facets, including the following: reduced physical activity, the exposure to artificial light, also acknowledged as light pollution, sedentary behavior coupled with consuming energy-dense nutriments, irregular eating frameworks, disruptions in sleep patterns (inadequate quality and duration), engagement in shift work, and the phenomenon known as social jetlag. The rapid evolution of contemporary life and domestic routines has significantly outpaced the rate of genetic adaptation. Consequently, the underlying circadian rhythms are exposed to multiple shifts, thereby elevating the susceptibility to disease predisposition. This comprehensive review endeavors to synthesize existing empirical evidence that substantiates the conceptual integration of the circadian clock, biochemical molecular homeostasis, oxidative stress, and the stimuli imparted by physical exercise, sleep, and nutrition.

Two oscillatory components detected by forced splitting of the sleep-wake cycle in humans

The sleep-wake cycle of human subjects was artificially split into two episodes by imposing an 8-h light and 4-h dark cycle (LD 8:4) twice a day for 7 days, which was followed by a 3-day free-running session. Sleep was permitted only in the dark period. The subjects in the ordinary group were exposed to ordinary light (ca. 500 lx) in the 8-h light period, and those in the bright light group to bright (ca. 5,000 lx) and ordinary light alternatively with bright light after the first dark period (2400-400). Split sleeps persisted in the free-running session with the major episode around the first dark period and the minor episode around the second dark period. By contrast, circadian melatonin rhythm in the free-running session significantly phase delayed in the ordinary light group, but phase advanced in the bright light group, keeping the melatonin rhythm unsplit. The length of nocturnal melatonin secretion (NMS) was significantly shortened in the bright light group. Interestingly, the falling phase of NMS advanced significantly further than the rising phase. Such a difference was not detected in the ordinary light group. Similar differences were observed in the body temperature rhythm. These findings indicated oscillatory mechanisms underlying split sleeps distinct from the circadian pacemaker and suggested an involvement of different circadian oscillators in the rising and falling phases of NMS, which is consistent with the dual oscillator model proposed for the circadian system of nocturnal rodents.NEW & NOTEWORTHY The present study demonstrated that human sleep was separated into two essentially identical components, which persisted under constant conditions, suggesting circadian oscillator underlying split-sleep episodes. The study also indicated differential light sensitivities in the rising and falling phases of circadian melatonin rhythm, indicating the involvement of two different oscillators. These results consisted of the evening and morning dual-oscillator hypothesis for the circadian pacemaker and the hierarchical model for the pacemaker and sleep-wake cycle.

Relationship between Circadian Phase Delay without Morning Light and Phase Advance by Bright Light Exposure the Following Morning

Humans have a circadian rhythm for which the period varies among individuals. In the present study, we investigated the amount of natural phase delay of circadian rhythms after spending a day under dim light (Day 1 to Day 2) and the amount of phase advance due to light exposure (8000 lx, 4100 K) the following morning (Day 2 to Day 3). The relationships of the phase shifts with the circadian phase, chronotype and sleep habits were also investigated. Dim light melatonin onset (DLMO) was investigated as a circadian phase marker on each day. In the 27 individuals used for the analysis, DLMO was delayed significantly (-0.24 ± 0.33 h, p < 0.01) from Day 1 to Day 2 and DLMO was advanced significantly (0.18 ± 0.36 h, p < 0.05) from Day 2 to Day 3. There was a significant correlation between phase shifts, with subjects who had a greater phase delay in the dim environment having a greater phase advance by light exposure (r = -0.43, p < 0.05). However, no significant correlations with circadian phase, chronotype or sleep habits were found. These phase shifts may reflect the stability of the phase, but do not account for an individual's chronotype-related indicators.

Effects of exercise on circadian rhythms in humans

The biological clock system is an intrinsic timekeeping device that integrates internal physiology and external cues. Maintaining a healthy biological clock system is crucial for life. Disruptions to the body's internal clock can lead to disturbances in the sleep-wake cycle and abnormalities in hormone regulation, blood pressure, heart rate, and other vital processes. Long-term disturbances have been linked to the development of various common major diseases, including cardiovascular diseases, metabolic disorders, tumors, neuropsychiatric conditions, and so on. External factors, such as the diurnal rhythm of light, have a significant impact on the body's internal clock. Additionally, as an important non-photic zeitgeber, exercise can regulate the body's internal rhythms to a certain extent, making it possible to become a non-drug intervention for preventing and treating circadian rhythm disorders. This comprehensive review encompasses behavioral, physiological, and molecular perspectives to provide a deeper understanding of how exercise influences circadian rhythms and its association with related diseases.

Metabolic Basis of Circadian Dysfunction in Parkinson's Disease

Parkinson's disease (PD) is one of the most common neurodegenerative disorders. The management of PD is a challenging aspect for general physicians and neurologists. It is characterized by the progressive loss of dopaminergic neurons. Impaired α-synuclein secretion and dopamine release may cause mitochondrial dysfunction and perturb energy metabolism, subsequently altering the activity and survival of dopaminergic neurons, thus perpetuating the neurodegenerative process in PD. While the etiology of PD remains multifactorial, emerging research indicates a crucial role of circadian dysfunction in its pathogenesis. Researchers have revealed that circadian dysfunction and sleep disorders are common among PD subjects and disruption of circadian rhythms can increase the risk of PD. Hence, understanding the findings of circadian biology from translational research in PD is important for reducing the risk of neurodegeneration and for improving the quality of life. In this review, we discuss the intricate relationship between circadian dysfunction in cellular metabolism and PD by summarizing the evidence from animal models and human studies. Understanding the metabolic basis of circadian dysfunction in PD may shed light on novel therapeutic approaches to restore circadian rhythm, preserve dopaminergic function, and ameliorate disease progression. Further investigation into the complex interplay between circadian rhythm and PD pathogenesis is essential for the development of targeted therapies and interventions to alleviate the burden of this debilitating neurodegenerative disorder.

