Sleep and academic performance in undergraduates: a multi-measure, multi-predictor approach

The present study examined the associations of sleep patterns with multiple measures of academic achievement of undergraduate university students and tested whether sleep variables emerged as significant predictors of subsequent academic performance when other potential predictors, such as class attendance, time devoted to study, and substance use are considered. A sample of 1654 (55% female) full-time undergraduates 17 to 25 yrs of age responded to a self-response questionnaire on sleep, academics, lifestyle, and well-being that was administered at the middle of the semester. In addition to self-reported measures of academic performance, a final grade for each student was collected at the end of the semester. Univariate analyses found that sleep phase, morningness/eveningness preference, sleep deprivation, sleep quality, and sleep irregularity were significantly associated with at least two academic performance measures. Among 15 potential predictors, stepwise multiple regression analysis identified 5 significant predictors of end-of-semester marks: previous academic achievement, class attendance, sufficient sleep, night outings, and sleep quality (R(2)=0.14 and adjusted R(2)=0.14, F(5, 1234)= 40.99, p < .0001). Associations between academic achievement and the remaining sleep variables as well as the academic, well-being, and lifestyle variables lost significance in stepwise regression. Together with class attendance, night outings, and previous academic achievement, self-reported sleep quality and self-reported frequency of sufficient sleep were among the main predictors of academic performance, adding an independent and significant contribution, regardless of academic variables and lifestyles of the students.     

CHRONIC SLEEP DEFICIT AND PERFORMANCE OF A SUSTAINED ATTENTION TASK—AN ELECTROOCULOGRAPHY STUDY

Electrooculography (EOG) was used to explore performance differences in a sustained attention task during rested wakefulness (RW) and after 7 days of partial sleep deprivation (SD). The RW condition was based on obtaining regular sleep, and the SD condition involved sleep restriction of 3?h/night for a week resulting in a total sleep debt of 21?h. The study used a counterbalanced design with a 2-wk gap between the conditions. Participants performed a sustained attention task for 45?min on four occasions: 10:00–11:00, 14:00–15:00, 18:00–19:00, and 22:00–23:00?h. The task required moving gaze and attention as fast as possible from a fixation point to a target. In each session, 120 congruent and 34 incongruent stimuli were presented, totaling 1232 observations/participant. Correct responses plus errors of omission (lapses) and commission (false responses) were recorded, and the effect of time-of-day on sustained attention following SD was investigated. The analysis of variance (ANOVA) model showed that SD affected performance on a sustained attention task and manifested itself in a higher number of omission errors: congruent stimuli (F_(1,64)?=?13.3, p?<?.001) and incongruent stimuli (F_(1,64)?=?14.0, p?<?.001). Reaction times for saccadic eye movements did not differ significantly between experimental conditions or by time-of-day. Commission errors, however, exhibited a decreasing trend during the day. The visible prevalence of omissions in SD versus RW was observed during the mid-afternoon hours (the so-called post-lunch dip) for both congruent and incongruent stimuli (F_(1,16)?=?5.3, p?=?.04 and F_(1,16)?=?5.6, p?=?.03, respectively), and at 18:00?h for incongruent stimuli (F_(1,13)?=?5.7, p?=?.03). (Author correspondence: magda.fafrowicz@uj.edu.pl)     

LIGHT INTENSITY EXPOSURE,SLEEP DURATION,PHYSICAL ACTIVITY,AND BIOMARKERS OF MELATONIN AMONG ROTATING SHIFT NURSES

Long-term, night shiftwork has been identified as a potential carcinogenic risk factor. It is hypothesized that increased light at night exposure during shiftwork reduces melatonin production, which is associated with increased cancer risk. Sleep duration has been hypothesized to influence both melatonin levels and cancer risk, and it has been suggested that sleep duration could be used as a proxy for melatonin production. Finally, physical activity has been shown to reduce cancer risk, and laboratory studies indicate it may influence melatonin levels. A cross-sectional study of light exposure, sleep duration, physical activity, and melatonin levels was conducted among 61 female rotating shift nurses (work schedule: two 12?h days, two 12?h nights, five days off). Light intensity was measured using a light-intensity data logger, and sleep duration and physical activity were self-reported in a study diary and questionnaire. Melatonin concentrations were measured from urine and saliva samples. The characteristics of nurses working day and night shifts were similar. Light intensity was significantly higher during sleep for those working at night (p<?0.0001), while urinary melatonin levels following sleep were significantly higher among those working days (p?=?0.0003). Mean sleep duration for nurses working during the day (8.27?h) was significantly longer than for those working at night (4.78?h, p<?0.0001). An inverse association (p?=?0.002) between light exposure and urinary melatonin levels was observed; however, this was not significant when stratified by shift group. There was no significant correlation between sleep duration and melatonin, and no consistent relationship between physical activity and melatonin. Analysis of salivary melatonin levels indicated that the circadian rhythms of night workers were not altered, meaning peak melatonin production occurred at night. This study indicates that two nights of rotating shift work may not change the timing of melatonin production to the day among those working at night. Additionally, in this study, sleep duration was not correlated with urinary melatonin levels, suggesting it may not be a good proxy for melatonin production. (Author correspondence: anne.grundy@queensu.ca)     

