Sleep in relation to age, sex, and chronotype in Japanese workers

The quantity and quality of scientific evidence about the health of working women in occupational health of Japan: A scoping review

OBJECTIVE

We aim to investigate the quantity and quality of scientific evidence dealing with comprehensive health issues of working women in occupational health.

METHODS

This scoping review of original articles that investigated comprehensive health issues of working women aged 19-64 years in Japan was published in PubMed (1967-2022) and Igaku Chuo Zasshi (or Ichu-shi, 1982-2022). Using identical broad search terms, we first identified 17 122 English and 6154 Japanese articles. We excluded those with clinically relevant topics, or ethnicity other than Japanese and included 853 English and 855 Japanese articles for review and classified them into nine research areas considered to be critical factors for women in the workforce and five study design groups to investigate the quality of the evidence accumulated.

RESULTS

Among 853 English-language articles in PubMed, "Mental health" was the most frequent area studied, followed by "Work-related disease" and "Lifestyle-related disease." Among 855 Japanese-language articles from Ichu-shi, "Mental health" was the most frequently studied area followed by "Work and balance," and "Work-related disease." "Infertility, pregnancy, and childbirth" and "Menstruation, menopause, and genital disease" were well studied in Ichu-shi but scarcely published in PubMed. "Harassment and discrimination" were sparsely reported in both databases. As for research designs, many articles in both PubMed and Ichu-shi employed descriptive or cross-sectional study designs. However, a few studies employed cohort/longitudinal or interventional studies.

CONCLUSION

The results underscored the need for higher-quality study designs with more scientific evidence on working women's health in the field of occupational health.

Subjective sleep quality, quantitative sleep features, and their associations dependent on demographic characteristics, habitual sleep–wake patterns, and distinction of weekdays/weekends

Generally applicable qualifications of sleep and principles for achieving better sleep are difficult to design, because sleep quality can depend on individual demographic characteristics and lifestyles. In this study, the static and dynamic features of sleep–wake patterns were analyzed in association with quantitative sleep-related parameters and self-rated sleep quality to serve as a practical selection of sleep–wake patterns fitted to individual conditions. Data obtained over a 2-week period by actigraphy from university students and information technology workers were measured to obtain a daily subjective rating of sleep quality using the Oguri–Shirakawa–Azumi (OSA) sleep inventory. Qualitative sleep quality in terms of OSA score and quantitative sleep-related and chronobiological features were analyzed with regard to their dependency on the demographic characteristics, habitual sleep–wake patterns (HSWP), and distinction of weekdays/weekends. Multi-factor ANOVA was used to further investigate their dependencies regarding multiple ways of interactions between the demographic characteristics, HSWP, and distinction of weekdays/weekends. Subjective sleep quality and quantitative sleep-related parameters depended on the demographic characteristics, and so did their associations. The classification of day-to-day variations in HSWP showed four clusters that were effective factors for understanding their dependencies. Multi-factor analysis revealed demographic characteristics, HSWP, distinction of weekdays/weekends, and their multi-way interactions up to 3rd order as significant effectors of qualitative and quantitative quality of sleep. This study clarified how quantitative sleep-related parameters, subjective sleep quality, and their associations depended on demographic characteristics. Furthermore, their dependency was understood as a combination of multi-way interactions between the demographic characteristics, HSWP, and the distinction of weekdays/weekends. Our findings could provide a basis for the design of individually matched sleep–wake patterns.

Sleep-Scheduling Strategies in Hospital Shiftworkers

INTRODUCTION

Shiftwork causes circadian disruption and results in impaired performance, sleep, and health. Often, individuals on non-standard shifts cannot modify work schedules. At-home sleep schedules are a potentially modifiable point of intervention, yet sleep-scheduling strategies remain relatively understudied. Specifically, the adoption of multiple strategies and the employment of strategies for not only night shifts, but also early starts on days, have yet to be formally examined to our knowledge. We studied how adoption of specific and/or multiple sleep-scheduling strategies for day and night shifts relates to measures of adaptation to shiftwork, self-reported on-shift sleepiness, and individual characteristics (eg, age, chronotype, education in circadian and sleep health). We hypothesized: 1) strategies would differ by shift type, 2) individuals would adopt multiple strategies, 3) strategies better aligned with circadian principles would relate to measures of adaptation, and 4) individual characteristics, such as having dependents, would relate to strategy selection.

