Journal Description
Clocks & Sleep
Clocks & Sleep
is a peer-reviewed, open access journal that investigates a wide range of sleep related topics and is published quarterly online by MDPI. The Australasian Chronobiology Society, Society for Light, Rhythms, and Circadian Health, and Swiss Society of Sleep Research, Sleep Medicine and Chronobiology are affiliated with Clocks & Sleep and their society members receive a discount on the article processing charges.
- Open Access— free for readers, with article processing charges (APC) paid by authors or their institutions.
- High visibility: indexed within Scopus, ESCI (Web of Science), PubMed, PMC, FSTA, and other databases.
- Journal Rank: JCR - Q2 (Clinical Neurology)
- Rapid Publication: manuscripts are peer-reviewed and a first decision is provided to authors approximately 23.2 days after submission; acceptance to publication is undertaken in 4.6 days (median values for papers published in this journal in the first half of 2026).
- Recognition of Reviewers: reviewers who provide timely, thorough peer-review reports receive vouchers entitling them to a discount on the APC of their next publication in any MDPI journal, in appreciation of the work done.
- Journal Cluster of Neurosciences: Brain Sciences, Neurology International, NeuroSci, Clinical and Translational Neuroscience, Neuroimaging, Neuroglia, Psychiatry International, Clocks & Sleep and Journal of Dementia and Alzheimer's Disease.
Impact Factor:
3.2 (2025);
5-Year Impact Factor:
3.0 (2025)
Latest Articles
Mechanisms of Heat-Induced Sleep Disruption in Aging: A Narrative Review
Clocks & Sleep 2026, 8(3), 43; https://doi.org/10.3390/clockssleep8030043 - 8 Jul 2026
Abstract
Rising global temperatures and more frequent heat waves pose a growing threat to public health, particularly among older adults. Age-related declines in thermoregulatory capacity such as reduced sweating, impaired vasodilation, and diminished hypothalamic responsiveness make it more difficult to cope with elevated nighttime
[...] Read more.
Rising global temperatures and more frequent heat waves pose a growing threat to public health, particularly among older adults. Age-related declines in thermoregulatory capacity such as reduced sweating, impaired vasodilation, and diminished hypothalamic responsiveness make it more difficult to cope with elevated nighttime temperatures. These thermal challenges disrupt sleep by prolonging sleep onset, fragmenting slow-wave and REM sleep, and suppressing melatonin secretion. Importantly, sex-related differences in thermoregulatory aging—particularly menopause-associated vasomotor instability in women and testosterone-related autonomic changes in men—further modulate individual vulnerability to heat-induced sleep disruption. Beyond sleep, heat-induced stress affects metabolic, cardiovascular, and immune systems, promoting insulin resistance, endothelial dysfunction, sympathetic overactivation, and chronic inflammation. Socioeconomic disparities, urban heat island exposure, and differential access to cooling infrastructure function as critical environmental modifiers that amplify biological vulnerability, particularly in disadvantaged older populations. This narrative review aims to synthesize current knowledge on the specific thermoregulatory mechanisms of sleep disruption induced by heat stress in older adults. Understanding these interactions is crucial for developing effective interventions, including environmental cooling, circadian-aligned behaviors, and targeted public health strategies, to mitigate the compounded risks of heat exposure and preserve healthy sleep in aging populations. However, many proposed mechanistic pathways are primarily derived from animal models, and controlled human studies specifically targeting heat-exposed older adults remain scarce.
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(This article belongs to the Section Human Basic Research & Neuroimaging)
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Open AccessReview
Sleep–Wake Dysregulation in Human African Trypanosomiasis: From Neuroinvasion to Neuronal Dysfunction
by
Seithikurippu R. Pandi-Perumal, Ahmed S. BaHammam and Konda Mani Saravanan
Clocks & Sleep 2026, 8(3), 42; https://doi.org/10.3390/clockssleep8030042 - 8 Jul 2026
Abstract
Human African trypanosomiasis (HAT) or sleeping sickness is a neglected tropical disease with a progressive central nervous system (CNS) involvement and marked sleep and circadian rhythm abnormalities. Even though this is a prominent feature of HAT, the connection between parasite neuroinvasion, neuroinflammation, circadian
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Human African trypanosomiasis (HAT) or sleeping sickness is a neglected tropical disease with a progressive central nervous system (CNS) involvement and marked sleep and circadian rhythm abnormalities. Even though this is a prominent feature of HAT, the connection between parasite neuroinvasion, neuroinflammation, circadian dysfunction, and neurological impairment is not fully understood. This narrative review aims to summarize the most up-to-date knowledge about sleep and circadian disturbance in HAT and proposes an integrated approach for the Trypanosome-Associated Sleep Disorder (TASD). The relevant literature was identified by searching major biomedical databases for HAT, sleep disorders, circadian rhythms, neuroinflammation, and CNS invasion. The review covers the steps by which the CNS becomes invaded, how the barriers are disrupted, how the CNS becomes activated by inflammatory responses, and how the hypothalamic and circadian regulatory networks are disrupted. The evidence suggests that excessive daytime sleepiness, fragmented nocturnal sleep, circadian misalignment, and neuropsychiatric manifestations are related to the activation of inflammatory cytokines, altered neurotransmitter signaling, activation of the kynurenine pathway, dysregulation of clock genes, and disruption of the suprachiasmatic nucleus. We also discuss TASD as a syndrome-like phenotype of CNS involvement and propose a three-stage model of sleep–wake dysfunction in HAT. The review unites these integral mechanisms in a single mechanistic framework to offer a unified understanding of the sleep pathology associated with HAT. There are still important gaps in our knowledge of biomarkers, disease staging, and irreversible neuronal damage, which indicate priorities for future research and better clinical management.