Shine light on sleep: Morning bright light improves nocturnal sleep and next morning alertness among college students

The relationship between daytime light, especially morning light and sleep, has not been well documented. People who work in an office spend most of their time indoors and thus have less access to high-level daylight. The current study employed a field intervention approach to investigate whether exposure to 1.5 h of bright electric light in the early morning for 1 workweek would benefit sleep among students who spent most of their time in an office at the university. Twelve students (24.92 ± 1.78 years) underwent a 2 workday baseline measurement and two inconsecutive 5 workday interventions (with 1 week washout) with morning bright light and regular office light (1000 lx, 6500 K vs. 300 lx, 4000 K, at eye level). The sleep outcomes were recorded with actigraphy and a sleep diary. In addition, self-ratings of daytime sleepiness, mood, mental fatigue, perceived effort, and next morning sleepiness were measured each workday. The results showed that exposure to morning bright light versus regular office light yielded a higher sleep efficiency (83.82% ± 1.60 vs. 80.35% ± 1.57, p = 0.02), a smaller fragmentation index (15.26% ± 1.31 vs. 17.18% ± 1.28, p = 0.05), and a shorter time in bed (7.12 ± 0.13 vs. 7.51 ± 0.12, p = 0.03). Meanwhile, an earlier sleep onset time, shorter sleep latency, and lower morning sleepiness were observed after a 5 workday morning bright light intervention compared with the baseline (ps <0.05), no such benefit was found for self-ratings (ps >0.05). These findings support existing evidence that morning bright light could function as an enhancer of sleep and alertness for office occupants.

Shift Work and Obesity Risk-Are There Sex Differences?

PURPOSE OF REVIEW

Shift work is prevalent among the working population and is linked to an array of adverse health outcomes. This review summarizes current evidence on the relation between shift work and risk of obesity, with a particular emphasis on potential sex differences.

RECENT FINDINGS

Observational data strongly point towards an association between shift work and heightened risk of prevalent and incident obesity, and particularly abdominal obesity. Circadian misalignment and unhealthy lifestyle behaviors are the primary culprits mediating such association. As it pertains to sex differences in the impact of shift work on obesity, few studies have examined this aspect, and findings are conflicting. Shift work is an important risk factor for obesity, with likely multiple biological and behavioral mediators. However, whether there is a sex-dependent vulnerability to the obesogenic effects of shift work is unclear. This area presents opportunities for future research.

Gene Expression Profile Associated with Asmt Knockout-Induced Depression-Like Behaviors and Exercise Effects in Mouse Hypothalamus

Sleep disorder caused by abnormal circadian rhythm is one of the main symptoms and risk factors of depression. As a known hormone regulating circadian rhythms, melatonin (MT) is also namely N-acetyl-5-methoxytryptamine. N-acetylserotonin methyltransferase (Asmt) is the key rate-limiting enzyme of MT synthesis and has been reportedly associated with depression. Although 50–90% of patients with depression have sleep disorders, there are no effective treatment ways in the clinic. Exercise can regulate circadian rhythm and play an important role in depression treatment. In the present study, we showed that Asmt knockout induced depression-like behaviors, which were ameliorated by swimming exercise. Moreover, swimming exercise increased serum levels of MT and 5-hydroxytryptamine (5-HT) in Asmt knockout mice. In addition, the microarray data identified 10 differentially expressed genes (DEGs) in KO mice compared with WT mice and 29 DEGs in KO mice after swimming exercise. Among the DEGs, the direction and magnitude of change in epidermal growth factor receptor pathway substrate 8-like 1 (Eps8l1) and phospholipase C-β 2 (Plcb2) were confirmed by qRT-PCR partly. Subsequent bioinformatic analysis showed that these DEGs were enriched significantly in the p53 signaling pathway, long-term depression and estrogen signaling pathway. In the protein–protein interaction (PPI) networks, membrane palmitoylated protein 1 (Mpp1) and p53-induced death domain protein 1 (Pidd1) were hub genes to participate in the pathological mechanisms of depression and exercise intervention. These findings may provide new targets for the treatment of depression.

The impacts of a combined exercise on executive function in children with ADHD: A randomized controlled trial

PURPOSE

The purpose of this study was to examine the effects of aerobic and neurocognitive exercise with moderate-to-vigorous physical activity levels on executive functions (EFs) and sleep quality in children with attention-deficit/hyperactivity disorder (ADHD).

METHODS

In a parallel two-group randomized controlled trial (RCT) design, 80 children with ADHD aged 6-12 years (Mage = 8.46 ± 1.50) were assigned to either a 12-week combined aerobic-and neurocognitive-exercise experimental group (EG; three sessions per week for 60-min) or a wait-list control group (CG). Forty children with typical development aged 6-12 years (Mage = 8.49 ± 1.51) were recruited as healthy controls (HC). A Polar heart rate (HR) monitor was used to track the exercise intensity (60%-80% predicted HRmax) throughout the intervention. Three core EFs (inhibitory control [IC], working memory [WM], and cognitive flexibility [CF]) were assessed by computer-based neurocognitive tasks, and sleep quality and physical activity (PA) levels were assessed by self-report questionnaires.

RESULTS

The results showed that the exercise intervention was beneficial for improving three core EFs, shortening sleep latency and decreasing sleep disturbances. The intervention effects on EFs and sleep quality appeared to be sustained for at least 12 weeks in EG. In addition, children with ADHD after intervention showed non-significant differences in IC, CF and multiple sleep quality outcomes compared with HC. Furthermore, a significant PA-EFs-sleep correlation was found in children with ADHD after the intervention.

CONCLUSION

The findings suggest that a 12-week combined aerobic and neurocognitive exercise intervention appears to be an effective treatment program for EFs and sleep quality in children with ADHD.

