The neuroendocrine control of the circadian system: adolescent chronotype

Chronotype changes after sex hormone use: A prospective cohort study in transgender users of gender-affirming hormones

Chronotype, an individual's preferred sleep-wake timing, is influenced by sex and age. Men sometimes report a later chronotype than women and older age is associated with earlier chronotype. The sex-related changes in chronotype coincide with puberty and menopause. However, the effects of sex hormones on human chronotype remain unclear. To examine the impact of 3 months of gender-affirming hormone therapy (GAHT) on chronotype in transgender persons, this study used data from 93 participants from the prospective RESTED cohort, including 49 transmasculine (TM) participants starting testosterone and 44 transfeminine (TF) participants starting estrogens and antiandrogens. Midpoint of sleep and sleep duration were measured using the ultra-short Munich ChronoType Questionnaire (µMCTQ). After 3 months of GAHT, TM participants' midpoint of sleep increased by 24 minutes (95% CI: 3 to 45), whereas TF participants' midpoint of sleep decreased by 21 minutes (95% CI: -38 to -4). Total sleep duration did not change significantly in either group. This study provides the first prospective assessment of sex hormone use and chronotype in transgender persons, showing that GAHT can change chronotype in line with cisgender sex differences. These findings provide a basis for future studies on biological mechanisms and clinical consequences of chronotype changes.

Delayed sleep wake phase disorder in adolescents: an updated review

PURPOSE OF REVIEW

This review examines the most common circadian rhythm disorder in adolescents, delayed sleep phase disorder. It explores the etiology, prevalence, clinical features, diagnostic tools and criteria, and treatment options to identify sleep disorders early in the course. This is important to help improve youths in terms of education and quality of life.

RECENT FINDINGS

Recent studies indicate that delayed sleep wake phase disorder has a range of prevalence between 1% and 16%. It is often associated with neurodevelopmental disorders (i.e. attention deficit hyperactivity disorder and autism spectrum disorder) as well as psychopathology (i.e. substance use, anxiety, and depression). It can present with a myriad of symptoms, such as insomnia, restless sleep, and poor daytime cognitive function, often seen in pediatric practice. Important diagnostic measures incorporate history-taking, sleep logs, actigraphy (i.e. Apple watches) and measurement of dim light melatonin onset. Treatments include improved sleep hygiene, chronotherapy, exogenous melatonin administration, and bright light therapy.

SUMMARY

There are many environmental and genetic factors that can predispose an individual to circadian rhythm disorders. Delayed sleep phase disorder has detrimental effects on overall health, cognition, and behavior. It is important to screen for this disorder in routine pediatric clinic visits. The goal of early intervention is to prevent health and behavioral complications and treat adolescents using a multimodal approach, especially those with affective/neurodevelopmental conditions, who are prone to having delayed sleep wake phase disorder.

Sleep, Nutrition, and Injury Risk in Adolescent Athletes: A Narrative Review

This narrative review explores the impact of sleep and nutrition on injury risk in adolescent athletes. Sleep is viewed as essential to the recuperation process and is distinguished as an active participant in recovery through its involvement in growth, repair, regeneration, and immunity. Furthermore, the literature has shown that the sleep of athletes impacts elements of athletic performance including both physical and cognitive performance, recovery, injury risk, and mental well-being. For sleep to have a restorative effect on the body, it must meet an individual's sleep needs whilst also lasting for an adequate duration and being of adequate quality, which is age-dependent. The literature has suggested that athletes have increased sleep needs compared to those of the general population and thus the standard recommendations may not be sufficient for athletic populations. Therefore, a more individualised approach accounting for overall sleep health may be more appropriate for addressing sleep needs in individuals including athletes. The literature has demonstrated that adolescent athletes achieve, on average, ~6.3 h of sleep, demonstrating a discrepancy between sleep recommendations (8-10 h) and actual sleep achieved. Sleep-wake cycles undergo development during adolescence whereby adaptation occurs in sleep regulation during this phase. These adaptations increase sleep pressure tolerance and are driven by the maturation of physiological, psychological, and cognitive functioning along with delays in circadian rhythmicity, thus creating an environment for inadequate sleep during adolescence. As such, the adolescent period is a phase of rapid growth and maturation that presents multiple challenges to both sleep and nutrition; consequently, this places a significant burden on an adolescent athletes' ability to recover, thus increasing the likelihood of injury. Therefore, this article aims to provide a comprehensive review of the available literature on the importance of sleep and nutrition interactions in injury risk in adolescent athletes. Furthermore, it provides foundations for informing further investigations exploring the relation of sleep and nutrition interactions to recovery during adolescence.

Is evening chronotype associated with higher alcohol consumption? A systematic review and meta-analysis

A broader understanding of whether and to what extent chronotype should be considered a risk factor for alcohol consumption is needed. The aim of this systematic review was to summarize the evidence on the association between evening chronotype and alcohol consumption. A systematic search of observational studies on this association was conducted in the PubMed, Scopus, Web of Science, Cochrane Library and PsycINFO databases up to April 30th, 2023. Random-effect models estimated the pooled odds ratio (OR) of alcohol consumption according to chronotype. The Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines and Quality Assessment tool for Observational Cohorts and Cross-sectional Studies from the National Heart, Lung and Blood Institute were followed. A total of 33 studies involving 28 207 individuals (age range: 18-93 years) were included in this review. Overall, most studies indicated a higher volume and frequency of alcohol consumption in evening-type individuals than in individuals with different chronotypes. Additionally, a meta-analysis including 13 studies showed that evening-type individuals were 41% more likely to consume alcohol than those with other chronotypes (OR = 1.41, 95% confidence interval: 1.16-1.66; I2 = 38.0%). Limitations of the present findings are the predominance of cross-sectional studies and varied definitions of alcohol consumption. The available evidence supports an association between the evening chronotype and alcohol consumption. The evening-type population, especially young adults, is a specific target for educational interventions for preventing or reducing alcohol consumption.PROSPERO number: CRD42022343778.

Narrative review: The role of circadian rhythm on sports performance, hormonal regulation, immune system function, and injury prevention in athletes

Objectives

This study was a narrative review of the importance of circadian rhythm (CR), describes the underlying mechanisms of CR in sports performance, emphasizes the reciprocal link between CR, endocrine homeostasis and sex differences, and the unique role of the circadian clock in immune system function and coordination.

Method

As a narrative review study, a comprehensive search was conducted in PubMed, Scopus, and Web of Science (core collection) databases using the keywords "circadian rhythm", "sports performance", "hormonal regulation", "immune system", and "injury prevention". Inclusion criteria were studies published in English and peer-reviewed journals until July 2023. Studies that examined the role of CR in sports performance, hormonal status, immune system function, and injury prevention in athletes were selected for review.

Results

CR is followed by almost all physiological and biochemical activities in the human body. In humans, the superchiasmatic nucleus controls many daily biorhythms under solar time, including the sleep-wake cycle. A body of literature indicates that the peak performance of essential indicators of sports performance is primarily in the afternoon hours, and the evening of actions occurs roughly at the peak of core body temperature. Recent studies have demonstrated that the time of day that exercise is performed affects the achievement of good physical performance. This review also shows various biomarkers of cellular damage in weariness and the underlying mechanisms of diurnal fluctuations. According to the clock, CR can be synchronized with photonic and non-photonic stimuli (i.e., temperature, physical activity, and food intake), and feeding patterns and diet changes can affect CR and redox markers. It also emphasizes the reciprocal links between CR and endocrine homeostasis, the specific role of the circadian clock in coordinating immune system function, and the relationship between circadian clocks and sex differences.