METHODS

A retrospective, online questionnaire (including items from the Survey of Shiftworkers and items related to sleep-scheduling strategies) was administered to both permanent and rotating hospital staff in four wards working 12-h day and/or night shifts (n=89). Additionally, reasons for strategy selection were explored.

RESULTS

Level of adaptation varied by sleep-scheduling strategy, with the least adaptation for those utilizing the Incomplete Shifter strategies. For night shifts, Night Stay and Switch Sleeper-N strategies were related to lower mid-shift sleepiness. Many night workers reported using strategies that restricted sleep, and most reported using multiple strategies, both of which also related to lower adaptation. Domestic considerations were the most common rationale for strategy selection. Strategies varied by several individual characteristics, including chronotype, dependents, and level of sleep education.

DISCUSSION

Future work should investigate sleep strategies and circadian interventions to help mitigate the effects of circadian and sleep disruption in hospital staff.

Sleep Quality, Sleep Structure, and PER3 Genotype Mediate Chronotype Effects on Depressive Symptoms in Young Adults

Depression and its related mood disorders are a major global health issue that disproportionately affects young adults. A number of factors that influence depressive symptoms are particularly relevant to the young adult developmental stage, including sleep loss, poor sleep quality, and the tendency toward eveningness in circadian preferences. However, relatively few studies have examined the relationship between sleep and circadian phenotypes, and their respective influences on mood, or considered potential molecular mechanisms driving these associations. Here, we use a multi-year, cross-sectional study of 806 primarily undergraduates to examine the relationships between sleep-wake chronotype, sleep disturbance, depression and genotypes associated with the PER3 variable number of tandom repeats (VNTR) polymorphism-circadian gene variants associated with both chronotype and sleep homeostatic drive. In addition, we use objective, Fitbit-generated sleep structure data on a subset of these participants (n = 67) to examine the relationships between chronotype, depression scores, actual measures of sleep duration, social jetlag, and the percent of deep and rapid eye movement (REM) sleep per night. In this population, chronotype is weakly associated with depressive symptoms and moderately correlated with self-reported sleep disturbance. Sleep disturbance is significantly associated with depression scores, but objective sleep parameters are not directly correlated with Beck Depression Inventory (BDI-II) scores, with the exceptions of a moderate correlation between social jetlag and depression scores in females and a marginal correlation between sleep duration and depression scores. Multiple regression and path analyses reveal that chronotype effects on depressive symptoms in this population are mediated largely by sleep disturbance. The PER3 VNTR genotype significantly predicts depressive symptoms in a model with objective sleep parameters, but it does not significantly predict depressive symptoms in a model with chronotype or subjective sleep disturbance. Interestingly, PER35,5 genotypes, in males only, are independently related to chronotype and depression scores. Our results support hypotheses linking subjective sleep quality and chronotype and provide a first step in understanding how objective sleep structure may be linked to chronotype and depressive symptoms. Our results also suggest that circadian gene variants may show sex-specific effects linking sleep duration and sleep structure to depression.

Moderating effects of depressive symptoms on the relationship between problematic use of the Internet and sleep problems in Korean adolescents

BACKGROUND

Adolescence is a period of marked sleep pattern changes and sleep problems, which may result from both endogenous and exogenous factors. Among the various factors affecting adolescent sleep, depression and problematic Internet use (PIU) have received considerable attention. We examined if there is a different PIU effect on sleep between depressed group and non-depressed groups.

METHODS

Data for a total of 766 students' between 7th and 11th grades were analyzed. We assessed various variables related sleep to problems and depression and compared those variables between an adolescent group with problematic Internet use (PIUG) and an adolescent group with normal Internet use (NIUG).

RESULTS

One hundred fifty two participants were classified as PIUG, and 614 were classified as NIUG. Compared with the NIUG, the members of the PIUG were more prone to insomnia, excessive daytime sleepiness and sleep-wake behavior problems. The PIUG also tended to include more evening types than the NIUG. Interestingly, the effect of Internet use problems on sleep problems appeared to be different according to the presence or absence of the moderating effect of depression. When we considered the moderating effect of depression, the effect of Internet use problems on sleep-wake behavior problems, insomnia and excessive daytime sleepiness increased with increasing Young's Internet Addiction Scale (IAS) scores in the non-depressed group. However, in the depressed group, the effects of Internet use problems on sleep-wake behavior problems and insomnia did not change with increasing Internet use problems, and the effect of Internet use problems on excessive daytime sleepiness was relatively decreased with increasing Internet use problems in the depressed group.

