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The Relationships between Sleep-Wake Cycle and Academic Performance in Medical Students


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Survey and laboratory studies suggest that several factors, such as social and academic demands, part-time jobs and irregular school schedules, affect the sleep-wake cycle of college students. In this study, we examined the sleep-wake pattern and the role played by academic schedules and individual characteristics on the sleep-wake cycle and academic performance. The subjects were 36 medical students (male = 21 and female = 15), mean age = 20.7 years, SD = 2.2. All students attended the same school schedule, from Monday to Friday. The volunteers answered a morningness-eveningness questionnaire, the Pittsburgh Sleep Quality Index (PSQI) and kept a sleep-wake diary for two weeks. The relationships between sleep-wake cycle, PSQI, chronotypes and academic performance were analyzed by a multiple regression technique. The results showed that 38.9% of the students had a poor sleep quality according to the PSQI. When the medical students were evening type or moderate evening type the PSQI showed a tendency of poor sleep. The multiple regression analysis showed a correlation between sleep onset, sleep irregularity and sleep length with academic performance. These results suggest that chronotypes influence the quality of the sleep-wake cycle and that irregularity of the sleep-wake cycle, as well as sleep deprivation (average length was 6:52), influence the learning of college students.
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The Relationships between Sleep-Wake Cycle and
Academic Performance in Medical Students
Ana Ligia D. Medeiros, Denise B.F. Mendes, Patrícia F. Lima and John F. Araujo
Laboratório de Cronobiologia, Depto. Fisiologia, UFRN, Natal, Brazil
Survey and laboratory studies suggest that several factors, such as social and academic
demands, part-time jobs and irregular school schedules, affect the sleep-wake cycle of
college students. In this study, we examined the sleep-wake pattern and the role played
by academic schedules and individual characteristics on the sleep-wake cycle and aca-
demic performance. The subjects were 36 medical students (male = 21 and female =
15), mean age = 20.7 years, SD = 2.2. All students attended the same school schedule,
from Monday to Friday. The volunteers answered a morningness-eveningness ques-
tionnaire, the Pittsburgh Sleep Quality Index (PSQI) and kept a sleep-wake diary for
two weeks. The relationships between sleep-wake cycle, PSQI, chronotypes and aca-
demic performance were analyzed by a multiple regression technique. The results
showed that 38.9% of the students had a poor sleep quality according to the PSQI. When
the medical students were evening type or moderate evening type the PSQI showed a
tendency of poor sleep. The multiple regression analysis showed a correlation between
sleep onset, sleep irregularity and sleep length with academic performance. These
results suggest that chronotypes influence the quality of the sleep-wake cycle and that
irregularity of the sleep-wake cycle, as well as sleep deprivation (average length was
6:52), influence the learning of college students.
Keywords: Medical student, academic performance, sleep-wake cycle, chronotype,
circadian rhythms.
Survey and laboratory studies suggest that a number of factors, such as social and aca-
demic demands, affect the pattern of the sleep-wake cycle of healthy college students.
Other factors, including work and study schedules, influence sleep length and sleep-
wake cycle regularity. The circadian pacemaker controls the sleep-wake cycle and is
synchronized by light-dark cycle and by social contact. Results from Valdez et al.
Address correspondence to: Partrícia F. Lima, Laboratório de Cronobiologia, Depto. Fisiologia, UFRN,
Caixa Postal 1506, Natal, RN, Brazil. E-mail:
Biological Rhythm Research 0165-0424/01/3202-263$16.00
2001, Vol. 32, No. 2, pp. 263–270 © Swets & Zeitlinger
(1996) suggested that prolonged sleep during weekends are due to reduction of sleep
during workdays, whereas the delay of bedtime seems to be associated with a tendency
of the human circadian system to maintain a delayed phase. Machado et al. (1998)
showed that the tendency of phase delay on weekends was differently expressed accord-
ing to study’s schedules and work. They also suggested that the waking time on week-
days is set by study schedules, working schedules and other external factors.
