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1.  "Sleepiness" is serious in adolescence: Two surveys of 3235 Canadian students 
BMC Public Health  2006;6:116.
Evidence is growing that sleep problems in adolescents are significant impediments to learning and negatively affect behaviour, attainment of social competence and quality of life. The objectives of the study were to determine the level of sleepiness among students in high school, to identify factors to explain it, and to determine the association between sleepiness and performance in both academic and extracurricular activities
A cross-sectional survey of 2201 high school students in the Hamilton Wentworth District School Board and the Near North District School Board in Ontario was conducted in 1998/9. A similar survey was done three years later involving 1034 students in the Grand Erie District School Board in the same Province. The Epworth Sleepiness Scale (ESS) was used to measure sleepiness and we also assessed the reliability of this tool for this population. Descriptive analysis of the cohort and information on various measures of performance and demographic data were included. Regression analysis, using the generalised estimating equation (GEE), was utilized to investigate factors associated with risk of sleepiness (ESS>10).
Seventy per cent of the students had less than 8.5 hours weeknight sleep. Bedtime habits such as a consistent bedtime routine, staying up late or drinking caffeinated beverages before bed were statistically significantly associated with ESS, as were weeknight sleep quantity and gender. As ESS increased there was an increase in the proportion of students who felt their grades had dropped because of sleepiness, were late for school, were often extremely sleepy at school, and were involved in fewer extracurricular activities. These performance measures were statistically significantly associated with ESS. Twenty-three percent of the students felt their grades had dropped because of sleepiness. Most students (58–68%) reported that they were "really sleepy" between 8 and 10 A.M.
Sleep deprivation and excessive daytime sleepiness were common in two samples of Ontario high school students and were associated with a decrease in academic achievement and extracurricular activity. There is a need to increase awareness of this problem in the education and health communities and to translate knowledge already available to strategies to address it.
PMCID: PMC1464124  PMID: 16670019
2.  Sleep complaints and daytime sleepiness among pharmaceutical students in Tripoli 
The Libyan Journal of Medicine  2012;7:10.3402/ljm.v7i0.18930.
The effect of sleep difficulties has achieved a great deal of attention recently, with university students considered as a homogenized population, particularly affected by sleep habits.
The objective of this study was to investigate whether Libyan college students experience sleep disturbance during their academic programmes.
A cross-sectional survey was conducted in the college of Pharmacy, Tripoli University, during February 2010. A total of 201 students, including 179 females (89.05%) and 22 males (10.95%), were recruited from different academic levels. Data were collected using a structured questionnaire and included a number of life-style variables. Epworth Sleepiness Scale (ESS) was used for the assessment of daytime sleepiness.
This study showed that the total sleep time (TST) on a weeknight was 6.40 h and 67 students reported napping during daytime. The TST plus naps totalled 7.39 h. Out of eight possible dozing situations, we found that the mean score for ESS was 8.78. In addition, 79 students showed an ESS score of >10. Furthermore, our results showed that the majority of students (>92%) reported poor sleep satisfaction with quality and duration of sleep hours. Thinking about difficulty of study but not increasing education programs or tea/coffee consumption is associated with sleep difficulties reported. Moreover, 77.6% of students reported an irregular sleep–wake schedule.
These findings indicate that students experienced excessive daytime sleepiness. The TST of pharmaceutical students in Libya, as in other developing countries, is less than those reported by Western students. Students experienced various environmental demands during their college years and, their quality of sleep was negatively affected.
PMCID: PMC3485400  PMID: 23118811
college students; sleep habits; sleep disorders; Epworth Sleepiness Scale
3.  Circadian Preference and Sleep-Wake Regularity: Associations With Self-Report Sleep Parameters in Daytime-Working Adults 
Chronobiology international  2011;28(9):802-809.
The aim of this study was to explore how interindividual differences in circadian type (morningness) and sleep timing regularity might be related to subjective sleep quality and quantity. Self-report circadian phase preference, sleep timing, sleep quality, and sleep duration were assessed in a sample of 62 day-working adults (33.9% male, age 23–48 yrs). The Pittsburgh Sleep Quality Index (PSQI) measured subjective sleep quality and the Sleep Timing Questionnaire (STQ) assessed habitual sleep latency and minutes awake after sleep onset. The duration, timing, and stability of sleep were assessed using the STQ separately for work-week nights (Sunday–Thursday) and for weekend nights (Friday and Saturday). Morningness-eveningness was assessed using the Composite Scale of Morningness (CSM). Daytime sleepiness was measured using the Epworth Sleepiness Scale (ESS). A morning-type orientation was associated with longer weekly sleep duration, better subjective sleep quality, and shorter sleep-onset latency. Stable weekday rise-time correlated with better self-reported sleep quality and shorter sleep-onset latency. A more regular weekend bedtime was associated with a shorter sleep latency. A more stable weekend rise-time was related to longer weekday sleep duration and lower daytime sleepiness. Increased overall regularity in rise-time was associated with better subjective sleep quality, shorter sleep-onset latency, and higher weekday sleep efficiency. Finally, a morning orientation was related to increased regularity in both bedtimes and rise-times. In conclusion, in daytime workers, a morning-type orientation and more stable sleep timing are associated with better subjective sleep quality.
PMCID: PMC4143130  PMID: 22080786
Chronotype; Human; Regularity; Sleep
4.  Associations of Executive Function with Sleepiness and Sleep Duration in Adolescents 
Pediatrics  2009;123(4):e701-e707.
Sleep deprivation and sleepiness are associated with poorer school performance, impaired neurobehavioral functioning and behavioral problems.
To determine whether adolescents with high levels of sleepiness or short sleep duration have impaired executive functioning.
Design, Setting, and Participants
Cross-sectional analysis of data from 236 healthy adolescents in a community-based cohort study. Sleepiness was measured using a modified version of the Epworth Sleepiness Scale (ESS). Participants underwent 5–7 day wrist actigraphy at home prior to overnight polysomnography. Exposure variables were excessive sleepiness (ESS ≥ 11) and weekday mean sleep duration.
Main Outcome Measures
The Global Executive Composite (GEC) scale from the Behavior Rating Inventory of Executive Function (BRIEF) and the Tower Test – Total Achievement score from the Delis-Kaplan Executive Functioning System (D-KEFS).