CONCLUSIONS

This study demonstrated that the effect of PIU on sleep presented differently between the depressed and non-depressed groups. PIU is associated with poorer sleep in non-depressed adolescents but not in depressed adolescents. This finding might be observed because PIU may be the biggest contributor to sleep problems in the problematic Internet user without depression, but in the problematic Internet user with depression, depression might be a more important contributor to sleep problems; thus, the influence of PIU on sleep effect might be diluted.

Nocturnal sleep mediates the relationship between morningness-eveningness preference and the sleep architecture of afternoon naps in university students

The present study investigated the parameters of nocturnal sleep that mediate the relationship between morningness-eveningness preference and the sleep architecture of naps in university students. This study had a cross-sectional, descriptive correlational design. The sleep architecture of 52 students invited to take an afternoon nap in the laboratory was recorded. The morningness-eveningness questionnaire (MEQ) was used to evaluate morningness-eveningness preference. An actigraph was used to collect students' nighttime sleep data in the week preceding the study. Polysomnography was used to measure the sleep architecture of the participants' naps. After adjustments for potential factors, although the MEQ did not directly correlate with the percentage of sleep stages in naps, the effects of the MEQ on the percentage of Stage 1 sleep, slow-wave sleep, and rapid eye movement sleep; sleep duration; and sleep efficiency of naps were mediated by the total sleep time in the preceding week. This preliminary study suggests that nap quality was affected by morningness-eveningness preference through the mediation of total nocturnal sleep time. Therefore, future studies should be carefully designed to consider nighttime sleep patterns when analyzing the effects of chronotypes on daytime sleep.

Correlates and prognostic relevance of sleep irregularity in inter-episode bipolar disorder

OBJECTIVES

Sleep-wake disturbances, such as sleep irregularity, are common in bipolar disorder. Early studies suggest that sleep irregularity is associated with mood symptoms in bipolar disorder, but little research has been conducted to identify other correlates of sleep irregularity. We investigated the relationship between sleep irregularity and sleep quality, social rhythms, eveningness, sleep-related cognitions and behaviors, and past and future mood episodes in 84 patients with inter-episode bipolar I or II disorder.

METHODS

This is a retrospective and prospective, naturalistic follow-up study. The Expanded Consensus Sleep Diary, Pittsburgh Sleep Quality Index (PSQI), Social Rhythm Metric (SRM-II-5), Composite Scale of Morningness (CSM), Dysfunctional Beliefs and Attitudes About Sleep Scale (DBAS-16), and Sleep Hygiene Practice Scale (SHPS) were administered. The Square Successive Difference (SSD), derived from a week-long sleep diary, was used as an index of sleep irregularity. Multilevel modeling analysis, which adjusts for biases in parameter estimates, was used to minimize the impact of missing data. Bonferroni correction was performed to account for multiple testing.

RESULTS

Higher SSD scores of sleep diary variables were significantly associated with higher PSQI, SRM-II-5, DBAS-16, and SHPS scores. Irregularity in total sleep time was related to more depressive episodes in the past 5years (p=.002), while irregularity in wake after sleep onset predicted the onset of depressive episodes over the next 2years (p=.002).

CONCLUSION

Sleep irregularity was associated with poor sleep quality, irregular social rhythms, dysfunctional sleep-related cognitions and behaviors, and greater number of depressive episodes in bipolar disorder.

The relationship between chronotype and mood fluctuation in the general population

There is a lack of evidence for the relationship between chronotype and subthreshold mood fluctuation. The present study aims to investigate the relationship between chronotypes and mood fluctuation in the general population. Participants (n=302) who have had no experience of major mood episodes were included. The Korean version of the Composite Scale of Morningness (CSM) was used to classify participants according to three chronotypes. Mood fluctuation was measured using the Mood Disorder Questionnaire (MDQ) and the Bipolar Spectrum Diagnostic Scale (BSDS). Mean scores achieved by the three chronotype groups on the MDQ and the BSDS were compared. There were no significant differences in the frequency of positive responses on the MDQ for the three chronotype groups. However, there was a significant group difference in total BSDS scores. The eveningness group had significantly higher BSDS-D scores than did either the morningness or the intermediate group have. In addition, the eveningness group had significantly higher BSDS-M scores than the morningness group. After adjusting for age by the analysis of covariance (ANCOVA), there were still significant group differences in total BSDS scores. The present results suggest that eveningness may be more related to mood fluctuation than morningness. The eveningness may be an important factor related to soft bipolarity or mood fluctuation.