A fixed single meal in the subjective day prevents free-running of the human sleep-wake cycle but not of the circadian pacemaker under temporal isolation

Effects of a fixed single meal per day were examined on the circadian pacemaker and sleep-wake cycle in subjects under temporal isolation. When the time of single meal was allowed to take at any time of day (Ad-lib meal), the sleep-wake cycle as well as the circadian rhythms in plasma melatonin, cortisol and core body temperature were significantly phase-delayed in 8 days. On the other hand, when the time of meal was fixed at 1800 h in local time (RF meal), the phase-shift of sleep-wake cycle was not significant, while those of the circadian rhythms were significant. The differential effects of a fixed single meal schedule were confirmed in most individual subjects. There was no evidence for the prefeeding increase in plasma cortisol and leptin levels under the fixed single meal schedule. The plasma ghrelin level was apparently high before meal in both Ad-lib and RF meal groups, which was, however, likely sculptured by a non-specific prandial drop and gradual increase after meal intake. Single meal augmented the prandial increase of plasma insulin levels by 4-5 times. These findings indicate that a single meal at fixed time of day during the subjective day failed to prevent the human circadian pacemaker but prevented the sleep-wake cycle to free-run at least 8 days under temporal isolation, suggesting that meal time was a potent non-photic time cue for the human sleep-wake cycle.

Clocks Ticking in the Dark: A Review of Biological Rhythms in Subterranean African Mole-Rats

Biological rhythms are rhythmic fluctuations of biological functions that occur in almost all organisms and on several time scales. These rhythms are generated endogenously and entail the coordination of physiological and behavioural processes to predictable, external environmental rhythms. The light-dark cycle is usually the most prominent environmental cue to which animals synchronise their rhythms. Biological rhythms are believed to provide an adaptive advantage to organisms. In the present review, we will examine the occurrence of circadian and seasonal rhythms in African mole-rats (family Bathyergidae). African mole-rats are strictly subterranean, they very rarely emerge aboveground and therefore, do not have regular access to environmental light. A key adaptation to their specialised habitat is a reduction in the visual system. Mole-rats exhibit both daily and seasonal rhythmicity in a range of behaviours and physiological variables, albeit to different degrees and with large variability. We review previous research on the entire circadian system of African mole-rats and discuss output rhythms in detail. Laboratory experiments imply that light remains the strongest zeitgeber for entrainment but in the absence of light, animals can entrain to ambient temperature rhythms. Field studies report that rhythmic daily and seasonal behaviour is displayed in their natural habitat. We suggest that ambient temperature and rainfall play an important role in the timing of rhythmic behaviour in mole-rats, and that they likely respond directly to these zeitgebers in the field rather than exhibit robust endogenous rhythms. In the light of climate change, these subterranean animals are buffered from the direct and immediate effects of changes in temperature and rainfall, partly because they do not have robust circadian rhythms, however, on a longer term they are vulnerable to changes in their food sources and dispersal abilities.

A Growing Link between Circadian Rhythms, Type 2 Diabetes Mellitus and Alzheimer's Disease

Type 2 diabetes mellitus (T2DM) patients are at a higher risk of developing Alzheimer’s disease (AD). Mounting evidence suggests the emerging important role of circadian rhythms in many diseases. Circadian rhythm disruption is considered to contribute to both T2DM and AD. Here, we review the relationship among circadian rhythm disruption, T2DM and AD, and suggest that the occurrence and progression of T2DM and AD may in part be associated with circadian disruption. Then, we summarize the promising therapeutic strategies targeting circadian dysfunction for T2DM and AD, including pharmacological treatment such as melatonin, orexin, and circadian molecules, as well as non-pharmacological treatments like light therapy, feeding behavior, and exercise.

Circadian acclimatization of performance, sleep, and 6-sulfatoxymelatonin using multiple phase shifting stimuli

Misalignment between the environment and one's circadian system is a common phenomenon (e.g., jet lag) which can have myriad negative effects on physical and mental health, mental and physiological performance, and sleep. Absent any intervention, the circadian system adjusts only 0.5-1.0 h per day to a shifted light-dark and sleep-wake schedule. Bright light facilitates circadian adjustment, but in field studies, bright light is only modestly better than no stimulus. Evidence indicates that exercise and melatonin can be combined with bright light to elicit larger shifts but no study has combined all of these stimuli or administered them at the times that are known to elicit the largest effects on the circadian system. The aims of this study are to compare the effects of different treatments on circadian adjustment to simulated jet lag in a laboratory. Following 2 weeks of home recording, 36 adults will spend 6.5 consecutive days in the laboratory. Following an 8 h period of baseline sleep recording on the participant's usual sleep schedule on Night 1 (e.g., 0000-0800 h), participants will undergo a 26 h circadian assessment protocol involving 2 h wake intervals in dim light and 1 h of sleep in darkness, repeated throughout the 26 h. During this protocol, all urine voidings will be collected; mood, sleepiness, psychomotor vigilance, and pain sensitivity will be assessed every 3 h, forehead temperature will be assessed every 90 min, and anaerobic performance (Wingate test) will be tested every 6 h. Following, the circadian assessment protocol, the participant's sleep-wake and light dark schedule will be delayed by 8 h compared with baseline (e.g., 0800-1400 h), analogous to travelling 8 times zones westward. This shifted schedule will be maintained for 3 days. During the 3 days on the delayed schedule, participants will be randomized to one of 3 treatments: (1) Dim Red Light + Placebo Capsules, (2) Bright Light Alone, (3) Bright Light + Exercise + Melatonin. During the final 26 h, all conditions and measures of the baseline circadian protocol will be repeated. Acclimatization will be defined by shifts in circadian rhythms of aMT6s, psychomotor vigilance, Wingate Anaerobic performance, mood, and sleepiness, and less impairments in these measures during the shifted schedule compared with baseline. We posit that Bright Light Alone and Bright Light + Exercise + Melatonin will elicit greater shifts in circadian rhythms and less impairments in sleep, mood, performance, and sleepiness compared with Dim Red Light + Placebo Capsules. We also posit that Bright Light + Exercise + Melatonin will elicit greater shifts and less impairments than Bright Light Alone.