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(This article belongs to the Section Human Basic Research & Neuroimaging)
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Open AccessArticle
Time-of-Day Variations and Effects of Total Sleep Deprivation on Attention Assessed with the Attentional Demands Task
by
Ilaria Di Pompeo, Martina Marcaccio, Giorgia Capitani, Assunta Pompili, Simone Migliore and Giuseppe Curcio
Clocks & Sleep 2026, 8(3), 41; https://doi.org/10.3390/clockssleep8030041 - 2 Jul 2026
Abstract
Circadian rhythms, sleep homeostasis, and chronotype interact to modulate cognitive processes such as attention and executive functions, leading to fluctuations in performance throughout the day and significant impairments under conditions of misalignment or sleep deprivation. The study was conducted in two phases and
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Circadian rhythms, sleep homeostasis, and chronotype interact to modulate cognitive processes such as attention and executive functions, leading to fluctuations in performance throughout the day and significant impairments under conditions of misalignment or sleep deprivation. The study was conducted in two phases and included the assessment of subjective measures of sleepiness, vigor, affect, sleep quality, and individual chronotype. In the first phase, 32 healthy participants (19 females; mean age = 24.9 ± 3.14) were tested at four different times of the day to examine diurnal variations in attentional performance. In the second phase, a subsample of 8 participants (4 females; mean age = 24.4 ± 2.20) underwent a total sleep-deprivation protocol and completed the AD-Task over two consecutive days to evaluate the impact of prolonged wakefulness on attentional and executive functioning. In the first phase, results revealed a progressive decline in selective attention across the day (F(3.93) = 3.188; p = 0.027; η2p = 0.093) and significantly slower reaction times in divided attention during the morning (F(3.93) = 7.3134; p < 0.001; η2p = 0.191), indicating a time-of-day modulation of attentional resources. In the second phase, total sleep deprivation led to a marked impairment in performance, reflected by slower reaction times (F(11.77) = 1.948; p = 0.046; η2p = 0.218) and reduced discriminative ability (d′; F(11.77) = 13.438; p < 0.001; η2p = 0.657), particularly in task-switching conditions. These findings suggest increased vulnerability of executive functions under sleep deprivation, likely associated with reduced efficiency of prefrontal cortical processes. The results confirm that time of the day and pressure of sleep significantly affect attention and cognitive flexibility and further affirm the validity of the AD-Task as a reliable instrument for detecting these variations under ecologically relevant conditions.
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(This article belongs to the Section Human Basic Research & Neuroimaging)
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Open AccessArticle
Sleep Quality, Not Sleep Duration, Is Independently Associated with Internalized Weight Bias: The Greek Lifestyle and Obesity-Related Bias Survey
by
Athina Tzifopoulou, Despoina Dragataki, Maria G. Grammatikopoulou, Eleni C. Pardali, Maria Dimitriou and Dimitrios Poulimeneas
Clocks & Sleep 2026, 8(3), 40; https://doi.org/10.3390/clockssleep8030040 - 29 Jun 2026
Abstract
Internalized weight bias—the self-directed endorsement of weight-related stereotypes—has emerged as a psychologically potent correlate of health outcomes in individuals with overweight and obesity, yet its relationship with sleep remains largely unexplored. In a cross-sectional manner, 495 Greek adults with a history of overweight/obesity
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Internalized weight bias—the self-directed endorsement of weight-related stereotypes—has emerged as a psychologically potent correlate of health outcomes in individuals with overweight and obesity, yet its relationship with sleep remains largely unexplored. In a cross-sectional manner, 495 Greek adults with a history of overweight/obesity were assessed regarding sleep quality and duration, internalized weight bias (Modified Weight Bias Internalization Scale; WBIS-M), and expressed anti-fat attitudes (Anti-Fat Attitudes Questionnaire, AFA: Dislike, Fear of Fat, Willpower). Insomnia prevalence, assessed with the Athens Insomnia Scale (AIS), was high at 57.6%—nearly doubling across ascending WBIS-M tertiles (39.9% to 73.1%). In hierarchical linear regression models, AIS score remained independently associated with WBIS-M after adjustment for depression, anxiety, BMI, and a comprehensive range of sociodemographic and clinical covariates (B = 0.058; 95% CI: 0.036–0.079; p < 0.001), with the fully adjusted model explaining 58.5% of total variance in WBIS-M. AFA subscales did not remain significant in the model post-full adjustment, and sleep duration failed to show independent association with either bias dimensions. The sleep–weight bias association was therefore specific to the internalized dimension and to sleep quality, rather than quantity. These findings highlight a clinically relevant and dimension-specific link between insomnia symptoms and internalized weight stigma, and suggest that routine sleep assessment may be warranted in individuals with a history of overweight or obesity presenting with elevated internalized weight bias—and vice versa.