Conclusion

The interaction between insufficient sleep and time of day on performance has been established in this study because it is crucial to balance training, recovery, and sleep duration to attain optimal sports performance.

CARE as a wearable derived feature linking circadian amplitude to human cognitive functions

Circadian rhythms are crucial for regulating physiological and behavioral processes. Pineal hormone melatonin is often used to measure circadian amplitude but its collection is costly and time-consuming. Wearable activity data are promising alternative, but the most commonly used measure, relative amplitude, is subject to behavioral masking. In this study, we firstly derive a feature named circadian activity rhythm energy (CARE) to better characterize circadian amplitude and validate CARE by correlating it with melatonin amplitude (Pearson's r = 0.46, P = 0.007) among 33 healthy participants. Then we investigate its association with cognitive functions in an adolescent dataset (Chinese SCHEDULE-A, n = 1703) and an adult dataset (UK Biobank, n = 92,202), and find that CARE is significantly associated with Global Executive Composite (β = 30.86, P = 0.016) in adolescents, and reasoning ability, short-term memory, and prospective memory (OR = 0.01, 3.42, and 11.47 respectively, all P < 0.001) in adults. Finally, we identify one genetic locus with 126 CARE-associated SNPs using the genome-wide association study, of which 109 variants are used as instrumental variables in the Mendelian Randomization analysis, and the results show a significant causal effect of CARE on reasoning ability, short-term memory, and prospective memory (β = -59.91, 7.94, and 16.85 respectively, all P < 0.0001). The present study suggests that CARE is an effective wearable-based metric of circadian amplitude with a strong genetic basis and clinical significance, and its adoption can facilitate future circadian studies and potential intervention strategies to improve circadian rhythms and cognitive functions.

Use of a Fitbit-like device in rats: Sex differences, relation to EEG sleep, and use to measure the long-term effects of adolescent ethanol exposure

BACKGROUND

Sleep difficulties and rhythm disturbances are some of the problems associated with adolescent binge drinking. Recently, animal models of alcohol-induced insomnia have been developed. However, studies in human subjects have recently focused not only on nighttime EEG findings but also on daytime sleepiness and disrupted activity levels as typically measured by activity tracking devices such as the "Fitbit." We sought to develop and test a Fitbit-like device (the "FitBite") in rats and use it to track rest-activity cycles following adolescent alcohol exposure.

METHODS

The effects of 5 weeks of adolescent ethanol vapor or control conditions were evaluated in 48 male and female Wistar rats using FitBite activity while intoxicated, and during acute (24 h post-vapor exposure) and chronic withdrawal (4 weeks post-vapor exposure). Data were analyzed using activity count and cosinor analyses. Fourteen rats were subsequently implanted with cortical electrodes, and data from the FitBite were compared with EEG data to determine how well the FitBite could identify sleep and activity cycles.

RESULTS

Female rats were generally more active than males, with higher circadian rhythm amplitudes and mesors (rhythm-adjusted means) across a 24-h period. There were significant correlations between EEG-estimated sleep and activity counts using the FitBite. When the rats were tested during intoxication after 4 weeks of ethanol vapor exposure, they had significantly less overall activity. Disruptions in circadian rhythm were also found with significant decreases in the circadian amplitude, mesor, and a later shift in the acrophase. At 24 h of ethanol withdrawal, rats had more episodes of activity with shorter durations during the daytime, when rats are expected to spend more of their time sleeping. This effect remained at 4 weeks following withdrawal, but circadian rhythm disruptions were no longer present.

CONCLUSIONS

A Fitbit-like device can be successfully used in rats to assess rest-activity cycles. Adolescent alcohol exposure produced circadian rhythm disturbances that were not observed after withdrawal. Fragmentation of ultradian rest-activity cycles during the light period was found at 24 h and 4 weeks after withdrawal and support data demonstrating the presence of sleep disturbance long after alcohol withdrawal.

[Cross-sectional study on sleep habits and new technologies use in high school students.]

OBJECTIVE

During lasts years, the use of information and communication technologies (ICTs) have boomed up, as well as their related- harmful behaviours. Parallel, time and quality of sleep has reduced along current society, which implies negatively in health in medium and long-terms. The present study aims to evaluate the association between lifestyle habits and quality of sleep of a subpopulation of young students.

METHODS

An observational transversal study has been performed in Certificate of Medium and Higher Education from a High school of Alcázar de San Juan (Ciudad Real, Spain), who filled up a survey related to their lifestyle habits and the use of ICTs. Furthermore, the survey also included several variables related to quality of sleep by using Pittsburgh test. Bivariate comparisons using student test or Mann-Whitney U test, or Chi-square or exact test depending on the variable were performed. Afterwards, logistic regression was also done.

RESULTS

The study sample were 286 students (43.4% women) were included being 22.2±7.3 years old on average. 99.7% of them owned mobile phone, using it 42 hours per week. Average total score of Pittsburgh test was 6.4±3.5, being higher in women (7.36±3.8) than in men (5.62±3.1). Moreover, 51.7% of surveyed students suffered from sleep disorders, being associated to several risk factors, such us using mobile phone while lying and without light (OR=2.04; CI95% [1.12-3.73]), using mobile phone in the middle of the night (OR=1.9; CI95% [1.06-3.42]) and drinking and smoking (OR=2.28; CI95% [1.14-4.55]). On the other hand, practising sports was defined as protector factor (OR=0.43; CI95% [0.26-0.72]).

CONCLUSIONS

More than half of surveyed suffer from sleep disorders, mainly derived from the inadequate use of ICTs, showing differences between genders.

Continuous body temperature as a window into adolescent development

Continuous body temperature is a rich source of information on hormonal status, biological rhythms, and metabolism, all of which undergo stereotyped change across adolescence. Due to the direct actions of these dynamic systems on body temperature regulation, continuous temperature may be uniquely suited to monitoring adolescent development and the impacts of exogenous reproductive hormones or peptides (e.g., hormonal contraception, puberty blockers, gender affirming hormone treatment). This mini-review outlines how traditional methods for monitoring the timing and tempo of puberty may be augmented by markers derived from continuous body temperature. These features may provide greater temporal precision, scalability, and reduce reliance on self-report, particularly in females. Continuous body temperature data can now be gathered with ease across a variety of wearable form factors, providing the opportunity to develop tools that aid in individual, parental, clinical, and researcher awareness and education.

Sleep Deprivation and Insomnia in Adolescence: Implications for Mental Health

Sleep changes significantly throughout the human lifespan. Physiological modifications in sleep regulation, in common with many mammals (especially in the circadian rhythms), predispose adolescents to sleep loss until early adulthood. Adolescents are one-sixth of all human beings and are at high risk for mental diseases (particularly mood disorders) and self-injury. This has been attributed to the incredible number of changes occurring in a limited time window that encompasses rapid biological and psychosocial modifications, which predispose teens to at-risk behaviors. Adolescents’ sleep patterns have been investigated as a biunivocal cause for potential damaging conditions, in which insufficient sleep may be both a cause and a consequence of mental health problems. The recent COVID-19 pandemic in particular has made a detrimental contribution to many adolescents’ mental health and sleep quality. In this review, we aim to summarize the knowledge in the field and to explore implications for adolescents’ (and future adults’) mental and physical health, as well as to outline potential strategies of prevention.