Exercise as a Peripheral Circadian Clock Resynchronizer in Vascular and Skeletal Muscle Aging

Aging is characterized by several progressive physiological changes, including changes in the circadian rhythm. Circadian rhythms influence behavior, physiology, and metabolic processes in order to maintain homeostasis; they also influence the function of endothelial cells, smooth muscle cells, and immune cells in the vessel wall. A clock misalignment could favor vascular damage and indirectly also affect skeletal muscle function. In this review, we focus on the dysregulation of circadian rhythm due to aging and its relationship with skeletal muscle changes and vascular health as possible risk factors for the development of sarcopenia, as well as the role of physical exercise as a potential modulator of these processes.

Factors Contributing to Diurnal Variation in Athletic Performance and Methods to Reduce Within-Day Performance Variation: A Systematic Review

ABSTRACT

Kusumoto, H, Ta, C, Brown, SM, and Mulcahey, MK. Factors contributing to diurnal variation in athletic performance and methods to reduce within-day performance variation: A systematic review. J Strength Cond Res 35(12S): S119-S135, 2021-For many individuals, athletic performance (e.g., cycle ergometer output) differs based on the time of day (TOD). This study identified factors contributing to diurnal variation in athletic performance and methods to reduce TOD performance variation. Comprehensive searches of PubMed, Ovid, EMBASE, Web of Science, and Cochrane Libraries were conducted in accordance with Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. Peer-reviewed publications reporting quantitative, significant diurnal variation (p ≤ 0.05) of athletic performance with explanations for the differences were included. Studies providing effective methods to reduce diurnal variation were also included. Literature reviews, studies involving nonhuman or nonadult subjects, studies that intentionally manipulated sleep duration or quality, and studies deemed to be of poor methodological quality using NIH Quality Assessment Tools were excluded. Forty-nine studies met the inclusion criteria. Body temperature differences (n = 13), electromyographic parameters (n = 10), serum biomarker fluctuations (n = 5), athlete chronotypes (n = 4), and differential oxygen kinetics (n = 3) were investigated as significant determinants of diurnal variation in sports performance. Successful techniques for reducing diurnal athletic performance variability included active or passive warm-up (n = 9), caffeine ingestion (n = 2), and training-testing TOD synchrony (n = 3). Body temperature was the most important contributor to diurnal variation in athletic performance. In addition, extended morning warm-up was the most effective way to reduce performance variation. Recognizing contributors to diurnal variation in athletic performance may facilitate the development of more effective training regimens that allow athletes to achieve consistent performances regardless of TOD.

Recent Progress in Non-motor Features of Parkinson's Disease with a Focus on Circadian Rhythm Dysregulation

Parkinson's disease (PD) is the second most common neurodegenerative disease, which manifests with both motor and non-motor symptoms. Circadian rhythm dysregulation, as one of the most challenging non-motor features of PD, usually appears long before obvious motor symptoms. Moreover, the dysregulated circadian rhythm has recently been reported to play pivotal roles in PD pathogenesis, and it has emerged as a hot topic in PD research. In this review, we briefly introduce the circadian rhythm and circadian rhythm-related genes, and then summarize recent research progress on the altered circadian rhythm in PD, ranging from clinical features to the possible causes of PD-related circadian disorders. We believe that future comprehensive studies on the topic may not only help us to explore the mechanisms of PD, but also shed light on the better management of PD.

Basic concepts and unique features of human circadian rhythms: implications for human health

Most physiological functions and behaviors exhibit a robust approximately 24-hour rhythmicity (circadian rhythm) in the real world. These rhythms persist under constant conditions, but the period is slightly longer than 24 hours, suggesting that circadian rhythms are endogenously driven by an internal, self-sustained oscillator. In mammals, including humans, the central circadian pacemaker is located in the hypothalamic suprachiasmatic nucleus. The primary zeitgeber for this pacemaker is bright sunlight, but nonphotic time cues also affect circadian rhythms. The human circadian system uniquely exhibits spontaneous internal desynchronization between the sleep-wake cycle and core body temperature rhythm under constant conditions and partial entrainment of the sleep-wake cycle in response to nonphotic time cues. Experimental and clinical studies of human circadian rhythms must take into account these unique features. This review covers the basic concepts and unique features of the human circadian system, the mechanisms underlying phase adjustment of the circadian rhythms by light and nonphotic time cues (eg, physical exercise), and the effects of eating behavior (eg, chewing frequency) on the circadian rhythm of glucose metabolism.

Assessment of Selected Clock Proteins (CLOCK and CRY1) and Their Relationship with Biochemical, Anthropometric, and Lifestyle Parameters in Hypertensive Patients

BACKGROUND

Circadian rhythms misalignment is associated with hypertension. The aim of the study was to evaluate the concentration of selected clock proteins-cryptochrome 1 (CRY1) and circadian locomotor output cycles kaput (CLOCK) to determine their relationships with biochemical and anthropometric parameters and lifestyle elements (diet, physical activity, and quality of sleep) in hypertensive patients.

METHODS

In 31 females with hypertension (HT) and 55 non-hypertensive women (NHT) the CRY1 and CLOCK concentrations, total antioxidant status (TAS), lipid profile, and glycemia were analyzed. Blood pressure and anthropometric measurements, nutritional, exercise, and sleep analyses were performed.

