Opioid Use Disorder (OUD) carries a high risk of psychiatric comorbidities, such as depression, sleep disturbances and suicidal behaviour. Recent findings emphasise the impact of chronotype and biological rhythm disturbances on the severity of addiction and suicidality. This study examined the associations between chronotype, biological rhythm characteristics, sleep quality, depressive symptoms and suicidal behaviour in individuals with OUD. A total of 159 patients diagnosed with OUD and 154 healthy controls were evaluated using validated scales, including the Columbia Suicide Severity Rating Scale, Biological Rhythm Assessment Interview, Morningness-Eveningness Questionnaire, Pittsburgh Sleep Quality Index, Beck Depression Inventory and Addiction Profile Index. The results showed that individuals with OUD had significantly higher rates of suicidal ideation and attempts, poorer sleep quality, more irregular biological rhythms and more severe depressive symptoms than the control group. An evening chronotype was more prevalent in the OUD group and was associated with greater addiction severity, disrupted rhythms, poor sleep quality, and increased suicidality. Higher depression severity was significantly associated with lower morningness preferences, and sleep quality was found to explain a significant portion of the shared variance between depressive symptoms and suicidal outcomes. These findings suggest that assessing chronotype and circadian dysregulation could help to identify high-risk patients and inform the development of targeted interventions to improve outcomes in OUD treatment.

Chronotype and meal timing are associated with sleep, yet their joint relationships remain understudied in physically active university students. This study investigated associations among chronotype, caloric intake timing, and sleep characteristics and hypothesized that later first and last caloric intake would independently predict lower Morningness-Eveningness Questionnaire (MEQ) scores. This single-university cross-sectional study included 200 students aged 18-25 years who had exercised ≥3 days/week and ≥150 min/week for the preceding six months. Chronotype, sleep behavior, sleep characteristics, and dietary intake timing were assessed using the MEQ, Athlete Sleep Behavior Questionnaire, three-day sleep diary, and three-day food record, respectively. Multiple linear regression evaluated continuous MEQ score as the primary outcome; group comparisons and correlations were secondary or exploratory. A dummy-coded model tested the robustness of the meal-timing results. Later first and last caloric intake were independently associated with lower MEQ scores (β = -0.435 and -0.422, respectively; both p < 0.001), and the model explained 51.1% of the variance. The sensitivity analysis showed the same graded pattern. Evening-type participants had poorer sleep behaviors, longer sleep latency, lower sleep efficiency, more nocturnal awakenings, poorer subjective sleep quality, and later caloric intake than morning-type participants (all p < 0.001). Total energy and macronutrient intake were unrelated to the evaluated sleep outcomes. Later caloric intake timing was independently associated with greater eveningness, while evening chronotype co-occurred with less favorable sleep characteristics. Given the cross-sectional design, causality and temporal direction cannot be inferred.

Women and evening (late) chronotypes more often than men and morning (early) chronotypes report problems with health, mood, and sleep. Can we expect that, in turn, women report evening preference more often than men? Instead, the literature on chronotypes suggests that men report a slightly larger evening preference than women. To explain this paradoxical finding, we investigated the role of morning and evening components of earliness-lateness. Previous studies have shown that preferences for earliness-lateness (i.e. morningness-eveningness) can vary depending on whether the morning or evening hours are considered. Therefore, we tested the following hypotheses: 1. Sex is unrelated to the combination of lateness in the morning hours with lateness in the evening hours because women more often than men combine morning lateness with evening earliness rather than with evening lateness. 2. Only morning lateness is associated with sleep, mood, and health problems, while evening lateness is not. Paired assessments of morning and evening earliness-lateness and problems with health, mood, and sleep were reported by 439 male and 1143 female university students. We examined relationships between these problems, sex, morning lateness, evening lateness, and their combination. Results supported the study hypotheses. Evening lateness did not contribute to the link of combination of morning and evening lateness to health, mood, and sleep problems and 2) this combination was unrelated to sex of students. Namely, female students less often than male students reported evening lateness that did not contribute to the association of combination of morning and evening lateness with health, mood, and sleep problems. Instead, they more often reported morning lateness that was also associated with health, mood, and sleep problems. As a result, they more often reported problems with health, mood, and sleep, while sex of students was not related to combination of morning lateness with evening lateness (i.e. with morning-evening preference).

