Sex differences in phase angle of entrainment and melatonin amplitude in humans

Sex differences in the circadian misalignment effects on energy regulation

Shift work causes circadian misalignment and is a risk factor for obesity. While some characteristics of the human circadian system and energy metabolism differ between males and females, little is known about whether sex modulates circadian misalignment effects on energy homeostasis. Here we show-using a randomized cross-over design with two 8-d laboratory protocols in 14 young healthy adults (6 females)-that circadian misalignment has sex-specific influences on energy homeostasis independent of behavioral/environmental factors. First, circadian misalignment affected 24-h average levels of the satiety hormone leptin sex-dependently (P < 0.0001), with a ∼7% decrease in females (P < 0.05) and an ∼11% increase in males (P < 0.0001). Consistently, circadian misalignment also increased the hunger hormone ghrelin by ∼8% during wake periods in females (P < 0.05) without significant effect in males. Females reported reduced fullness, consistent with their appetite hormone changes. However, males reported a rise in cravings for energy-dense and savory foods not consistent with their homeostatic hormonal changes, suggesting involvement of hedonic appetite pathways in males. Moreover, there were significant sex-dependent effects of circadian misalignment on respiratory quotient (P < 0.01), with significantly reduced values (P < 0.01) in females when misaligned, and again no significant effects in males, without sex-dependent effects on energy expenditure. Changes in sleep, thermoregulation, behavioral activity, lipids, and catecholamine levels were also assessed. These findings demonstrate that sex modulates the effects of circadian misalignment on energy metabolism, indicating possible sex-specific mechanisms and countermeasures for obesity in male and female shift workers.

Predictability of individual circadian phase during daily routine for medical applications of circadian clocks

BACKGROUNDCircadian timing of treatments can largely improve tolerability and efficacy in patients. Thus, drug metabolism and cell cycle are controlled by molecular clocks in each cell and coordinated by the core body temperature 24-hour rhythm, which is generated by the hypothalamic pacemaker. Individual circadian phase is currently estimated with questionnaire-based chronotype, center-of-rest time, dim light melatonin onset (DLMO), or timing of core body temperature (CBT) maximum (acrophase) or minimum (bathyphase).METHODSWe aimed at circadian phase determination and readout during daily routines in volunteers stratified by sex and age. We measured (a) chronotype, (b) every minute (q1min) CBT using 2 electronic pills swallowed 24 hours apart, (c) DLMO through hourly salivary samples from 1800 hours to bedtime, and (d) q1min accelerations and surface temperature at anterior chest level for 7 days, using a teletransmitting sensor. Circadian phases were computed using cosinor and hidden Markov modeling. Multivariate regression identified the combination of biomarkers that best predicted core temperature circadian bathyphase.RESULTSAmong the 33 participants, individual circadian phases were spread over 5 hours, 10 minutes (DLMO); 7 hours (CBT bathyphase); and 9 hours, 10 minutes (surface temperature acrophase). CBT bathyphase was accurately predicted, i.e., with an error less than 1 hour for 78.8% of the subjects, using a new digital health algorithm (INTime), combining time-invariant sex and chronotype score with computed center-of-rest time and surface temperature bathyphase (adjusted R2 = 0.637).CONCLUSIONINTime provided a continuous and reliable circadian phase estimate in real time. This model helps integrate circadian clocks into precision medicine and will enable treatment timing personalization following further validation.FUNDINGMedical Research Council, United Kingdom; AP-HP Foundation; and INSERM.

Eveningness is associated with greater subjective cognitive impairment in individuals with self-reported symptoms of unipolar depression

BACKGROUND

Eveningness is associated with depression diagnosis and increased depressive symptom severity. Time-of-day preference has been linked with differences in cognitive function in the general population, with cognitive difficulties being a major factor in psychosocial impairment in depression. We therefore investigated the impact of time-of-day preference and self-reported depressed state on subjective cognitive function.

METHODS

Participants over the age of 18 with a self-reported history of depression completed an online questionnaire. They provided demographic and mental health information, and completed self-report scales assessing depression symptoms, time-of-day preference, and cognition. Participants were classified as "currently" or "previously depressed" based on self-reported symptoms, and as having a morning, neither, or evening time-of-day preference.

RESULTS

A total of 804 participants reporting a history of unipolar depression were included. Currently-depressed participants reported more cognitive difficulties in all areas measured. Evening types reported more complex attentional and retrospective memory difficulties than neither types, and reported more executive and prospective memory difficulties than both neither and morning types. There was an additive effect of mood state and time-of-day preference, with self-reported depressed evening types reporting the most cognitive problems.

LIMITATIONS

Depression history, time-of-day preference, and cognitive function were assessed using unsupervised self-report measures. Time-of-day preference does not necessarily reflect the physiological circadian system.

CONCLUSIONS

Both depressed state and evening preference were individually associated with subjective cognitive complaints in people with a self-reported history of unipolar depression. The additive effect of poor mood and eveningness is important given the high prevalence of eveningness in depression. Assessment of time-of-day preference could help to identify those susceptible to cognitive symptoms, and inform treatment.

Decreased sensitivity of the circadian system to light in current, but not remitted depression

BACKGROUND

Misalignment of circadian timing in patients with depression has commonly been reported, but the underlying mechanisms are not known. Individual differences in the sensitivity of the circadian system to light affect how the biological clock synchronizes with the external environment and can lead to misalignment of rhythms. We investigated the sensitivity of the circadian system to light in unmedicated (for >3 months) women with a current or previous diagnosis of major depression, and healthy controls.

METHODS

Baseline melatonin levels in dim light (<1 lux) were assessed, followed by melatonin levels in normal indoor lighting of 100 lux in order to determine melatonin suppression.

RESULTS

Patients currently experiencing a depressive episode showed significantly lower levels of melatonin suppression to light compared to remitted patients and controls, with large effect sizes. Remitted patients and controls showed similar suppression.

LIMITATIONS

The relatively small sample, and lack of long-term, within subject assessments, make it difficult to determine the potential causal role of reduced light sensitivity in the development of circadian disruption.

CONCLUSIONS

We conclude that hyposensitivity of the circadian system to light may contribute to circadian misalignment in patients with depression. Interventions that increase sensitivity to light or provide stronger light cues may assist in normalizing circadian clock function.

Advanced melatonin onset relative to sleep in women with unmedicated major depressive disorder

Studies on circadian timing in depression have produced variable results, with some investigations suggesting phase advances and others phase delays. This variability may be attributable to differences in participant diagnosis, medication use, and methodology between studies. This study examined circadian timing in a sample of unmedicated women with and without unipolar major depressive disorder. Participants were aged 18-28 years, had no comorbid medical conditions, and were not taking medications. Eight women were experiencing a major depressive episode, nine had previously experienced an episode, and 31 were control participants with no history of mental illness. Following at least one week of actigraphic sleep monitoring, timing of salivary dim light melatonin onset (DLMO) was assessed in light of <1 lux. In currently depressed participants, melatonin onset occurred significantly earlier relative to sleep than in controls, with a large effect size. Earlier melatonin onset relative to sleep was also correlated with poorer mood for all participants. Our results indicate that during a unipolar major depressive episode, endogenous circadian phase is advanced relative to sleep time. This is consistent with the early-morning awakenings often seen in depression. Circadian misalignment may represent a precipitating or perpetuating factor that could be targeted for personalized treatment of major depression.