Circadian Phenotype Composition is a Major Predictor of Diurnal Physical Performance in Teams

Team performance is a complex phenomenon involving numerous influencing factors including physiology, psychology, and management. Biological rhythms and the impact of circadian phenotype have not been studied for their contribution to this array of factors so far despite our knowledge of the circadian regulation of key physiological processes involved in physical and mental performance. This study involved 216 individuals from 12 different teams who were categorized into circadian phenotypes using the novel RBUB chronometric test. The composition of circadian phenotypes within each team was used to model predicted daily team performance profiles based on physical performance tests. Our results show that the composition of circadian phenotypes within teams is variable and unpredictable. Predicted physical peak performance ranged from 1:52 to 8:59 p.m. with performance levels fluctuating by up to 14.88% over the course of the day. The major predictor for peak performance time in the course of a day in a team is the occurrence of late circadian phenotypes. We conclude that circadian phenotype is a performance indicator in teams that allows new insight and a better understanding of team performance variation in the course of a day as often observed in different groupings of individuals.

Distribution of Chronotypes among a Sample of Iraqi Kurdish Medical Students

OBJECTIVES

The aim of this study was to assess the distribution of chronotypes in a sample of Iraqi Kurdish medical students.

METHODS

A descriptive cross-sectional study was conducted at the Hawler Medical University College of Medicine in Erbil City, Iraq, between 1(st) January and 31(st) March 2013. A total of 580 students were given the reduced version of the Horne and Ostberg Morningness-Eveningness Questionnaire (MEQr), a close-ended self-administered questionnaire.

RESULTS

Of the 580 students, 130 (22.4%) were male and 450 (77.6%) were female. The mean age ± standard deviation was 20.3 ± 1.45 years, with a range of 17-24 years. Most of the students (52.6%) were in the intermediate class, followed by morning type (24.1%) and evening type (23.3%). Significant gender differences were detected in the proportion of morning, intermediate and evening types (P <0.001). The mean scores for the female students were 14.8 ± 2.2 and the mean scores for the male students were 14.6 ± 7.3, with no statistically significant differences (P = 0.45).

CONCLUSION

Students in the College of Medicine were mostly classified as intermediate types. The morning type was more common among this student population, particularly male students, than has been reported in similar age groups in some Western countries. There was a significant gender difference in the proportion of MEQr types.

Circadian preference and sleep-wake regularity: associations with self-report sleep parameters in daytime-working adults

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. (Author correspondence: asoehner@berkeley.edu ).

Chronotype and diurnal cortisol profile in working women: differences between work and leisure days

The influence of chronotype on the diurnal profile of salivary cortisol was examined in a sample of 187 healthy women: 21 evening chronotype, 24 morning chronotype and 142 intermediate chronotype. Saliva samples were collected at waking, 30 min post-awakening, at 1000 h, 1200 h, 1500 h, 1700 h and at bedtime on one work and one leisure day. Several components of the diurnal profile were examined including the cortisol awakening response, the total cortisol output and the diurnal profile on both the work and the leisure day, a significant main effect of time emerged (both p<0.01). After adjustment for age, smoking status, self-rated health, time of waking, and sleep problems, no effect of chronotype was evident for cortisol in the evening, the cortisol awakening response, or total cortisol output over the working day. However, on the leisure day, total cortisol output was greater in evening-types than intermediate or morning-types, after adjustment for covariates (p=0.029). The present data indicate that chronotype has a limited impact on the diurnal cortisol profile of healthy women, and may be somewhat impervious to individual preferences for morning or evening activity.

Distribution of chronotypes in a large sample of young adult Saudis

BACKGROUND AND OBJECTIVES

There are no published data on the chronotypes of young Saudi adults. This study assessed the distribution of chronotypes in college-aged Saudis.

DESIGN AND SETTING

Cross-sectional survey of college students.

PATIENTS AND METHODS

A validated abridged version of the original Horne and Ostberg morningness-eveningness questionnaire (MEQr) was used to assess the chronotype of 759 subjects.

RESULTS

Of 540 (71.1%) males and 219 (28.9%) females participated in this study ( age range, 18-32 years), 138 (18.2%) were "morning-types," 417 (54.9%) were "neither-types" and 204 (26.9%) were "evening-types." There was no significant gender difference in MEQr typology. In Saudis, particularly males, the frequency of morning typology was somewhat higher than that reported for individuals in similar age groups in some Western countries.