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(This article belongs to the Section Human Basic Research & Neuroimaging)
Open AccessArticle
Association of Sleep Patterns and Sleep Quality with Academic Performance Among Female University Students: Insights Supporting SDG 3 (Good Health and Well-Being)
by
Noorah Saleh Al-Sowayan and Lama Essam Aboselmiya
Clocks & Sleep 2026, 8(3), 39; https://doi.org/10.3390/clockssleep8030039 - 29 Jun 2026
Abstract
Background: Sleep quality plays an essential role in cognitive performance, memory consolidation, learning efficiency, and overall wellbeing. University students are particularly vulnerable to sleep disturbances because of academic stress, irregular sleep schedules, and lifestyle-related factors. Poor sleep quality has been associated with impaired
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Background: Sleep quality plays an essential role in cognitive performance, memory consolidation, learning efficiency, and overall wellbeing. University students are particularly vulnerable to sleep disturbances because of academic stress, irregular sleep schedules, and lifestyle-related factors. Poor sleep quality has been associated with impaired academic performance and reduced cognitive functioning. Objective: This study aimed to evaluate the relationship between sleep patterns, sleep quality, and academic performance among female university students. Methods: A cross-sectional study was conducted among 201 female university students at Qassim University, Saudi Arabia. Data were collected using an electronic self-administered questionnaire that included demographic characteristics, sleep-related behaviors, and the Pittsburgh Sleep Quality Index (PSQI). Academic performance was assessed using self-reported Grade Point Average (GPA). Statistical analysis included descriptive statistics, Spearman correlation analysis, one-way ANOVA with Tukey post hoc analysis, Chi-square tests, and multiple linear regression analysis. Results: The mean GPA of the participants was 4.13 ± 0.60 (on a 5-point scale), while the mean PSQI score was 8.81 ± 3.26, indicating generally poor sleep quality. A significant negative correlation was observed between PSQI score and GPA (rho = −0.200, p = 0.0047). Students with good sleep quality demonstrated significantly higher GPA scores compared with students with poor sleep quality (F(2,194) = 6.31, p = 0.0022). Significant associations were also identified between sleep quality and both bedtime (p = 0.0009) and sleep duration category (p = 0.0002). However, after adjustment for other variables, the independent effect of PSQI on GPA was attenuated and did not reach statistical significance (p = 0.138). This discrepancy between the significant bivariate correlation (rho = −0.200, p = 0.005) and the non-significant multivariate result represents the most important finding of this study, suggesting that sleep quality alone does not independently predict GPA when other academic and behavioral factors are considered. Conclusion: Poor sleep quality was highly prevalent among female university students and showed a significant bivariate association with lower academic performance, though this relationship was attenuated in the multivariate model. Promoting healthy sleep behaviors may support student wellbeing and academic functioning, cognitive wellbeing, quality of life, and the advancement of Sustainable Development Goal 3 (Good Health and Well-Being).
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(This article belongs to the Section Human Basic Research & Neuroimaging)
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Open AccessOpinion
Melatonin in Clinical Practice: Grey Zones Between Chronobiology, Insomnia and Consumer Supplementation
by
Alexandros Kalkanis, Aliki Karkala and Athanasia Pataka
Clocks & Sleep 2026, 8(3), 38; https://doi.org/10.3390/clockssleep8030038 - 24 Jun 2026
Abstract
Melatonin occupies a paradoxical position in contemporary sleep medicine: despite its physiological role as a regulator of circadian timing, it is frequently used and perceived as a nonspecific “natural” hypnotic. Although melatonin demonstrates modest benefits for sleep initiation and clearer efficacy in circadian
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Melatonin occupies a paradoxical position in contemporary sleep medicine: despite its physiological role as a regulator of circadian timing, it is frequently used and perceived as a nonspecific “natural” hypnotic. Although melatonin demonstrates modest benefits for sleep initiation and clearer efficacy in circadian rhythm sleep–wake disorders, its clinical use is often undermined by diagnostic imprecision, inappropriate dosing, mistimed administration, inconsistent formulations, and inadequate patient counseling. Circadian disorders can be misclassified as primary insomnia, leading to symptomatic treatment approaches that fail to address the underlying phase misalignment. At the same time, supraphysiological doses and reflexive bedtime administration have become normalized despite evidence that melatonin acts primarily as a chronobiotic whose effects depend more on timing than dose. Regulatory inconsistencies and substantial variability in over-the-counter preparations further complicate safe and reproducible use. These factors contribute to avoidable treatment failure, inaccurate labeling of nonresponse, and persistent misconceptions regarding melatonin’s mechanism of action. Therefore, melatonin should be approached as a pharmacological intervention requiring the same diagnostic rigor, individualized dosing, and longitudinal assessment expected of other sleep therapeutics, particularly when integrated with behavioral and circadian interventions.
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(This article belongs to the Section Disorders)
Open AccessReview
Effects of Heatwaves and Tropical Nights on Sleep in Middle-Aged and Older Adults: A Scoping Review
by
Jelena Krčum, Neriman Ezgin, Nikola Šutulović, Nemanja Rajković, Emilija Djurić, Dušan Mladenović, Milena Vesković, Arif E. Cetin, Aleksandra Rašić-Marković, Olivera Stanojlović and Dragan Hrnčić
Clocks & Sleep 2026, 8(3), 37; https://doi.org/10.3390/clockssleep8030037 - 23 Jun 2026
Abstract
Heatwaves and tropical nights are emerging as significant public health challenges under accelerating climate change, with middle-aged and older adults demonstrating heightened vulnerability. This scoping review maps the existing evidence on how nocturnal heat affects sleep in middle-aged and older adults aged 45
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Heatwaves and tropical nights are emerging as significant public health challenges under accelerating climate change, with middle-aged and older adults demonstrating heightened vulnerability. This scoping review maps the existing evidence on how nocturnal heat affects sleep in middle-aged and older adults aged 45 and above, synthesizing findings from experimental and observational studies published in English over the past decade. A comprehensive search of PubMed and Scopus, supplemented by reference screening, identified 31 relevant studies. Data on study design, population characteristics, heat exposure metrics, sleep outcomes, and interventions were charted and synthesized narratively due to methodological heterogeneity. Across studies, elevated nighttime temperatures consistently reduced total sleep time and sleep efficiency, increased wake after sleep onset, and disrupted sleep architecture, particularly REM and N3 stages. Environmental, behavioral, and physiological interventions such as improved ventilation, targeted cooling strategies, and pre-sleep thermal management partially mitigated heat-related sleep disruption. Overall, the findings highlight gaps in standardized exposure metrics and harmonized sleep assessment, providing guidance for future research and public health strategies aimed at protecting sleep health in middle-aged and aging populations amid increasingly frequent extreme heat events.