Participants (n=236) were 13.7 ± 0.8 years, 52.1% were male. Mean weekday sleep duration was 7.70 ± 1.03 hours; 11% slept < 6.5 hrs on average on weekdays and 26% reported excessive sleepiness. In unadjusted analyses, sleepy adolescents had poorer executive functioning on the BRIEF GEC (5.30 ± 1.67, p=0.002) and D-KEFS Tower Test Total Achievement (−1.11 ± 0.46, p=0.02). Analyses adjusted for potential confounders resulted in a modest attenuation of the association with the BRIEF and a larger attenuation for the D-KEFS. Caregiver education modified the association between sleepiness and the BRIEF outcomes; Among sleepy adolescents, those with less educated caregivers had greater impairment on the BRIEF-GEC. Sleep duration was not significantly associated with executive functioning outcomes.
Decrements in selected executive function scales are associated with subjective sleepiness, but not sleep duration, in adolescents. The association between sleepiness and executive functioning is strongest among adolescents with primary caregivers who have lower levels of education, suggesting an increased susceptibility. Pediatricians and public health officials should consider sleepiness as a potentially important contributor to adolescent functioning.
PMCID: PMC4430079  PMID: 19336360
Sleep; Adolescent; Sleepiness; Cognition
5.  Sleep patterns and habits in high school students in Iran 
Sleep patterns and habits in high school students in Iran have not been well studied to date. This paper aims to re-address this balance and analyse sleep patterns and habits in Iranian children of high school age.
The subjects were 1,420 high school students randomly selected by stratified cluster sampling. This was a self-report study using a questionnaire which included items about usual sleep/wake behaviours over the previous month, such as sleep schedule, falling asleep in class, difficulty falling asleep, tiredness or sleepiness during the day, difficulty getting up in the morning, nightmares, and taking sleeping pills.
The mean duration of night sleep was 7.7 h, with no difference between girls, boys, and school year (grade). The mean time of waking in the morning was not different between genders. About 9.9% of the girls and 4.6% of the boys perceived their quality of sleep as being bad, and 58% of them reported sleepiness during the day. About 4.2% of the subjects had used medication to enhance sleep. The time of going to bed was associated with grade level and gender. Sleep latency was not associated with gender and grade leve, l and 1.4% experienced bruxism more than four times a week.
Our results are in contrast with that of previous studies that concluded sleep duration is shorter in Asia than in Europe, that boys woke-up significantly later than girls, and that the frequency of sleep latency category was associated with gender and grade level. The magnitude of the daytime sleepiness, daytime sleepiness during classes, sleep latency, and incidences of waking up at night represent major public health concerns for Iran.
PMCID: PMC2292723  PMID: 18339201
6.  Effects of an irregular bedtime schedule on sleep quality, daytime sleepiness, and fatigue among university students in Taiwan 
BMC Public Health  2009;9:248.
An irregular bedtime schedule is a prevalent problem in young adults, and could be a factor detrimentally affecting sleep quality. The goal of the present study was to explore the association between an irregular bedtime schedule and sleep quality, daytime sleepiness, and fatigue among undergraduate students in Taiwan.
A total of 160 students underwent a semi-structured interview and completed a survey comprising 4 parts: Pittsburgh Sleep Quality Index (PSQI), Epworth Sleepiness Scale (ESS), Fatigue Severity Scale (FSS), and a rating of irregular bedtime frequency. Participants were grouped into 3 groups in terms of irregular bedtime frequency: low, intermediate, or high according to their 2-week sleep log. To screen for psychological disorders or distress that may have affected responses on the sleep assessment measures, the Chinese health questionnaire-12 (CHQ-12) was also administered.
We found an increase in bedtime schedule irregularity to be significantly associated with a decrease in average sleep time per day (Spearman r = -0.22, p = 0.05). Multivariate regression analysis revealed that irregular bedtime frequency and average sleep time per day were correlated with PSQI scores, but not with ESS or FSS scores. A significant positive correlation between irregular bedtime frequency and PSQI scores was evident in the intermediate (partial r = 0.18, p = 0.02) and high (partial r = 0.15, p = 0.05) frequency groups as compared to low frequency group.
The results of our study suggest a high prevalence of both an irregular bedtime schedule and insufficient sleep among university students in Taiwan. Students with an irregular bedtime schedule may experience poor sleep quality. We suggest further research that explores the mechanisms involved in an irregular bedtime schedule and the effectiveness of interventions for improving this condition.
PMCID: PMC2718885  PMID: 19615098
7.  Study of Sleep Habits and Sleep Problems Among Medical Students of Pravara Institute of Medical Sciences Loni, Western Maharashtra, India 
Good quality sleep and adequate amount of sleep are important in order to have better cognitive performance and avoid health problems and psychiatric disorders.
The aim of this study was to describe sleep habits and sleep problems in a population of undergraduates, interns and postgraduate students of Pravara Institute of Medical Sciences (Deemed University), Loni, Maharashtra, India.
Subject and Methods:
Sleep habits and problems were investigated using a convenience sample of students from Pravara Institute of Medical Sciences (Deemed University), Loni, Maharashtra, India. The study was carried out during Oct. to Dec. 2011 with population consisted of total 150 medical students. A self-administered questionnaire developed based on Epworth Daytime Sleepiness Scale and Pittsburgh Sleep Quality Index was used. Data was analyzed by using Statistical Package of Social Sciences (SPSS) version 16.0.
In this study, out of 150 medical students, 26/150 (17.3%) students had abnormal levels of daytime sleepiness while 20/150 (13.3%) were border line. Sleep quality in females was better than the male.
Disorders related to poor sleep qualities are significant problems among medical students in our institution. Caffeine and alcohol ingestion affected sleep and there was high level of daytime sleepiness. Sleep difficulties resulted in irritability and affected lifestyle and interpersonal relationships.
PMCID: PMC3634224  PMID: 23634330
Medical students; Sleep disorders; Sleep habits; Sleep quality
8.  Effect of animated movie in combating child sleep health problems 
SpringerPlus  2015;4:343.
Sleep deprivation among teens is a major health issue. Only 15% of teens get 8.5 h of sleep on school nights. Sleep deprivation can lead to poor grades, sleepiness and moodiness. We undertook a study to assess the prevalence of sleep habit disturbance among elementary school students in South Texas with Hispanic ethnicity predominance. We also found how much a video based on sleep education had an impact on these children.
Once the Corpus Christi Independent School District (CCISD) approved the collection of baseline sleep data, questionnaires were administered using the Children’s Sleep Habit Questionnaire (CSHQ.) These questionnaires were distributed prior to the viewing of the educational and animated movie KNIGHTS (Keep Nurturing and Inspiring Good Habits in Teen Sleep). Four months later, a random follow-up was performed and the children were requested to respond to the same CSHQ.