RESULTS

In the HT group, the CRY1 level was 37.38% lower than in the NHT group. No differences were noted in CLOCK concentration between groups. BMI, FBG, and TG were higher in the HT group compared to the NHT group, while TC, LDL, and HDL levels were similar. The study showed no relationship between CRY1 or CLOCK concentrations and glucose or lipids profile, amount of physical activity, or sleep quality, although CRY1 was associated with some anthropometric indicators. In the HT group, increased CLOCK and CRY1 values were associated with a high TAS level.

CONCLUSIONS

The serum level of CRY1 could be considered in a detailed diagnostic of hypertension risk in populations with abnormal anthropometric indices.

Regular exercise counteracts circadian shifts in core body temperature during long-duration bed rest

With NASA's plans for the human exploration of Mars, astronauts will be exposed to mission durations much longer than current spaceflight missions on the International Space Station. These mission durations will increase the risk for circadian misalignment. Exercise has gained increasing interest as a non-pharmacological aid to entrain the circadian system. To assess the potential of exercise as a countermeasure to mitigate the risk for circadian disorders during spaceflight, we investigated the effects of long-term head-down tilt bed rest (HDBR) with and without exercise on the circadian rhythm of core body temperature. Core body temperature was recorded for 24 h using a rectal probe in sixteen healthy men (age: 30.5 ± 7.5 years (mean ± SD)) after 7 days and 49 days of HDBR. Five participants underwent HDBR only (CTR), five participants underwent HDBR and performed resistive exercises (RE), and six participants underwent HDBR and performed resistive exercises superimposed with vibrations (RVE). The exercise was scheduled three times per week. CTR showed a phase delay of 0.69 h. In contrast, both exercise groups were characterized by a phase advance (0.45 h for RE and 0.45 h for RVE; p = 0.026 for interaction between time and group). These findings suggest that resistive exercise (with or without vibration) may also serve as a countermeasure during spaceflight to mitigate circadian misalignments. The results could also be important for increasing awareness about the role of circadian disorders in long-term bedridden patients.

Genomic perspectives on the circadian clock hypothesis of psychiatric disorders

Circadian rhythm disturbances are frequently described in psychiatric disorders such as major depressive disorder, bipolar disorder, and schizophrenia. Growing evidence suggests a biological connection between mental health and circadian rhythmicity, including the circadian influence on brain function and mood and the requirement for circadian entrainment by external factors, which is often impaired in mental illness. Mental (as well as physical) health is also adversely affected by circadian misalignment. The marked interindividual differences in this combined susceptibility, in addition to the phenotypic spectrum in traits related both to circadian rhythms and mental health, suggested the possibility of a shared genetic background and that circadian clock genes may also be candidate genes for psychiatric disorders. This hypothesis was further strengthened by observations in animal models where clock genes had been knocked out or mutated. The introduction of genome-wide association studies (GWAS) enabled hypothesis-free testing. GWAS analysis of chronotype confirmed the prominent role of circadian genes in these phenotypes and their extensive polygenicity. However, in GWAS on psychiatric traits, only one clock gene, ARNTL (BMAL1) was identified as one of the few loci differentiating bipolar disorder from schizophrenia, and macaque monkeys where the ARNTL gene has been knocked out display symptoms similar to schizophrenia. Another lesson from genomic analyses is that chronotype has an important genetic correlation with several psychiatric disorders and that this effect is unidirectional. We conclude that the effect of circadian disturbances on psychiatric disorders probably relates to modulation of rhythm parameters and extend beyond the core clock genes themselves.

Impaired function of the suprachiasmatic nucleus rescues the loss of body temperature homeostasis caused by time-restricted feeding

The suprachiasmatic nucleus (SCN) is the master circadian pacemaker that drives body temperature rhythm. Time-restricted feeding (TRF) has potential as a preventative or therapeutic approach against many diseases. The potential side effects of TRF remain unknown. Here we show that a 4-hour TRF stimulus in mice can severely impair body temperature homeostasis and can result in lethality. Nearly half of the mice died at 21 °C, and all mice died at 18 °C during 4-hour TRF. Moreover, this effect was modulated by the circadian clock and was associated with severe hypothermia due to loss of body temperature homeostasis, which is different from "torpor", an adaptive response under food deprivation. Disrupting the circadian clock by the SCN lesions or a non-invasive method (constant light) which disrupts circadian clock rescued lethality during TRF. Analysis of circadian gene expression in the dorsomedial hypothalamus (DMH) demonstrated that TRF reprograms rhythmic transcriptome in DMH and suppresses expression of genes, such as Ccr5 and Calcrl, which are involved in thermoregulation. We demonstrate a side effect of 4-hour TRF on the homeostasis of body temperature and a rescue function by impairing the SCN function. Altogether, our results suggested that constructing a circadian arrhythmicity may have a beneficial effect on the host response to an acute stress.

Obesity and Circadian Cycle of Sleep and Wakefulness: Common Points and Prospects of Therapy

The prevalence of obesity in recent years has assumed the character of a non-communicable epidemic. Wherein, the standard approaches for its treatment are not always successful. Meanwhile, obesity remains one of the main causes of the formation of a number of some serious diseases, such as cardiovascular, diabetes, cancer, etc. and death from them. In search of alternative and more adequate methods of obesity treatment and preventing its complications, recent studies are aimed at further identifying new associations and revealing the pathophysiological mechanisms underlying excessive weight gain. It should be noted an increasing amount of chronobiological studies that raised awareness of the key role of the body’s circadian rhythms and its main regulator, melatonin, responsible for the temporary organization of the main physiological (including metabolism) processes throughout the 24-h day, in the development and progression of obesity. This review is devoted to the consideration of mutually directed interactions between the circadian system and metabolism; attempts have been made to explain the role of sleep-wake cycle disruptions in the excess accumulation of adipose tissue and the formation of obesity and its comorbidities, as well as detailed therapeutic principles based on normalizing disruption of body clocks using time-coordinated approaches to food intake, physical activity, the effects of non-drug methods and pharmacological substances (chronobiotics), which represents a novel and promising ways to prevent or treat obesity and associated diseases.