Factors Underpinning the Shift to Eveningness during Early Adolescence: Pubertal Development and Family Conflicts

Biological and psychosocial factors have been related to the shift to eveningness during early adolescence but it is necessary to study them from a longitudinal perspective. This longitudinal study examined the contribution of these factors to the onset of a shift towards eveningness in early adolescence. A sample of 440 (49.9% boys) Spanish adolescents were assessed for pubertal development, family conflicts, and morningness/eveningness. The same measures were taken twice at the age of 12 and one year later (T1: M = 12.47, SD = 0.75 and T2: M = 13.64, SD = 0.78). Pubertal development and family conflicts were considered predictors of morningness/eveningness in a mixed-effects multilevel model. The developmental shift towards eveningness appeared in girls but not in boys. The shift was related to more advanced pubertal development and more conflicts in the family. This study has implications for shaping healthy sleep habits in adolescents and possible interventions focused on family dynamics.

Circle(s) of Life: The Circadian Clock from Birth to Death

Most lifeforms on earth use endogenous, so-called circadian clocks to adapt to 24-h cycles in environmental demands driven by the planet’s rotation around its axis. Interactions with the environment change over the course of a lifetime, and so does regulation of the circadian clock system. In this review, we summarize how circadian clocks develop in humans and experimental rodents during embryonic development, how they mature after birth and what changes occur during puberty, adolescence and with increasing age. Special emphasis is laid on the circadian regulation of reproductive systems as major organizers of life segments and life span. We discuss differences in sexes and outline potential areas for future research. Finally, potential options for medical applications of lifespan chronobiology are discussed.

Integration of Time-Based Recommendations with Current Pediatric Health Behavior Guidelines: Implications for Obesity Prevention and Treatment in Youth

PURPOSE OF REVIEW

Youth-onset obesity is associated with negative health outcomes across the lifespan including cardiovascular diseases, type 2 diabetes, obstructive sleep apnea, dyslipidemias, asthma, and several cancers. Pediatric health guidelines have traditionally focused on the quality and quantity of dietary intake, physical activity, and sleep.

RECENT FINDINGS

Emerging evidence suggests that the timing (time of day when behavior occurs) and composition (proportion of time spent allocated to behavior) of food intake, movement (i.e., physical activity, sedentary time), and sleep may independently predict health trajectories and disease risks. Several theoretically driven interventions and conceptual frameworks feature behavior timing and composition (e.g., 24 h movement continuum, circadian science and chronobiology, intermittent fasting regimens, structured day hypothesis). These literatures are, however, disparate, with little crosstalk across disciplines. In this review, we examine dietary, sleep, and movement guidelines and recommendations for youths ages 0-18 in the context of theoretical models and empirical findings in support of time-based approaches. The review aims to inform a unifying framework of health behaviors and guide future research on the integration of time-based recommendations into current quantity and quality-based health guidelines for children and adolescents.

Multidimensional self-rating biological rhythm disorder and its association with depression and anxiety symptoms among adolescents aged 11-23 years: a school-based cross-sectional study from China

BACKGROUND

Depression and anxiety are topical concerns worldwide, especially among adolescents. Besides, biological rhythm disorder as a candidate mechanism for mood disorders is highly prevalent, but relevant research among adolescents in China is presently limited. We conducted the present study to investigate the distribution of multi-dimensional self-rating biological rhythm disorder and the association of self-rating biological rhythm disorders with depression and anxiety symptoms among Chinese adolescents in different academic stages.

METHODS

In the cross-sectional study, 3693 students aged 11-23 from Zhengzhou City, Henan Province, China were included. The Patient Health Questionnaire (PHQ-9) and General Anxiety Disorder (GAD-7) were used to evaluate symptoms of depression and anxiety, respectively. Additionally, the Self-Rating of Biological Rhythm Disorder for Adolescents (SBRDA) was used to assess status of biological rhythm disorders. Multivariate logistic regression was developed to explore factors potentially associated with symptoms of depression and anxiety stratified by academic stages.

RESULTS

Among all participants, 44.14 and 36.15% suffered from depression and anxiety symptoms, respectively. On average, participants scored 74.66 ± 19.37 on the measure of total biological rhythm disorder. Adjusted for demographic confounding factors, the logistic regression analysis showed higher scores of total biological rhythm disorder were associated with more severe depression (OR = 14.38, 95%CI: 11.38-18.16) and anxiety symptoms (OR = 11.63, 95%CI: 9.14-14.81). The similar results were also found in the stratified analysis by academic stages.

CONCLUSIONS

Self-rating biological rhythm disorders are significantly associated with depression and anxiety symptoms among adolescents. Discrepancy across academic stages should also be taken into account in establishing public health strategies.

Constitutional delay of growth and puberty in female mice is induced by circadian rhythm disruption in utero

Constitutional delay of growth and puberty (CDGP) refers to the late onset of puberty. CDGP is associated with poor psychosocial outcomes and elevated risk of cardiovascular and osteoporotic diseases, especially in women. The environmental factors that contribute to CDGP are poorly understood. Here, we investigated the effects of chronic circadian disturbance (CCD) during the fetal stage on the pubertal development of female mice. Compared to non-stressed female (NS-F) mice that were not exposed to CCD in utero, adolescent CCD female (CCD-F) mice exhibited phenotypes that were consistent with CDGP, including lower body weight, reduced levels of circulating gonadal hormones, decreased expression of gonadal hormones and steroid synthesis-related enzymes in the ovary and hypothalamus, irregular estrus cycles, and tardive vaginal introitus initial opening (VO) days (equivalent to the menarche). Phenotypic differences in the above-noted parameters were not observed in CCD-F mice once they had reached adulthood. The expression of genes involved in fatty acid metabolism was perturbed in the ovary and hypothalamus of CCD-F mice. In addition, the ovaries of these animals exhibited altered diurnal expression profiles of circadian clock genes. Together, our findings not only suggest that CCD during fetal development may result in delayed puberty in female mice, they also offer insights on potential mechanisms that underlie CDGP.

What time do you plan to sleep tonight? An intense longitudinal study of adolescent daily sleep self-regulation via planning and its associations with sleep opportunity

BACKGROUND

Most adolescents are sleep deprived on school days, yet how they self-regulate their sleep-wake behaviours is poorly understood. Using ecological momentary assessment, this intense longitudinal study explored patterns of adolescents' daily bedtime and risetime planning and execution, and whether these behaviours predicted sleep opportunity.

METHODS

Every afternoon, for 2 school weeks and the subsequent 2 vacation weeks, 205 (54.1% female, 64.4% non-White) adolescents from year 10 to 12 (M ± SD_age  = 16.9 ± 0.9) reported their plans for bedtime (BT) that evening, and for risetimes (RT) the following day. Actual daily sleep was measured via actigraphy and sleep diary.