264 children from two elementary schools participated in this educational program. At baseline, 55.56% of the children had trouble sleeping. When the questionnaire was administered four months later, only 23.26% (p < 0.05) had trouble sleeping. Additionally, at baseline, approximately 60–70% children had some baseline bedtime resistance, anxiety dealing with sleep, issues with sleep duration and/or awakenings in the middle of the night. In the follow up questionnaire, results showed significant improvements in overall sleep habits, bedtime resistance, sleep anxiety and night awakenings amongst students (p < 0.05). However, no significant differences were seen in sleep duration and daytime sleepiness.
Sleep deprivation and good sleep habits remain as a pervasive challenge among elementary school students. Administering an animated video about sleep education along with a provider-based education may be an effective tool for educating elementary school students and decreasing the prevalence of these sleep-related issues. Future prospective randomized studies are suggested.
PMCID: PMC4501343  PMID: 26191471
Sleep deprivation; Teen sleep; Video based learning; Sleep education
9.  Sleep Problems among Pre-School Children in Qazvin, Iran 
Background: Sleep problems are one of the main health issues raised by families. Therefore, we aimed to evaluate the sleep problems of pre-school children in Iran.
Methods: Five hundred and seventy-nine children aged 3–6 years were randomly recruited from 15 kindergartens in the city of Qazvin in Iran. The Iranian version of BEARS (Bedtime problems, Excessive daytime sleepiness, Awakenings during the night, Regularity and duration of sleep and Snoring) and the Children’s Sleep Habits questionnaire (CSHQ) were completed by interviewers. Data analysis was performed using SPSS version 19. The data were analysed with a Student’s t-test, chi-square and Fisher’s exact tests. A P value < 0.05 was considered significant.
Results: The study population consisted of 299 boys (51.6%) and 280 (48.3%) girls with a mean age of 4.1 years (SD 0.8). The mean body mass index (BMI) of the children was 15 (SD 2.1). The average sleep duration among the children was 10:54 h/day (SD 00:48). They went to bed late (23:18 h SD 00:48) and woke early (09:26 h; SD 01:00). Daytime sleepiness was reported by 6.9% of the participants. The incidence of awakening during the night, sleep-disordered breathing and snoring was 13.9%, 1.2% and 2.7%, respectively. Most of the children shared a room with their parents (87%) (P > 0.05).
Conclusion: The children had sleep-related problems, including a late bedtime, delayed sleep onset, daytime sleepiness, midnight awakening, sleep-disordered breathing, and snoring. Sharing a room was very common among the Iranian children.
PMCID: PMC4391455  PMID: 25897283
sleep; habits; child; pre-school; questionnaires
10.  Circadian melatonin rhythm and excessive daytime sleepiness in Parkinson’s disease 
JAMA neurology  2014;71(4):463-469.
Diurnal fluctuations of motor and non-motor symptoms and high prevalence of sleep/wake disturbances in Parkinson’s disease (PD) suggest a role of the circadian system in the modulation of these symptoms. Yet, surprisingly little is known regarding circadian function in PD, and whether circadian dysfunction is involved in the development of sleep/wake disturbances in PD.
The objective of this study was to determine the relationship between the timing and amplitude of the 24-hour melatonin rhythm, a marker of endogenous circadian rhythmicity, with self-reported sleep quality, the severity of daytime sleepiness and disease metrics.
A cross-sectional study, (2009–2012).
PD and Movement Disorders Center, Northwestern University, Chicago.
Twenty PD patients on stable dopaminergic therapy and 15 age-matched controls underwent blood sampling for the measurement of serum melatonin levels at 30-minute intervals for 24 hours under modified constant routine conditions.
Main Outcome Measure(s)
Clinical and demographic data, self-reported measures of sleep quality (Pittsburgh Sleep Quality Index (PSQI)) and daytime sleepiness (Epworth Sleepiness Scale (ESS)), circadian markers of the melatonin rhythm, including the amplitude, area-under-the-curve (AUC), and phase of the 24-hour rhythm.
Participants with PD had a blunted circadian rhythms of melatonin secretion compared to controls; both the amplitude of the melatonin rhythm and the 24-hour AUC for circulating melatonin levels were significantly lower in PD participants compared with controls (p<0.001). Markers of circadian phase were not significantly different between the two groups. Among PD participants, those with excessive daytime sleepiness (ESS score ≥10) had a significantly lower amplitude of the melatonin rhythm and the 24-hour melatonin AUC compared with PD participants without excessive sleepiness (p=0.001). Disease duration, UPDRS scores, levodopa equivalent dose and global PSQI scores in the PD group were not significantly related to measures of the melatonin circadian rhythm.
Conclusion and Relevance
These results indicate that circadian dysfunction may underlie excessive sleepiness in PD. The nature of this association needs to be further explored in longitudinal studies. Approaches aimed to strengthen circadian function, such as timed bright light and exercise, might potentially serve as complementary therapies for the non-motor manifestations of PD.
PMCID: PMC4078989  PMID: 24566763
11.  Association between delayed bedtime and sleep-related problems among community-dwelling 2-year-old children in Japan 
Although delayed sleep timing causes many socio-psycho-biological problems such as sleep loss, excessive daytime sleepiness, obesity, and impaired daytime neurocognitive performance in adults, there are insufficient data showing the clinical significance of a ‘night owl lifestyle’ in early life. This study examined the association between habitual delayed bedtime and sleep-related problems among community-dwelling 2-year-old children in Japan.
Parents/caregivers of 708 community-dwelling 2-year-old children in Nishitokyo City, Tokyo, participated in the study. The participants answered a questionnaire to evaluate their child’s sleep habits and sleep-related problems for the past 1 month.
Of the 425 children for whom complete data were collected, 90 (21.2%) went to bed at 22:00 or later. Children with delayed bedtime showed significantly more irregular bedtime, delayed wake time, shorter total sleep time, and difficulty in initiating and terminating sleep. Although this relationship indicated the presence of sleep debt in children with delayed bedtime, sleep onset latency did not differ between children with earlier bedtime and those with delayed bedtime. Rather, delayed bedtime was significantly associated with bedtime resistance and problems in the morning even when adjusting for nighttime and daytime sleep time.