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(This article belongs to the Section Human Basic Research & Neuroimaging)
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Open AccessBrief Report
Who Blames the Moon for Poor Sleep? An Exploratory Online Survey
by
Christian Cajochen
Clocks & Sleep 2026, 8(2), 36; https://doi.org/10.3390/clockssleep8020036 - 22 Jun 2026
Abstract
The belief that the moon disturbs sleep is widespread, but the factors associated with it remain poorly understood. I therefore examined how frequently poor sleep is attributed to moon phases, whether this varied across the lunar cycle, and which personal and environmental factors
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The belief that the moon disturbs sleep is widespread, but the factors associated with it remain poorly understood. I therefore examined how frequently poor sleep is attributed to moon phases, whether this varied across the lunar cycle, and which personal and environmental factors were associated with “moon blaming”. Data were derived from an ongoing online survey. At the time of analysis, 1815 participants had completed a 16-item questionnaire assessing sleep quality, sleep duration, sleep timing on workdays and free days, alarm clock use, environmental and personal sleep-disturbing factors, residential setting, age, gender, attention to lunar phases, and whether the moon was perceived as a cause of poor sleep. The primary outcome was endorsement of the moon as a sleep-disturbing factor. Logistic regression with stepwise Akaike information criterion selection was used to identify the strongest predictors of attributing the moon for poor sleep. Questionnaire timing was also examined across the lunar cycle. Among environmental factors, the moon was the most frequently endorsed cause of poor sleep (36%), followed by outdoor temperature (31%), indoor noise (26%), and bad weather (22%). Rumination was the most commonly reported personal factor (73%), but it did not predict moon attribution. Instead, the strongest correlates were weather-related sleep complaints, tracking lunar phases, age, and gender, with endorsement increasing with age and being more common among women. Moon-related complaints also peaked during the week after the full moon. These findings suggest that perceived lunar effects on sleep are shaped, at least in part, by attributional and expectation-related processes.
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(This article belongs to the Section Society)
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Open AccessArticle
Short- and Long-Term Chrono-Immune Consequences of Dim Light at Night Exposure in Male Mice at Different Life Stages
by
Carlos A. Trujillo, Fernando Miranda and José Sarmiento
Clocks & Sleep 2026, 8(2), 35; https://doi.org/10.3390/clockssleep8020035 - 17 Jun 2026
Abstract
The current use of artificial light during the natural dark phase has acquired contaminant dimensions, known as “light pollution”. It is well known that exposure to dim light at night (dLAN) during the postnatal period severely impairs the immune system and related organs,
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The current use of artificial light during the natural dark phase has acquired contaminant dimensions, known as “light pollution”. It is well known that exposure to dim light at night (dLAN) during the postnatal period severely impairs the immune system and related organs, but few reports have demonstrated the effects of dLAN during the fetal period. This study, therefore, examines whether exposure to dim light at night during two critical developmental windows (i.e., prenatal and postnatal periods) leads to long-lasting dysregulation of circadian, behavioral, and immune organization, as well as spleen immune responses, in early adulthood. To address this question, these outcomes were assessed using two defined sampling time points. To answer this question, we exposed two groups of C57BL/6J male mice to dim night light during the gestational and postnatal periods and compared them with control groups that were exposed to light–dark conditions (12 h each, LD). Parametric and non-parametric activity/rest values were analyzed with circular statistics. Compared to their controls, we found differences in alpha, onset, offset, M10, and L5 start time in dLAN groups. We also assessed the transcript levels of clock genes and inflammatory mediators in spleen tissue and found a dampening of daily variation in mRNA expression in both experimental groups. Finally, we used an ovalbumin (OVA) allergy challenge to test the B-cell response in the spleen and found a significantly higher cell recruitment to the spleen and more anti-OVA IgE. Together, these results clearly show that dLAN, at two ZT sampling points, affects peripheral molecular clocks and responses in the spleen, and that these effects are independent of the life stage at which exposure to dim light at night occurs.
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(This article belongs to the Section Impact of Light & other Zeitgebers)
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Open AccessArticle
Sleep Quality and Its Sociodemographic, Behavioural, Clinical, and Regional Correlates Among Adults in Kazakhstan: A National Cross-Sectional Survey
by
Yerlan Ismoldayev, Anel Ibrayeva, Alfiya Shamsutdinova, Marat Shoranov, Bolat Sadykov, Altynay Sadykova, Timur Saliev, Shynar Tanabayeva and Ildar Fakhradiyev
Clocks & Sleep 2026, 8(2), 34; https://doi.org/10.3390/clockssleep8020034 - 12 Jun 2026
Abstract
Population-based evidence on sleep quality in Kazakhstan remains limited. This study describes sleep quality as a multidimensional construct among adults in Kazakhstan using data collected during the first national survey wave after the adoption of a single national time zone. The survey was
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Population-based evidence on sleep quality in Kazakhstan remains limited. This study describes sleep quality as a multidimensional construct among adults in Kazakhstan using data collected during the first national survey wave after the adoption of a single national time zone. The survey was designed as a national post-transition baseline assessment and not as an evaluation of the causal impact of the time-zone reform. Associations with socio-demographic, behavioural, clinical, and regional factors were examined. We conducted a nationally representative cross-sectional survey of adults aged 18–69 years in Kazakhstan from May to October 2025 using a multistage stratified cluster design. Sleep quality was assessed with the Pittsburgh Sleep Quality Index (PSQI). Poor sleep quality was defined as a global PSQI score > 5. Complete PSQI data were available for 5872 participants. Descriptive analyses examined the global PSQI score and the seven component scores. Survey-weighted multivariable logistic regression was used to identify factors independently associated with poor sleep quality. The weighted prevalence of poor sleep quality was 28.1%, and the weighted mean global PSQI score was 4.43. The greatest component burden was attributable to sleep latency (mean 0.87), subjective sleep quality (0.82), and sleep disturbances (0.80), whereas use of sleep medication contributed minimally (0.11). Poor sleep quality was more common among women, older adults, urban residents, and participants with diabetes, current smoking, heavy episodic drinking, and depressive symptoms. In the adjusted model, female sex (aOR 1.37, 95% CI 1.19–1.57), age 55 years or older versus 18–24 years (1.98, 1.53–2.55), diabetes (1.47, 1.22–1.78), current smoking (1.28, 1.10–1.50), heavy episodic drinking (1.43, 1.16–1.76), and depressive symptoms (4.26, 3.52–5.15) were independently associated with higher odds of poor sleep quality. Rural residence was inversely associated with the outcome (0.71, 0.61–0.84). Compared with the North, higher odds were observed in the Central region (2.00, 1.46–2.74), East (1.94, 1.48–2.53), West (1.48, 1.17–1.88), and Almaty city (2.18, 1.72–2.76). Poor sleep quality is common among adults in Kazakhstan and is characterized primarily by difficulties with sleep initiation, perceived sleep quality, and nocturnal disturbances. The findings provide national post-transition baseline evidence and suggest that sleep health surveillance in Kazakhstan should prioritize demographic, mental health, behavioural, and regional inequalities while avoiding causal interpretation of the time-zone reform itself.