Daylight exposure is an environmental determinant of human health, yet measuring real-world exposure at scale remains a major challenge. Large population studies frequently rely on self-reported time spent outdoors as a proxy for daylight exposure, although the validity of this measure remains uncertain. We evaluated the agreement between daily self-reported outdoor daylight exposure and objective light measurements obtained from wearable sensors and investigated whether depressive symptoms influence this agreement. A total of 172 adults living in two Brazilian metropolitan regions were monitored for up to 44 consecutive days, yielding over 5,800 matched days of subjective and objective exposure data. Objective measures included device output illuminance, photopic illuminance, and melanopic equivalent daylight illuminance (EDI). Agreement was assessed across the light exposure thresholds and durations using Lin's concordance correlation coefficient and ROC analyses. Moderate agreement was observed between self-reported and actigraphy-based daylight exposure. The highest concordance occurred at light levels consistent with outdoor daylight (>1000 l× for photopic illuminance and melanopic EDI; >750 l× for device illuminance). A minimum of 30 min of outdoor daylight exposure was the duration most accurately self-reported. Depressive symptoms did not affect these agreement patterns. These findings support the use of simple self-report questionnaires to estimate outdoor daylight exposure in clinical applications and in studies examining how environmental factors shape health.

Chronotype and social jetlag are important correlates of sleep and health, yet their joint relationship with somatic symptom burden remains insufficiently studied in medical students. This cross-sectional study examined the associations among chronotype, social jetlag, sleep quality, and somatic symptoms in 500 undergraduate medical students aged 18-26 y. Chronotype was assessed with the Morningness-Eveningness Questionnaire (MEQ), sleep quality with the Pittsburgh Sleep Quality Index (PSQI), social jetlag (SJL) from weekday-weekend mid-sleep differences, and somatic symptoms with the DSM-5 Level 2-Somatic Symptom-Adult scale. Higher morningness was associated with lower social jetlag, better sleep quality, and fewer somatic symptoms. Social jetlag was positively associated with poorer sleep quality and higher somatic symptom scores, whereas sleep quality showed the strongest association with somatic symptoms. In multivariable analyses, higher morningness predicted lower social jetlag and better sleep quality, and greater social jetlag independently predicted poorer sleep quality. However, after accounting for sleep quality, neither chronotype nor social jetlag remained independently associated with somatic symptoms. Serial mediation analysis showed that the chronotype-somatic symptom association was largely accounted for by indirect pathways, predominantly through sleep quality, with an additional smaller serial pathway through social jetlag and sleep quality.

The circadian system regulates physiological and metabolic processes, and exercise timing may influence metabolism and adiposity. To investigate the time-of-day effects of high-intensity interval resistance training (HIRT) on metabolism, adiposity, and adipogenic markers, male Swiss mice (n = 111) were allocated to control or HIRT groups during the light (C6 and T6) or dark phase (C18 and T18). HIRT was performed for 8 weeks (3 sessions/week) on a ladder at 90% of maximal load until exhaustion. Metabolic biomarkers, adiposity, adipocyte morphology, and protein expression of PPARγ and adiponectin were assessed. Maximal strength increased in trained groups. Training-time interactions were observed for triglycerides and total cholesterol, with higher values in T6 than in C6 and T18. Glucose and PPARγ were higher during the dark phase. PPARγ was also higher in trained than control groups, irrespective of the time of day. HIRT reduced adiposity across multiple depots regardless of training time. No significant differences were observed for adipocyte area, adiponectin, insulin, or HOMA-IR. HIRT reduced adiposity independently of training time, suggesting that chronic adaptations in adipose tissue were primarily driven by the training. However, time of day modulated metabolic responses, particularly lipid metabolism.

Platelet indices provide valuable information on platelet activation, heterogeneity, and production kinetics, yet their physiological variability remains poorly characterized in horses. Although seasonal changes in platelet count have been described, the seasonal modulation of derived platelet indices in mares remains poorly understood. The aim of this study was to evaluate the seasonal variation of platelet count and derived platelet indices in clinically healthy mares from the Valencia region (Spain), and to assess their interrelationships. Forty clinically healthy Spanish Purebred mares (6-12 y) were monitored over one year under natural environmental conditions. Monthly blood samples were collected and analyzed for platelet count (PLT) and derived indices using an automated hematology analyzer. Seasonal effects were evaluated using non-parametric repeated-measures analysis. Significant seasonal variation was observed in most platelet indices (p < 0.05), while PCT and aggregation index remained unchanged. Platelet count was lowest in autumn, whereas indices reflecting platelet size and heterogeneity increased during both warm and cold seasons. Correlation analysis revealed consistent associations among platelet size, mass, and heterogeneity, as well as inverse relationships between platelet density and activation-related variables. These findings demonstrate a clear seasonal modulation of platelet dynamics in mares, likely reflecting adaptive responses to environmental conditions. The results highlight the importance of considering seasonal variation when interpreting platelet indices and support the need for season-adjusted reference intervals in clinical practice.