Even in 2-year-old children, delayed bedtime was associated with various sleep-related problems. The causal factors may include diminished homeostatic sleep drive due to prolonged daytime nap as well as diurnal preference (morning or night type) regulated by the biological clock.
PMCID: PMC4364649  PMID: 25858638
Sleep habits; Sleep problems; Toddlers; Prevalence; Cross-sectional study
12.  Genome-wide association of sleep and circadian phenotypes 
BMC Medical Genetics  2007;8(Suppl 1):S9.
Numerous studies suggest genetic influences on sleepiness and circadian rhythms. The Sleep Heart Health Study collected questionnaire data on sleep habits and sleepiness from 2848 Framingham Heart Study Offspring Cohort participants. More than 700 participants were genotyped using the Affymetrix 100K SNP GeneChip, providing a unique opportunity to assess genetic linkage and association of these traits.
Sleepiness (defined as the Epworth Sleepiness Scale score), usual bedtime and usual sleep duration were assessed by self-completion questionnaire. Standardized residual measures adjusted for age, sex and BMI were analyzed. Multipoint variance components linkage analysis was performed. Association of SNPs to sleep phenotypes was analyzed with both population-based and family-based association tests, with analysis limited to 70,987 autosomal SNPs with minor allele frequency ≥10%, call rate ≥80%, and no significant deviation from Hardy-Weinberg equilibrium (p ≥ 0.001).
Heritability of sleepiness was 0.29, bedtime 0.22, and sleep duration 0.17. Both genotype and sleep phenotype data were available for 749 subjects. Linkage analysis revealed five linkage peaks of LOD >2: four to usual bedtime, one to sleep duration. These peaks include several candidate sleep-related genes, including CSNK2A2, encoding a known component of the circadian molecular clock, and PROK2, encoding a putative transmitter of the behavioral circadian rhythm from the suprachiasmatic nucleus. Association tests identified an association of usual bedtime with a non-synonymous coding SNP in NPSR1 that has been shown to encode a gain of function mutation of the neuropeptide S receptor, whose endogenous ligand is a potent promoter of wakefulness. Each copy of the minor allele of this SNP was associated with a 15 minute later mean bedtime. The lowest p value was for association of sleepiness with a SNP located in an intron of PDE4D, which encodes a cAMP-specific phosphodiesterase widely expressed in human brain. Full association results are posted at .
This analysis confirms prior reports of significant heritability of sleepiness, usual bedtime, and usual sleep duration. Several genetic loci with suggestive linkage to these traits are identified, including linkage peaks containing circadian clock-related genes. Association tests identify NPSR1 and PDE4D as possible mediators of bedtime and sleepiness.
PMCID: PMC1995620  PMID: 17903308
13.  Depressive Symptoms and Subjective And Objective Sleep In Community-Dwelling Older Women 
To examine the relationship between depressive symptoms and subjective and objective sleep in older women.
Four US clinical centers.
3045 community-dwelling women ≥70 years.
Depressive symptoms were assessed with the Geriatric Depression Scale categorizing participants as “normal” (0–2, referent), “some depressive symptoms” (3–5), or “depressed” (≥6). Subjective sleep quality and daytime sleepiness were assessed using the Pittsburgh Sleep Quality Index (PSQI) and Epworth Sleepiness Scale (ESS). Objective sleep measures were assessed with wrist actigraphy.
In multivariable-adjusted models, there were graded associations between increased level of depressive symptoms and both worse subjective sleep quality and more subjective daytime sleepiness (p-trends <0.001). Women with some depressive symptoms (OR 1.82, CI 1.48–2.24) and depressed (OR 2.84, CI 2.08–3.86) women had greater odds of reporting poor sleep (PSQI>5). Women with some depressive symptoms (OR 1.97, CI 1.47–2.64) and depressed women (OR 1.70, CI 1.12–2.58) had greater odds of reporting excessive daytime sleepiness (ESS>10). There were also graded associations between increased level of depressive symptoms and objectively measured wake after sleep onset (WASO) (p-trend = 0.030) and long wake episodes >5 minutes (p-trend 0.006). Depressed women had modestly increased odds of WASO ≥1 hour (OR 1.37, CI 1.03–1.83). Women with some depressive symptoms (OR 1.49, CI 1.19–1.86) and depressed women (OR 2.04, CI 1.52–2.74) had greater odds of being in the highest quartile for number of nap episodes >5 minutes. No associations between depressive symptom level and prolonged sleep latency, reduced sleep efficiency, or reduced or increased total sleep time were found.
Greater depressive symptom levels were associated with more subjective sleep disturbance and objective evidence of sleep fragmentation and napping.
PMCID: PMC3517685  PMID: 22428562
Depression; sleep; actigraphy; elderly; age
14.  The Association between the Phenotype of Excessive Daytime Sleepiness and Blood Pressure in Patients with Obstructive Sleep Apnea-Hypopnea Syndrome 
Objective Investigate the clinical features and the blood pressure (BP) pattern of the phenotype of excessive daytime sleepiness (EDS) in OSAHS.
Methods A total of 508 Chinese adults with suspected OSAHS were referred to our sleep laboratory from October 2009 to May 2012. On the same night of polysomnography (PSG), the levels of blood pressure were measured before sleeping (bedtime BP) and immediately after waking up in the next morning (morning BP). EDS was recognized as Epworth Sleepiness Scale (ESS)≥9. Subjects were classified into four groups based on the apnea-hypopnea index (AHI) from PSG as follows: control (simple snoring) group (control, n=104) with AHI<5; mild group (mild, n=89) with AHI≥5 and <15; moderate group (moderate, n=70) with AHI≥15 and<30; and severe group (severe, n=245) with AHI ≥30. The differences and correlations between BP and PSG parameters in EDS and non-EDS group of OSAHS patients were analyzed.
Results In all subjects, ESS was positively correlated with morning diastolic blood pressure (DBP), Mean arterial pressure (MAP) and bedtime DBP (r=0.144, 0.102 and 0.114, respectively, each P value<0.05). In OSAHS patients, ESS was only positively correlated with morning DBP (r=0.137, P<0.05). OSAHS patients with EDS phenotype were younger and were more likely to have the symptom of waking up feeling tired (36.1% vs. 23.2%, p=0.023), who had lower MSaO2, longer SIT90 (the ratio of time of SpO2 below 90% in total sleep time) and higher DBP (bedtime as well as morning). In patients with AHI≥15, ESS was correlated positively with both bedtime and morning DBP after controlling the confounding effects of age, sex, BMI, AHI and nadir nocturnal oxygen saturation( r=0.126,0.143, respectively, both P values<0.05). And in OSAHS patients of EDS phenotype, the bedtime DBP, bedtime MAP, morning DBP, and morning MAP were 3~5 mm Hg higher than that in patients of non-EDS phenotype(P<0.05). In the moderate and severe OSAHS group, patients with EDS phenotype were younger and had a lower mean blood oxygen saturation (MSaO2), longer time of SpO2 below 90% and higher SIT90 than patients with non-EDS phenotype (P<0.05). In hypertensive OSAHS patients, patients with EDS were also younger and had higher micro-arousal index (MiI), as well as higher morning DBP, morning MAP and bedtime DBP than that in non-EDS group (P<0.05).