RESULTS

Some adolescents never planned bedtime (school 19.5%, non-school 53.2%) or risetime (school 1.5%, non-school 24.4%). More adolescents planned consistently (≥75% of days) on school (BT = 29.9%, RT = 61.3%) compared to non-school nights (BT = 3.5%, RT = 2.5%). On average, adolescents went to bed later than planned, with longer delays on non-school (71 min) compared to school nights (46 min). Of those who executed their plans within ≤15 min, more did it consistently (≥75% of days) on school (BT = 40.9%, RT = 67.7%) than on non-school nights/days (BT = 29.7%, RT = 58.6%). Mixed effects models utilizing daily data, controlling for sex, race, and study day, showed that bedtime planning predicted longer time in bed (TIB; p < .01) on school and shorter TIB on non-school nights (p < .01); and greater delay in actual (compared to planned) BT predicted shorter TIB (p < .001).

CONCLUSIONS

Adolescents may require support during the transition from parent-controlled to autonomous sleep self-regulation. Bedtime planning on school nights and going to bed as planned are two modifiable sleep regulatory behaviours that are protective and potential therapeutic targets for increasing sleep opportunity in adolescents.

Sex Differences in Pubertal Circadian and Ultradian Rhythmic Development Under Semi-naturalistic Conditions

Biological rhythms in core body temperature (CBT) provide informative markers of adolescent development under controlled laboratory conditions. However, it is unknown whether these markers are preserved under more variable, semi-naturalistic conditions, and whether CBT may therefore prove useful in a real-world setting. To evaluate this possibility, we examined fecal steroid concentrations and CBT rhythms from pre-adolescence (p26) through early adulthood (p76) in intact male and female Wistar rats under natural light and climate at the Stephen Glickman Field Station for the Study of Behavior, Ecology and Reproduction. Despite greater environmental variability, CBT markers of pubertal onset and its rhythmic progression were comparable with those previously reported in laboratory conditions in female rats and extend actigraphy-based findings in males. Specifically, sex differences emerged in CBT circadian rhythm (CR) power and amplitude prior to pubertal onset and persisted into early adulthood, with females exhibiting elevated CBT and decreased CR power compared with males. Within-day (ultradian rhythm [UR]) patterns also exhibited a pronounced sex difference associated with estrous cyclicity. Pubertal onset, defined by vaginal opening, preputial separation, and sex steroid concentrations, occurred later than previously reported under lab conditions for both sexes. Vaginal opening and increased fecal estradiol concentrations were closely tied to the commencement of 4-day oscillations in CBT and UR power. By contrast, preputial separation and the first rise in testosterone concentration were not associated with adolescent changes to CBT rhythms in male rats. Together, males and females exhibited unique temporal patterning of CBT and sex steroids across pubertal development, with tractable associations between hormonal concentrations, external development, and temporal structure in females. The preservation of these features outside the laboratory supports CBT as a strong candidate for translational pubertal monitoring under semi-naturalistic conditions in females.

The impact of COVID-19 on Italian adolescents' sleep and its association with psychological factors

Insomnia and circadian dysregulation during adolescence represent important risk factors for emotional and psychological problems. Recent studies have shown that the coronavirus disease 2019 (COVID‐19) pandemic has been linked to a high prevalence of behavioural sleep problems in the general population. This study aimed to provide two pictures of two different time points of the pandemic regarding the prevalence of sleep problems in adolescents and their association with psychological health variables. Two different independent large samples of Italian adolescents aged 13–17 years were recruited at two pandemic time points. A total of 1,146 adolescents at Time 1 (T1; April 2020) and 1,406 at Time 2 (T2; April 2021) took part in the study. Measures of insomnia symptoms, sleep hygiene, chronotype, psychological distress and emotion regulation were collected. Prevalence of insomnia was 12.13% at T1 and 23.19% at T2. Furthermore, high levels of poor sleep habits (late bedtime, poor sleep hygiene, use of electronic devices at bedtime) were also detected at both time points. Insomnia symptoms strongly correlated with poor sleep hygiene, higher psychological distress, and emotional suppression at both time points. Results highlighted an alarming picture for two large samples at two different time points of the pandemic that showed a potential negative impact of the COVID‐19 pandemic, in both the first outbreak and in the later phase of the pandemic, on sleep habits, psychological distress and insomnia symptoms in adolescents. This strongly suggests the need for monitoring these variables and their interaction in the post‐pandemic period and to develop and promote interventions for insomnia and circadian disturbances during adolescence.

Chronotype at the beginning of secondary school and school timing are both associated with chronotype development during adolescence

The misalignment between late chronotypes and early school start times affect health, performance and psychological well-being of adolescents. Here we test whether, and how, the baseline chronotype (i.e. chronotype at the beginning of secondary school) and the school timing affect the magnitude and the direction of the developmental change in chronotype during adolescence. We evaluated a sample of Argentinian students (n = 259) who were randomly assigned to attend school in the morning (07:45 a.m.–12:05 p.m.), afternoon (12:40 p.m.–05:00 p.m.) or evening (05:20 p.m.–09:40 p.m.) school timings. Importantly, chronotype and sleep habits were assessed longitudinally in the same group of students along secondary school (at 13–14 y.o. and 17–18 y.o.). Our results show that: (1) although chronotypes partially align with class time, this effect is insufficient to fully account for the differences observed in sleep-related variables between school timings; (2) both school timing and baseline chronotype are independently associated with the direction and the magnitude of change in chronotype, with greater delays related to earlier baseline chronotypes and later school timings. The practical implications of these results are challenging and should be considered in the design of future educational timing policies to improve adolescents’ well-being.

Sex differences in the relationship between morningness-eveningness components, mood and well-being among Bangladeshi university students

On the Morningness/Eveningness (M/E) continuum, eveningness has been related to mood disorder and poor well-being. M/E differs between men and women throughout their lifespan. However, there is a lack of information on sex differences in the relationship between M/E, mood, and well-being. This study aimed to test sex differences in the M/E, mood, and well-being relationship with consideration of two components of M/E, morning affect, and morning preference. A sample of 981 Bangladeshi university students (607 men) aged 18 to 27 (M = 21.95) completed Bangla versions of the Composite Scale of Morningness (CSM), BRUnel Mood Scale (BRUMS), and Positive Mental Health scale (PMH-scale) through an online survey. Multiple regression analyses were used to test the relationship of M/E components with mood and well-being. The results showed that the relationship between M/E, mood, and well-being was greater in women than in men. A lower score on both M/E components was related to higher negative moods (anger, confusion, depression, fatigue, and tension) and poor well-being. In regression analysis, only morning affect was found to be significant, which means that morning affect mainly contributes to the relation between M/E, mood, and well-being. Finally, sex by morning affect interaction indicated that the relation was higher for women. Therefore, higher eveningness could be more hazardous for women than men. Greater insight into the independent contribution of morning affect may facilitate understanding of the chronotype effects on psychological outcomes in men and women.