Serum 25-hydroxyvitamin D [25(OH)D] exhibits a seasonal pattern in temperate populations, typically peaking in late summer and declining in winter. It is still not clear whether this pattern also exists in tropical monsoon climates. To characterize the annual pattern of 25(OH)D in a tropical megacity and identify environmental synchronizers of its seasonal variation, a laboratory-based retrospective cross-sectional study was performed on 1,202 adult outpatients from Dhaka, Bangladesh. Serum 25(OH)D was measured with chemiluminescence immunoassay method. Thirty‑day moving averages of weather variables UV Index, temperature, relative humidity, cloud cover, and AQI were linked to each specimen date. Multivariable linear and logistic regression was performed. A phase shifted seasonal l rhythm was observed: 25(OH)D peaked in December (22.96 ng/mL) and declined in July (12.94 ng/mL). Deficiency prevalence doubled during monsoon months (May-August, OR 2.03-2.27 vs. January). Humidity was negatively associated with 25(OH)D (β = -0.764, p = 0.005), while cloud cover showed a positive association (β = 0.267, p = 0.015). UV index did not independently predict 25(OH)D after adjustment for calendar month. Age was protective against deficiency (OR = 0.975 per year, p < 0.001). In tropical monsoon Dhaka, the seasonal rhythm of 25(OH)D is phase-shifted relative to temperate populations, with summer nadir and winter peak. This pattern may be better explained by behavioral responses to heat and humidity than by UV availability alone. Chronobiological models of seasonal Vitamin D rhythms require climate-specific parameters.

Evening chronotype is overrepresented in adults with attention-deficit/hyperactivity disorder (ADHD), yet how circadian preference relates to specific symptom dimensions remains unclear. Cognitive Disengagement Syndrome (CDS; formerly Sluggish Cognitive Tempo), characterized by daydreaming, mental fogginess, and hypoarousal, is considered distinct from ADHD despite overlap and may be relevant to associations among chronotype, sleep, and attentional symptoms. This cross-sectional study tested an a priori serial mediation model in 100 treatment-seeking adults with attentional complaints and no prior ADHD diagnosis or pharmacotherapy. Participants completed the Morningness-Eveningness Questionnaire, Pittsburgh Sleep Quality Index, Barkley Adult Sluggish Cognitive Tempo Rating Scale, and Adult ADHD Self-Report Scale (ASRS-v1.1). Eveningness was associated with poorer sleep quality, and poorer sleep quality with higher CDS symptoms. CDS was strongly associated with both inattention and hyperactivity/impulsivity. The serial indirect effects through sleep quality and CDS were significant for both dimensions, whereas simple indirect effects were not. The full models explained 50.0% and 21.3% of the variance in inattention and hyperactivity/impulsivity, respectively. Supplementary analyses localized this effect to the Daydreaming rather than Sluggishness subdimension. Findings were robust to age- and sex-adjustment. These findings suggest sleep quality and CDS are clinically relevant correlates of ADHD symptom dimensions, though longitudinal confirmation is needed.

This study examined the associations among chronotype, sleep quality, and risky health behaviors in early adolescents and explored the independent contribution of chronotype to these outcomes after controlling for sociodemographic covariates. This cross-sectional study enrolled 295 seventh- and eighth-grade students (48.5% female; mean age 13.29 ± 0.63 y) from two public middle schools in Muş, eastern Türkiye. Data were collected using the Morningness-Eveningness Scale for Children (MESC), the Pittsburgh Sleep Quality Index (PSQI), and the Risky Behavior Scale (RBS). Normality was evaluated with the Shapiro-Wilk test and skewness/kurtosis values. Pearson correlation, independent-samples t-test, one-way ANOVA with Bonferroni post-hoc comparisons, hierarchical multiple regression, and Baron-Kenny mediation analysis with 2,000 bootstrap resamples were employed. Most students displayed an intermediate chronotype (61.0%), and 76.6% had poor sleep quality (PSQI > 5). MESC scores were negatively correlated with PSQI (r = -.297, 95% CI [-.398, -.189], p < 0.001) and RBS (r = -.495, 95% CI [-.577, -.404], p < 0.001). After Benjamini-Hochberg FDR correction, MESC independently explained 7.1% additional variance in sleep quality (ΔR2 = .071, p < 0.001) and 18.0% in risky behaviors (ΔR2 = .180, p < 0.001) beyond demographic predictors. Sleep quality partially mediated the chronotype - risky behavior association (indirect β = -.047, 95% CI [-.086, -.014]). Male sex, single-parent family structure, paternal unemployment, and smoking were additional significant risk factors. Chronotype was independently associated with both sleep quality and risky behaviors in early adolescents, with sleep quality functioning as a partial statistical mediator in this relationship. These findings highlight the potential value of chronotype assessment in school health contexts, though longitudinal and intervention studies are needed to confirm these associations and evaluate targeted strategies.