Gender differences in chronotype diminish with age: a meta-analysis based on morningness/chronotype questionnaires

Chronotype is an individual difference trait that is closely linked to biological variables. Usually, men and women differ in their chronotype with men being more evening oriented than women. The aim of the study was to assess gender differences in chronotype based on a systematic review and meta-analysis. In addition, many recent studies do not report gender differences any more although researchers collected data on men and women. This motivated us to contact many researchers directly to obtain and use these additional data. We included 164 studies giving 201 effect size measures in a data set, which only included the most commonly used questionnaires (MEQ, rMEQ and CSM) totaling 186,289 participants in total, of which 75,622 were men and 110,667 were women. We calculated an effect size of the standardized mean difference of -0.072 (95% CI from -0.062 to -0.082) in the fixed effects and of -0.066 (95% CI from -0.043 to- 0.089) in the random effects model. Men were on average more evening oriented than women. Type of questionnaire did not influence the standardized mean difference in chronotype between genders. Mean age, standard deviation of age and publication year (p ≤ 0.05) were found to have significant effects on the standardized mean difference in chronotype between genders. The standardized mean difference in chronotype between genders is predicted to change from negative to positive with increasing mean age (young women were more morning orientated than young men, but older women were less morning orientated than older men). This suggests that the differences between men and women diminish with time. The standardized mean difference in chronotype between genders is decreasing with increasing publication year, as well as with high variation in age of the samples. Abbreviations: CSM: Composite Scale of Morningness (Smith et al. 1989); MEQ: Morningness-Eveningness Questionnaire (Horne and Ostberg, 1976); rMEQ: reduced Morningness-Eveningness Questionnaire (Adan & Almiral, 1991); SMD: standardized mean difference (measure of effect size).

Chronotype Genetic Variant in PER2 is Associated with Intrinsic Circadian Period in Humans

The PERIOD2 (PER2) gene is a core molecular component of the circadian clock and plays an important role in the generation and maintenance of daily rhythms. Rs35333999, a missense variant of PER2 common in European populations, has been shown to associate with later chronotype. Chronotype relates to the timing of biological and behavioral activities, including when we sleep, eat, and exercise, and later chronotype is associated with longer intrinsic circadian period (cycle length), a fundamental property of the circadian system. Thus, we tested whether this PER2 variant was associated with circadian period and found significant associations with longer intrinsic circadian period as measured under forced desynchrony protocols, the 'gold standard' for intrinsic circadian period assessment. Minor allele (T) carriers exhibited significantly longer circadian periods when determinations were based on either core body temperature or plasma melatonin measurements, as compared to non-carriers (by 12 and 11 min, respectively; accounting for ~7% of inter-individual variance). These findings provide a possible underlying biological mechanism for inter-individual differences in chronotype, and support the central role of PER2 in the human circadian timing system.

Chronotypical characteristics and related miR-142-3p levels of children with attention deficit and hyperactivity disorder

To compare children with Attention Deficit and Hyperactivity Disorder (ADHD) and a healthy control group in terms of chronotype characteristics and miRNA-142-3p/miRNA-378 levels. 50 children with ADHD and 44 healthy children were included in the study. Childhood Chronotype Questionnaire was used to identify the chronotype preferences of children. Serum miR-142-3p and miR- 378 levels were determined. Preference for nighttime was higher in children with ADHD. Additionally, a night preference was found to be associated with attention deficit in both groups. While a significant correlation was found between the psychopathology rate in mothers and the presence of ADHD, there was no such correlation in fathers. In the comparison between children with ADHD and the control group, no significant difference was found between miRNA levels. Both the miR-142-3p and miR-378 values of the children with ADHD that have immediate relatives with a psychiatric disorder were lower, compared to control group. We found that shift to night preference in the circadian rhythm was higher and this preference was associated with attention deficit in the children with ADHD. In addition, the presence of psychopathology in the family and the mother's psychopathology affected the miR-142-3p and miR378 levels.

The Influence of Circadian Timing on Olfactory Sensitivity

Olfactory sensitivity has traditionally been viewed as a trait that varies according to individual differences but is not expected to change with one's momentary state. Recent research has begun to challenge this position and time of day has been shown to alter detection levels. Links between obesity and the timing of food intake further raise the issue of whether odor detection may vary as a function of circadian processes. To investigate this question, 37 (21 male) adolescents (M age = 13.7 years) took part in a 28-h forced desynchrony (FD) protocol with 17.5 h awake and 10.5 h of sleep, for 7 FD cycles. Odor threshold was measured using Sniffin' Sticks 6 times for each FD cycle (total threshold tests = 42). Circadian phase was determined by intrinsic period derived from dim light melatonin onsets. Odor threshold showed a significant effect of circadian phase, with lowest threshold occurring on average slightly after the onset of melatonin production, or about 1.5○ (approximately 21:08 h). Considerable individual variability was observed, however, peak olfactory acuity never occurred between 80.5○ and 197.5○ (~02:22-10:10 h). These data are the first to show that odor threshold is differentially and consistently influenced by circadian timing, and is not a stable trait. Potential biological relevance for connections between circadian phase and olfactory sensitivity are discussed.

Shift Work Disrupts Circadian Regulation of the Transcriptome in Hospital Nurses

Circadian misalignment between sleep and behavioral/feeding rhythms is thought to lead to various health impairments in shift workers. Therefore, we investigated how shift work leads to genome-wide circadian dysregulation in hospital nurses. Female nurses from the University of Alabama at Birmingham (UAB) Hospital working night shift ( n = 9; 29.6 ± 11.4 y) and day shift ( n = 8; 34.9 ± 9.4 y) participated in a 9-day study measuring locomotor activity and core body temperature (CBT) continuously. Additionally, cortisol and melatonin were assayed and peripheral blood mononuclear cells (PBMCs) were harvested for RNA extraction every 3 h on a day off from work. We saw phase desynchrony of core body temperature, peak cortisol, and dim light melatonin onset in individual night-shift subjects compared with day-shift subjects. This variability was evident even though day- and night-shift nurses had similar sleep timing and scheduled meal times on days off. Surprisingly, the phase and rhythmicity of the expression of the clock gene, PER1, in PBMCs were similar for day-shift and night-shift subjects. Genome-wide microarray analysis of PBMCs from a subset of nurses revealed distinct gene expression patterns between night-shift and day-shift subjects. Enrichment analysis showed that day-shift subjects expressed pathways involved in generic transcription and regulation of signal transduction, whereas night-shift subjects expressed pathways such as RNA polymerase I promoter opening, the matrisome, and endocytosis. In addition, there was large variability in the number of rhythmic transcripts among subjects, regardless of shift type. Interestingly, the amplitude of the CBT rhythm appeared to be more consistent with the number of cycling transcripts for each of the 6 subjects than was melatonin rhythm. In summary, we show that shift-work patterns affect circadian alignment and gene expression in PBMCs.

The elite athlete as a special risk traveler and the jet lag's effect: lessons learned from the past and how to be prepared for the next Olympic Games 2020 Tokyo

BACKGROUND

Elite athletes have to travel long-haul distances and cross multiple meridians; thus, a unique syndrome named as jet-lag is induced. Furthermore, traveler athletes are submitted to several factors negatively affecting their well-being and athletic performance. This qualitative descriptive study aims to promote safely and future promising participations of elite athletes in great events, such as the next Olympic Games 2020 Tokyo, based on the chronobiology of jet-lag, factors affecting the traveler athlete and previous experiences from the 2014 FIFA World Cup Brazil, the 2018 FIFA World Cup Russia and the Olympic Games Rio 2016.

METHODS

A narrative review of the literature across a broad cross-section of the chronobiology of jet-lag and factors affecting the traveler athlete was undertaken. In addition, a general analysis based on the past sport events aforementioned is also included.