Conclusions EDS in OSAHS patients is a special phenotype, which was characterized by younger age, higher DBP and more severe hypoxic load. This feature is mainly manifested in moderate and severe OSAHS patients. It is very important to identify the phenotype of EDS in patients with OSAHS, who may meet more benefits from effective treatment of OSAHS by correcting the intermittent nocturnal hypoxia and sleep fragmentation.
PMCID: PMC4025171  PMID: 24843321
Obstructive sleep apnea hypopnea syndrome (OSAHS); Epworth sleepiness scale (ESS); excessive daytime sleepiness (EDS); Blood pressure (BP); AHI; Chinese adults.
15.  Sleep Patterns Among Rural Chinese Twin Adolescents 
Sleep medicine  2008;10(4):479-489.
To examine sleep patterns and influencing factors (age, gender, Tanner Stage, weekday vs. weekend, and pre-sleep activity) among rural Chinese adolescents.
This is a prospective study among 621 adolescents aged 11–20 years (341 males) using both a questionnaire and sleep diary to obtain bedtime, wake-up time, sleep latency, and total sleep time (TST).
The median TST was 8.6 hours on weekdays and 9.4 hours on weekends. Despite absence of late night social pressure and computers, a U-shaped TST pattern was observed across age and Tanner stage, with a nadir around age 15–16 years or Tanner IV. Bedtimes became progressively later with age and Tanner Stage, while wake-up time was considerably earlier for school students or up to Tanner IV. Later wake-up times and longer TST on weekends were seen in school students, but not in non-school adolescents (>17 years). Pre-sleep activity, like reading or studying, was related to later bedtime, earlier wake-up time, and shorter TST in both genders.
Age, Tanner stage, and pre-sleep activity affected sleep patterns in this sample of rural Chinese adolescents. Later bedtime coupled with earlier wake-up time associated with academic demand appear to be important contributors to sleep loss among school students.
PMCID: PMC2753967  PMID: 18752997
Age; gender; puberty; Tanner stages; sleep patterns; wake-up time; bedtime; total sleep time
16.  Predictors of poor sleep quality among Lebanese university students: association between evening typology, lifestyle behaviors, and sleep habits 
Adequate, good night sleep is fundamental to well-being and is known to be influenced by myriad biological and environmental factors. Given the unavailability of sleep data about Lebanon, the cultural shifts and socioeconomic pressures that have affected many aspects of society, particularly for students and working adults, as well as our understanding of sleep in university students in other countries, we conducted a national study to assess sleep quality and factors contributing to sleep and general health in a culture-specific context. A self-filled questionnaire, inquiring about sociodemographics, health-risk behaviors, personal health, and evaluating sleep quality and chronotype using standard scales was completed by 540 students at private and public universities in Lebanon. Overall, they reported sleeping 7.95±1.34 hours per night, although 12.3% reported sleeping <6.5 hours and more than half scored in the poor-sleeper category on the Pittsburgh Sleep Quality Index (PSQI). Sleep timing differed markedly between weekdays and weekends, with bedtimes and wake-up times delayed by 1.51 and 2.43 hours, respectively, on weekends. While most scored in the “neither type” category on the Morningness–Eveningness Questionnaire (MEQ), 24.5% were evening types and 7.3% were morning types. MEQ score was significantly correlated with smoking behavior and daily study onset, as well as with PSQI score, with eveningness associated with greater number of cigarettes, later study times, and poor sleep. We conclude that the prevalence of poor sleep quality among Lebanese university students is associated with reduced sleep duration and shifts in sleep timing between weekdays and weekends, especially among evening types. While chronotype and certain behavioral choices interact to affect sleep dimensions and quality, raising awareness about the importance of obtaining adequate nighttime sleep on daily performance and avoiding risky behaviors may help Lebanese students make better choices in school and work schedules.
PMCID: PMC3894960  PMID: 24470782
bedtime irregularities; chronotype; Lebanon; PSQI; sleep duration; behavioral habits
17.  Daytime Sleepiness in Parkinson’s Disease: A Reappraisal 
PLoS ONE  2014;9(9):e107278.
Excessive daytime sleepiness is a frequent complaint in Parkinson’s disease (PD); however the frequency and risk factors for objective sleepiness remain mostly unknown. We investigated both the frequency and determinants of self-reported and objective daytime sleepiness in patients with Parkinson’s disease (PD) using a wide range of potential predictors.
One hundred and thirty four consecutive patients with PD, without selection bias for sleep complaint, underwent a semi-structured clinical interview and a one night polysomnography followed by a multiple sleep latency test (MSLT). Demographic characteristics, medical history, PD course and severity, daytime sleepiness, depressive and insomnia symptoms, treatment intake, pain, restless legs syndrome, REM sleep behaviour disorder, and nighttime sleep measures were collected. Self-reported daytime sleepiness was defined by an Epworth Sleepiness Scale (ESS) score above 10. A mean sleep latency on MSLT below 8 minutes defined objective daytime sleepiness.
Of 134 patients with PD, 46.3% had subjective and only 13.4% had objective sleepiness with a weak negative correlation between ESS and MSLT latency. A high body mass index (BMI) was associated with both ESS and MSLT, a pain complaint with ESS, and a higher apnea/hypopnea index with MSLT. However, no associations were found between both objective and subjective sleepiness, and measures of motor disability, disease onset, medication (type and dose), depression, insomnia, restless legs syndrome, REM sleep behaviour disorder and nighttime sleep evaluation.
We found a high frequency of self-reported EDS in PD, a finding which is however not confirmed by the gold standard neurophysiological evaluation. Current treatment options for EDS in PD are very limited; it thus remains to be determined whether decreasing pain and BMI in association with the treatment of sleep apnea syndrome would decrease significantly daytime sleepiness in PD.