Wever (1988) suggested that the desyncronization of circadian rhythms causes a
troublesome increase of stress and Jean-Louis et al. (1998) showed that students who
fell asleep in school experienced substantially greater negative mood states than those
who did not. The importance of the sleep-wake cycle for the physical, mental and
social health was shown by Pilcher and Ott (1998). The same study suggested that
the students submitted to stress, such as academic demands, had irregular sleep-wake
patterns and were presumably not as alert as they should be. In the present work, we
study the sleep-wake cycle patterns of a group of students, and the role played by the
irregularity of the sleep-wake patterns and individual characteristics on the quality of
sleep and academic performance.
Materials and Methods
The subjects were 35 medical students of the UFRN, with average age of 20.54 years
(SD = 2), 20 male and 15 female. They attended the same school schedules, with
classes beginning at 8:00 on Mondays, Wednesdays and Fridays and at 7:00 on Tues-
days and Thursdays. There were also classes from 14:00 to 17:00 on Mondays,
Wednesdays and Fridays. In the first day of the study, every student filled out an iden-
tification form with personal information, including their daily activities and health
problems, if they had any. All students were volunteers. They signed a term agreeing
to participate in the research and no monetary compensation was given. For two
weeks, the students recorded their sleeping and waking up schedules, as well as their
naps. The subjective sleep assessment, self-reported data on sleep diary and sleep
habits are frequently used in sleep-related research and have been highly correlated
with polygraphic measures of the sleep and wrist-worn activity monitor, the actigra-
phy (Lockley et al., 1999; Usui et al., 1999). It is important to know that all methods
that attempt to measure sleep, measure different things, i.e., subjetive recolletion of
sleep, electrical activity of the brain or motor activity.
A Portuguese version of the Horne & Östberg questionnaire (Horne & Östberg,
1976) was used to classify the participants of the research in morning type, evening
type or indifferent type, differentiating the moderate and extreme types, based on the
obtained value:
16–30: extreme evening type
31–41: moderate evening type
42–58: indifferent type
59–69: moderate morning type
70–86: extreme morning type
264 A.L.D. Medeiros et al.
The subjects completed the Pittsburgh Sleep Quality Index (PSQI) questionnaire,
which consists of 10 questions related with the normal sleep habits (Buysse et al.,
1989). It was applied during the second week of the data collection. Sleep quality
was considered bad for individuals who obtained a score higher than 5.
Sleep onset and sleep length were studied, as well as its deviation pattern. As quali-
tative variables, the chronotype and the quality of the sleep were analyzed. The results
of an exam taken during the collection of data were used to analyze the students’ aca-
demic performance. The standard deviation of sleep onset was used as an index of
irregularity of the sleep-wake cycle. For the statistical analysis of the data, a linear
regression test was applied with ANOVA to detect correlation among the several
studied variables.
Our volunteers had a normal distribution of morningness-eveningness scoring
range (Fig. 1A), which was 25 indifferent types, 5 moderate morning types,
4 moderate evening types and 1 extreme evening type. The average of the sleep onset
was 0:03 ± 93min, and female students (23:44 ± 98min) went to sleep earlier than
male students (0:17 ± 90min). The average sleep length was 6:52 ± 93 min, which
is less than the general population, suggesting that our samples had partial sleep
The relationship between chronotype and sleep onset was statistically signifi-
cant (p < 0.04, Fig. 1B), which confirms that the data obtained in the Horne &
Östberg questionnaire are coherent. There was no statistically significant relationship
between chronotype and sleep length (p > 0.8), showing that, in spite of the differ-
ence in sleep schedules, sleep length was similar among morning and evening
The standard deviation of the sleep onset of each student was used as an index of
irregularity of the sleep-wake cycle. The results showed a negative correlation
between irregularity of the sleep and score of the chronotype (p < 0.001), revealing
that the students who presented values tending to eveningness had a more irregular
The analysis of the PSQI showed that 38.9% of the students had a poor sleep
quality during the study period. This high percentage is a result of the contribution
of the components 1 and 3 of the PSQI (subjective sleep quality and sleep length).
42.8% of the students had an irregular pattern of sleep-wake cycle (Fig. 2). A corre-
lation was also found between the irregularity of sleep and the PSQI (p < 0.05),
proving that irregularity of sleep implies bad quality of sleep.