RESULTS

The jet-lag disorder may occur after transmeridian travel over more than three time-zones and the resynchronization is dependent on the direction and number of the time-zones crossed and the availability and the intensity of local circadian time cues. Also the athlete's ability to sleep, eat, get hydrated and train, are essential, as well as, others individual tolerance differences, such as age, gender, chronotype and ethnic differences. Athletes should arrive a number of days before the competition according to the number of time-zone transitions experienced.

CONCLUSIONS

Jet-lag is usually benign and self-limited, but can occasionally have serious consequences for the athlete's mental and physical health and performance. A good plan concerning the athlete's traveling schedule, sleeping, eating and training before and after travelling is mandatory.

Misaligned core body temperature rhythms impact cognitive performance of hospital shift work nurses

Circadian rhythms greatly influence 24-h variation in cognition in nearly all organisms, including humans. Circadian clock impairment and sleep disruption are detrimental to hippocampus-dependent memory and negatively influence the acquisition and recall of learned behaviors. The circadian clock can become out of sync with the environment during circadian misalignment. Shift work represents a real-world model of circadian misalignment that can be studied for its physiological implications. The present study aimed to test the hypothesis that circadian misalignment disrupts vigilance and cognitive performance on occupationally relevant tasks using shift work as a model. As such, we sought to (1) explore the general effects of night- and day-shift worker schedules on sleep-wake parameters and core body temperature (CBT) phase, and (2) determine whether shift-type and CBT phase impact cognitive performance and vigilance at the end of a 12-h shift. We observed a sample of day-shift and night-shift hospital nurses over a 10-day period. At the end of three, consecutive, 12-h shifts (7 pm-7am or 7am-7 pm), participants completed a cognitive battery assessing vigilance, cognitive throughput, and medication calculation fluency (via an investigator developed and tested metric). Night-shift nurses exhibited significantly greater sleep fragmentation as well as a greater disparity between their wake-time and time of CBT minimum compared to day-shift nurses. Night-shift nurses exhibited significantly slower cognitive proficiency at the end of their shifts, even after adjustment for CBT phase. These results suggest that circadian disruption and reduced sleep quality both contribute to cognitive functioning and performance.

Sleep Physiology, Circadian Rhythms, Waking Performance and the Development of Sleep-Wake Therapeutics

Disturbances of the sleep-wake cycle are highly prevalent and diverse. The aetiology of some sleep disorders, such as circadian rhythm sleep-wake disorders, is understood at the conceptual level of the circadian and homeostatic regulation of sleep and in part at a mechanistic level. Other disorders such as insomnia are more difficult to relate to sleep regulatory mechanisms or sleep physiology. To further our understanding of sleep-wake disorders and the potential of novel therapeutics, we discuss recent findings on the neurobiology of sleep regulation and circadian rhythmicity and its relation with the subjective experience of sleep and the quality of wakefulness. Sleep continuity and to some extent REM sleep emerge as determinants of subjective sleep quality and waking performance. The effects of insufficient sleep primarily concern subjective and objective sleepiness as well as vigilant attention, whereas performance on higher cognitive functions appears to be better preserved albeit at the cost of increased effort. We discuss age-related, sex and other trait-like differences in sleep physiology and sleep need and compare the effects of existing pharmacological and non-pharmacological sleep- and wake-promoting treatments. Successful non-pharmacological approaches such as sleep restriction for insomnia and light and melatonin treatment for circadian rhythm sleep disorders target processes such as sleep homeostasis or circadian rhythmicity. Most pharmacological treatments of sleep disorders target specific signalling pathways with no well-established role in either sleep homeostasis or circadian rhythmicity. Pharmacological sleep therapeutics induce changes in sleep structure and the sleep EEG which are specific to the mechanism of action of the drug. Sleep- and wake-promoting therapeutics often induce residual effects on waking performance and sleep, respectively. The need for novel therapeutic approaches continues not at least because of the societal demand to sleep and be awake out of synchrony with the natural light-dark cycle, the high prevalence of sleep-wake disturbances in mental health disorders and in neurodegeneration. Novel approaches, which will provide a more comprehensive description of sleep and allow for large-scale sleep and circadian physiology studies in the home environment, hold promise for continued improvement of therapeutics for disturbances of sleep, circadian rhythms and waking performance.

Neuroendocrine Control of Sleep

Sleep is a phenomenon in animal behavior as enigmatic as it is ubiquitous, and one deeply tied to endocrine function. Though there are still many unanswered questions about the neurochemical basis of sleep and its functions, extensive interactions have been identified between sleep and the endocrine system, in both the endocrine system's effect on sleep and sleep's effect on the endocrine system. Unfortunately, until recent years, much research on sleep behavior largely disregarded its connections with the endocrine system. Use of both clinical studies and rodent models to investigate interactions between neuroendocrine function, including biological sex, and sleep therefore presents a promising area of further exploration. Further investigation of the neurobiological and neuroendocrine basis of sleep could have wide impact on a number of clinical and basic science fields. In this review, we summarize the state of basic sleep biology and its connections to the field of neuroendocrine biology, as well as suggest key future directions for the neuroendocrine regulation of sleep that may significantly impact new therapies for sleep disorders in women and men.

Gender differences in the association between melatonin secretion and diabetes in elderly: The HEIJO-KYO cohort

OBJECTIVE

Reportedly, melatonin protects the pancreatic islets and decreases insulin resistance; thus, it may contribute to preventing diabetes. Epidemiological data suggested that lower melatonin secretion is associated with higher incidence of diabetes in female nurses. Such associations are unknown in the general population. We evaluated the association between melatonin secretion and diabetes in a general population, including both genders.

DESIGN

Cross-sectional study.

PARTICIPANTS

A total of 1096 community-based elderly males (n = 519) and females (n = 577) (mean age, 71.8 years) were enrolled.

MEASUREMENTS

Overnight urinary 6-sulfatoxymelatonin excretion (UME) and diabetes prevalence were measured.

RESULTS

The median UME was 6.7 μg (interquartile range, 4.0-10.5); the prevalence of diabetes was 17.5% in males and 10.7% in females. The prevalence of diabetes decreased with increasing UME quartiles among males (P for trend = 0.009) but not among females (P for trend = 0.96). In a multivariable logistic regression analysis adjusting for potential confounding factors, such as age, smoking and drinking habits, economic status, caloric intake, and physical activity, the odds ratio (OR) for diabetes was significantly lower in the highest UME quartile group compared with the lowest quartile group among males (OR, 0.35; 95% CI, 0.17-0.70; P = 0.003) but not females (OR, 0.94; 95% CI, 0.45-1.95; P = 0.87). Consistent results were observed in the analysis after adjusting for clinical parameters or using continuous UME data.

CONCLUSIONS

Melatonin secretion was significantly and inversely associated with diabetes in males but not in females. This association was independent of several important confounding factors.

Sex Differences in the Association between Night Shift Work and the Risk of Cancers: A Meta-Analysis of 57 Articles

Objectives

To identify the association between night shift work and the risk of various cancers with a comprehensive perspective and to explore sex differences in this association.

Methods

We searched PubMed, Embase, and Web of Science for studies on the effect of night shift work on cancer, including case-control, cohort, and nested case-control studies. We computed risk estimates with 95% confidence intervals (CIs) in a random or fixed effects model and quantified heterogeneity using the I ² statistic. Subgroup, metaregression, and sensitivity analyses were performed to explore potential sources of heterogeneity. Contour-enhanced funnel plots and the trim and fill method were used together to analyze bias. Linear dose-response analysis was used to quantitatively estimate the accumulative effect of night shift work on the risk of cancer.