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(This article belongs to the Section Human Basic Research & Neuroimaging)
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Open AccessArticle
Hyperuricemia as a Biomarker for Circadian Syndrome: A Cross-Sectional Study
by
Joud AlBashtawi, Hana Zeidan, Abdulrahman Al-Tairi, Najlaa Al-Marri, Mohammed Abdel Hamid, Reem Odaiba, Shaikha Al-Kurbi, Ramez Jaradat, Susu M. Zughaier and Habib H. Farooqui
Clocks & Sleep 2026, 8(2), 33; https://doi.org/10.3390/clockssleep8020033 - 4 Jun 2026
Abstract
Circadian Syndrome (CircS) links metabolic, behavioral, and mental health challenges to disrupted circadian rhythm. Hyperuricemia (HUA) is associated with cardiometabolic disorders; however, its connection to CircS remains incompletely understood. This study aims to determine if HUA can serve as a biomarker for CircS.
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Circadian Syndrome (CircS) links metabolic, behavioral, and mental health challenges to disrupted circadian rhythm. Hyperuricemia (HUA) is associated with cardiometabolic disorders; however, its connection to CircS remains incompletely understood. This study aims to determine if HUA can serve as a biomarker for CircS. We analyzed the National Health and Nutrition Examination Survey (NHANES) data (2005–2020) from 27,410 adults. CircS was defined as the presence of at least five out of eight components, encompassing the traditional metabolic syndrome criteria plus three additional factors: short sleep duration, depression, and non-alcoholic fatty liver disease (NAFLD). HUA was set at serum uric acid levels >6 mg/dL (357 µmol/L) for females and >7 mg/dL (416 µmol/L) for males. Multivariable logistic regression identified predictors of CircS, and dose–response relationships were explored. Of 27,410 participants, 2076 (7.57%) had CircS. HUA was found to be the strongest independent predictor of CircS, with an odds ratio (OR) of 3.26 (95% uncertainty interval (UI) 2.80–3.80, p < 0.001). Other important risk factors included chronic kidney disease (CKD) (OR 2.80), female sex (OR 1.44), and smoking (OR 1.29). In addition, older age, lower educational level, and lower income were also linked with higher risk. Higher uric acid levels were consistently linked to metabolic components of CircS more strongly than to depression and short sleep. In conclusion, HUA is linked with a greater risk of CircS. Although testing is simple and widely available, it could be used for early risk detection. Future studies should determine if lowering uric acid improves circadian health.
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(This article belongs to the Section Disorders)
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Open AccessSystematic Review
Circadian Regulation and Pain: A Systematic Review of the Association Between Rest–Activity Rhythm and Pain-Related Outcomes
by
Aline Van Stallen, Manon De deyne, Céline Labie and Liesbet De Baets
Clocks & Sleep 2026, 8(2), 32; https://doi.org/10.3390/clockssleep8020032 - 28 May 2026
Abstract
The rest–activity rhythm (RAR) is a key marker of circadian regulation and is commonly assessed using actigraphy. Emerging evidence suggests that characteristics of RAR, such as amplitude, stability, and regularity, may be associated with pain-related outcomes. However, no systematic review has yet synthesized
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The rest–activity rhythm (RAR) is a key marker of circadian regulation and is commonly assessed using actigraphy. Emerging evidence suggests that characteristics of RAR, such as amplitude, stability, and regularity, may be associated with pain-related outcomes. However, no systematic review has yet synthesized this evidence across populations and pain conditions. This systematic review aimed to provide an overview of current approaches to measuring and defining RAR and to examine its associations with pain outcomes in both healthy individuals and clinical populations experiencing acute or chronic pain. A systematic search of PubMed, Web of Science, Scopus, and Embase was conducted, with the final search completed on 20 May 2025. Observational studies reporting associations between at least one RAR characteristic and a pain outcome were eligible. Article selection and risk-of-bias assessment using the ROBINS-E tool were performed independently by two reviewers, and findings were synthesized narratively. Seven cross-sectional studies were included, employing diverse analytic methods such as cosinor and non-parametric analyses. Overall, the findings were heterogeneous, suggesting that associations between RAR and pain vary according to the RAR metric used, the analytical approach, and the population studied. Nevertheless, the evidence generally indicates that more robust and well-consolidated circadian rhythms are associated with lower pain, whereas regularity and timing appear to play more context-dependent roles, highlighting the potential relevance of RAR metrics as modifiable targets and the need for standardized measurement approaches.