The regression test also showed a correlation between sleep onset and academic
performance (p < 0.001) (Fig. 3A), between sleep length and academic perfor-
mance (p < 0.02, Fig. 3B) and between irregularity of sleep and academic per-
formance (p < 0.03, Fig. 3C), implying that the students with a more irregular
sleep-wake cycle and a shorter length of the sleep presented worse academic
Sleep-Wake Cycle and Academic Performance 265
Other studies have shown that students without sleep deprivation (with sleep length
of 7:30h), but with an irregular pattern of the sleep-wake cycle presented sleepiness
during the day (Manber et al., 1996). Jean-Louis et al. (1998) showed a relationship
between day sleepiness and poor mood states in college students.
Billiard et al. (1987) showed that 13.6% of the students self-reported snoring.
Ficker et al. (1999) reported that 11.9% of the students snore frequently and are more
likely than non-snorers to have lower examination scores or even to fail their exams.
In our study, 13.8% of the students reported snoring but we did not find any
relationship between snoring and academic performance.
The decrement of academic performance on students who have an irregular sleep-
wake cycle could be explained by the internal desynchronization of the subjects’
rhythms. We are unable to demonstrate that these students are internally desynchro-
266 A.L.D. Medeiros et al.
Figure 1. Distribution of morningness-eveningness scoring range and the relationship
between the chronotype and the sleep onset of subjects.
Sleep-Wake Cycle and Academic Performance 267
Figure 2. Graphic of regular (a) and irregular (b) pattern sleep-wake cycle of subjects.
nized, but the irregularity of the sleep-wake cycle suggests this. Furthermore, these
students are under academic pressure. The irregularity of the sleep-wake cycle and,
perhaps, the internal desynchronization could be causing an increase of stress, and
the stress could be influencing their academic performance (Wever, 1988).
Several measures of human performance are controlled by circadian system and
recent research has proposed an endogenous two-oscillator model of the human cir-
cadian system, with one oscillator indicated by the core body temperature rhythm and
a second oscillator responsible for the daily sleep-wake cycle. When the subjects are
under altered sleep-wake pattern, the temperature rhythm and the sleep-wake cycle
may be separated from one another and run with different periods. This condition can
decrease performance efficiency, like in jet-lag and shift-work.
Students who showed a more regular sleep-wake cycle and longer sleep length
reported better academic performance. This is an evidence of the consequences of
insufficient sleep and irregular sleep-wake cycle. Although these consequences seem
obvious, unfortunately they are still often ignored. The results that showed worse aca-
demic performance in students who had irregular sleep-wake cycle and shorter sleep
length could reveal only one part of the consequences. Jean-Louis et al. (1998) pro-
posed a cascade into catastrophic events, such as decrement in academic performance,
disturbance of mood and behavior, and increased vulnerability to substance use.
Several published data appear to indicate that sleep deprivation or sleep fragmenta-
tion may impair the consolidation of newly learned information and the formation
268 A.L.D. Medeiros et al.
Figure 3. The linear regression shows a relationship between sleep onset (A), sleep length
(B), sleep irregularity (C) and academic performance.
of permanent memory trace during sleep (Giuditta et al., 1995). It is important to
emphasize that in our study and in others, we can only demonstrate statistical
relationships between chronotype and sleep irregularity and between sleep irregular-
ity and academic performance, without being able to prove a causal relationship. We
propose, however, that several exogenous factors, such as school schedules and
academic demands, and endogenous factors, such as chronotype and others, influence
the sleep-wake cycle and the quality of sleep, and that irregularity of the sleep-
wake cycle and poor sleep quality, as well as other factors, influence academic
Our results suggest that irregularity of the sleep-wake cycle as well as deprivation
of sleep (average length 6:52) influence the academic performance of college students.
We suggest that it is necessary to rethink the school schedules and to guide the students’
sleeping habits with the goal of reducing these negative effects on their learning.
We are grateful for the collaboration of the students. This work was supported by
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... It is reasonable to suppose that university students who develop such sleep patterns may have poor academic performances. Studies on this topic include Carskadom and Davis (1989), Lack, 1986, Medeiros, et al. (2001, Hicks and Pellegrino (1991), Gomes (2002), and Gray and Watson (2002). ...