Results

Fifty-eight studies were eligible for our meta-analysis, including 5,143,838 participants. In the random effects model, the pooled odds ratio (OR) of cancers was 1.15 (95% CI = 1.08-1.22, P < 0.001; I ² = 76.2%). Night shift work increased the cancer risk in both men (OR = 1.14, 95% CI = 1.05-1.25, P = 0.003) and women (OR = 1.12, 95% CI = 1.04-1.20, P = 0.002). Subgroup analyses showed that night shift work positively increased the risk of breast (OR = 1.22, 95% CI = 1.08-1.38), prostate (OR = 1.26, 95% CI = 1.05-1.52), and digestive system (OR = 1.15, 95% CI = 1.01-1.32) cancers. For every 5 years of night shift work, the cancer risk increased by 3.2% (OR = 1.032, 95% CI = 1.013-1.051).

Conclusion

This is the first meta-analysis identifying the positive association between night shift work and the risk of cancer and verifying that there is no sex difference in the effect of night shift work on cancer risk. Cancer risk increases with cumulative years of night shift work.

Impact of Shift Work on the Circadian Timing System and Health in Women

Women who do shift work are a sizable part of the workforce. Shift workers experience circadian misalignment due to shifted sleep periods, with potentially far-reaching health consequences, including elevated risk of sleep disturbances, metabolic disorders, and cancer. This review provides an overview of the circadian timing system and presents the sex differences that can be observed in the functioning of this system, which may account for the lower tolerance to shift work for women compared with men. Recent epidemiologic findings on female-specific health consequences of shift work are discussed.

Low maternal melatonin level increases autism spectrum disorder risk in children

BACKGROUND

It is assumed that autism spectrum disorder (ASD) is caused by a combination of de novo inherited variation and common variation as well as environmental factors. It often co-occurs with intellectual disability (ID). Almost eight hundred potential causative genetic variations have been found in ASD patients. However, not one of them is responsible for more than 1% of ASD cases. Low melatonin levels are a frequent finding in ASD patients. Melatonin levels are negatively correlated with severity of autistic impairments, it is important for normal neurodevelopment and is highly effective in protecting DNA from oxidative damage. Melatonin deficiency could be a major factor, and well a common heritable variation, that increases the susceptibility to environmental risk factors for ASD. ASD is already present at birth. As the fetus does not produce melatonin, low maternal melatonin levels may be involved.

METHODS

We measured 6-sulfatoxymelatonin in urine of 60 mothers of a child with ASD and controls.

RESULTS

6-sulfatoxymelatonin levels were significantly lower in mothers with an ASD child than in controls (p = 0.012).

CONCLUSIONS

Low parental melatonin levels could be one of the contributors to ASD and possibly ID etiology. Our findings need to be duplicated on a larger scale. If our hypothesis is correct, this could lead to policies to detect future parents who are at risk and to treatment strategies to ASD and intellectual disability risk.

Increased sensitivity of the circadian system to light in delayed sleep-wake phase disorder

KEY POINTS

This is the first study to demonstrate an altered circadian phase shifting response in a circadian rhythm sleep disorder. Patients with delayed sleep-wake phase disorder (DSWPD) demonstrate greater sensitivity of the circadian system to the phase-delaying effects of light. Increased circadian sensitivity to light is associated with later circadian timing within both control and DSWPD groups. DSWPD patients had a greater sustained pupil response after light exposure. Treatments for DSWPD should consider sensitivity of the circadian system to light as a potential underlying vulnerability, making patients susceptible to relapse.

ABSTRACT

Patients with delayed sleep-wake phase disorder (DSWPD) exhibit delayed sleep-wake behaviour relative to desired bedtime, often leading to chronic sleep restriction and daytime dysfunction. The majority of DSWPD patients also display delayed circadian timing in the melatonin rhythm. Hypersensitivity of the circadian system to phase-delaying light is a plausible physiological basis for DSWPD vulnerability. We compared the phase shifting response to a 6.5 h light exposure (∼150 lux) between male patients with diagnosed DSWPD (n = 10; aged 20.8 ± 2.3 years) and male healthy controls (n = 11; aged 22.4 ± 3.3 years). Salivary dim light melatonin onset (DLMO) was measured under controlled conditions in dim light (<3 lux) before and after light exposure. Correcting for the circadian time of the light exposure, DSWPD patients exhibited 31.5% greater phase delay shifts than healthy controls. In both groups, a later initial melatonin phase was associated with a greater magnitude phase shift, indicating that increased circadian sensitivity to light may be a factor that contributes to delayed phase, even in non-clinical groups. DSWPD patients also had reduced pupil size following the light exposure, and showed a trend towards increased melatonin suppression during light exposure. These findings indicate that, for patients with DSWPD, assessment of light sensitivity may be an important factor that can inform behavioural therapy, including minimization of exposure to phase-delaying night-time light.

Melatonin receptor 1B -1193T>C polymorphism is associated with diurnal preference and sleep habits

BACKGROUND

Melatonin modulates the master circadian clock through the activation of G-protein-coupled receptors MT1 and MT2. It is presumed, therefore, that genetic variations in melatonin receptors can affect both sleep and circadian phase. We investigated whether the -1193T > C (rs4753426) polymorphism in the promoter of MT2 receptor gene (MTNR1B) is associated with diurnal preference and sleep habits. This polymorphism was previously associated with sunshine duration, suggesting a role in circadian entrainment.

METHODS

A total of 814 subjects who completed the Morningness-Eveningness and the Munich Chronotype questionnaires were genotyped for the selected polymorphism. Linear and multinomial regression were performed to test the interaction between gene variants and diurnal preference/sleep habits.

RESULTS

The -1193C variant was associated with the extreme morningness phenotype in a codominant model (C/C vs. T/T), recessive model (C/C + C/T vs. T/T) and alleles (C vs. T). A negative correlation was found between -1193C alleles and social jetlag scores. The frequency of -1193T allele was higher in the group that stay in bed more than 8 h/night compared to the group that stay in bed less than 8 h/night on weekends.

CONCLUSION

To the best of our knowledge, these data provide the first insights into the role of MTNR1B gene in the regulation of sleep, biological rhythms, and entrainment in humans.

INSOMNIA AND CIRCADIAN RHYTHMS OF MELATONIN IN MENOPAUSAL WOMEN

The aim of the review is to analyze literature data about sleep homeostasis and the role of the one of circadian system key elements – melatonin – in the regulation of the sleep-wake cycle in women in menopause. It was shown that the prevalence and structure of sleep disorders depends on the menopausal phase. It was revealed that the melatonin content in the body, determined in various biological media (blood, saliva, urine), depends on age, sex, race, and chronotype. It was shown that morning melatonin can be used as a biological marker for determining the chronotype. Most studies indicated a decrease in melatonin level with aging. Moreover, women have lower melatonin level than men. In case of insomnia, lower melatonin level was found, although the results of the studies are ambiguous. The shift in the peak of hormone secretion in the early morning hours was described in menopausal women. Also, the dependence of melatonin circadian rhythm on the menopausal phase was revealed, which determines different approaches to insomnia therapy. We revealed the association of melatonin secretion circadian rhythms with Clock 3111T/C gene polymorphism in Caucasian patients with insomnia, which allows considering 3111T allele as risky in the formation of melatonin circadian rhythm disturbances in these patients.

Chronotherapy for Hypertension

PURPOSE OF REVIEW

Given the emerging knowledge that circadian rhythmicity exists in every cell and all organ systems, there is increasing interest in the possible benefits of chronotherapy for many diseases. There is a well-documented 24-h pattern of blood pressure with a morning surge that may contribute to the observed morning increase in adverse cardiovascular events. Historically, antihypertensive therapy involves morning doses, usually aimed at reducing daytime blood pressure surges, but an absence of nocturnal dipping blood pressure is also associated with increased cardiovascular risk.