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(This article belongs to the Section Human Basic Research & Neuroimaging)
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Open AccessArticle
Efficacy and Safety of Sustained-Release Melatonin Capsules (2 mg) in Healthy Adults with Poor Sleep Quality: A Randomized, Double-Blind, Placebo-Controlled Trial
by
Shefali Thanawala, Rajat Shah, Alphy Lopes, Milind Kulkarni, Bharat Jain and Niranjan Andhalkar
Clocks & Sleep 2026, 8(2), 31; https://doi.org/10.3390/clockssleep8020031 - 27 May 2026
Abstract
Sleep disturbances and poor sleep quality are growing public health concerns, adversely affecting both physical and mental health. While exogenous melatonin supplements are used to manage the condition, there is limited evidence available on the efficacy of sustained-release (SR) melatonin formulations. This multicenter,
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Sleep disturbances and poor sleep quality are growing public health concerns, adversely affecting both physical and mental health. While exogenous melatonin supplements are used to manage the condition, there is limited evidence available on the efficacy of sustained-release (SR) melatonin formulations. This multicenter, randomized, double-blind, placebo-controlled clinical trial evaluated the efficacy and safety of melatonin-SR capsules (2 mg) in healthy adults with poor sleep quality. Participants aged 30–60 years with poor sleep quality received melatonin-SR (2 mg) or a placebo capsule at night for 28 days. Changes from baseline to day 28 in polysomnography (PSG)-derived sleep parameters, Pittsburgh Sleep Quality Index (PSQI), WHO-5 Well-Being Index, sleep diary parameters, and safety profile were evaluated. Of 62 enrolled participants, 59 (melatonin-SR, n = 28; placebo, n = 31) completed the study. Compared with placebo, melatonin-SR supplementation resulted in significant improvements at day 28 in PSG-derived sleep efficiency (change from baseline: 3.49 for melatonin-SR vs. −6.30% for placebo; p = 0.001) and total sleep time (change from baseline: 23.83 for melatonin-SR vs. −39.25 min for placebo; p = 0.001), along with significant reductions in sleep onset latency (change from baseline: −10.28 for melatonin-SR vs. 16.70 min for placebo; p = 0.031) and wake after sleep onset (change from baseline: −14.92 for melatonin-SR vs. 24.71 min for placebo; p = 0.001). Melatonin-SR supplementation demonstrated a large treatment effect for the improvement in sleep efficiency compared with placebo (Cohen’s d = 0.9). A significant reduction in PSQI global scores was observed in the melatonin-SR group from day 07 onwards (change from baseline on day 07: −2.21 vs. −0.23; day 14: −4.86 vs. −0.65; and day 28: −5.61 vs. −0.65 for melatonin-SR and placebo, respectively; p = 0.001). Improvement in subjective psychological well-being was significant from day 14 onwards (change from baseline on day 14: 9.86 vs. 0.77; and day 28: 13.29 vs. 0.77 for melatonin-SR and placebo, respectively; p = 0.001). A significant improvement in subjective sleep parameters at day 28 (p < 0.05) was observed. Reported adverse events in both groups were mild and transient in nature. Supplementation with melatonin-SR 2 mg capsule at night for 28 days was found to be effective and safe in improving objective and subjective sleep quality outcomes and overall well-being in the trial population.
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(This article belongs to the Section Human Basic Research & Neuroimaging)
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Open AccessArticle
Temporal Dynamics of Sleep During Bright-Light Therapy for Depression and Their Relation to Symptom Improvement
by
Emma Visser, Niki Antypa, Machteld C. Marcelis, Claudia J. P. Simons and Yvonne A. W. de Kort
Clocks & Sleep 2026, 8(2), 30; https://doi.org/10.3390/clockssleep8020030 - 26 May 2026
Abstract
Sleep disturbance is a central feature of depression and a proposed pathway through which Bright-Light Therapy (BLT) exerts antidepressant effects. However, little is known about how sleep reorganises day by day during BLT or whether these dynamics relate to symptom improvement. We analysed
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Sleep disturbance is a central feature of depression and a proposed pathway through which Bright-Light Therapy (BLT) exerts antidepressant effects. However, little is known about how sleep reorganises day by day during BLT or whether these dynamics relate to symptom improvement. We analysed daily sleep diaries from 66 patients with depression undergoing three weeks of BLT in routine outpatient care. Generalised Additive Mixed Models characterised daily trajectories in sleep timing, continuity, duration, and Subjective Sleep Quality, and weekly changes in sleep regularity were assessed using Root Mean Square of the Successive Differences. Structural Equation Modelling examined whether within-person deviations in sleep parameters mediated changes in depressive symptoms. Sleep timing showed gradual adjustment across treatment, with a progressive 48 min advance in weekday sleep onset. Sleep regularity improved from Week 1 to Week 2 before partially reversing, and the probability of nocturnal awakenings followed a non-linear trajectory. Other sleep parameters showed weaker directional trends. Improvements in Subjective Sleep Quality accounted for a modest portion of the association between treatment progression and reductions in depressive symptoms, whereas changes in sleep timing and regularity were not associated with symptom change. These findings indicate that sleep reorganises gradually during outpatient BLT, with different sleep dimensions evolving on distinct timescales and Subjective Sleep Quality emerging as one observable component linked to symptom improvement. More broadly, the results highlight the value of day-to-day modelling for understanding sleep–mood dynamics during real-world chronotherapy.