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... Ergänzend wird ein Zusammenhang zwischen Chronotyp und akademischen Leistungen diskutiert, in dem der Chronotyp assoziierte Schlafparameter beeinflusst, die wiederum die Leistungsfähigkeit von Studierenden beeinflussen kann. So war beispielsweise die akademische Leistung besser, je früher Studierende schlafen gingen (Anmerkung: Schlafzeiten hängen mit dem Chronotyp zusammen) und je länger die Schlafdauern (Anmerkung: späte Chronotypen schlafen unter der Woche oftmals zu kurz) waren (Medeiros et al. 2001). Dieses Ergebnis wird ergänzt durch Erkenntnisse, nach denen das Merkmal Chronotyp nicht direkt Auswirkungen auf die Leistung ausübt, sondern als Mediator auf u. a. auch Aspekte wie Gewissenhaftigkeit wirkt. ...
... Lack of sleep is highly correlated with low academic performance, decreased learning abilities, and reduced memory [23,24]. Medeiros suggested that irregular sleep-wake cycle is linked to poor students performance in medical college [25,26]. Rodriguez RN observed that students who did not get enough sleep did not perform well on their final examinations compared to the others [27]. ...
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Introduction: Sleep disorders are extremely prevalent in the general population. College students are more susceptible to sleep problems. This is due to the increased competition in getting a job position and the current alterations in the labor market. Poor sleep is prevalent and has deleterious effects on college students, but its frequency among college students has not been documented in Jordan. So, the aims of this study are to assess the prevalence of daytime sleepiness among medical college students in Jordan and to look for any links between daytime sleepiness and academic performance. Methods: A cross-sectional study performed on medical and paramedical specialties students and Epworth sleepiness Sscale (ESS) was used. To assess the students' academic performance, the cumulative grade point average was utilized. Results: 977 students from five medical colleges participated in the study. ESS scores were abnormal in 34.4% of students and were considered to have daytime sleepiness. Significant lower ESS scores were associated with students who reported good sleep quality than students who reported poor sleep quality. Significant lower ESS scores were reported by students who slept more than 7 hours compared with students who slept less than 6 hours. The ESS scores were not significantly associated with students' CPGA. Conclusion: Daytime sleepiness is highly prevalent among medical students in Jordan. The data of this study might be very helpful to assess the academic policy makers to develop intervention strategies that resolve the sleep disturbances in college students and reduce its impact on the academic achievements.
... 18 The use of different measures for assessment of sleep-related problems in the medical students have yielded prevalence ranging from 16 % to as high as 90% in the available literature. 19 Thus, the extent of poor sleep quality observed in the present study is comparable to that reported in some previous studies, 18,21 and is slightly more than that reported in few other studies. 22,23 This prevalence of poor sleep quality is in line with a population based study done in western Nepal among adolescents which reported poor sleep quality among 39% of respondents Nepal. ...
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Background: The use of the internet is growing rapidly worldwide with easier availability and affordability in developing countries like Nepal. Apart from several benefits, it has also led to deleterious effects on certain individuals' physical and mental well-being. The present study aimed to assess the burden of internet addiction among nursing, dental and medical undergraduates at a medical school, and examine its relationship with depression and sleep quality. Methods: A cross-sectional study among 494 students pursuing nursing, dental and medical undergraduate courses at the same medical college in Nepal was conducted. The burden of internet addiction, depression, and sleep disturbance was assessed using Young's Internet addiction test, Beck's depression inventory, and Pittsburgh Sleep Quality Index questionnaires respectively. Results: The majority of respondents reported either controlled use of internet or mild problem with internet use. However, 4.7% of respondents reported significant problems due to internet use. Further, about 42.3% reported poor sleep quality, and 8.9% screened positive for depression. In both chi-square and logistic regression analyses, internet addiction was significantly associated with poor sleep quality and depression. Conclusions: The study shows that about half of the participants experienced at least some problems and a small but significant proportion of them reported severe problems due to internet use. This warrants the need to address the issue of internet addiction among medical and allied sciences students in Nepal. Further, internet addiction is associated with both depression and poor sleep quality, highlighting a need to develop effective interventions targeting all three problems holistically.