Identifying Environmental Endocrine Disruptors Associated With the Age at Menarche by Integrating a Transcriptome-Wide Association Study With Chemical-Gene-Interaction Analysis

Menarche is the first occurrence of menstrual bleeding and one of the most important events of female puberty. Alarmingly, over the last several decades, the mean age at menarche (AAM) has decreased. Environmental endocrine disruptors (EEDs) are chemicals that may interfere with the endocrine system, resulting in adverse developmental, immunological, neurological, and reproductive effects in humans. Thus, the effects of EEDs on fertility and reproduction are growing concerns in modern societies. In this study, we aimed to determine the influence of genetic and environmental factors on AAM. We used data from an AAM genome-wide association study of 329,345 women to conduct a transcriptome-wide association study (TWAS) with FUSION software. As references, we determined the gene-expression levels in the hypothalamus, pituitary gland, ovaries, uterus, and whole blood. We performed Gene Ontology and Kyoto Encyclopedia of Genes and Genomes enrichment analyses using the significantly dysregulated genes identified by the TWAS. Using the STRING database, we also generated a protein-protein-interaction network to analyze common AAM-specific genes identified by the TWAS with different tissues. We performed chemical-related gene set enrichment analysis (CGSEA) and identified significant TWAS genes to uncover relationships between different chemicals and AAM. The TWAS identified 9,848 genes; among these, 1580 genes were significant (P < 0.05), and 11 genes were significant among the hypothalamus, pituitary, ovary, uterus, and whole blood. CGSEA identified 1,634 chemicals, including 120 chemicals significantly correlated with AAM. In summary, we performed a TWAS (for genetic factors) and CGSEA (for environmental factors) focusing on AAM and identified several AAM-associated genes and EEDs. The results of this study expand our understanding of genetic and environmental factors related to the onset of female puberty.

Changes in chronotype and social jetlag during adolescence and their association with concurrent changes in BMI-SDS and body composition, in the DONALD Study

BACKGROUND/OBJECTIVES

Adolescence is a critical period for both the development of overweight and the transition toward a later chronotype, often accompanied by an increase in social jetlag. This study assessed whether changes in chronotype and social jetlag, are linked to changes in body composition during adolescence.

SUBJECTS/METHODS

We used data from the DONALD open cohort study, collected between 2014 and 2019, from 213 adolescents (9-17 years at baseline, 45% females) having at least two measures of chronotype and anthropometry (N = 572). Chronotype was assessed with the Munich Chronotype Questionnaire and defined as: midpoint of sleep corrected for sleep-debt (MSFsc) accumulated over the week (later MSFsc represents later chronotype). Social jetlag (SJL) defines the difference between midpoint of sleep during week and weekend. Calculations for Fat Free Mass Index (FFMI [kg/m²)]) and Fat Mass Index (FMI) [kg/m²)]) were based on body fat percentage, weight, and height. To analyze the associations, we used linear mixed-effect regression models. Finally, the total cohort was split into three biologically relevant age groups (cut-off set at <12 years, ≥12 to ≤15 years and >15 years).

RESULTS

Median follow-up was 2.1 years. Overall, change toward a later chronotype was significantly related with an increase in FMI (ß: 0.05, 95% CI: 0.01-0.08). A 1 h increase in social jetlag predicted an increase in BMI-SDS of 0.08 SDS units (95% CI: 0.01-0.14) and in FMI of 0.04 kg/m2 (95% CI: 0.003-0.08). Associations were stronger for the age group ≥12 to ≤15 years (p for interaction: <0.001). No relationship was found with FFMI.

CONCLUSIONS

Changes in MSFsc and SJL during adolescence were associated with concurrent changes in BMI-SDS and FMI. The age ≥12 to ≤15 years appears to be a sensitive period in which chronobiological changes were clearly associated with increasing body fatness.

Synchronizing Our Clocks as We Age: The Influence of the Brain-Gut-Immune Axis on the Sleep-Wake Cycle Across the Lifespan

The microbes that colonize the small and large intestines, known as the gut microbiome, play an integral role in optimal brain development and function. The gut microbiome is a vital component of the bi-directional communication pathway between the brain, immune system, and gut, also known as the brain-gut-immune axis. To date there has been minimal investigation into the implications of improper development of the gut microbiome and the brain-gut-immune axis on the sleep-wake cycle, particularly during sensitive periods of physical and neurological development, such as childhood, adolescence, and senescence. Therefore, this review will explore the current literature surrounding the overlapping developmental periods of the gut microbiome, brain, and immune system from birth through to senescence, while highlighting how the brain-gut-immune axis affects maturation and organisation of the sleep-wake cycle. We also examine how dysfunction to either the microbiome or the sleep-wake cycle negatively affects the bidirectional relationship between the brain and gut, and subsequently the overall health and functionality of this complex system. Additionally, this review integrates therapeutic studies to demonstrate when dietary manipulations, such as supplementation with probiotics and prebiotics, can modulate the gut microbiome to enhance health of the brain-gut-immune axis and optimize our sleep-wake cycle.

Long-term consequences of peri-adolescent social isolation on social preference, anxiety-like behaviour, and vasopressin neural circuitry of male and female rats

Social isolation during the juvenile and adolescent stages (peri-adolescent social isolation) can have long-term consequences for behavioural and neural development. Most of this research, however, has relied on data from males, and very few studies have included both sexes. The present study investigated the impact of peri-adolescent social isolation on social preference, anxiety-like behaviour, and vasopressin neural circuitry of male and female Long Evans rats. Rats were either housed alone for 3 weeks beginning at weaning (Isolated) or in groups (Group-housed). In adulthood, rats were tested in social preference, open field, marble burying, and light/dark box tests, and brains were processed for vasopressin immunohistochemistry. Isolated males exhibited a lower social preference score and spent more time in the light zone of the light/dark box than their group-housed counterparts. Isolated and Group-housed females did not differ in these measures. Peri-adolescent social isolation did not alter vasopressin fibre density in target areas known to influence social and anxiety-like behaviours (the lateral septum or lateral habenula), but increased fibre density in an output pathway of the circadian pacemaker (projections to the paraventricular nucleus of the thalamus); an effect detected across both sexes. A previously unreported sex difference was also detected for vasopressin fibre density in the paraventricular nucleus of the thalamus (females > males). These findings demonstrate long-term consequences of peri-adolescent social isolation on social preference, anxiety-like behaviour, and the circadian vasopressin pathway and suggest that socio-affective development of males is more vulnerable to social stressors during the juvenile and adolescent stages.

Adolescent Development of Biological Rhythms in Female Rats: Estradiol Dependence and Effects of Combined Contraceptives

Adolescence is a period of continuous development, including the maturation of endogenous rhythms across systems and timescales. Although, these dynamic changes are well-recognized, their continuous structure and hormonal dependence have not been systematically characterized. Given the well-established link between core body temperature (CBT) and reproductive hormones in adults, we hypothesized that high-resolution CBT can be applied to passively monitor pubertal development and disruption with high fidelity. To examine this possibility, we used signal processing to investigate the trajectory of CBT rhythms at the within-day (ultradian), daily (circadian), and ovulatory timescales, their dependence on estradiol (E2), and the effects of hormonal contraceptives. Puberty onset was marked by a rise in fecal estradiol (fE2), followed by an elevation in CBT and circadian power. This time period marked the commencement of 4-day rhythmicity in fE2, CBT, and ultradian power marking the onset of the estrous cycle. The rise in circadian amplitude was accelerated by E2 treatment, indicating a role for this hormone in rhythmic development. Contraceptive administration in later adolescence reduced CBT and circadian power and resulted in disruption to 4-day cycles that persisted after discontinuation. Our data reveal with precise temporal resolution how biological rhythms change across adolescence and demonstrate a role for E2 in the emergence and preservation of multiscale rhythmicity. These findings also demonstrate how hormones delivered exogenously in a non-rhythmic pattern can disrupt rhythmic development. These data lay the groundwork for a future in which temperature metrics provide an inexpensive, convenient method for monitoring pubertal maturation and support the development of hormone therapies that better mimic and support human chronobiology.