Chronotype-Dependent Changes in Sleep Habits Associated with Dim Light Melatonin Onset in the Antarctic Summer

Dim light melatonin onset (DLMO) is the most reliable measure of human central circadian timing. Its modulation by light exposure and chronotype has been scarcely approached. We evaluated the impact of light changes on the interaction between melatonin, sleep, and chronotype in university students (n = 12) between the Antarctic summer (10 days) and the autumn equinox in Montevideo, Uruguay (10 days). Circadian preferences were tested by validated questionnaires. A Morningness–Eveningness Questionnaire average value (47 ± 8.01) was used to separate late and early participants. Daylight exposure (measured by actimetry) was significantly higher in Antarctica versus Montevideo in both sensitive time windows (the morning phase-advancing and the evening phase-delaying). Melatonin was measured in hourly saliva samples (18–24 h) collected in dim light conditions (<30 lx) during the last night of each study period. Early and late participants were exposed to similar amounts of light in both sites and time windows, but only early participants were significantly more exposed during the late evening in Antarctica. Late participants advanced their DLMO with no changes in sleep onset time in Antarctica, while early participants delayed their DLMO and sleep onset time. This different susceptibility to respond to light may be explained by a subtle difference in evening light exposure between chronotypes.

Circadian reinforcement therapy in combination with electronic self-monitoring to facilitate a safe post-discharge period of patients with depression by stabilizing sleep: protocol of a randomized controlled trial

BACKGROUND

The transition phase from inpatient to outpatient care for patients suffering from Major Depressive Disorder represents a vulnerable period associated with a risk of depression worsening and suicide. Our group has recently found that the sleep-wake cycle in discharged depressive patients became irregular and exhibited a drift towards later hours, associated with worsening of depression. In contrast, an advancement of sleep phase has earlier been shown to have an antidepressant effect. Thus, methods to prevent drift of the sleep-wake cycle may be promising interventions to prevent or reduce worsening of depression after discharge.

METHODS

In this trial, we apply a new treatment intervention, named Circadian Reinforcement Therapy (CRT), to patients discharged from inpatient psychiatric wards. CRT consists of a specialized psychoeducation on the use of regular time signals (zeitgebers): daylight exposure, exercise, meals, and social contact. The aim is to supply stronger and correctly timed zeitgebers to the circadian system to prevent sleep drift and worsening of depression. The CRT is used in combination with an electronic self-monitoring system, the Monsenso Daybuilder System (MDB). By use of the MDB system, all patients self-monitor their sleep, depression level, and activity (from a Fitbit bracelet) daily. Participants can inspect all their data graphically on the MDB interface and will have clinician contact. The aim is to motivate patients to keep a stable sleep-wake cycle. In all, 130 patients referred to an outpatient service will be included. Depression rating is blinded. Patients will be randomized 1:1 to a Standard group or a CRT group. The intervention period is 4 weeks covering the transition phase from inpatient to outpatient care. The primary outcome is score change in interviewer rated levels of depression on the Hamilton Depression Rating Scale. A subset of patients will be assessed with salivary Dim Light Melatonin Onset (DLMO) as a validator of circadian timing. The trial was initiated in 2016 and will end in 2020.

DISCUSSION

If the described intervention is beneficial it could be incorporated into usual care algorithms for depressed patients to facilitate a better and safer transition to outpatient treatment.

TRIAL REGISTRATION

Posted prospectively at ClinicalTrials.gov at February 10, 2016 with identifier NCT02679768 .

Human circadian phase-response curves for exercise

KEY POINTS

Exercise elicits circadian phase-shifting effects, but additional information is needed. The phase-response curve describing the magnitude and direction of circadian rhythm phase shifts, depending on the time of the zeigeber (time cue) stimulus, is the most fundamental chronobiological tool for alleviating circadian misalignment and related morbidity. Fifty-one older and 48 young adults followed a circadian rhythms measurement protocol for up to 5.5 days, and performed 1 h of moderate treadmill exercise for 3 consecutive days at one of eight times of the day/night. Temporal changes in the phase of 6-sulphatoxymelatonin (aMT6s) were measured from evening onset, cosine acrophase, morning offset and duration of excretion. Significant phase-response curves were established for aMT6 onset and acrophase with large phase delays from 7:00 pm to 10:00 pm and large phase advances at both 7:00 am and from 1:00 pm to 4:00 pm. Delays or advances would be desired, for example, for adjustment to westward or eastward air travel, respectively. Along with known synergism with bright light, the above PRCs with a second phase advance region (afternoon) could support both practical and clinical applications.

ABSTRACT

Although bright light is regarded as the primary circadian zeitgeber, its limitations support exploring alternative zeitgebers. Exercise elicits significant circadian phase-shifting effects, but fundamental information regarding these effects is needed. The primary aim of the present study was to establish phase-response curves (PRCs) documenting the size and direction of phase shifts in relation to the circadian time of exercise. Aerobically fit older (n = 51; 59-75 years) and young adults (n = 48; 18-30 years) followed a 90 min laboratory ultrashort sleep-wake cycle (60 min wake/30 min sleep) for up to 5½ days. At the same clock time on three consecutive days, each participant performed 60 min of moderate treadmill exercise (65-75% of heart rate reserve) at one of eight times of day/night. To describe PRCs, phase shifts were measured for the cosine-fitted acrophase of urinary 6-sulphatoxymelatonin (aMT6s), as well as for the evening rise, morning decline and change in duration of aMT6s excretion. Significant PRCs were found for aMT6s acrophase, onset and duration, with peak phase advances corresponding to clock times of 7:00 am and from 1:00 pm to 4:00 pm, delays from 7:00 pm to 10:00 pm, and minimal shifts around 4:00 pm and 2:00 am. There were no significant age or sex differences. The amplitudes of the aMT6s onset and acrophase PRCs are comparable to expectations for bright light of equal duration. The phase advance to afternoon exercise and the exercise-induced PRC for change in aMT6s duration are novel findings. The results support further research exploring additive phase-shifting effects of bright light and exercise and health benefits.