RECENT FINDINGS

To more effectively reduce nocturnal blood pressure and still counteract the morning surge in blood pressure, a number of studies have examined moving one or more antihypertensives from morning to bedtime dosing. More recently, such studies of chronotherapy have studied comorbid populations including obstructive sleep apnea, chronic kidney disease, or diabetes. Here, we summarize major findings from recent research in this area (2013-2017). In general, nighttime administration of antihypertensives improved overall 24-h blood pressure profiles regardless of disease comorbidity. However, inconsistencies between studies suggest a need for more prospective randomized controlled trials with sufficient statistical power. In addition, experimental studies to ascertain mechanisms by which chronotherapy is beneficial could aid drug design and guidelines for timed administration.

Validation of the Munich ChronoType Questionnaire in Korean Older Adults

OBJECTIVE

This study aimed to evaluate psychometric properties of the Munich ChronoType Questionnaire (MCTQ) in a sample of Korean older adults.

METHODS

One-hundred ninety two participants aged 65 and over completed interview-based questionnaires about chronotype, insomnia, depression, and anxiety. Additionally, a small subset of subjects completed a 7-day sleep diary and actigraphy measurements.

RESULTS

Morningness-Eveningness Questionnaire (MEQ) scores were significantly negatively correlated with Midpoint of sleep on free days corrected for sleep debt accumulated through weekdays (MSFsc) (r=-0.45, p<0.01) assessed by the MCTQ. MSFsc using the MCTQ was significantly positively correlated with MSFsc assessed by both the sleep diary (r=0.74, p<0.05) and actigraphy (r=0.76, p<0.05). Additionally, MSFsc assessed by the MCTQ was significantly positively correlated with insomnia (r=0.26, p<0.01), depression (r=0.25, p<0.01), and anxiety (r=0.18, p<0.05). Finally, based on MEQ scores, we derived a cut-off score for the MCTQ that distinguishes morning type and other types (intermediate/evening types) in older adults.

CONCLUSION

The results of these studies supported the validity of the MCTQ in Korean older adults. Additionally, while sleep rhythms in elder adults may be more advanced, eveningness tendency may be still important and indicative of sleep and psychological disturbance.

Melatonin Relations With Respiratory Quotient Weaken on Acute Exposure to High Altitude

High altitude (HA) exposure may affect human health and performance by involving the body timing system. Daily variations of melatonin may disrupt by HA exposure, thereby possibly affecting its relations with a metabolic parameter like the respiratory quotient (RQ). Sea level (SL) volunteers (7 women and 7 men, 21.0 ± 2.04 y) were examined for daily changes in salivary melatonin concentration (SMC). Sampling was successively done at SL (Antofagasta, Chile) and, on acute HA exposure, at nearby Caspana (3,270 m asl). Saliva was collected in special vials (Salimetrics Oral Swab, United Kingdom) at sunny noon (SMC_D) and in the absence of blue light at midnight (SMC_N). The samples were obtained after rinsing the mouth with tap water and were analyzed for SMC by immunoassay (ELISA kit; IBL International, Germany). RQ measurements (n = 12) were realized with a portable breath to breath metabolic system (Oxicon^TM Mobile, Germany), between 8:00 PM and 10:00 PM, once at either location. At SL, SMC_D, and SMC_N values (mean ± SD) were, respectively, 2.14 ± 1.30 and 11.6 ± 13.9 pg/ml (p < 0.05). Corresponding values at HA were 8.83 ± 12.6 and 13.7 ± 16.7 pg/ml (n.s.). RQ was 0.78 ± 0.07 and 0.89 ± 0.08, respectively, at SL and HA (p < 0.05). Differences between SMC_N and SMC_D (SMC_N-SMC_D) strongly correlate with the corresponding RQ values at SL (r = -0.74) and less tight at HA (r = -0.37). Similarly, mean daily SMC values (SMC) tightly correlate with RQ at SL (r = -0.79) and weaker at HA (r = -0.31). SMC_N-SMC_D, as well as, SMC values at SL, on the other hand, respectively, correlate with the corresponding values at HA (r = 0.71 and r = 0.85). Acute exposure to HA appears to loosen relations of SMC with RQ. A personal profile in daily SMC variation, on the other hand, tends to be conserved at HA.

The immune system as a chronotoxicity target of the anticancer mTOR inhibitor everolimus

The circadian timing system controls many biological functions in mammals including xenobiotic metabolism, detoxification, cell proliferation, apoptosis and immune functions. Everolimus is a mammalian target of rapamycin inhibitor, whose immunosuppressant properties are both desired in transplant patients and unwanted in cancer patients, where it is indicated for its antiproliferative efficacy. Here we sought whether everolimus circadian timing would predictably modify its immunosuppressive effects so as to optimize this drug through timing. C57BL/6J mice were synchronized with light-dark 12h:12h, with L onset at Zeitgeber Time (ZT) 0. Everolimus was administered orally to male (5 mg/kg/day) and female mice (15 mg/kg/day) at ZT1, during early rest span or at ZT13, during early activity span for 4 weeks. Body weight loss, as well as hematological, immunological and biochemical toxicities, were determined. Spleen and thymus were examined histologically. Everolimus toxicity was less severe following dosing at ZT13, as compared to ZT1, as shown with least body weight inhibition in both genders; least reductions in thymus weight both in males (p < 0.01) and females (p < 0.001), least reduction in female spleen weight (p < 0.05), and less severe thymic medullar atrophy both in males (p < 0.001) and females (p < 0.001). The mean circulating counts in total leukocytes, total lymphocytes, T-helper and B lymphocytes displayed minor and non-significant changes following dosing at ZT13, while they were decreased by 56.9% (p < 0.01), 45.5% (p < 0.01), 43.1% (p < 0.05) and 48.7% (p < 0.01) after everolimus at ZT1, respectively, in only male mice. Chronotherapy of everolimus is an effective way to increase the general tolerability and decrease toxicity on the immune system.

Phase Relationship between DLMO and Sleep Onset and the Risk of Metabolic Disease among Normal Weight and Overweight/Obese Adults

Circadian misalignment is hypothesized to contribute to increased diabetes and obesity among shift workers and individuals with late sleep timing. Accordingly, the goal of our study was to identify-among normal and overweight/obese adults-associations between circadian timing (dim light melatonin onset; DLMO) and circadian misalignment (the interval between DLMO and sleep onset) with metabolic disease risk. This was a secondary analysis of data from a larger study. Participants ages 18 to 50 years without depression, diabetes, or shift work, with sleep duration 6.5 h or more, completed the following evaluations: 7 days of wrist actigraphy, circadian timing assessment (DLMO), and a fasting blood draw to measure glucose and insulin and calculate the Homeostatic Model of Assessment-Insulin Resistance (HOMA-IR). Data were analyzed using correlation and regression analyses controlling for age, sex, DLMO, and sleep duration. Analyses were conducted for the entire sample ( n = 54) and stratified by normal weight ( n = 36) and overweight/obese groups ( n = 18). Mean age was 26.4 years (SD = 7.1 years). Average sleep duration was 436.2 min (SD = 55.1 min), DLMO was 2250h (SD = 01:31), and interval between DLMO and sleep onset was 2 h 18 min (SD = 53 min). Average BMI was 24.3 kg/m² (SD = 4.5 kg/m²). Circadian timing and interval between DLMO and sleep onset were not associated with glucose, insulin, or HOMA-IR in the main analyses. Among overweight/obese participants, a shorter interval between DLMO and sleep onset was associated with higher insulin ( B[SE] = -5.12 [2.24], p = 0.04) and HOMA-IR ( B[SE] = -1.32 [0.57], p = 0.04). Results of our multivariable model indicated that among overweight/obese participants, insulin was 5.1 pmol/L higher and HOMA was 1.3 µU/mL higher for every hour closer that sleep onset was to DLMO. The strengths of this study include the use of objective measures of circadian timing, but results should be considered hypothesis generating due to the small sample size and use of subgroup analyses.