PMCID: PMC4157859  PMID: 25198548
18.  Effects of a selective educational system on fatigue, sleep problems, daytime sleepiness, and depression among senior high school adolescents in Taiwan 
The aim of the study reported here was to clarify the effects of academic pressure on fatigue, sleep problems, daytime sleepiness, and depression among senior high school adolescents in Taiwan.
This cross-sectional study enrolled 757 senior high school adolescents who were classified into four groups: Grade 1 (n=261), Grade 2 (n=228), Grade 3T (n=199; Grade 3 students who had another college entrance test to take), and Grade 3S (n=69; Grade 3 students who had succeeded in their college application). Fatigue, sleep quality, daytime sleepiness, and depression were assessed using the Chinese version of the Multidimensional Fatigue Symptom Inventory – Short Form, Pittsburgh Sleep Quality Index-Taiwan Form, the Chinese version of the Epworth Sleepiness Scale, and the Chinese version of the Beck Depression Inventory®-II (BDI-II), respectively.
Physical, emotional, and mental fatigue scores were all higher in higher-grade groups. The Grade 3T (test) students had the worst fatigue severity, and the Grade 3S (success) students had the least fatigue severity. More than half of the students (60.9%) went to bed after 12 am, and they had on average 6.0 hours of sleep per night. More than 30% of the students in Grade 2 (37.3%) and Grades 3T/S (30.2%/30.4%) possibly had daily sleepiness problems. The students in Grade 3T had the worst BDI-II score (13.27±9.24), and the Grade 3S students had a much lower BDI-II score (7.91±6.13).
Relatively high proportions of fatigue, sleep problems, daytime sleepiness, and depression among senior high school adolescents were found in our study. The severities of fatigue, sleep problems, and depression were significantly diminished in the group under less academic stress (Grade 3S). Our findings may increase the understanding of the mental health of senior high school students under academic pressure in Taiwan. Further large sample size and population-based study should be done for better understanding about this topic.
PMCID: PMC4372029  PMID: 25834449
academic stress; students; mental health; hours of sleep; school performance
19.  Longitudinal Change in Sleep and Daytime Sleepiness in Postpartum Women 
PLoS ONE  2014;9(7):e103513.
Sleep disruption strongly influences daytime functioning; resultant sleepiness is recognised as a contributing risk-factor for individuals performing critical and dangerous tasks. While the relationship between sleep and sleepiness has been heavily investigated in the vulnerable sub-populations of shift workers and patients with sleep disorders, postpartum women have been comparatively overlooked. Thirty-three healthy, postpartum women recorded every episode of sleep and wake each day during postpartum weeks 6, 12 and 18. Although repeated measures analysis revealed there was no significant difference in the amount of nocturnal sleep and frequency of night-time wakings, there was a significant reduction in sleep disruption, due to fewer minutes of wake after sleep onset. Subjective sleepiness was measured each day using the Karolinska Sleepiness Scale; at the two earlier time points this was significantly correlated with sleep quality but not to sleep quantity. Epworth Sleepiness Scores significantly reduced over time; however, during week 18 over 50% of participants were still experiencing excessive daytime sleepiness (Epworth Sleepiness Score ≥12). Results have implications for health care providers and policy makers. Health care providers designing interventions to address sleepiness in new mothers should take into account the dynamic changes to sleep and sleepiness during this initial postpartum period. Policy makers developing regulations for parental leave entitlements should take into consideration the high prevalence of excessive daytime sleepiness experienced by new mothers, ensuring enough opportunity for daytime sleepiness to diminish to a manageable level prior to reengagement in the workforce.
PMCID: PMC4117520  PMID: 25078950
20.  Prostatic hyperplasia is highly associated with nocturia and excessive sleepiness: a cross-sectional study 
BMJ Open  2012;2(3):e000505.
The objective of this study is to assess the impact of nocturia on sleep in patients with lower urinary tract symptoms (LUTS)/benign prostatic enlargement (BPE) (nocturia≥2).
Cross-sectional survey.
798 urologists and general practitioners randomly selected from the overall population of urologists and general practitioners of every French region.
A total of 2179 LUTS/BPE men (aged 67.5±7.5 years old) were recruited.
Primary and secondary outcome measures
Validated patients' self-administered questionnaires were used to assess the severity of LUTS/BPE (the International Prostate Symptom Score), sleep characteristics (sleep log) and sleep disorders (the International Classification of Sleep Disorders (ICSD-2) and the DSM-IV). Sleepiness was assessed with the Epworth Sleepiness Scale (ESS). The volume of 24 h diuresis (1500 ml) was measured.
Participants had on average 2.9±0.9 nocturia episodes (three or more episodes in 67%) and the International Prostate Symptom Score of 15.8±5.7; 60.9% complained of insomnia according to the ICSD-2, 7.9% of restless leg syndrome and 6.4% of obstructive sleep apnoea. 32.3% had excessive sleepiness (ESS >10) and 3.1% severe excessive sleepiness (ESS >16). Insomnia was mainly nocturnal awakenings with an average wake after sleep onset of 89±47 min. The number of episodes of nocturia per night correlated significantly with wake after sleep onset and ESS but not with total sleep time and sleep latency.
Nocturia is significantly associated with sleep maintenance insomnia and sleepiness in men with BPE.
Article summary
Article focus
Complaint of nocturia and its links with excessive sleepiness.
Assessment of the impact of nocturia on sleep.
Key messages
By being disruptive to sleep, the nocturia episodes affected sleep efficiency and quality.
The number of nocturia episodes was associated with an increased sleepiness in men with benign prostatic hyperplasia.
Strengths and limitations of this study
This is a cross-sectional study. It would have been more convincing to compare our subjects to a similar group of older people with no benign prostatic hyperplasia. However, our study focused on the frequency of insomnia and on the correlates between benign prostatic hyperplasia and insomnia.
PMCID: PMC3367152  PMID: 22649170
21.  Association between the melanopsin gene polymorphism OPN4*Ile394Thr and sleep/wake timing in Japanese university students 
In our previous studies, we found that the Ile394Thr SNP in the melanopsin gene (OPN4) was functionally associated with the pupillary light reflex. This indicates the possibility that OPN4*Ile394Thr is associated with other non-image forming responses. The aim of this study was therefore to determine whether OPN4*Ile394Thr is associated with sleep/wake timing.