Blind Spot for Sedentarism: Redefining the Diseasome of Physical Inactivity in View of Circadian System and the Irisin/BDNF Axis

Introduction: The term "diseasome of physical inactivity" was coined by Pedersen to explain clustering of chronic diseases linked to physical inactivity. Accordingly, physical inactivity per se contributes to the accumulation of visceral fat, which, generates chronic low-grade systemic inflammation, contributes to emergence of chronic, non-communicable diseases. Diversity of these disorders posits the possible involvement of a supraphysiological system. Methods: Hypothesis driven literature search and deductive reasoning was used to review relevant literature and formulate a novel theory. Results: We have identified the circadian system, omnipresent in virtually every cell, as a possible vehicle for brain muscle crosstalk, explaining some aspects of the diseasome of physical inactivity This system is hierarchically organized, with the suprachiasmatic nucleus (SCN) being the master clock that entrains to the dark/light cycle and synchronizes subsidiary molecular clocks in the periphery. Insufficient photic entrainment also causes chronic disease evolution. The recently identified irisin, was shown to induce brain-derived neurotrophic factor (BDNF) production in several brain areas. BDNF assumes significant role in gating light's influence in the retinohypothalamic synapse, by having a permissive effect on glutamate signal transduction underlying photic entrainment. Conclusions: Here we provide theoretical evidence to support the hypothesis that irisin may facilitate photic entrainment of the SCN, via BDNF. By this irisin opens up possible pathways for peripheral non-photic entrainment signals to exert influence on the master clock that is otherwise resistant to these. Furthermore, we suggest that intertwining processes of circadian, redox, inflammatory, and myokine systems lay underneath the diseasome of physical inactivity.

Circadian rhythm in bipolar disorder: A review of the literature

Sleep disturbances and circadian rhythm dysfunction have been widely demonstrated in patients with bipolar disorder (BD). Irregularity of the sleep-wake rhythm, eveningness chronotype, abnormality of melatonin secretion, vulnerability of clock genes, and the irregularity of social time cues have also been well-documented in BD. Circadian rhythm dysfunction is prominent in BD compared with that in major depressive disorders, implying that circadian rhythm dysfunction is a trait marker of BD. In the clinical course of BD, the circadian rhythm dysfunctions may act as predictors for the first onset of BD and the relapse of mood episodes. Treatments focusing on sleep disturbances and circadian rhythm dysfunction in combination with pharmacological, psychosocial, and chronobiological treatments are believed to be useful for relapse prevention. Further studies are therefore warranted to clarify the relation between circadian rhythm dysfunction and the pathophysiology of BD to develop treatment strategies for achieving recovery in BD patients.

Circadian Rhythms, Exercise, and Cardiovascular Health

Human circadian rhythmicity is driven by a circadian clock comprised of two distinct components: the central clock, located in the suprachiasmatic nucleus (SCN) within the hypothalamus, and the peripheral clocks, located in almost all tissues and organ systems in the body. Entrainment, or alignment, of circadian rhythmicity is dependent upon time of day and can occur through environmental influences such as light cues and physical activity exerted on skeletal muscle. Entrainment of the circadian clock through exercise has been reported to improve health by reducing risk of conditions such as cardiovascular disease (CVD), but further research is still needed. The purpose of this review is to discuss the effects exercise has on the regulation of circadian rhythmicity, specifically with respect to CVD risk factors – including hormonal levels, sleep/wake cycles, blood pressure, and heart rate. Additionally, the impact of exercise-induced circadian entrainment is discussed relative to hormone regulation, nocturnal blood pressure dipping, post-exercise hypotension, and overall cardiovascular health.

Entrainment of the mouse circadian clock: Effects of stress, exercise, and nutrition

The circadian clock system in mammals plays a fundamental role in maintaining homeostasis. Entrainment is an important characteristic of the internal clock, by which appropriate timing is maintained according to external daily stimuli, such as light, stress, exercise, and/or food. Disorganized entrainment or a misaligned clock time, such as jet lag, increases health disturbances. The central clock in the suprachiasmatic nuclei, located in the hypothalamus, receives information about arousal stimuli, such as physical stress or exercise, and changes the clock time by modifying neural activity or the expression of circadian clock genes. Although feeding stimuli cannot entrain the central clock in a normal light-dark cycle, the central clock can partially detect the metabolic status. Local clocks in the peripheral tissues, including liver and kidney, have a strong direct response to the external stimuli of stress, exercise, and/or food that is independent of the central clock. The mechanism underlying entrainment by stress/exercise is mediated by glucocorticoids, sympathetic nerves, oxidative stress, hypoxia, pH, cytokines, and temperature. Food/nutrition-induced entrainment is mediated by fasting-induced hormonal or metabolic changes and re-feeding-induced insulin or oxyntomodulin secretion. Chrono-nutrition is a clinical application based on chronobiology research. Future studies are required to elucidate the effects of eating and nutrient composition on the human circadian clock. Here, we focus on the central and peripheral clocks mostly in rodents' studies and review the findings of recent investigations of the effects of stress, exercise, and food on the entrainment system.