Bed- and risetimes of human ad lib sleep are determined by the endogenous mechanism of sleep-wake regulation. However, humans are capable to volitionally prolong (i.e. without any external influences) the wake phase of their sleep-wake cycle to early night hours. We hypothesized that the conscious behaviors mostly known under the terms "bedtime procrastination" and "mind-bedtime procrastination" can compete with the biological sleep-wake regulator for setting bedtimes on weekdays and/or weekends and thus this behavior can contribute to the delay of sleep relative to the bedtime signal from this regulator. University students (5375 in total) were grouped in accord with their earlier or later weekday and weekend bedtimes. To test the hypothesis, the group-averaged sleep times were calculated and simulated. Near 8% of students reported later weekday than weekend bedtimes. The simulations of their sleep times suggested that these times cannot be explained by a model of sleep-wake regulator without the additional assumption of bedtime delay caused by the volitional missing the bedtime signal from this regulator (i.e. this missing can be a result of such volitional behavior as mind-bedtime procrastination on weekdays rather than on weekends). We concluded that the concept of two conflicting - biological and "social" - "clocks" that was introduced in this journal 20 years ago can be extended to the concept of three conflicting "clocks." Bed- and risetimes on weekdays and weekends can reflect the competition between three - biological, "social," and, additionally, "mental" - "clocks." In accord with the concept of two "conflicting clocks," weekday risetimes can be mostly determined by "social clocks" competing with the biological clocks that can be solely responsible for weekend risetimes. However, weekday and/or weekend bedtimes cannot be always set by the biological clocks. Sometimes, they are determined by the additional conflict of "mental (mind) clocks" with the biological (body) clocks. This conflict can lead to weekday sleep insufficiency and can be, in particular, explained by such kind of conscious behavior as mind-bedtime procrastination.

Depression is a serious mental and psychological disorder, characterized by a high incidence rate, high disability rate and high recurrence rate. It is a major problem that urgently needs to be solved in the field of global public health. Circadian rhythms regulate various physiological and behavioral processes in the human body. Previous studies have shown that there is a close connection between circadian rhythmicity and depression. Factors such as shift work, jet lag, social jet lag, chronotypes, and light at night exposure are all related to the occurrence and development of depression. An in-depth exploration of the neural mechanisms related to circadian rhythms and depression can help us better understand the relationship between the two. At present, non-pharmacological intervention methods based on circadian rhythm regulation, such as light therapy, sleep deprivation and cognitive behavioral therapy for insomnia have demonstrated clinical value in improving depression. Future research can also focus on the in-depth application of wearable devices, explore diverse and precise intervention methods, conduct in-depth longitudinal studies, and use various brain imaging devices to explore neural mechanisms, etc. providing theoretical basis and practical directions for the early prevention, precise diagnosis and personalized treatment of depression.

The phase delay on the sleep-wake cycle resulting from biopsychosocial changes related with adolescence is exacerbated by the level of urbanization. However, early school start times conflict with this delay, leading to several negative consequences. This study aims to compare sleep habits and quality, daytime sleepiness, and attention between adolescents from morning and afternoon shifts across different urbanization levels. A total of 159 Brazilian adolescents from technical high school (15.3 ± 0.8 years old; 101 girls/58 boys) completed the following questionnaires: "Health and Sleep," the Pittsburgh Sleep Quality Index, and the Pediatric Daytime Sleepiness Scale, in addition to a 10-d sleep diary that included the Maldonado Sleepiness Scale. Attention was evaluated by a continuous performance task. Sleep and attention were compared between shifts (Morning: n = 78/Afternoon: n = 81) and degrees of urbanization (High: n = 97/Low: n = 62) using MANCOVA. Independent of urbanization level, morning-shift students woke-up earlier, had a shorter time in bed at night and over a 24-h period (nocturnal sleep + nap), showing higher irregularities in wake-up times, along with higher sleep debt at night and over 24-h, social jetlag, daytime sleepiness, sleepiness upon wake-up time, frequency of naps, and non-spontaneous waking during the week than those in the afternoon shift. However, there were no differences in attention performance. Independent of shift, students from higher urbanization regions showed later bed and wake-up times and a shorter time in bed at night and over 24 h on weekends, and higher sleepiness upon wake-up time on weekdays. Despite longer reaction time in phasic alertness and selective attention, they showed a lower percentage of wrong responses in tonic and phasic alertness, selective attention, and a higher time‑on‑task stability. Thus, early school starting time is a strong modulator for adolescents' sleep-wake cycle regardless of the urbanization level. Further studies are necessary to analyze the relationship between attention and school shift.