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(This article belongs to the Section Impact of Light & other Zeitgebers)
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Open AccessArticle
Influences of Diurnal Rhythms on Gut Microbiota and Clock Gene Expression in Procambarus clarkii
by
Lin Feng, Zhengyan Zhou, Yubo Ma, Yingying Zhao, Hua Wei and Xiaochen Zhu
Clocks & Sleep 2026, 8(2), 29; https://doi.org/10.3390/clockssleep8020029 - 25 May 2026
Abstract
This study investigated the diurnal dynamics of the gut microbiota and core clock gene expression in the red swamp crayfish, Procambarus clarkii. Samples were collected at four time points (06:00, 12:00, 18:00, and 24:00) over a 24 h period. Gut microbiota characteristics
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This study investigated the diurnal dynamics of the gut microbiota and core clock gene expression in the red swamp crayfish, Procambarus clarkii. Samples were collected at four time points (06:00, 12:00, 18:00, and 24:00) over a 24 h period. Gut microbiota characteristics were analyzed using 16S rRNA gene sequencing, while quantitative real-time polymerase chain reaction (qPCR) was used to examine the expression patterns of core clock genes, including Cycle (Cyc), Clock (Clk), and cryptochrome type 1 (Cry1), in the hepatopancreas and eyestalk. The results showed that Kruskal–Wallis tests for α-diversity indices (Shannon, Simpson, ACE, Chao1) and PERMANOVA for β-diversity (Bray–Curtis) of the gut microbiota revealed no significant diurnal variation across the four time points (all p > 0.05). Firmicutes, Proteobacteria, and Bacteroidota were the dominant phyla, with norank_o_RsaHf231, ZOR0006, and Bacteroides as the predominant genera. Although the overall microbial structure remained stable, several taxa, including unclassified_c_Bacilli, unclassified_f_Caulobacteraceae, Gemmobacter, unclassified_f_Rhodobacteraceae, Allorhizobium–Neorhizobium–Pararhizobium–Rhizobium, Lactobacillus, and unclassified_f_Vibrionaceae exhibited time-dependent fluctuations. In addition, the relative mRNA expression levels of Cyc, Clk, and Cry1 in the hepatopancreas and eyestalk showed significant diurnal variation. This study reveals the diurnal dynamic characteristics of the gut microbiota and core clock gene expression in P. clarkii, providing a foundation for further investigation of diurnal regulatory mechanisms and physiological adaptations.
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(This article belongs to the Special Issue Circadian Rhythm Research in Aquatic Animals)
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Open AccessReview
Obstructive Sleep Apneas and Cardiovascular Diseases
by
Vincenzo Castiglione, Paolo Morfino, Iacopo Fabiani, Francesco Gentile, Edoardo Airò, Benedetta Volpi, Daniela Cardinale, Claudio Passino, Alberto Giannoni and Michele Emdin
Clocks & Sleep 2026, 8(2), 28; https://doi.org/10.3390/clockssleep8020028 - 21 May 2026
Abstract
Obstructive sleep apnea (OSA) is a sleep-disordered breathing condition characterized by recurrent upper-airway obstruction, leading to intermittent hypoxemia, sleep fragmentation, and sympathetic activation. OSA is highly prevalent in patients with cardiovascular diseases and is strongly associated with hypertension, atrial fibrillation, coronary artery disease,
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Obstructive sleep apnea (OSA) is a sleep-disordered breathing condition characterized by recurrent upper-airway obstruction, leading to intermittent hypoxemia, sleep fragmentation, and sympathetic activation. OSA is highly prevalent in patients with cardiovascular diseases and is strongly associated with hypertension, atrial fibrillation, coronary artery disease, heart failure, and adverse prognosis. This review summarizes current evidence on the pathophysiology of OSA, its cardiovascular consequences, and available diagnostic and therapeutic strategies, with particular attention to clinical implications in cardiology practice. We discuss established treatments such as lifestyle interventions, continuous positive airway pressure, mandibular advancement devices, and selected surgical options, as well as emerging therapies, including pharmacological approaches targeting weight loss and ventilatory control. While OSA treatment improves symptoms and quality of life, evidence for cardiovascular event reduction remains heterogeneous and appears strongly influenced by patient selection and treatment adherence. Identifying patients most likely to benefit from targeted OSA management remains a key challenge.
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(This article belongs to the Special Issue Emerging Trends in Obstructive Sleep Apnea)
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Open AccessReview
Obstructive Sleep Apnea in Critically Ill Patients: A Structured Narrative Review of Prevalence, Diagnostic Barriers, and Clinical Implications in the ICU
by
Christine Gharib, Catherine Kim, Jun Ling and Madhu Varma
Clocks & Sleep 2026, 8(2), 27; https://doi.org/10.3390/clockssleep8020027 - 20 May 2026
Abstract
Obstructive sleep apnea (OSA) is a highly prevalent yet frequently underdiagnosed condition that is associated with significant cardiopulmonary, metabolic, and neurocognitive outcomes. Risk factors for OSA overlap with illnesses commonly observed in intensive care unit (ICU) patients, resulting in a disproportionately elevated burden
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Obstructive sleep apnea (OSA) is a highly prevalent yet frequently underdiagnosed condition that is associated with significant cardiopulmonary, metabolic, and neurocognitive outcomes. Risk factors for OSA overlap with illnesses commonly observed in intensive care unit (ICU) patients, resulting in a disproportionately elevated burden on healthcare. This structured narrative review synthesizes current evidence regarding the prevalence, diagnostic challenges, and clinical implications of obstructive sleep apnea (OSA) in critically ill adults admitted to intensive care units (ICUs) using PubMed, EMBASE, and Scopus. Key search terms included “obstructive sleep apnea,” “ICU,” and “critical illness.” Results showed that OSA is present in up to 60–70% of ICU patients, yet only ~5% are formally diagnosed during hospitalization. Underdiagnosis is linked to prolonged mechanical ventilation, extubation failure rates as high as 30%, 2-fold higher perioperative complication rates, cardiovascular instability, 1.8-fold greater 30-day ICU readmission rates, and 2.2-fold mortality. Standard screening tools have limited applicability in ICU patients. Emerging alternatives, such as overnight oximetry, polygraphy, and machine learning models lack validation. Our analyses reveal that current diagnostic and treatment strategies are poorly adapted to critically ill patients. Integration of OSA as a part of ICU management, diagnosis, and intervention may reduce readmissions and mortality.