A New Perspective for Parkinson's Disease: Circadian Rhythm

Circadian rhythm is manifested by the behavioral and physiological changes from day to night, which is controlled by the pacemaker and its regulator. The former is located at the suprachiasmatic nuclei (SCN) in the anterior hypothalamus, while the latter is composed of clock genes present in all tissues. Circadian desynchronization influences normal patterns of day-night rhythms such as sleep and alertness cycles, rest and activity cycles. Parkinson's disease (PD) exhibits diurnal fluctuations. Circadian dysfunction has been observed in PD patients and animal models, which may result in negative consequences to the homeostasis and even exacerbate the disease progression. Therefore, circadian therapies, including light stimulation, physical activity, dietary and social schedules, may be helpful for PD patients. However, the cellular and molecular mechanisms that underlie the circadian dysfunction in PD remain elusive. Further research on circadian patterns is needed. This article summarizes the existing research on the circadian rhythms in PD, focusing on the clinical symptom variations, molecular changes, as well as the available treatment options.

The mammalian circadian clock and its entrainment by stress and exercise

The mammalian circadian clock regulates day-night fluctuations in various physiological processes. The circadian clock consists of the central clock in the suprachiasmatic nucleus of the hypothalamus and peripheral clocks in peripheral tissues. External environmental cues, including light/dark cycles, food intake, stress, and exercise, provide important information for adjusting clock phases. This review focuses on stress and exercise as potent entrainment signals for both central and peripheral clocks, especially in regard to the timing of stimuli, types of stressors/exercises, and differences in the responses of rodents and humans. We suggest that the common signaling pathways of clock entrainment by stress and exercise involve sympathetic nervous activation and glucocorticoid release. Furthermore, we demonstrate that physiological responses to stress and exercise depend on time of day. Therefore, using exercise to maintain the circadian clock at an appropriate phase and amplitude might be effective for preventing obesity, diabetes, and cardiovascular disease.

Chronobesity: role of the circadian system in the obesity epidemic

Although obesity is considered to result from an imbalance between energy uptake and energy expenditure, the strategy of dietary changes and physical exercise has failed to tackle the global obesity epidemic. In search of alternative and more adequate treatment options, research has aimed at further unravelling the mechanisms underlying this excessive weight gain. While numerous studies are focusing on the neuroendocrine alterations that occur after bariatric Roux-en-Y gastric bypass surgery, an increasing amount of chronobiological studies have started to raise awareness concerning the pivotal role of the circadian system in the development and exacerbation of obesity. This internal timekeeping mechanism rhythmically regulates metabolic and physiological processes in order to meet the fluctuating demands in energy use and supply throughout the 24-h day. This review elaborates on the extensive bidirectional interaction between the circadian system and metabolism and explains how disruption of body clocks by means of shift work, frequent time zone travelling or non-stop consumption of calorie-dense foods can evoke detrimental metabolic alterations that contribute to obesity. Altering the body's circadian rhythms by means of time-related dietary approaches (chrononutrition) or pharmacological substances (chronobiotics) may therefore represent a novel and interesting way to prevent or treat obesity and associated comorbidities.

Morning and evening physical exercise differentially regulate the autonomic nervous system during nocturnal sleep in humans

Effects of daily physical exercise in the morning or in the evening were examined on circadian rhythms in plasma melatonin and core body temperature of healthy young males who stayed in an experimental facility for 7 days under dim light conditions (<10 lux). Sleep polysomnogram (PSG) and heart rate variability (HRV) were also measured. Subjects performed 2-h intermittent physical exercise with a bicycle ergometer at ZT3 or at ZT10 for four consecutive days, where zeitgeber time 0 (ZT0) was the time of wake-up. The rising phase of plasma melatonin rhythm was delayed by 1.1 h without exercise. Phase-delay shifts of a similar extent were detected by morning and evening exercise. But the falling phase shifted only after evening exercise by 1.0 h. The sleep PSG did not change after morning exercise, while Stage 1+2 sleep significantly decreased by 13.0% without exercise, and RE sleep decreased by 10.5% after evening exercise. The nocturnal decline of rectal temperature was attenuated by evening exercise, but not by morning exercise. HRV during sleep changed differentially. Very low frequency (VLF) waves increased without exercise. VLF, low frequency (LF), and high frequency (HF) waves increased after morning exercise, whereas HR increased after evening exercise. Morning exercise eventually enhanced the parasympathetic activity, as indicated by HRV, while evening exercise activated the sympathetic activity, as indicated by increase in heart rate in the following nocturnal sleep. These findings indicated differential effects of morning and evening exercise on the circadian melatonin rhythm, PSG, and HRV.

Free access to a running-wheel advances the phase of behavioral and physiological circadian rhythms and peripheral molecular clocks in mice

Behavioral and physiological circadian rhythms are controlled by endogenous oscillators in animals. Voluntary wheel-running in rodents is thought to be an appropriate model of aerobic exercise in humans. We evaluated the effects of chronic voluntary exercise on the circadian system by analyzing temporal profiles of feeding, core body temperature, plasma hormone concentrations and peripheral expression of clock and clock-controlled genes in mice housed under sedentary (SED) conditions or given free access to a running-wheel (RW) for four weeks. Voluntary wheel-running activity advanced the circadian phases of increases in body temperature, food intake and corticosterone secretion in the mice. The circadian expression of clock and clock-controlled genes was tissue- and gene-specifically affected in the RW mice. The temporal expression of E-box-dependent circadian clock genes such as Per1, Per2, Nr1d1 and Dbp were slightly, but significantly phase-advanced in the liver and white adipose tissue, but not in brown adipose tissue and skeletal muscle. Peak levels of Per1, Per2 and Nr1d1 expression were significantly increased in the skeletal muscle of RW mice. The circadian phase and levels of hepatic mRNA expression of the clock-controlled genes that are involved in cholesterol and fatty acid metabolism significantly differed between SED and RW mice. These findings indicated that endogenous clock-governed voluntary wheel-running activity provides feedback to the central circadian clock that systemically governs behavioral and physiological rhythms.