Shift work is increasingly common in modern societies but is strongly associated with misalignments of natural circadian rhythms, which may negatively impact dietary behaviour and psychosocial well-being. Chronotype, an individual's natural sleep-wake preference, influences adaptation to shift work and its associated lifestyle challenges. This systematic review aimed to examine the relationship between chronotype on both eating behaviour and psychosocial well-being among shift workers. A systematic search was conducted in accordance with PRISMA 2020 guidelines. Literature searches were performed in Web of Science, Scopus, PubMed, and Cochrane from database inception until April 2026. Eligible studies included research involving adult shift workers reporting on chronotype in relation to eating behaviour and psychosocial aspects. Quality appraisal was performed using the Joanna Briggs Institute (JBI) Critical Appraisal Tools. Twenty-nine studies met the inclusion criteria, comprising primarily nurses and healthcare workers, with additional representation from manufacturing and services sectors. Evening chronotypes consistently exhibited less healthy dietary habits, including irregular meal timing, skipping breakfast, delayed food intake, greater consumption of energy-dense foods, lower fibre intake, and higher alcohol use. Additionally, psychosocial outcomes showed similar patterns, with evening types reported significantly higher levels of depression, anxiety, stress, emotional exhaustion, and burnout compared to morning and intermediate types. Misalignment between chronotype and shift schedule further amplifies these effects, whereas alignment improved job satisfaction and well-being. Sleep disturbances, a contributing factor that can exacerbate psychosocial issues, were observed to be more common in evening types as compared to morning and intermediate types. Evening chronotype is a key vulnerability factor for both unhealthy eating habits and impaired psychosocial well-being among shift workers. Organisational strategies such as chronotype-sensitive scheduling, access to healthier food options, and tailored psychosocial support may mitigate these risks. Future longitudinal and interventional research is needed to establish causal pathways and to evaluate the effectiveness of chronotype-based workplace interventions.

Sleep-wake disturbances commonly occur in Alzheimer's disease (AD). However, the precise mechanisms underlying the breakdown of the circadian gene network remain elusive. This study examined 23 circadian genes in 253 post-mortem samples (80 AD, 173 controls) from the hippocampus, entorhinal cortex, and superior frontal cortex, using three metrics: a Circadian Disruption Index (CDI), a Network Coherence Score (NCS), and a Circadian Entropy Index (CEI). AD brains showed a modest overall shift in circadian gene expression (CDI = 0.101), concentrated mainly in CRY2, PER3, and PER2. The PER3-CRY2 gene pair showed the most significant co-expression alteration of any gene pair examined, a 60.4% reduction in coherence (∆ρ 0.604). Network-wide coherence (NCS) and CEI, averaged across all 23 genes, did not differ significantly between the AD and control groups (NCS: 6.7% reduction, p = 0.356; CEI: -0.4% change, p = 0.923), suggesting the alteration is concentrated in specific gene relationships rather than global network collapse. Regional CDI did not differ significantly across brain areas (p = 0.724). A 10-gene panel classified AD versus control with cross‑validated area under the curve (AUC) = 0.759 ± 0.069 (nested cross-validation AUC = 0.759 ± 0.069, zero optimism bias), though external validation in an independent cohort (GSE5281) did not exceed chance level (AUC = 0.500). These results identify the PER3-CRY2 co-expression change as a specific, reproducible molecular signature of AD and support a validated circadian gene-based classifier, while showing that global circadian network disruption is not a consistent feature of this cohort. The findings identify a localized alteration in circadian gene co-expression in AD brain tissue, with potential implications for future therapeutic targeting of the PER3-CRY2 interaction.