A total of 348 healthy Japanese university students participated in this study. Scalp hair was used to genotype the Ile394Thr SNP of OPN4. Sleep habits, including bedtime, wake time and sleep duration, were assessed separately for weekdays and weekends. A total of 328 samples, including 223 samples with TT genotype, 91 with TC genotype and 14 with CC genotype, were used for statistical analysis. No significant difference in age or male/female distribution was found among the three genotype groups.
There was no significant difference in circadian preference among the genotype groups. During weekdays, bedtime, wake time and midpoint of sleep for CC subjects were significantly later than those for TT and TC subjects. However, there was no difference between TT and TC subjects in any of their sleep habits. During weekends, bedtime of CC subjects was significantly later than those of TT and TC subjects, and the midpoint of sleep of CC subjects was significantly later than that of TC subjects.
Our findings demonstrated that OPN4*Ile394Thr is associated with sleep/wake timing. We also found that the sleep/wake timing of subjects with the CC genotype was later than that of subjects with the TT or TC genotype.
PMCID: PMC4048048  PMID: 24887407
Genotype; Human; Melanopsin gene (OPN4); Single nucleotide polymorphism (SNP); Non-image forming responses; Sleep
22.  Adolescent Sleep Patterns and Night-Time Technology Use: Results of the Australian Broadcasting Corporation's Big Sleep Survey 
PLoS ONE  2014;9(11):e111700.
Electronic devices in the bedroom are broadly linked with poor sleep in adolescents. This study investigated whether there is a dose-response relationship between use of electronic devices (computers, cellphones, televisions and radios) in bed prior to sleep and adolescent sleep patterns.
Adolescents aged 11–17 yrs (n = 1,184; 67.6% female) completed an Australia-wide internet survey that examined sleep patterns, sleepiness, sleep disorders, the presence of electronic devices in the bedroom and frequency of use in bed at night.
Over 70% of adolescents reported 2 or more electronic devices in their bedroom at night. Use of devices in bed a few nights per week or more was 46.8% cellphone, 38.5% computer, 23.2% TV, and 15.8% radio. Device use had dose-dependent associations with later sleep onset on weekdays (highest-dose computer adjOR  = 3.75: 99% CI  = 2.17–6.46; cellphone 2.29: 1.22–4.30) and weekends (computer 3.68: 2.14–6.32; cellphone 3.24: 1.70–6.19; TV 2.32: 1.30–4.14), and later waking on weekdays (computer 2.08: 1.25–3.44; TV 2.31: 1.33–4.02) and weekends (computer 1.99: 1.21–3.26; cellphone 2.33: 1.33–4.08; TV 2.04: 1.18–3.55). Only ‘almost every night’ computer use (: 2.43: 1.45–4.08) was associated with short weekday sleep duration, and only ‘almost every night’ cellphone use (2.23: 1.26–3.94) was associated with wake lag (waking later on weekends).
Use of computers, cell-phones and televisions at higher doses was associated with delayed sleep/wake schedules and wake lag, potentially impairing health and educational outcomes.
PMCID: PMC4229101  PMID: 25390034
23.  Obstructive Sleep Apnea and Risk of Cardiovascular Events and All-Cause Mortality: A Decade-Long Historical Cohort Study 
PLoS Medicine  2014;11(2):e1001599.
Tetyana Kendzerska and colleagues explore the association between physiological measures of obstructive sleep apnea other than the apnea-hypopnea index and the risk of cardiovascular events.
Please see later in the article for the Editors' Summary
Obstructive sleep apnea (OSA) has been reported to be a risk factor for cardiovascular (CV) disease. Although the apnea-hypopnea index (AHI) is the most commonly used measure of OSA, other less well studied OSA-related variables may be more pathophysiologically relevant and offer better prediction. The objective of this study was to evaluate the relationship between OSA-related variables and risk of CV events.
Methods and Findings
A historical cohort study was conducted using clinical database and health administrative data. Adults referred for suspected OSA who underwent diagnostic polysomnography at the sleep laboratory at St Michael's Hospital (Toronto, Canada) between 1994 and 2010 were followed through provincial health administrative data (Ontario, Canada) until May 2011 to examine the occurrence of a composite outcome (myocardial infarction, stroke, congestive heart failure, revascularization procedures, or death from any cause). Cox regression models were used to investigate the association between baseline OSA-related variables and composite outcome controlling for traditional risk factors. The results were expressed as hazard ratios (HRs) and 95% CIs; for continuous variables, HRs compare the 75th and 25th percentiles. Over a median follow-up of 68 months, 1,172 (11.5%) of 10,149 participants experienced our composite outcome. In a fully adjusted model, other than AHI OSA-related variables were significant independent predictors: time spent with oxygen saturation <90% (9 minutes versus 0; HR = 1.50, 95% CI 1.25–1.79), sleep time (4.9 versus 6.4 hours; HR = 1.20, 95% CI 1.12–1.27), awakenings (35 versus 18; HR = 1.06, 95% CI 1.02–1.10), periodic leg movements (13 versus 0/hour; HR = 1.05, 95% CI 1.03–1.07), heart rate (70 versus 56 beats per minute [bpm]; HR = 1.28, 95% CI 1.19–1.37), and daytime sleepiness (HR = 1.13, 95% CI 1.01–1.28).The main study limitation was lack of information about continuous positive airway pressure (CPAP) adherence.
OSA-related factors other than AHI were shown as important predictors of composite CV outcome and should be considered in future studies and clinical practice.
Please see later in the article for the Editors' Summary
Editors' Summary
Obstructive sleep apnea (OSA) is a common sleep-related breathing disorder, particularly among middle-aged and elderly people. It is characterized by apnea—a brief interruption in breathing that lasts at least 10 seconds—and hypopnea—a decrease of more than 50% in the amplitude of breathing that lasts at least 10 seconds or clear but smaller decrease in amplitude associated with either oxygen desaturation or an arousal. Patients with OSA experience numerous episodes of apnea and hypopnea during the night; severe OSA is defined as having 30 or more episodes per hour (an apnea-hypopnea index [AHI] of >30). These breathing interruptions occur when relaxation of the upper airway muscles decreases the airflow, which lowers the amount of oxygen in the blood. As a result, affected individuals frequently wake from deep sleep as they struggle to breathe. Symptoms of OSA include loud snoring and daytime sleepiness. Treatments include lifestyle changes such as losing weight (excess fat around the neck increases airway collapse) and smoking cessation. For severe OSA, doctors recommend continuous positive airway pressure (CPAP), in which a machine blows pressurized air through a face mask into the airway to keep it open.