CONCLUSION

Most Saudi college students had no preference for morningness or eveningness and were classified as "intermediate-types." Morningness appears to be slightly more common in Saudis, especially males, than in individuals of some Western societies.

Differential impact of chronotype on weekday and weekend sleep timing and duration

Most recommendations are that adults should obtain 7-8 hours of sleep per night, although there are individual differences in self-reported sleep need. Chronotype (preference for early or late sleep timing), in combination with social demands, may affect the ability to obtain adequate sleep. This questionnaire study assessed perceived sleep need and self-reported sleep timing and duration during the week and on the weekend with respect to chronotype in visitors to the Museum of Science in Boston. Increasing age was associated with greater morningness. After adjusting for age, we found no significant association between chronotype and self-reported sleep need, or between chronotype and weekday sleep duration. However, we did find that greater eveningness was associated with a larger gap between self-reported sleep need and weekday sleep duration. On weekends, greater eveningness was associated with a longer sleep duration and greater extension of sleep, with the sleep extension achieved by later wake times. Together, these findings suggest that evening types accumulate a sleep debt during the week, despite reporting a similar sleep need and duration as morning types, and evening types then attempt to make up for that lost weekday sleep on the weekends. Studies of sleep need and sleep duration should take chronotype into account, and studies of chronotype may be confounded by the association between age and morningness, and must account for this potential confound in selection criteria and/or analysis.

Comparison of the Munich Chronotype Questionnaire with the Horne‐Östberg's Morningness‐Eveningness score

We report on results from an Internet survey of sleeping habits in a Dutch population using the Munich Chronotype Questionnaire (MCTQ), supplemented with the Horne-Ostberg Morningness-Eveningness Questionnaire (MEQ). The MCTQ was completed by 5,055 responders, of which 2,481 also completed the MEQ. MEQ score correlated well with the MCTQ assessment of time of mid-sleep on free days (MSF; r = - 0.73) and on workdays (MSW; r = - 0.61). MEQ was more strongly correlated with MSF (50% of sleep time) than with sleep onset (0%), rise time (100%), or with any other percentile (10 to 40, 60% to 90%) of sleep on free days. The study shows that chronotype (based on MSF as measured by the MCTQ) strongly correlates with morningness-eveningness (as measured by the MEQ). However, the MCTQ collects additional detailed information on sleep-wake behavior under natural conditions.

Relationship between depressive mood and chronotype in healthy subjects

AIM

The endogenous circadian clock generates daily variations of physiological and behavior functions such as the endogenous interindividual component (morningness/eveningness preferences). Also, mood disorders are associated with a breakdown in the organization of ultradian rhythm. Therefore, the purpose of the present study was to assessed the association between chronotype and the level of depressive symptoms in a healthy sample population. Furthermore, the components of the depression scale that best discriminate the chronotypes were determined.

METHODS

This cross-sectional study involved 200 volunteers, aged 18-99 years, 118 women and 82 men. The instruments were the Montgomery-Asberg Depression Rating Scale (MADRS), the Morningness/Eveningness Questionnaire, the Self-Reporting Questionnaire-20, and the future self-perception questionnaire.

RESULTS

Logistic regression showed that subjects with the eveningness chronotype had a higher chance of reporting more severe depressive symptoms compared to morning- and intermediate-chronotypes, with an odds ratio (OR) of 2.83 and 5.01, respectively. Other independent cofactors associated with a higher level of depressive symptoms were female gender (OR, 3.36), minor psychiatric disorders (OR, 3.70) and low future self-perception (OR, 3.11). Younger age, however, was associated with a lower level of depressive symptoms (OR, 0.97). The questions in the MADRS that presented higher discriminate coefficients among chronotypes were those related to sadness, inner tension, sleep reduction and pessimism.

CONCLUSION

Identification of an association between evening typology and depressive symptoms in healthy samples may be useful in further investigation of circadian typology and the course of depressive disease.