... These evening online sessions resulted in late night sleep, long term mobile/computer exposure, and disturbed sleep pattern [6]. Due to this reason, diurnal preferences of the students changed and many students altered their active lifestyle to evening [7]. Earlier studies reported that altered sleep-wake cycle disturbs a person psychologically, physically, and socially [8][9][10][11]. ...
Background: COVID-19 emerged as a serious pandemic in 2019 and billions of people were infected. Various precautionary methods were taken to contain the spread of virus such as social distancing, public lockdown, sanitation, and closure of schools and colleges. Many colleges started online classes to resume their syllabus and to complete the course curriculum. These evening online sessions resulted in late night sleep, long term mobile/computer exposure, and disturbed sleep pattern. Objective: The present study aimed to determine the impact of COVID-19 online classes on morningness- eveningness personality and to compare it with different age groups, gender, and body mass index. Methods: The cluster sampling method was used to collect the subjects from the total of 1153 adult college students, 897 subjects were selected based on the selection criteria and instructed to submit an online survey consists of the Morningness-eveningness Questionnaire and demographic and anthropometric data through mail, social media, or through a researcher by direct interview. Results: The mean score for the 897 participants is 56.7, indicating Intermediate morningness-eveningness personality type. On comparing the different groups, the youngest group (18-20 years) scored 4.23%(mean = 46.7), female subjects scored 6.13%(mean = 58.1), the underweight 2.67%(mean = 59.2) and overweight groups scored 2.89%(mean = 59.7) indicating definite eveningness. Among the 897 collected samples of the population 8.13%of the subjects experienced definite eveningness, 14.93%has moderate eveningness, 17.38%are under intermediate category, 22.4%have moderate morningness, and 37.11%have definite morningness. Conclusions: Subjects with eveningness personality have high risk of developing mental illness, thus it's important to determine the eveningness personality among student population to avoid serious complications in later age.
... Multiple studies have correlated poor academic performance with bad sleeping habits [45][46][47]. Interestingly, our study has shown that the PSQI score was not associated with a low GPA. ...
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Background: Sleep quality ensures better physical and psychological well-being. It is regulated through endogenous hemostatic, neurogenic, and circadian processes. Nonetheless, environmental and behavioral factors also play a role in sleep hygiene. Electronic device use is increasing rapidly and has been linked to many adverse effects, raising public health concerns. Objective: This study aimed to investigate the impact of electronic device addiction on sleep quality and academic performance among health care students in Saudi Arabia. Methods: A descriptive cross-sectional study was conducted from June to December 2019 at 3 universities in Jeddah. Of the 1000 students contacted, 608 students from 5 health sciences disciplines completed the questionnaires. The following outcome measures were used: Smartphone Addiction Scale for Adolescents-short version (SAS-SV), Pittsburgh Sleep Quality Index (PSQI), and grade point average (GPA). Results: The median age of participants was 21 years, with 71.9% (437/608) being female. Almost all of the cohort used smartphones, and 75.0% (456/608) of them always use them at bedtime. Half of the students (53%) have poor sleep quality, while 32% are addicted to smartphone use. Using multivariable logistic regression, addiction to smartphones (SAS-SV score >31 males and >33 females) was significantly associated with poor sleep quality (PSQI >5) with an odds ratio of 1.8 (1.2-2.7). In addition, male gender and older students (age ≥21 years) were significantly associated with lower GPA (<4.5), with an odds ratio of 1.6 (1.1-2.3) and 2.3 (1.5-3.6), respectively; however, addiction to smartphones and poor sleep quality were not significantly associated with a lower GPA. Conclusions: Electronic device addiction is associated with increased risk for poor sleep quality; however, electronic device addiction and poor sleep quality are not associated with increased risk for a lower GPA.
... When analyzing the results of the sleep habits of students of the medical course, it is concluded that these group have considerable sleep disorders, excessive daytime sleepiness and use of stimulating and inhibiting substances. (PINAUD et al., 2002;MEDEIROS et al., 2001;SANTOS et al., 2014). ...