Why Was This Study Done?
OSA can be life-threatening. Most directly, daytime sleepiness can cause accidents, but OSA is also associated with an increased risk of developing cardiovascular disease (CVD, disease that affects the heart and the circulation). To date, studies that have investigated the association between OSA and the risk of myocardial infarction (heart attack), congestive heart failure, stroke, and other CVDs have used the AHI to diagnose and categorize the severity of OSA. However, by focussing on AHI, clinicians and researchers may be missing opportunities to improve their ability to predict which patients are at the highest risk of CVD. In this historical cohort study, the researchers investigate the association between other OSA-related variables (for example, blood oxygen saturation and sleep fragmentation) and the risk of cardiovascular events and all-cause mortality (death). A historical cohort study examines the medical records of groups of individuals who have different characteristics at baseline for the subsequent occurrence of specific outcomes.
What Did the Researchers Do and Find?
The researchers used administrative data (including hospitalization records and physicians' claims for services supplied to patients) to follow up adults referred for suspected OSA who underwent diagnostic polysomnography (a sleep study) at a single Canadian hospital between 1994 and 2010. A database of the polysomnography results provided information on OSA-related variables for all the study participants. Over an average follow-up of about 6 years, 11.5% of the 10,149 participants were hospitalized for a myocardial infarction, stroke, or congestive heart failure, underwent a revascularization procedure (an intervention that restores the blood supply to an organ or tissue after CVD has blocked a blood vessel), or had died from any cause. After adjusting for multiple established risk factors for CVD such as smoking and age in Cox regression models (a statistical approach that examines associations between patient variables and outcomes), several OSA-related variables (but not AHI) were significant predictors of CVD. The strongest OSA-related predictor of cardiovascular events or all-cause mortality was total sleep time spent with oxygen saturation below 90%, which increased the risk of a cardiovascular event or death by 50%. Other statistically significant OSA-related predictors (predictors that were unlikely to be associated with the outcome through chance) of cardiovascular events or death included total sleep time, number of awakenings, frequency of periodic leg movements, heart rate, and daytime sleepiness.
What Do These Findings Mean?
These findings indicate that OSA-related factors other than AHI are important predictors of the composite outcome of a cardiovascular event or all-cause mortality. Indeed, although AHI was significantly associated with the researchers' composite outcome in an analysis that did not consider other established risk factors for CVD (“confounders”), the association became non-significant after controlling for potential confounders. The accuracy of these findings, which need to be confirmed in other settings, is likely to be limited by the lack of information available about the use of CPAP by study participants and by the lack of adjustment for some important confounders. Importantly, however, these findings suggest that OSA-related factors other than AHI should be considered as predictors of CVD in future studies and in clinical practice.
Additional Information
Please access these websites via the online version of this summary at
The US National Heart Lung and Blood Institute has information (including several videos) about obstructive sleep apnea (in English and Spanish), sleep studies, heart disease, and other cardiovascular diseases (some information in English and Spanish)
The UK National Health Service Choices website provides information (including personal stories) about sleep apnea and about cardiovascular disease
The not-for-profit American Sleep Apnea Association provides detailed information about sleep apnea for patients and health-care professionals, including personal stories about the condition
The MedlinePlus encyclopedia has pages on obstructive sleep apnea and on polysomnography; MedlinePlus provides links to further information and advice about obstructive sleep apnea, heart diseases, and vascular diseases (in English and Spanish)
PMCID: PMC3913558  PMID: 24503600
24.  Causes and consequences of sleepiness among college students 
Daytime sleepiness, sleep deprivation, and irregular sleep schedules are highly prevalent among college students, as 50% report daytime sleepiness and 70% attain insufficient sleep. The consequences of sleep deprivation and daytime sleepiness are especially problematic to college students and can result in lower grade point averages, increased risk of academic failure, compromised learning, impaired mood, and increased risk of motor vehicle accidents. This article reviews the current prevalence of sleepiness and sleep deprivation among college students, contributing factors for sleep deprivation, and the role of sleep in learning and memory. The impact of sleep and sleep disorders on academics, grade point average, driving, and mood will be examined. Most importantly, effective and viable interventions to decrease sleepiness and sleep deprivation through sleep education classes, online programs, encouragement of naps, and adjustment of class time will be reviewed. This paper highlights that addressing sleep issues, which are not often considered as a risk factor for depression and academic failure, should be encouraged. Promotion of university and college policies and class schedules that encourage healthy and adequate sleep could have a significant impact on the sleep, learning, and health of college students. Future research to investigate effective and feasible interventions, which disseminate both sleep knowledge and encouragement of healthy sleep habits to college students in a time and cost effective manner, is a priority.
PMCID: PMC4075951  PMID: 25018659
grade point average; GPA; sleep deprivation; academic performance; adolescence; sleep education programs
25.  Rapid-Eye-Movement-Sleep (REM) Associated Enhancement of Working Memory Performance after a Daytime Nap 
PLoS ONE  2015;10(5):e0125752.
The main objective was to study the impact of a daytime sleep opportunity on working memory and the mechanism behind such impact. This study adopted an experimental design in a sleep research laboratory. Eighty healthy college students (Age:17-23, 36 males) were randomized to either have a polysomnography-monitored daytime sleep opportunity (Nap-group, n=40) or stay awake (Wake-group, n=40) between the two assessment sessions. All participants completed a sleep diary and wore an actigraph-watch for 5 days before and one day after the assessment sessions. They completed the state-measurement of sleepiness and affect, in addition to a psychomotor vigilance test and a working memory task before and after the nap/wake sessions. The two groups did not differ in their sleep characteristics prior to and after the lab visit. The Nap-group had higher accuracy on the working memory task, fewer lapses on the psychomotor vigilance test and lower state-sleepiness than the Wake-group. Within the Nap-group, working memory accuracy was positively correlated with duration of rapid eye movement sleep (REM) and total sleep time during the nap. Our findings suggested that “sleep gain” during a daytime sleep opportunity had significant positive impact on working memory performance, without affecting subsequent nighttime sleep in young adult, and such impact was associated with the duration of REM. While REM abnormality has long been noted in pathological conditions (e.g. depression), which are also presented with cognitive dysfunctions (e.g. working memory deficits), this was the first evidence showing working memory enhancement associated with REM in daytime napping in college students, who likely had habitual short sleep duration but were otherwise generally healthy.
PMCID: PMC4430242  PMID: 25970511

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