Class Start Times,Sleep, and Academic Performance in College: A Path Analysis

Path analysis was used to examine the relationship between class start times, sleep, circadian preference, and academic performance in college-aged adults. Consistent with observations in middle and high school students, college students with later class start times slept longer, experienced less daytime sleepiness, and were less likely to miss class. Chronotype was an important moderator of sleep schedules and daytime functioning; those with morning preference went to bed and woke up earlier and functioned better throughout the day. The benefits of taking later classes did not extend to academic performance, however; grades were somewhat lower in students with predominantly late class schedules. Furthermore, students taking later classes were at greater risk for increased alcohol consumption, and among all the factors affecting academic performance, alcohol misuse exerted the strongest effect. Thus, these results indicate that later class start times in college, while allowing for more sleep, also increase the likelihood of alcohol misuse, ultimately impeding academic success. (Author correspondence: sonyper@stlawu.edu)     

Morningness: Protective Factor for Sleep-Related and Emotional Problems in Childhood and Adolescence?

The relationship between morningness/eveningness, sleep, and psychological problems is well documented in adults as well as in adolescents. However, research on the circadian orientation and its concomitants in younger children is scarce. The authors investigated the distribution of morningness/eveningness and its connection to sleeping and psychological problems in 91 children and 151 adolescents in Austria. The authors found that morning (M) types had less sleep-related and psychological problems than intermediate (I) and evening (E) types, respectively. Among children, M-types suffered less from daytime sleepiness (females: χ²₍₂₎?=?8.1, p?=?.017; males: χ²₍₂₎?=?14.8, p?=?.001). Among adolescents, M-types showed fewer sleep-wake problems (females: χ²₍₂₎?=?17.5, p?<?.001; males: χ²₍₂₎?=?19.8, p?<?.001), and female M-types showed less externalizing (χ²₍₂₎?=?8.7, p?=?.013) as well as internalizing problem behavior (χ²₍₂₎?=?9.0, p?=?.011). In conclusion, these findings indicate that morningness may act as a protective factor against the development of sleep-related problems in childhood and sleep-related and psychological problems in adolescence, especially in females. (Author correspondence: gloriagelbmann@gmx.at)     

Prevalence of sleep disorders and their impact on academic performance in medical students/University of Duhok

Full-time students experiencing high levels of stress due to a high bulk of teaching materials and academic performance demands are the most susceptible population class for different types of sleep disorders. The current study examined the prevalence of sleep disorders and their impacts on academic performance of a random sample of medical college students. In this regard, a random sample of 316 medical students of a large public university in Iraq participated in a cross-sectional study. The participants completed the SLEEP-50 self-reported questionnaire and questions about socio-demographic factors. The variables set included sleep apnea, insomnia, narcolepsy, restless legs syndrome, circadian rhythm sleep disorder, sleepwalking, nightmares, grade point average, and some socio-demographic characteristics. The study showed that to some extent, the students suffer from different types of sleep disorders with no substantial difference between males and females. Students with worse level of sleep disorders had a lower grade point average compared with those with normal sleep patterns (p = 0.001). The study confirmed that students with sleep disorders had poorer academic performance at college.