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A obra intitulada “Ciências da saúde: teorias e práticas vol. 1”, publicada pela Brazilian Journals Publicações de Periódicos e Editora, apresenta um conjunto de quatorze capítulos que visa abordar diversos assuntos do conhecimento relacionados com a área da saúde. Logo, os artigos apresentam as seguintes temáticas: a investigação dos efeitos da metformina na resposta imunológica e inflamatória contra o mycobacterium tuberculosis durante o tratamento para TB em pacientes diabéticos. A utilização do hormônio do crescimento na rede pública de saúde de uma cidade de São Paulo. Em seguida é discutido o impacto de um programa de melhoria contínua na redução da incidência de PAV na UTI adulto de um Hospital Público no interiorda Amazônia. Posteriormente é apresentado um estudo para analisar a freqüência das etiologias para predição da progressão da DRC em pacientes submetidos à hemodiálise em São João del Rei-MG. Em seguida, é abordada a influência do sono na qualidade de vida e, principalmente, no desempenho acadêmico dos discentes do curso de medicina, buscando compreender os impactos dele em suas funções laborais. A descoberta da terapia anti-retroviral (ART) que aumenta a expectativa de vida das pessoas vivendo com HIV (PLHIV) com mis de 50 anos de idade, entre outros estudos. Dessa forma, agradecemos aos autores por todo esforço e dedicação que contribuíram para a construção dessa obra, e esperamos que este livro possa colaborar para a discussão e entendimento de temas relevantes para a área da saúde, orientando docentes, estudantes, gestores e pesquisadores à reflexão sobre os assuntos aqui apresentados.
Individual preference for morning or evening activities (chronotype), affect, hardiness, and talent are associated with a variety of performance outcomes. This longitudinal study was designed to investigate the degree to which these variables are associated with academic, physical, and military performance. Self-reported measures of chronotype, affect, and hardiness were collected from 1149 cadets from the Class of 2016 upon entry to the United States Military Academy. Talent, a composite of academic, leadership, and physical fitness scores were drawn from cadet records. Academic, military, and physical performance measures were collected at graduation 4 years later. The results indicated that a morning orientation was associated with better physical and military performance. Higher talent scores, as well as lower levels of negative affect, were associated with better performance across all three performance measures. Hardiness was only associated with military performance. The findings suggest that a morning orientation and less negative affect may result in better performance overall within a challenging and structured military environment. Future studies of chronotype shifts may provide further insight into associated performance benefits.
The purpose of this study was to investigate the relationship between chronotype, learning style, and academic achievement. The study sample consisted of 1884 volunteer undergraduate students from 58 different universities across Turkey. The data were collected online during distance education because of the Covid-19 pandemic. Turkish version of Morningness-Eveningness Questionnaire (MEQ) and Big16 Learning Modality Inventory were used for data collection. The correlation between chronotype and cumulative grade point average (CGPA) scores was analyzed using Spearman's rho, and differences among the chronotypes were analyzed with Kruskal-Wallis test. Chi-square tests with pairwise z-test were used to analyze the relationships between the participants' learning style preferences and chronotypes. Also, ANCOVA analyses were performed to evaluate the interactions of gender × chronotype and gender × learning style on CGPA scores. The results revealed that participants' preference for visual and auditory styles differed by chronotype. Visual learning style was more dominant among morning (M) types, while auditory style was more dominant among evening (E) types. However, the most preferred learning style was visual, followed by auditory and kinesthetic styles for all chronotypes. No relationship was found between chronotype and academic achievement. The CGPA scores of the participants with kinesthetic learning style were lower than the participants with auditory and visual learning styles. The female participants had higher CGPA score than males. However, the CGPA scores did not differ for both male and female participants with different chronotype and learning style preferences. From the results, we suggest that academic achievement can be enhanced by consideration of students' learning style preferences for all chronotypes.