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(This article belongs to the Special Issue Emerging Trends in Obstructive Sleep Apnea)
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Open AccessArticle
Association of Healthy Lifestyle with Insomnia Among Chinese Older Adults: A Cross-Sectional Study
by
Lu Liu, Wen Zhou, Yu Luo, Yueyi Zhang, Dongxi Wang, Ming Chen, Zhiming Wang and Yan Zeng
Clocks & Sleep 2026, 8(2), 26; https://doi.org/10.3390/clockssleep8020026 - 9 May 2026
Abstract
Insomnia is common among older adults and is associated with adverse health outcomes, yet evidence on its relationship with healthy lifestyle in Chinese older adults is limited. This study included 4929 participants from the Hubei Memory and Aging Cohort Study (HMACS). A healthy
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Insomnia is common among older adults and is associated with adverse health outcomes, yet evidence on its relationship with healthy lifestyle in Chinese older adults is limited. This study included 4929 participants from the Hubei Memory and Aging Cohort Study (HMACS). A healthy lifestyle score (range 0–6) was constructed based on body weight, drinking alcohol, smoking, regular exercise, diet, and cognitive activity. Participants were categorized into unfavorable (0–2), average (3), and favorable (4–6) lifestyle groups. Insomnia was defined using the Athens Insomnia Scale (AIS ≥ 6), or the Pittsburgh Sleep Quality Index (PSQI > 5). Multivariable logistic regression models were applied to assess the associations of overall and individual healthy behaviors with insomnia risk. Stratified analyses by smoking status and substitution analyses were conducted. Healthier lifestyle was associated with lower risk of insomnia. Compared with the unfavorable group, participants with favorable lifestyle had a 17.5% lower risk of insomnia. Among individual lifestyle behaviors, healthy diet and active cognitive activity were associated with reduced insomnia risk. Stratified analyses showed these associations were only evident among non-current smokers. Substitution analyses suggested that replacing unhealthy behaviors with healthy ones was associated with a lower insomnia risk. Favorable lifestyle, particularly healthy diet and active cognitive activity, is associated with lower insomnia risk among older adults, with stronger associations observed among non-current smokers.
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(This article belongs to the Section Disorders)
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Open AccessCommunication
Pet Co-Sleeping and Well-Being: Evidence from Two Cross-Sectional Online Surveys of Youths and Adults
by
Kaori Endo, Keiichi Shimatani and Norimichi Suzuki
Clocks & Sleep 2026, 8(2), 25; https://doi.org/10.3390/clockssleep8020025 - 7 May 2026
Abstract
While the health benefits of pet ownership are well-documented, research on co-sleeping with pets has yielded conflicting results, often contrasting objective sleep disturbances with subjective satisfaction. This study examined the association between dog or cat co-sleeping and well-being across two age groups: adults
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While the health benefits of pet ownership are well-documented, research on co-sleeping with pets has yielded conflicting results, often contrasting objective sleep disturbances with subjective satisfaction. This study examined the association between dog or cat co-sleeping and well-being across two age groups: adults and youths. Data were collected through two cross-sectional online surveys involving adults (n = 2675) and youths (n = 1050). Participants reported their pet ownership, co-sleeping status, and well-being using the five-item World Health Organization Well-being Index (WHO-5). Analysis of covariance (ANCOVA) was used to compare WHO-5 scores among three groups: non-owners, owners who do not co-sleep, and co-sleepers. In adults, dog co-sleepers exhibited significantly higher well-being scores compared to non-owners (p = 0.025). However, no significant associations were observed in the youth sample. These findings suggest that while pet co-sleeping is often perceived as disruptive, it may be positively associated with subjective well-being in adult populations. Further longitudinal research is needed to clarify the causal relationship and the specific mechanisms underlying this “pet effect” in the context of shared sleep environments.
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(This article belongs to the Section Human Basic Research & Neuroimaging)
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Sleep Hygiene and Symptom Burden in Multiple Sclerosis: A Cross-Sectional Study
by
Michalina Rzepka, Aleksandra Buczek, Tomasz Chmiela, Weronika Galus, Joanna Siuda and Ewa Krzystanek
Clocks & Sleep 2026, 8(2), 24; https://doi.org/10.3390/clockssleep8020024 - 30 Apr 2026
Abstract
Sleep disturbances are common in multiple sclerosis (MS) and contribute to increased symptom burden. Behavioral sleep hygiene practices are potentially modifiable factors influencing sleep and related symptoms, yet their role in MS remains insufficiently explored. This cross-sectional study comprised 175 MS patients. Sleep
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Sleep disturbances are common in multiple sclerosis (MS) and contribute to increased symptom burden. Behavioral sleep hygiene practices are potentially modifiable factors influencing sleep and related symptoms, yet their role in MS remains insufficiently explored. This cross-sectional study comprised 175 MS patients. Sleep hygiene was assessed using a behavioral checklist covering a regular sleep schedule, avoidance of daytime naps, limitation of evening caffeine intake, reduced evening screen exposure, and optimization of the sleep environment. The instruments included the Fatigue Severity Scale (FSS), the Modified Fatigue Impact Scale (MFIS), the Athens Insomnia Scale (AIS), the Epworth Sleepiness Scale (ESS), and the Hospital Anxiety and Depression Scale (HADS). Higher sleep hygiene adherence was associated with lower daytime sleepiness (ESS: r = −0.18, p = 0.020), anxiety (HADS-A: r = −0.16, p = 0.034), and depression (HADS-D: r = −0.15, p = 0.047). Patients with higher adherence (score ≥ 3) demonstrated significantly lower MFIS, AIS, ESS, and HADS-D scores compared with those with lower adherence (all p < 0.05). Multivariate regression showed that sleep hygiene adherence was independently associated with lower MFIS (β = −3.24, 95% CI: −6.06 to −0.41, p = 0.025), ESS (β = −0.85, 95% CI: −6.06 to −0.41, p = 0.016), HADS-A (β = −0.67, 95% CI: −1.23 to −0.11, p = 0.019), and HADS-D scores (β = −0.62, 95% CI: −1.17; −0.08, p = 0.026). Better adherence to sleep hygiene practices may be associated with a lower symptom burden in MS.
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(This article belongs to the Section Human Basic Research & Neuroimaging)
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