     

Sleep,Diurnal Preference,Health, and Psychological Well-being: A Prospective Single-Allelic-Variation Study

Individual differences in sleep and diurnal preference associate with physical and mental health characteristics, but few genetic determinants of these differences have been identified. A variable number tandem repeat (VNTR) polymorphism in the PERIOD3 (PER3) gene (rs57875989) has been reported to associate with diurnal preference, i.e., preferred timing of waking and sleep. Here, the authors investigate in a prospective single-candidate genetic variant study whether allelic variation for this polymorphism associates also with reported actual sleep timing and sleep duration, as well as psychological and health measures. Six hundred and seventy-five subjects, aged 20 to 35 yrs, completed questionnaires to assess sleep and psychological and health characteristics and were genotyped for the PER3 VNTR. Homozygosity for the longer allele (PER3^5/5) of the VNTR was associated with increased morning preference, earlier wake time and bedtime, and reduced daytime sleepiness. Separate analyses of work and rest days demonstrated that the increase in time in bed during rest days was greatest in PER3^5/5 homozygotes. PER3 genotype modified the effects of sleep timing and duration on fluid intelligence and body mass index. Genotype was not associated with physical or psychological characteristics as assessed by the SF-36 Health Questionnaire, the General Health Questionnaire, the Big Five Inventory, the Behavioral Inhibition System–Behavioral Activation System scales, and the Positive and Negative Affect Scale, even though these measures varied significantly with diurnal preference as assessed by the Morningness-Eveningness Questionnaire. Whereas diurnal preference also predicts mental health and psychological characteristics, as well as sleep timing, the PER3 VNTR specifically affects measures of sleep timing and may also modify the effects of sleep on health outcome measures. (Author correspondence: a.lazar@surrey.ac.uk)     

Seasonal Effect on Infants' Sleep Regulation: A Preliminary Study in a Mediterranean Climate

Infants' sleep-wake rhythms are influenced by multiple factors, including developmental and contextual aspects, as well as circadian cycles. Empirical studies that address the seasonal impact on infants' sleep are scarce. The present study examined aspects of sleep schedule and quality, comparing summer and winter months in a Mediterranean climate. This report is based on a convenience sample of 34 healthy 7-mo-olds, an age in which sleep is well consolidated and regulated compared with the first few months of life. Sleep was measured with actigraphy, in the home context. It was found that compared with winter, in the summer months, sleep onset occurred at a later hour, and more motor activity during sleep was detected. Although the overall sleep quality, as defined by sleep efficiency score, was similar in the two seasons, in the summer, more active sleep was observed. The authors discuss the finding in terms of circadian rhythms, developmental characteristics, as well as possible environmental factors and family routines, and call for more studies, in different climates and geographical zones, and in different developmental periods. (Author correspondence: cohen.dini@gmail.com or anats@edu.haifa.ac.il)     

Social jetlag negatively correlates with academic performance in undergraduates

Discrepancies between sleep timing on workdays and weekends, also known as social jetlag (SJL), affect the majority of the population and have been found to be associated with increased health risk and health-impairing behaviors. In this study, we explored the relationship between SJL and academic performance in a sample of undergraduates of the Semmelweis University. We assessed SJL and other sleep-related parameters with the Munich ChronoType Questionnaire (MCTQ) (n?=?753). Academic performance was measured by the average grade based on weekly test results as well as scores acquired on the final test (n?=?247). The average mid-sleep point on free days in the Hungarian sample fits well the regression line plotted for longitudes within the Central European Time Zone and chronotypes, confirming that sunlight has a major impact on chronotype. Multivariate analysis showed negative effect of SJL on the weekly average grade (p?=?0.028, n?=?247) during the lecture term with its highly regular teaching schedules, while this association disappeared in the exam period (p?=?0.871, n?=?247) when students had no scheduled obligations (lower SJL). We also analyzed the relationship between the time of the weekly tests and academic performance and found that students with later sleep times on free days achieved worse in the morning (p?=?0.017, n?=?129), while the inverse tendency was observed for the afternoon test-takers (p?=?0.10, n?=?118). We did not find significant association between academic performance and sleep duration or sleep debt on work days. Our data suggest that circadian misalignment can have a significant negative effect on academic performance. One possible reason for this misalignment is socially enforced sleep times.     