Influence of nocturnal asthma on chronotype

Individual differences in circadian rhythm have been studied since the past century. Chronotypes are a chronobiology classification based on the preferential times for beginning and ending activities throughout the day. Chronotypes can be classified as definitely morning, moderately morning, indifferent, moderately evening, and definitely evening. We aim to assess the distribution of chronotypes in asthmatics and the relationship of chronotype to the presence of nocturnal symptoms. Two hundred subjects were evaluated, 100 asthmatics and 100 non-asthmatics. The Morningness/Eveningness questionnaire was applied for chronotype determination. The asthmatics were subdivided according to the presence or absence of nocturnal symptoms. The chronotype distribution did not differ significantly between asthmatics and non-asthmatics. Thirty-five percent of the asthma group reported nocturnal symptoms. There was a significant difference in chronotype distribution between asthmatics with and without nocturnal worsening. The asthmatics with nocturnal symptoms had a lower prevalence of morning types and had a greater predominance of indifferent chronotype compared to asthmatics without nocturnal symptoms (p = 0.011). In conclusion, asthmatics with nocturnal symptoms present deviation from the chronotype distribution curve when compared to asthmatics without nocturnal symptoms. This is the first study to show the effect of a disease on chronotypes.

Influence of chronotype, season, and sex of subject on sleep behavior of young adults

The aim of this study was to investigate whether sex, season, and/or chronotype influence the sleep behavior of university students. Detailed data were collected on activity/rest patterns by wrist actigraphy combined with diaries. Thirty-four medical students (19 female and 15 male) were monitored by Actiwatch actometers for 15 consecutive days in May and again in November. The data of a modified Horne and Ostberg chronotype questionnaire, which were collected from 1573 female and 1124 male medical school students surveyed in the spring and autumn over an eight-year period, were evaluated. Actiwatch sleep analysis software was used to process the activity data with statistical analyses performed with ANOVA. We found no significant sex-specific differences in sleep efficiency, sleep onset latency, or actual sleep-time duration. However, we did find a difference in sleep efficiency between morning and evening types, with morning types having a higher sleep efficiency (87.9%, SD=1.3) than evening types (84.3%, SD=0.87%; p=0.007). Seasonal differences were also detected: the actual sleep-time duration in autumn was significantly longer (mean 6.9 h, SD=0.13 h) than in spring (6.6 h, SD=0.1 h; p=0.013). Evaluation of the chronotype questionnaire data showed that individuals with no special preference for morningness or eveningness (i.e., so-called intermediates) were most common. The distribution of chronotypes was related to the sex of subject. Men displayed eveningness significantly more often than women (28.9% males vs. 20.8% females; p<0.001), while females exhibited greater morningness (20.3% females vs.15.6% males; p<0.001). Sex influences chronotype distribution, but not actual sleep time-duration, sleep onset latency, or sleep efficiency. The latter, however, differed among chronotypes, while actual sleep-time duration was affected by season.

Morningness and eveningness: The free cortisol rise after awakening in “early birds” and “night owls”

We investigated salivary cortisol profiles in the first hour after awakening in morning versus evening chronotypes. Chronotypes were defined by Horne and Ostberg's Owl-and-Lark-Questionnaire. In a sample of 112 healthy, day-active young men, we identified 9 morning and 29 evening chronotypes. Saliva samples were collected 0, 30, 45, and 60min after awakening on 2 consecutive days. Log-transformed cortisol levels were analyzed with General Linear Model procedures (GLMs) and awakening time and sleep duration were entered as covariates. On both days, a significant main effect of chronotype emerged (both p=0.02), and this effect could not be explained by differences in awakening time or sleep duration. The present data support the idea that morning relative to evening chronotypes might show higher cortisol levels in the first hour after awakening. In sum, individual chronotype should be acknowledged as one further possible source of interindividual variability in the cortisol rise after awakening.

Sleepiness/alertness among healthy evening and morning type individuals

Objective: The aim of this study was to determine the level of sleepiness/alertness among different chronotypes.Background: The Horne-Ostberg Morningness-Eveningness Questionnaire (MEQ) has allowed the characterization of chronotypes that are associated with a number of biological factors including: body temperature, cortisol rhythm, sleep patterns, and architecture.Methods: Fifty-six consecutive normal volunteers underwent an 8-h polysomnogram followed by a multiple sleep latency test (MSLT). Each subject also completed the MEQ and the Sleep/Wake Activity Inventory.Results: Evening types (ET) reported significantly later bedtimes and risetimes than both morning types (MT) and neither types (NT, P<0.05). On nocturnal polysomnography, the ET documented significantly longer latencies to stage 1 and persistent sleep when compared to both the NT and MT (P<0.01). There were no significant differences in the level of sleepiness on the MSLT across the different chronotypes. However, the pattern of sleepiness differed among them. While ET and NT showed differential sleep latencies across nap opportunities, MT showed no evidence of circadian variation on their level of sleepiness.Conclusions: There were no overall differences in daytime sleepiness/alertness across chronotypes. However, a differential pattern of sleep latencies was noted on the MSLT.