Development and validation of the self-rating of biological rhythm disorder for Chinese adolescents

Modern lifestyles, and the popularization of artificial light at night, have led to maladjusted social time and internal circadian rhythm, so developing an instrument on biological rhythms is critical. A 36-item self-rated questionnaire assessing biological rhythm disorder in adolescents was developed according to the literature and expert evaluations. Based on a literature review, four dimensions, digital media use, sleep, eating habits, and activity, were determined. After preliminary item analysis, seven unqualified items were eliminated. A total of 1,152 college students and 8,082 middle school students were selected. Two independent sample t-tests, the Pearson correlations, and confirmatory factor analysis, were used to evaluate the reliability and validity of the questionnaire. The final questionnaire consisted of 4 dimensions covering 29 items, and the variance cumulative contribution was 62.65%. Cronbach's α for the total questionnaire was 0.950 and ranged from 0.817 to 0.904 for each dimension. The Pearson correlation coefficients between each item and the total score ranged from 0.360 to 0.755, and the Pearson correlation coefficient between each item and its dimension was between 0.575 and 0.841. Confirmatory factor analysis showed that the indices of CFI, TLI and RMSEA were 0.911, 0.901 and 0.043, respectively, which is a good degree of fit. The self-rating scale is consistent with the evaluation standard of psychometrics and can be used to evaluate the degree of biological rhythm disorder in adolescents.

Associations of circadian factors with insomnia symptoms and emotional and behavioral problems among school-age children

STUDY OBJECTIVES

To examine the associations of circadian characteristics (ie, chronotype and social jetlag) with insomnia symptoms and emotional and behavioral problems among school-age children.

METHODS

A total of 620 primary school children (median_age = 10.06, standard deviation = 1.16, 58.7% boys) were recruited and assessed by a set of parent-report questionnaires, including Children's Sleep Habit Questionnaire for measuring sleep-wake patterns and insomnia symptoms (bedtime resistance, sleep onset delay, and night waking), Children's Chronotype Questionnaire for assessing the child's chronotype preference, and Strength and Difficulties Questionnaire for assessing emotional and behavioral problems. Linear regression models were applied to examine the associations of chronotype and social jetlag with insomnia symptoms and mental health outcomes, in which age, sex, family income, and average sleep duration were entered as covariates.

RESULTS

Evening chronotype was significantly associated with bedtime resistance and sleep onset delay, while social jetlag was not related to insomnia symptoms. Evening chronotype was also significantly associated with externalizing symptoms after controlling for potential confounders.

CONCLUSIONS

Evening chronotype, but not social jetlag, was the risk factor for insomnia symptoms, and evening chronotype was further associated with increased behavioral problems in school-age children. Our findings underscored the roles of circadian factors in relation to sleep and mental health problems in this young population.

CITATION

Sun W, Kwok NTT, Chan NY, et al. Associations of circadian factors with insomnia symptoms and emotional and behavioral problems among school-age children. J Clin Sleep Med. 2021;17(10):2107-2114.

The role of chronotype and reward processing in understanding social hierarchies in adolescence

INTRODUCTION

Circadian rhythms shift toward an evening preference during adolescence, a developmental period marked by greater focus on the social domain and salience of social hierarchies. The circadian system influences maturation of cognitive architecture responsible for motivation and reward, and observation of responses to reward cues has provided insights into neurocognitive processes that underpin adolescent social development. The objective was to investigate whether circadian phase of entrainment (chronotype) predicted both reward-related response inhibition and social status, and to explore whether mediator and moderator relationships existed between chronotype, reward processing, and social status outcomes.

METHODS

Participants were 75 adolescents aged 13-14 years old (41 females) who completed an eye tracking paradigm that involved an inhibitory control task (antisaccade task) within a nonsocial reward (Card Guessing Game) and a social reward (Cyberball Game) context. Chronotype was calculated from weekend midsleep and grouped into early, intermediate, and later terciles. Participants indicated subjective social status compared with peers in seven domains.

RESULTS

An intermediate and later chronotype predicted improved inhibitory control in the social versus nonsocial reward context. Chronotype also predicted higher perceived social status in two domains (powerful, troublemaker). Intermediate chronotypes reported higher "Powerful" status whereas later chronotypes were higher on "Troublemaker." Improved social reward-related performance predicted only the higher powerful scores and chronotype moderated this relationship. Improved inhibitory control to social reward predicted higher subjective social status in the intermediate and later chronotype group, an effect that was absent in the early group.

CONCLUSION

This behavioral study found evidence that changes toward a later phase of entrainment predicts social facilitation effects on inhibitory control and higher perceived power among peers. It is proposed here that circadian delayed phase in adolescence is linked to approach-related motivation, and the social facilitation effects could reflect a social cognitive capacity involved in the drive to achieve social rank.

A daily diary study of sleep chronotype among Mexican-origin adolescents and parents: Implications for adolescent behavioral health

The current study used daily assessments of sleep to examine stability and change in sleep chronotype in adolescents and their parents. The study assessed adolescent sleep chronotype according to age, gender, and parent chronotype, and evaluated its associations with emotional and behavioral problems in youth. Participants included of 417 Mexican American adolescents (Mage = 16.0 years, Range = 13.9-20.0) and 403 caregivers, who reported bed and wake times daily for 2 consecutive weeks at two time points spaced 1 year apart. In addition, adolescents completed established self-report questionnaires of emotional and behavioral problems. Chronotype was computed as the midsleep point from bed to wake time on free days, correcting for sleep debt accumulated across scheduled days. Multilevel modeling showed a curvilinear association between adolescent age and chronotype, with a peak eveningness observed between ages 16 to 17. Adolescent and parent chronotypes were contemporaneously correlated, but each was only moderately stable over the 1-year period. Later adolescent chronotype was contemporaneously associated with more substance use in all adolescents. Individual development and the family context shape sleep chronotype in adolescents and parents. Sleep chronotype is implicated in adolescent behavioral health.

Sleep disturbance and the long-term impact of early adversity

Sleep disturbance may be a central, yet underappreciated mechanism by which early adversity has a long-term impact upon mental and physical health. The fundamental regulatory processes shaped by early adversity - neural, neuroendocrine, and immune - are also central to sleep. Sleep problems, in turn, lead to a similar constellation of chronic health problems that have been linked to early adversity. We bring together work from the fields of early adversity and sleep in order to suggest a model by which sleep disturbance plays a critical role in the far-reaching impacts of early adversity on health. Future research should employ more longitudinal designs and pay particular attention to the impact of developmental periods such as adolescence and midlife when maturational and environmental factors conspire to create a unique time of sleep disturbance. We also suggesting that intervening to minimize sleep disturbance may be a promising means by which to test the model, as well as potentially blunt the long-term impact of early adversity on health.

Sleep-Wake Timings in Adolescence: Chronotype Development and Associations with Adjustment

Adolescent sleep research has focused heavily on duration and quality with less work examining chronotype, defined as individual differences in sleep-wake timings driven by the circadian rhythm. This study filled a gap in the literature by utilizing actigraphy-based sleep estimates in an accelerated longitudinal design in order to better understand the developmental trajectory and individual stability of chronotype during adolescence, as well as the associations between chronotype with risky behaviors, substance use, and depressive symptoms. A total of 329 adolescents (57% female; 21% Asian American, 31% European American, 41% Latino, 7% other ethnicity) provided actigraphy-based estimates of sleep and completed questionnaires at up to three time points, two years apart, beginning at 14-17 years of age. Multilevel modeling revealed a non-linear developmental trend in chronotype whereby eveningness increased from 14 to 19 years of age followed by a trend toward morningness. Individual differences in chronotype exhibited modest stability during adolescent development. Furthermore, greater evening chronotype was associated with more risky behaviors and substance use among males, and more substance use among older adolescents, whereas depressive symptoms were not associated with chronotype. The findings from this study may have practical implications for adolescent behavioral health interventions targeted at reducing risky behaviors and substance use among youth.