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An English language self-assessment Morningness-Eveningness questionnaire is presented and evaluated against individual differences in the circadian vatiation of oral temperature. 48 subjects falling into Morning, Evening and Intermediate type categories regularly took their temperature. Circadian peak time were identified from the smoothed temperature curves of each subject. Results showed that Morning types and a significantly earlier peak time than Evening types and tended to have a higher daytime temperature and lower post peak temperature. The Intermediate type had temperatures between those of the other groups. Although no significant differences in sleep lengths were found between the three types, Morning types retired and arose significantly earlier than Evening types. Whilst these time significatly correlated with peak time, the questionnaire showed a higher peak time correlation. Although sleep habits are an important déterminant of peak time there are other contibutory factors, and these appear to be partly covered by the questionnaire. Although the questionnaire appears to be valid, further evaluation using a wider subject population is required.
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The present study evaluated the differential effects of two manipulations of sleep-wake schedules on daily subjective ratings of daytime sleepiness of college undergraduate students. Two experimental conditions were compared: a sleep only group and a regularity group. Subjects in both conditions were given a lower limit for total sleep time (7.5 hours). Subjects in the regularity group received an additional instruction to keep a regular sleep schedule. The study was longitudinal and prospective. Following a baseline period (12 days), the experimental conditions were introduced. The experimental phase lasted 4 weeks and overall compliance was good. A follow-up phase (1 week) began 5 weeks past termination of the experimental phase. The findings indicated that when nocturnal sleep is not deprived, regularization of sleep-wake schedules is associated with reduced reported sleepiness. Subjects in the regular schedule condition reported greater and longer lasting improvements in alertness compared with subjects in the sleep only condition and reported improved sleep efficiency.
College students usually exhibit an irregular sleep-wake cycle characterized by great phase delays on weekends and short sleep length on weekdays. As the temporal organization of social activities is an important synchronizer of human biological rhythms, we investigated the role played by study's schedules and work on the sleep-wake cycle. Three groups of female college students were investigated: (1) no-job morning group, (2) no-job evening group, (3) job evening group. The volunteers answered a sleep questionnaire in the classroom. The effects of day of the week and group on the sleep schedules and sleep length were analyzed by a two way ANOVA for repeated measures. The three groups showed delays in the wake up time on weekends. No-job evening and morning groups also delayed bedtime, but the job evening group slept at the same time on weekdays as on weekends. Sleep length increased on weekends for morning group and job evening group, whereas the no-job evening group maintained the amount of sleep from weekdays to weekends. This survey showed that the tendency of phase delay on weekends was differently expressed according to study's schedules and work.
Sleep is often assessed in circadian rhythm studies and long-term monitoring is required to detect any changes in sleep over time. The present study aims to investigate the ability of the two most commonly employed methods, actigraphy and sleep logs, to identify circadian sleep/wake disorders and measure changes in sleep patterns over time. In addition, the study assesses whether sleep measured by both methods shows the same relationship with an established circadian phase marker, urinary 6-sulphatoxymelatonin. A total of 49 registered blind subjects with different types of circadian rhythms were studied daily for at least four weeks. Grouped analysis of all study days for all subjects was performed for all sleep parameters (1062–1150 days data per sleep parameter). Good correlations were observed when comparing the measurement of sleep timing and duration (sleep onset, sleep offset, night sleep duration, day-time nap duration). However, the methods were poorly correlated in their assessment of transitions between sleep and wake states (sleep latency, number and duration of night awakenings, number of day-time naps). There were also large and inconsistent differences in the measurement of the absolute sleep parameters. Overall, actigraphs recorded a shorter sleep latency, advanced onset time, increased number and duration of night awakenings, delayed offset, increased night sleep duration and increased number and duration of naps compared with the subjective sleep logs. Despite this, there was good agreement between the methods for measuring changes in sleep patterns over time. In particular, the methods agreed when assessing changes in sleep in relation to a circadian phase marker (the 6-sulphatoxymelatonin (aMT6s) rhythm) in both entrained (n= 30) and free-running (n= 4) subjects.
Twenty-five young people (Y group), three elderly people and seven people with various sleep disorders (SD group) kept a sleep log for 2–7 days, and their wrist-activity was monitored simultaneously. The sensitivity and specificity of the sleep log, and the ratio of agreement between the sleep log and actigraphic sleep-wake state were calculated. The sensitivity and specificity in Y group were 87.93 ± 6.49% and 96.51 ± 2.37%, respectively. The sensitivity in SD group was significantly lower than in Y group. Even in Y group one-hour agreement ratios dropped during the sleep onset period.