Heritability of the melatonin synthesis variability in autism spectrum disorders

Autism Spectrum Disorders (ASD) are heterogeneous neurodevelopmental disorders with a complex genetic architecture. They are characterized by impaired social communication, stereotyped behaviors and restricted interests and are frequently associated with comorbidities such as intellectual disability, epilepsy and severe sleep disorders. Hyperserotonemia and low melatonin levels are among the most replicated endophenotypes reported in ASD, but their genetic causes remain largely unknown. Based on the biochemical profile of 717 individuals including 213 children with ASD, 128 unaffected siblings and 376 parents and other relatives, we estimated the heritability of whole-blood serotonin, platelet N-acetylserotonin (NAS) and plasma melatonin levels, as well as the two enzymes arylalkylamine N-acetyltransferase (AANAT) and acetylserotonin O-methyltransferase (ASMT) activities measured in platelets. Overall, heritability was higher for NAS (0.72 ± 0.091) and ASMT (0.59 ± 0.097) compared with serotonin (0.31 ± 0.078), AANAT (0.34 ± 0.077) and melatonin (0.22 ± 0.071). Bivariate analyses showed high phenotypic and genetic correlations between traits of the second step of the metabolic pathway (NAS, ASMT and melatonin) indicating the contribution of shared genetic factors. A better knowledge of the heritability of the melatonin synthesis variability constitutes an important step to identify the factors that perturb this pathway in individuals with ASD.

Sex differences in age-related changes in the sleep-wake cycle

Age-related changes in sleep and circadian regulation occur as early as the middle years of life. Research also suggests that sleep and circadian rhythms are regulated differently between women and men. However, does sleep and circadian rhythms regulation age similarly in men and women? In this review, we present the mechanisms underlying age-related differences in sleep and the current state of knowledge on how they interact with sex. We also address how testosterone, estrogens, and progesterone fluctuations across adulthood interact with sleep and circadian regulation. Finally, we will propose research avenues to unravel the mechanisms underlying sex differences in age-related effects on sleep.

Ovarian hormones, sleep and cognition across the adult female lifespan: An integrated perspective

Loss of ovarian function in women is associated with sleep disturbances and cognitive decline, which suggest a key role for estrogens and/or progestins in modulating these symptoms. The effects of ovarian hormones on sleep and cognitive processes have been studied in separate research fields that seldom intersect. However, sleep has a considerable impact on cognitive function. Given the tight connections between sleep and cognition, ovarian hormones may influence selective aspects of cognition indirectly, via the modulation of sleep. In support of this hypothesis, a growing body of evidence indicates that the development of sleep disorders following menopause contributes to accelerated cognitive decline and dementia in older women. This paper draws from both the animal and human literature to present an integrated view of the effects of ovarian hormones on sleep and cognition across the adult female lifespan.

Chronotypes in the US - Influence of age and sex

An individual’s chronotype reflects how the circadian system embeds itself into the 24-h day with rhythms in physiology, cognition and behavior occurring accordingly earlier or later. In view of an increasing number of people working at unusual times and linked health and safety risks, the wide range in human chronotypes may provide opportunities to allow people to work (and sleep) at times that are in synch with their circadian physiology. We aimed at estimating the distribution of chronotypes in the US population by age and sex. Twelve years (2003–2014) of pooled diary data from the American Time Use Survey were used to calculate chronotype based on mid-point of sleep on weekends (MSF^We, n = 53,689). We observed a near-normal distribution overall and within each age group. The distribution’s mean value is systematically different with age, shifting later during adolescence, showing a peak in ‘lateness’ at ~19 years, and shifting earlier thereafter. Men are typically later chronotypes than women before 40, but earlier types after 40. The greatest differences are observed between 15 and 25 for both sexes, equaling more than 50% of the total chronotype difference across all age groups. The variability in chronotype decreases with age, but is generally higher in males than females. This is the first study to estimate the distribution and prevalence of individual chronotypes in the US population based on a large-scale, nationally representative sample. Our finding that adolescents are on average the latest chronotypes supports delaying school start times to benefit their sleep and circadian alignment. The generally wide range in chronotypes may provide opportunities for tailored work schedules by matching external and internal time, potentially decreasing long- and short-term health and safety risks.

Differential menopause- versus aging-induced changes in oxidative stress and circadian rhythm gene markers

Menopause is characterized by the depletion of estrogen that has been proposed to cause oxidative stress. Circadian rhythm is an internal biological clock that controls physiological processes. It was analyzed the gene expression in peripheral blood mononuclear cells and the lipids and glucose levels in plasma of a subgroup of 17 pre-menopausal women, 19 men age-matched as control group for the pre-menopausal women, 20 post-menopausal women and 20 men age-matched as control group for the post-menopausal women; all groups were matched by body mass index. Our study showed a decrease in the expression of the oxidative stress-related gene GPX1, and an increase in the expression of SOD1 as consequence of menopause. In addition, we found that the circadian rhythm-related gene PER2 decreased as consequence of menopause. On the other hand, we observed a decrease in the expression of the oxidative stress-related gene GPX4 and an increase in the expression of CAT as a consequence of aging, independently of menopause. Our results suggest that the menopause-induced oxidative stress parallels a disruption in the circadian clock in women, and part of the differences in oxidative stress observed between pre- and post-menopausal women was due to aging, independent of menopause. Clinical Trials.gov.Identifier: NCT00924937.

Relationships between circadian measures, depression, and response to antidepressant treatment: A preliminary investigation

Few studies have examined relationships between circadian rhythms and unipolar major depressive disorder. Further, no study to date has examined circadian markers as predictors of response to depression treatment. In the present study, we examined associations between circadian timing and its alignment with sleep and depression severity in 30 adults with major depressive disorder who completed a randomized controlled trial of two weeks of time in bed (TIB) restriction administered adjunctive to fluoxetine, with a focus on sex differences. Thirty adults with major depressive disorder received 8 weeks of fluoxetine 20-40 mgs and were randomized to 8h TIB or 6h TIB for the first 2 weeks. Participants in the 6h TIB condition were further randomized to a delayed bedtime or advanced risetime group. Circadian measures included dim light melatonin onset (DLMO) and the difference between DLMO and midsleep point (i.e., phase angle difference). Depression was assessed using the Hamilton Rating Scale for Depression. For females, a phase delay after 2 weeks of fluoxetine and the experimental TIB manipulation was associated with a poorer response to fluoxetine, and depression severity was negatively correlated with phase angle difference, whereas males showed a positive correlation between depression severity and phase angle difference.

Conscientiousness but not agreeableness mediates females' tendency toward being a morning person

Individuals differ in their chronotype, and some are identified as morning ones and others as evening ones. Earlier studies showed that women were higher on morningness, conscientiousness, and agreeableness. In this study, we aimed at exploring the mediational effects of conscientiousness and agreeableness in the relationship of gender and morningness-eveningness. Participants were 669 university students. Results supported positive relationships between morningness and conscientiousness and agreeableness and between conscientiousness and agreeableness. Females were higher on all these three variables. Mediation analyses suggested that the effect of gender (here females) on chronotype (here morningness) was mediated by conscientiousness but not agreeableness so that after the mediation partially occurred, the gender's effect did not remain significant anymore. This study backed our hypothesis that conscientiousness might play a more pronounced role than the intrinsic diurnal rhythm concerning the sex differences in chronotype.