Circadian rhythms and substance use disorders: A bidirectional relationship

The circadian system organizes circadian rhythms (biological cycles that occur around 24 h) that couple environmental cues (zeitgebers) with internal functions of the organism. The misalignment between circadian rhythms and external cues is known as chronodisruption and contributes to the development of mental, metabolic and other disorders, including cancer, cardiovascular diseases and addictive disorders. Drug addiction represents a global public health concern and affects the health and well-being of individuals, families and communities. In this manuscript, we reviewed evidence indicating a bidirectional relationship between the circadian system and the development of addictive disorders. We provide information on the interaction between the circadian system and drug addiction for each drug or drug class (alcohol, cannabis, hallucinogens, psychostimulants and opioids). We also describe evidence showing that drug use follows a circadian pattern, which changes with the progression of addiction. Furthermore, clock gene expression is also altered during the development of drug addiction in many brain areas related to drug reward, drug seeking and relapse. The regulation of the glutamatergic and dopaminergic neurocircuitry by clock genes is postulated to be the main circadian mechanism underlying the escalation of drug addiction. The bidirectional interaction between the circadian system and drug addiction seems to be mediated by the effects caused by each drug or class of drugs of abuse. These studies provide new insights on the development of successful strategies aimed at restoring/stabilizing circadian rhythms to reduce the risk for addiction development and relapse.

Sex differences in the association between chronotype and risk of depression

Information on sex differences in the association between chronotype and depression is scarce. We aimed to investigate these differences using data from the Korea National Health and Nutrition Examination Survey in 2016. Chronotypes were categorised based on mid-sleep time on free days corrected by sleep debt accumulated on workdays (MSFsc): early type, < mean MSFsc - 1 standard deviation (SD); intermediate type, between mean MSFsc - 1 SD and MSFsc + 1 SD; and late type, > mean MSFsc + 1 SD. A Patient Health Questionnaire-9 score of ≥ 10 indicated depression. Among 5550 non-shift working adults aged 19-80 years, the prevalence rates of depression in the early, intermediate, and late chronotype groups were 7.4%, 4.5%, and 9.3%, respectively. Women with late chronotype (odds ratio [OR] = 2.9, 95% confidence interval [CI] = 1.8-4.7) showed a higher risk of depression than women with intermediate chronotype after adjusting for covariates. Women with early chronotype did not show a significant difference in depression risk (OR = 1.3, 95% CI = 0.9-2.0). In conclusion, late chronotype is associated with an increased risk of depression in women but not in men. Early chronotype is not associated with depression in women or men.

Adolescent sleep characteristics and body-mass index in the Family Life, Activity, Sun, Health, and Eating (FLASHE) Study

Sleep may play a role in overweight and obesity in adolescents. The objective of this study is to investigate the relationships between sleep duration and timing and overweight and obesity status in adolescents, with a special emphasis on weekday-weekend difference in sleep characteristics as well as sex-specific relationships. We examined 1,254 U.S. adolescents (12-17 years) self-reported sleep duration, timing, weekday-weekend differences in duration and timing in relation to overweight and obesity. We found an inverse association between sleep duration and overweight and obesity. Compared to 8-9 h of sleep, short sleep (< 7 h) on weekdays was associated with higher odds of overweight and obesity [Odds ratio (95% confidence interval), 1.73 (1.00, 2.97)] in the overall population, while long sleep (10+ h) on weekends was associated with lower odds, but only in males [0.56 (0.34, 0.92)]. We also found that a larger weekday-weekend difference in sleep duration was associated with overweight and obesity in females, but not in males. Specifically, the odds of overweight and obesity were significantly higher among females reporting longer sleep on weekends than weekdays by ≥ 2 h [2.31 (1.15, 4.63)] when compared to those reporting little weekday-weekend differences. Sleep timing, or weekday-weekend differences in sleep timing, were not associated with overweight and obesity in the overall population, although we found suggestive evidence linking later weekend sleep with overweight and obesity in females. Our findings support a role of sleep in adolescent obesity and suggest sex-differences in this relationship that warrant future studies.

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.

Disruption in daily eating-fasting and activity-rest cycles in Indian adolescents attending school

A lifestyle with erratic eating patterns and habits predisposes youngsters to obesity. Through a two-phase feasibility study among Indian students living in the Delhi area, we longitudinally examined the following: (1) the daily eating-fasting cycles of students (N = 34) in school and college using smartphones as they transition from high school (aged 13–15 years; n_IX = 13) to higher secondary school (HSSS; 16–18 years; n_XII = 9) to their first year (FY) of college (18–19 years; n_FC = 12); and (2) daily activity-rest cycles and light-dark exposure of 31 higher secondary school students (HSSS) using actigraphy. In phase 1, students’ food data were analyzed for temporal details of eating events and observable differences in diet composition, such as an energy-dense diet (fast food (FF)), as confounding factors of circadian health. Overall, the mean eating duration in high school, higher secondary and FY college students ranged from 14.1 to 16.2h. HSSS exhibited the shortest night fasting. Although FY college students exhibited the highest fast food percentage (FF%), a positive correlation between body mass index (BMI) and FF% was observed only among HSSS. Furthermore, the body weight of HSSS was significantly higher, indicating that FF, untimely eating and reduced night fasting were important obesity-associated factors in adolescents. Reduced night fasting duration was also related to shorter sleep in HSSS. Therefore, food data were supplemented with wrist actigraphy, i.e., activity-rest data, in HSSS. Actigraphy externally validated the increased obesogenic consequences of deregulated eating rhythms in HSSS. CamNtech motion watches were used to assess the relationship between disturbed activity cycles of HSSS and other circadian clock-related rhythms, such as sleep. Less than 50% of Indian HSSS slept 6 hours or more per night. Seven of 31 students remained awake throughout the night, during which they had more than 20% of their daily light exposure. Three nonparametric circadian rhythm analysis (NPCRA) variables revealed circadian disruption of activity in HSSS. The present study suggests that inappropriate timing and quality of food and sleep disturbances are important determinants of circadian disruptions in adolescents attending school.

Objective sleep patterns and validity of self-reported sleep monitoring across different playing levels in rugby union

Background

Growing evidence highlights that elite rugby union players experience poor sleep quality and quantity which can be detrimental for performance.

Objectives

This study aimed to i) compare objective sleep measures of rugby union players between age categories over a one week period, and ii) compare self-reported measures of sleep to wristwatch actigraphy as the criterion.

Methods

Two hundred and fifty-three nights of sleep were recorded from 38 players representing four different age groups (i.e. under 16, under 18, senior academy, elite senior) in a professional rugby union club in the United Kingdom (UK). Linear mixed models and magnitude-based decisions were used for analysis.