Despite the prevalence of sleep complaints among psychiatric patients, few questionnaires have been specifically designed to measure sleep quality in clinical populations. The Pittsburgh Sleep Quality Index (PSQI) is a self-rated questionnaire which assesses sleep quality and disturbances over a 1-month time interval. Nineteen individual items generate seven "component" scores: subjective sleep quality, sleep latency, sleep duration, habitual sleep efficiency, sleep disturbances, use of sleeping medication, and daytime dysfunction. The sum of scores for these seven components yields one global score. Clinical and clinimetric properties of the PSQI were assessed over an 18-month period with "good" sleepers (healthy subjects, n = 52) and "poor" sleepers (depressed patients, n = 54; sleep-disorder patients, n = 62). Acceptable measures of internal homogeneity, consistency (test-retest reliability), and validity were obtained. A global PSQI score greater than 5 yielded a diagnostic sensitivity of 89.6% and specificity of 86.5% (kappa = 0.75, p less than 0.001) in distinguishing good and poor sleepers. The clinimetric and clinical properties of the PSQI suggest its utility both in psychiatric clinical practice and research activities.
To investigate the prevalence of excessive daytime somnolence and contributing factors, 58,162 draftees between 17 and 22 years of age, registered in two selection centers of the French army, were screened by means of a 17-item questionnaire. In response, 8,201 subjects (14.1%) reported occasional daytime sleep episodes, 2,210 (3.8%) one or two daily episodes, and 640 (1.1%) more than two daily episodes. Of the total sample, five percent or 2,933 considered these sleep episodes to affect their lives. Different possible factors of daytime sleep episodes were investigated, including hours of nocturnal sleep, sleep-wake schedule, sleep difficulties, use of hypnotics, snoring, and occurrence of cataplexy. A strong association was found between these factors and excessive daytime somnolence. A stepwise multivariate analysis was performed on five of these factors: hours of nocturnal sleep, sleep-wake schedule, sleep difficulties, use of hypnotics, and snoring. All five factors were shown to be independently related to excessive daytime somnolence and were ranked in the following descending order: use of hypnotics, sleep difficulties, irregular sleep-wake schedule, snoring, and hours of sleep.
In addition to modulatory roles concerning bodily functions, sleep is assumed to play a main processing role with regard to newly acquired neural information. Elaboration of memory traces acquired during the waking period is assumed to require two sequential steps taking place during slow wave sleep (SWS) and eventually during paradoxical sleep (PS). This view is suggested by several considerations, not the least of which concerns the natural sequence of appearance of SWS and PS in the adult animal. While the involvement of PS in memory processing is well documented, the involvement of SWS is supported by the results of baseline and post-trial EEG analyses carried out in rats trained for a two-way active avoidance task or a spatial habituation task. Together with control analyses, these data indicate that the marked increase in the average duration of post-trial SWS episodes does not reflect the outcome of non-specific contingent factors, such as sleep loss or stress, but is related to memory processing events. Several considerations have furthermore led to the proposal that, during SWS, after a preliminary selection step, the first processing operation consists in the weakening of non-adaptative memory traces. The remaining memory traces would then be stored again under a better configuration during the ensuing PS episode. This view is in agreement with several relevant features of sleep, including the EEG waveforms prevailing during SWS and PS, as well as the ontogenetic sequence of appearance of SWS and PS. Some theoretical considerations on the role of sleep are also in agreement with the sequential hypothesis. More recent data indicate that the learning capacity of rats is correlated with several baseline EEG features of sleep and wakefulness. They include the average duration of PS episodes and of SWS episodes followed by wakefulness (longer in fast learning rats), and the waking EEG power spectrum of fast learning rats whose output is more balanced in the frequency range below 10 Hz than in slow learning and in non-learning rats. Additional EEG data suggest that fast learning rats may accomplish 'on line' processing of newly acquired information according to a sequence of events not dissimilar from the one proposed by the sequential hypothesis.