Circadian Rhythms in Plasma Brain-derived Neurotrophic Factor Differ in Men and Women

The measurement of circulating levels of brain-derived neurotrophic factor (BDNF) has been proposed to be a marker of disease and an indicator of recovery. Thus, knowing the temporal pattern and influence of potential circadian rhythms is important. Although several studies have measured BDNF at different times of day, no studies have done so while controlling for potential masking influences such as sleep and activity. Further, no previous study has examined circadian rhythms within individuals. We examined circadian rhythms in plasma BDNF while minimizing masking from behavioral and environmental factors using a 30-h constant routine (CR) protocol. In a sample of 39 healthy adults, we found significant circadian rhythms in 75% of women and 52% of men. The timing of the acrophase of the BDNF rhythm, however, was unrelated to clock time in women, while it was related to clock time in men. These results indicate that the use of single-sample measures of plasma BDNF as a marker of disease will be unreliable, especially in women. Repeated plasma BDNF samples over a 24-h period within individuals would be needed to reveal abnormalities related to disease states.

A single night light exposure acutely alters hormonal and metabolic responses in healthy participants

Many animal studies have reported an association between melatonin suppression and the disturbance of metabolic responses; yet, few human studies have investigated bright light effects on metabolic and hormonal responses at night. This study investigated the impact of light on plasma hormones and metabolites prior to, and after, an evening meal in healthy participants. Seventeen healthy participants, 8 females (22.2 ± 2.59 years, mean ± s.d.) and 9 males (22.8 ± 3.5 years) were randomised to a two-way cross-over design protocol; dim light (DL) (<5 lux) and bright light (BL) (>500 lux) sessions, separated by at least seven days. Saliva and plasma samples were collected prior to and after a standard evening meal at specific intervals. Plasma non-esterified fatty acid (NEFA) levels were significantly higher pre-meal in DL compared to BL (P < 0.01). Plasma glucose and insulin levels were significantly greater post-meal in the BL compared to DL session (P = 0.02, P = 0.001), respectively. Salivary melatonin levels were significantly higher in the DL compared to those in BL session (P = 0.005). BL at night was associated with significant increases in plasma glucose and insulin suggestive of glucose intolerance and insulin insensitivity. Raised pre-prandial NEFA levels may be due to changes in insulin sensitivity or the presence of melatonin and/or light at night. Plasma triglyceride (TAG) levels were the same in both sessions. These results may explain some of the health issues reported in shift workers; however, further studies are needed to elucidate the cause of these metabolic changes.

Gender and the circadian pattern of body temperature in normoxia and hypoxia

Circadian patterns are at the core of many physiological processes, and their disruption can have short- and long-term consequences. This essay focuses on one of the best known patterns, the daily oscillation of body temperature (Tb), and the possibility of its difference between genders. From human and animal studies globally considered, the tentative conclusion is reached that differences in Tb circadian pattern between genders are very small and probably limited to the timing of the rhythm, not to its amplitude. Such similarity between genders, despite the differences in hormonal systems, presumably testifies to the importance that the Tb circadian pattern plays in the economy of the organism and its survival against environmental challenges. The second part of the article presents some previously unpublished experimental data from behaving male and female rats during hypoxia in synchronized conditions. In adult rats hypoxia (10.5% O₂ for three days) caused a profound drop of the Tb daily oscillations; by day 3 they were 55% (♀) and 22% (♂) of the normoxic amplitudes, with a statistically significant gender difference. In pre-puberty rats (26-day old) hypoxia caused a major disruption of the circadian pattern qualitatively similar to the adults but not different between genders. Hence, on the basis of this preliminary set of data, it seems that sex-hormones may be a factor in how the Tb daily pattern responds to hypoxia. The implications of the effects of hypoxia on the circadian patterns, and the possibility that such effects may differ between genders, are matters that could have biological and clinical implications and deserve further investigations.

Circadian timing and alignment in healthy adults: associations with BMI, body fat, caloric intake and physical activity

Introduction

Disruption of circadian rhythms is one of the proposed mechanisms linking late sleep timing to obesity risk but few studies have evaluated biological markers outside of the laboratory. The goal of this study was to determine the relationship between the timing and alignment of melatonin and sleep onset (phase angle) with BMI, body fat and obesity related behaviors. We hypothesized that circadian alignment (relationship of melatonin to sleep timing) rather than circadian (melatonin) timing would be associated with higher BMI, body fat, dietary intake and lower physical activity.

Subjects/Methods

Adults with sleep duration ≥6.5 hours completed 7 days of wrist actigraphy, food diaries and SenseWear arm band monitoring. Circadian timing, measured by dim light melatonin onset (DLMO) was measured in the clinical research unit. Circadian alignment was calculated as the duration between dim light melatonin onset and average sleep onset time in the prior week (phase angle). Body fat was evaluated using dual-energy absorptiometry (DXA). Data were analyzed using bivariate correlations and multivariable regression analyses controlling for age, sex, sleep duration and evening light exposure.

Results

Participants included 97 adults (61 F, age 26.8 ± 7.3 years) with average sleep duration 443.7 (SD= 50.4) minutes. Average phase angle was 2.2 hours (SD= 1.5). Circadian alignment was associated with circadian timing (p<0.001) and sleep duration (p=.005). In multivariable analyses, later circadian timing was associated with lower BMI (p=.04). Among males only, circadian alignment was associated with percent body fat (p=.02) and higher android/gynoid fat ratio (p=0.04). Circadian alignment was associated with caloric intake (p=0.049) carbohydrate intake (p=0.04) and meal frequency (p=0.03) among both males and females.

Conclusion

Circadian timing and alignment were not associated with increased BMI or body fat, among healthy adults with ≥6.5 hours of sleep, but circadian alignment was associated with dietary intake. There may be sex differences in the relationship between circadian alignment and body fat.

Diurnal and circadian variation of sleep and alertness in men vs. naturally cycling women

This study quantifies sex differences in the diurnal and circadian variation of sleep and waking while controlling for menstrual cycle phase and hormonal contraceptive use. We compared the diurnal and circadian variation of sleep and alertness of 8 women studied during two phases of the menstrual cycle and 3 women studied during their midfollicular phase with that of 15 men. Participants underwent an ultradian sleep-wake cycle (USW) procedure consisting of 36 cycles of 60-min wake episodes alternating with 60-min nap opportunities. Core body temperature (CBT), salivary melatonin, subjective alertness, and polysomnographically recorded sleep were measured throughout this procedure. All analyzed measures showed a significant diurnal and circadian variation throughout the USW procedure. Compared with men, women demonstrated a significant phase advance of the CBT but not melatonin rhythms, as well as an advance in the diurnal and circadian variation of sleep measures and subjective alertness. Furthermore, women experienced an increased amplitude of the diurnal and circadian variation of alertness, mainly due to a larger decline in the nocturnal nadir. Our results indicate that women are likely initiating sleep at a later circadian phase than men, which may be one factor contributing to the increased susceptibility to sleep disturbances reported in women. Lower nighttime alertness is also observed, suggesting a physiological basis for a greater susceptibility to maladaptation to night shift work in women.

Diurnal variations of hormonal secretion, alertness and cognition in extreme chronotypes under different lighting conditions

Circadian rhythms in physiology and behavior are modulated by external factors such as light or temperature. We studied whether self-selected office lighting during the habitual waking period had a different impact on alertness, cognitive performance and hormonal secretion in extreme morning and evening chronotypes (N = 32), whose preferred bed- and wake-up times differed by several hours. The self-selected lighting condition was compared with constant bright light and a control condition in dim light. Saliva samples for hormonal analyses, subjective ratings of alertness, wellbeing, visual comfort and cognitive performance were regularly collected. Between the self-selected and the bright, but not the dim lighting condition, the onset of melatonin secretion in the evening (as marker for circadian phase) was significantly different for both chronotypes. Morning chronotypes reported a faster increase in sleepiness during the day than evening chronotypes, which was associated with higher cortisol secretion. Wellbeing, mood and performance in more difficult cognitive tasks were better in bright and self-selected lighting than in dim light for both chronotypes, whereas visual comfort was best in the self-selected lighting. To conclude, self-selection of lighting at work might positively influence biological and cognitive functions, and allow for inter-individual differences.