Results

The analysis of sleep schedules showed that U16 players went to bed and woke up later than their older counterparts (small differences). In general, players obtained seven hours of sleep per night, with trivial or unclear differences between age groups. The validity analysis highlighted a large relationship between objective and subjective sleep measures for bedtime (r = 0.56 [0.48 to 0.63]), and get up time (r = 0.70 [0.63 to 0.75]). A large standardised typical error (1.50 [1.23 to 1.88]) was observed for total sleep time.

Conclusion

This study highlights that differences exist in sleep schedules between rugby union players in different age categories that should be considered when planning training. Additionally, self-reported measures overestimated sleep parameters. Coaches should consider these results to optimise sleep habits of their players and should be careful with self-reported sleep measures.

Chronotype, social jetlag and sleep loss in relation to sex steroids

Chronotype describes preferences for functioning at different times of the day. At the onset of puberty, a sharp shift towards eveningness starts, reaching its peak at the end of adolescence, followed by a steady shift towards morningness as the ageing process occurs. Puberty is also the time when sex differences appear, with men being more inclined to eveningness than women, which diminishes around menopause; the described pattern of changes in chronotype leads to the hypothesis that reproductive hormones may be the driving factor behind this conversion. In the present study, we aimed to verify this hypothesis by analysing participants' testosterone, progesterone and dehydroepiandrosterone (DHEA) levels in the three months, as indicated by assays in 3-cm hair strands from the scalp. Participants (n = 239) of both sexes also completed the Munich Chronotype Questionnaire. The results showed that in men higher testosterone levels were related to eveningness and less sleep loss, whereas greater sleep loss was associated with lower levels of DHEA. In women, no associations between chronotype and levels of the analysed hormones were found. The results support the hypothesis that testosterone levels play a role in shaping eveningness. We further hypothesised that a possible cause of the higher secretion level of testosterone in men with the evening chronotype is a mechanism to offset the negative consequences of sleep loss.

Chronotype and Social Jetlag: A (Self-) Critical Review

The Munich ChronoType Questionnaire (MCTQ) has now been available for more than 15 years and its original publication has been cited 1240 times (Google Scholar, May 2019). Additionally, its online version, which was available until July 2017, produced almost 300,000 entries from all over the world (MCTQ database). The MCTQ has gone through several versions, has been translated into 13 languages, and has been validated against other more objective measures of daily timing in several independent studies. Besides being used as a method to correlate circadian features of human biology with other factors-ranging from health issues to geographical factors-the MCTQ gave rise to the quantification of old wisdoms, like "teenagers are late", and has produced new concepts, like social jetlag. Some like the MCTQ's simplicity and some view it critically. Therefore, it is time to present a self-critical view on the MCTQ, to address some misunderstandings, and give some definitions of the MCTQ-derived chronotype and the concept of social jetlag.

An Interdisciplinary Perspective on the Association Between Chronotype and Well-being

Individuals with a circadian preference for mental and physical activity later in the day ("Evening types") are consistently found to fare worse on most facets of well-being than individuals with a circadian preference for mental and physical activity earlier in the day ("Morning types"). Several explanatory hypotheses of this association between chronotype and well-being have been proposed, including shared genetic, biological, developmental, and psychosocial mechanisms. This paper presents a critical summary of these explanatory mechanisms and offers suggestions for their integration in an interdisciplinary biopsychosocial framework.

Pregnancy Induces an Earlier Chronotype in Both Mice and Women

Daily rhythms generated by endogenous circadian mechanisms and synchronized to the light-dark cycle have been implicated in the timing of birth in a wide variety of species. Although chronodisruption (e.g., shift work or clock gene mutations) is associated with poor reproductive outcomes, little is known about circadian timing during pregnancy. This study tested whether daily rhythms change during full-term pregnancies in mice and women. We compared running wheel activity continuously in both nonpregnant ( n = 14) and pregnant ( n = 13) 12- to 24-week-old C57BL/6NJ mice. We also monitored wrist actigraphy in women ( N = 39) for 2 weeks before conception and then throughout pregnancy and measured daily times of sleep onset. We found that on the third day of pregnancy, mice shift their activity to an earlier time compared with nonpregnant dams. Their time of daily activity onset was maximally advanced by almost 4 h around day 7 of pregnancy and then shifted back to the nonpregnant state approximately 1 week before delivery. Mice also showed reduced levels of locomotor activity during their last week of pregnancy. Similarly, in women, the timing of sleep onset was earlier during the first and second trimesters (gestational weeks 4-13 and 14-27) than before pregnancy and returned to the prepregnant state during the third trimester (weeks 28 until delivery). Women also showed reduced levels of locomotor activity throughout pregnancy. These results indicate that pregnancy induces changes in daily rhythms, altering both time of onset and amount of activity. These changes are conserved between mice and women.

Sleep Timing in Patients with Precocious and Delayed Pubertal Development

Previous studies have reported a shift in the timing of sleep during adolescence toward a later time. To date, it is unclear whether hormonal changes during puberty might contribute to this change in sleeping behavior. We systematically assessed pubertal development and sleep timing in a cross-sectional case-control study in girls with precocious (n = 42) and boys with delayed pubertal development (n = 19). We used the Munich ChronoType Questionnaire and the Children’s ChronoType Questionnaire to assess sleep timing in patients and age- and sex-matched controls (n = 309) and used the midpoint of sleep on free days, corrected for potential sleep debt accumulated during the school week, as a marker for sleep timing. Compared to the controls, girls with central precocious puberty showed a delay in sleep timing of 54 min, and girls with premature pubarche slept on average 30 min later. Male adolescents with delayed pubertal development showed an average sleep midpoint that was 40 min earlier compared to the control group. The results of this pilot study suggest an association between pubertal onset and shifts in sleep timing, which is a novel finding in human sleep behavior. Prospective studies in larger cohorts will be needed to examine the robustness and generalizability of the findings.

Rhythms of life: circadian disruption and brain disorders across the lifespan

Many processes in the human body - including brain function - are regulated over the 24-hour cycle, and there are strong associations between disrupted circadian rhythms (for example, sleep-wake cycles) and disorders of the CNS. Brain disorders such as autism, depression and Parkinson disease typically develop at certain stages of life, and circadian rhythms are important during each stage of life for the regulation of processes that may influence the development of these disorders. Here, we describe circadian disruptions observed in various brain disorders throughout the human lifespan and highlight emerging evidence suggesting these disruptions affect the brain. Currently, much of the evidence linking brain disorders and circadian dysfunction is correlational, and so whether and what kind of causal relationships might exist are unclear. We therefore identify remaining questions that may direct future research towards a better understanding of the links between circadian disruption and CNS disorders.

Sleep quality and adolescent default mode network connectivity

Sleep suffers during adolescence and is related to academic, emotional and social behaviors. How this normative change relates to ongoing brain development remains unresolved. The default mode network (DMN), a large-scale brain network important for complex cognition and socioemotional processing, undergoes intra-network integration and inter-network segregation during adolescence. Using resting state functional connectivity and actigraphy over 14 days, we examined correlates of naturalistic individual differences in sleep duration and quality in the DMN at rest in 45 human adolescents (ages 14-18). Variation in sleep quality, but not duration, was related to weaker intrinsic DMN connectivity, such that those with worse quality sleep evinced weaker intra-network connectivity at rest. These novel findings suggest sleep quality, a relatively unexplored sleep index, is related to adolescent brain function in a network that contributes to behavioral maturation and undergoes development during adolescence.