Circadian rhythmicity of cortisol and body temperature: morningness-eveningness effects

The purpose of this study was to describe and compare the circadian rhythm of body temperature and cortisol, as well as self-reported clock times of sleep onset and offset on weekdays and weekends in 19 healthy adult "larks" (morning chronotypes) and "owls" (evening chronotypes), defined by the Home and Ostberg questionnaire. Day-active subjects entered the General Clinical Research Center, where blood was sampled every 2 h over 38 h for later analysis for cortisol concentration by enzyme immunoassay. Rectal body temperature was measured continuously. Lights were turned off at 22:30 for sleep and turned on at 06:00, when subjects were awakened. The acrophases (peak times) of the cortisol and temperature rhythms occurred 55 minutes (P < or = .05) and 68 minutes (P < .01), respectively, earlier in the morningness group. The amplitude of the cortisol rhythm was lower in the eveningness than in the morningness group (P = n.s.). Subject groups differed on all indices of habitual and preferred timing of sleep and work weekdays and weekends (P = .05-.001).

Nocturnal sleep pattern in Native Brazilian Terena adults

Social-economic factors influence sleep habits. This research analyzes characteristics of nocturnal sleep in Brazilian Native Terena adults. Sixty-four adults (31 M; 33 F) from 18 to 75 years, with a mean age of 37.0, from the Indian Reservation village of Córrego do Meio, in the central region of Mato Grosso do Sul, an agriculturally oriented group were evaluated. Nocturnal sleep characteristics were evaluated by means of a standard questionnaire applied to each individual. It was observed that reported nocturnal sleep was longer, sleep onset was earlier and wake up time was also earlier than usually described in urban populations. The mean total time in bed was 8.5 h or more, in every age bracket. The seven-day prevalence rate of insomnia was 4.6%, while the seven-day prevalence rate of hypnotic use was 1.5%, both remarkably less than described in urban populations. These findings stress the need to consider ethnic influences on sleep patterns and disorders.

Siestas among Brazilian Native Terena adults : a study of daytime napping

Regular daytime napping behavior, also known as siesta culture, is influenced by circadian, cultural and environmental factors. This research analyzes characteristics of regular daytime napping in Brazilian Native Terenas. We evaluated 65 adults ( 32 M; 33 F ) from 18 to 75 years, with a mean age of 37.2, from the Indian Reservation village Córrego do Meio, in the central region of Mato Grosso do Sul. Daytime napping characteristics were evaluated by means of a standard questionnaire applied to each individual. It was observed that weekly daytime napping (at least once a week) was present in 72. 3% of the population. There was a tendency to occur in males. The effects of weekends was mild. Mean onset time of daytime sleep was 12.2 h, remarkably earlier than usually described in urban populations. This data stresses the need to consider ethnic influences in order to understand sleep habits.

Sleep and chronotype for children in Japan

To investigate the change in sleep-wake habits, Morningness-Eveningness preference, and sleep status by grade, 512 students aged from 6 to 18 years, were tested using the Morningness-Eveningness Questionnaire and Sleep Questionnaire. The habitual waking time showed no difference by grade, but the students above Grade 7 reported a significantly later habitual bedtime and had a shorter length of sleep on weekdays than the students below Grade 6. The students above Grade 7 reported a significant difference between habitual and preferred waking times but did not show a difference between habitual and preferred bedtimes. Although the sleep length during weekends became shorter from Grade 1, the sleep length of students above Grade 8 showed a significant difference between the weekdays and weekends; they had more than nine hours of sleep on the weekends. The percentage of students taking a nap during a school lesson significantly increased across Grades 8 to 12. The mean score on the questionnaire decreased across grades and the decrease was significant at Grade 7. Both the habitual and preferred bedtimes and waking times were later from the Morning, Intermediate, to the Evening types across grades. The difference by chronotype in preferred waking time increased for groups from the primary, junior high, to the high school. Also, the sleep lengths both weekdays and weekends decreased from the Morning, Intermediate, to the Evening type for all grades. We suggested that the delay of sleep phase, reduction of sleep length, increased daytime napping, and transition to Evening type were remarkably represented around Grade 7.