Constraint is associated with earlier circadian phase and morningness: Confirmation of relationships between personality and circadian phase using a constant routine protocol

Associations among personality, diurnal preference, and circadian phase were investigated using a constant routine laboratory protocol. One hundred and sixty-eight healthy participants aged 18-30 years (Women n = 68) completed either a 30- or 50-hour constant routine under dim-light conditions (<3 lux), during which circadian phase was measured from core body temperature and melatonin. Prior to laboratory admission, self-report measures of personality and diurnal preference were also obtained. The personality trait of Constraint correlated positively with morning diurnal preference and earlier circadian phase, with circadian phase partially mediating the relationship between Constraint and diurnal preference. No other personality variables correlated with circadian phase. Sex was an important covariate in several of the relationships investigated due to lower levels of Constraint and later CBT phase amongst men and was thus controlled for in all relevant analyses. Findings from this highly controlled study are consistent with previous field research in suggesting that earlier circadian phase is associated with the personality trait of Constraint.

Gender differences in sleep in older men and women

Sleep disturbances increase with increasing age in both males and females and become fairly common in the older community when compared to their younger counterparts. Even though these sleep disturbances increase with advancing age, there are nevertheless inherent differences in sleep disturbances between males and females. When compared to older men, older women will have a longer sleep latency (number of minutes it takes to fall asleep), more daytime sleepiness, will sleep about 20 min less per day, have less NREM stages 1 and 2 sleep, have more slow-wave sleep, and are more predisposed to REM sleep. Women have at least a 40% increased risk for developing insomnia, are at twice the risk for restless legs syndrome, will have different obstructive sleep apnea symptoms and more partial obstructions during sleep compared to men. They are also less likely to use antidepressants but will metabolize zolpidem 50% slower than men.

Neuroendocrine underpinnings of sex differences in circadian timing systems

There are compelling reasons to study the role of steroids and sex differences in the circadian timing system. A solid history of research demonstrates the ubiquity of circadian changes that impact virtually all behavioral and biological responses. Furthermore, steroid hormones can modulate every attribute of circadian responses including the period, amplitude and phase. Finally, desynchronization of circadian rhythmicity, and either enhancing or damping amplitude of various circadian responses can produce different effects in the sexes. Studies of the neuroendocrine underpinnings of circadian timing systems and underlying sex differences have paralleled the overall development of the field as a whole. Early experimental studies established the ubiquity of circadian rhythms by cataloging daily and seasonal changes in whole organism responses. The next generation of experiments demonstrated that daily changes are not a result of environmental synchronizing cues, and are internally orchestrated, and that these differ in the sexes. This work was followed by the revelation of molecular circadian rhythms within individual cells. At present, there is a proliferation of work on the consequences of these daily oscillations in health and in disease, and awareness that these may differ in the sexes. In the present discourse we describe the paradigms used to examine circadian oscillation, to characterize how these internal timing signals are synchronized to local environmental conditions, and how hormones of gonadal and/or adrenal origin modulate circadian responses. Evidence pointing to endocrinologically and genetically mediated sex differences in circadian timing systems can be seen at many levels of the neuroendocrine and endocrine systems, from the cell, the gland and organ, and to whole animal behavior, including sleep/wake or rest/activity cycles, responses to external stimuli, and responses to drugs. We review evidence indicating that the analysis of the circadian timing system is amenable to experimental analysis at many levels of the neuraxis, and on several different time scales, rendering it especially useful for the exploration of mechanisms associated with sex differences.

Sex differences in the circadian regulation of sleep and waking cognition in humans

The sleep-wake cycle and circadian rhythmicity both contribute to brain function, but whether this contribution differs between men and women and how it varies across cognitive domains and subjective dimensions has not been established. We examined the circadian and sleep-wake-dependent regulation of cognition in 16 men and 18 women in a forced desynchrony protocol and quantified the separate contributions of circadian phase, prior sleep, and elapsed time awake on cognition and sleep. The largest circadian effects were observed for reported sleepiness, mood, and reported effort; the effects on working memory and temporal processing were smaller. Although these effects were seen in both men and women, there were quantitative differences. The amplitude of the circadian modulation was larger in women in 11 of 39 performance measures so that their performance was more impaired in the early morning hours. Principal components analysis of the performance measures yielded three factors, accuracy, effort, and speed, which reflect core performance characteristics in a range of cognitive tasks and therefore are likely to be important for everyday performance. The largest circadian modulation was observed for effort, whereas accuracy exhibited the largest sex difference in circadian modulation. The sex differences in the circadian modulation of cognition could not be explained by sex differences in the circadian amplitude of plasma melatonin and electroencephalographic slow-wave activity. These data establish the impact of circadian rhythmicity and sex on waking cognition and have implications for understanding the regulation of brain function, cognition, and affect in shift-work, jetlag, and aging.

Sex Differences in Circadian Dysfunction in the BACHD Mouse Model of Huntington's Disease

Huntington's disease (HD) is an autosomal dominant neurodegenerative disorder that affects men and women in equal numbers, but some epidemiological studies indicate there may be sex differences in disease progression. One of the early symptoms of HD is disruptions in the circadian timing system, but it is currently unknown whether sex is a factor in these alterations. Since sex differences in HD could provide important insights to understand cellular and molecular mechanism(s) and designing early intervention strategies, we used the bacterial artificial chromosome transgenic mouse model of HD (BACHD) to examine whether sex differences in circadian behavioral rhythms are detectable in an animal model of the disease. Similar to BACHD males, BACHD females display circadian disruptions at both 3 and 6 months of age; however, deficits to BACHD female mouse activity levels, rhythm precision, and behavioral fragmentation are either delayed or less severe relative to males. These sex differences are associated with a smaller suprachiasmatic nucleus (SCN) in BACHD male mice at age of symptom onset (3 months), but are not associated with sex-specific differences in SCN daytime electrical activity deficits, or peptide expression (arginine vasopressin, vasoactive intestinal peptide) within the SCN. Notably, BACHD females exhibited delayed motor coordination deficits, as measured using rotarod and challenge beam. These findings suggest a sex specific factor plays a role both in non-motor and motor symptom progression for the BACHD mouse.

Artificial light at night: melatonin as a mediator between the environment and epigenome

The adverse effects of excessive use of artificial light at night (ALAN) are becoming increasingly evident and associated with several health problems including cancer. Results of epidemiological studies revealed that the increase in breast cancer incidents co-distribute with ALAN worldwide. There is compiling evidence that suggests that melatonin suppression is linked to ALAN-induced cancer risks, but the specific genetic mechanism linking environmental exposure and the development of disease is not well known. Here we propose a possible genetic link between environmental exposure and tumorigenesis processes. We discuss evidence related to the relationship between epigenetic remodelling and oncogene expression. In breast cancer, enhanced global hypomethylation is expected in oncogenes, whereas in tumour suppressor genes local hypermethylation is recognized in the promoter CpG chains. A putative mechanism of action involving epigenetic modifications mediated by pineal melatonin is discussed in relation to cancer prevalence. Taking into account that ALAN-induced epigenetic modifications are reversible, early detection of cancer development is of great significance in the treatment of the disease. Therefore, new biomarkers for circadian disruption need to be developed to prevent ALAN damage.