Association between circadian preference and academic achievement: A systematic review and meta-analysis

The association between circadian preference and academic achievement has been assessed through a systematic review and meta-analysis. The literature searches retrieved 1647 studies; 31 studies, with a total sample size of 27?309 participants, fulfilled the inclusion criteria and were included in the meta-analysis. With reference to all these 31 studies, before running the meta-analysis, the sign of the correlation between the investigated variables was set in a way that a positive correlation showed that eveningness was related to worse academic performance. The meta-analysis yielded a small overall effect size of 0.143 (CI [0,129; 0,156]) under a fixed effects model (Z?=?20.584, p?<?0.001, I^2?=?72.656; Q?=?109.715) and of 0.145 (CI [0.117; 0.172]) under a random effects model (Z?=?10.077, p?<?0.001). A random effects model with a grouping variable (participants) revealed 15 studies based on school pupils and 16 on university students. The random model showed a higher effect size in school pupils (0.166, CI from 0.127 to 0.206) compared to university students (0.121, CI from 0.080 to 0.163). Self-report measures of grades revealed a stronger effect size (0.171; CI: 0.137 to 0.206; N?=?20) compared to objective measures (0.093; CI: 0.047 to 0.140; N?=?19). Overall, the present results suggest that evening orientation is associated with a worse academic performance, both in school pupils and university students; for the first time, it has been shown that such relationship changes over time, being weaker in university students.     

Relation of Chronotype to Sleep Complaints in the General Finnish Population

Individuals show variation in their preference for the daily timing of activities. In this study the authors analyzed whether chronotypes associate with sleep duration and sleep-related complaints. The authors used the National FINRISK Study 2007 Survey data on 3696 women and 3162 men, representative of the Finnish population aged 25 yrs and older, for the assessment of chronotype and self-reported sleep. Evening types experienced insomnia symptoms, had nightmares, and had used recently hypnotics significantly more often than other chronotypes among both men and women. In a multinominal logistic regression model predicting insufficient sleep, the association of eveningness with insufficient sleep was not abolished after adjustment for sex, age, and sleep duration. The prevalence of short sleepers was significantly higher in evening types among men than among women, whereas that of long sleepers was significantly higher in evening types among both men and women, as compared with the other chronotypes. These results indicate that eveningness predisposes individuals to a range of sleep complaints. (Author correspondence: ilona.merikanto@helsinki.fi)     

INTERINDIVIDUAL DIFFERENCES IN NEUROBEHAVIORAL PERFORMANCE IN RESPONSE TO INCREASING HOMEOSTATIC SLEEP PRESSURE

Neurobehavioral function deteriorates with increasing homeostatic sleep pressure during wakefulness. It has been claimed that some individuals exhibit a quicker rate of such deterioration than others, thus being more vulnerable than others to the detrimental impact of increasing homeostatic sleep pressure. Evidence supporting the claim, however, has been limited by methodological issues. To overcome these limitations, the current study used a 12-calendar-day, 28-h forced desynchrony (FD) protocol (sleep:wake period?=?1:2) to study individual differences in the rate of change in neurobehavioral performance with increasing homeostatic sleep pressure. Neurobehavioral performance was assessed with a psychomotor vigilance task and a serial addition subtraction task. A significant performance decline on both tasks was revealed within as short as 17?h of wakefulness. The rates of decline of individual performance trajectories were, however, not different from the group average rate. This suggests that individuals are not differentially vulnerable to the detrimental impact of increasing homeostatic sleep pressure. (Author correspondence: xuan.zhou@unisa.edu.au)     

SLEEP PATTERNS IN HIGH SCHOOL AND UNIVERSITY STUDENTS: A LONGITUDINAL STUDY

We performed a longitudinal study to investigate whether changes in social zeitgebers and age alter sleep patterns in students during the transition from high school to university. Actimetry was performed on 24 high-school students (mean age?±?SD: 18.4?±?0.9 yrs; 12 females) for two weeks. Recordings were repeated in the same subjects 5 yrs later when they were university students. The sleep period duration and its center, the mid-sleep time, and total sleep time were estimated by actimetry. Actigraphic total sleep time was similar when in high school and at the university on school days (6.31?±?0.47 vs. 6.45?±?0.80?h, p?=?ns) and longer on leisure days by 1.10?±?1.10?h (p?<?0.0001 vs. school days) when in high school, but not at the university. Compared to the high school situation, the mid-sleep time was delayed when at the university on school days (03∶11?±?0.6 vs. 03∶55?±?0.7?h, p?<?0.0001), but not on leisure days. Individual mid-sleep times on school and leisure days when in high school were significantly correlated with the corresponding values 5 yrs later when at the university (r?=?0.58 and r?=?0.55, p?<?0.05, respectively). The large differences in total sleep time between school and leisure days when students attended high school and the delayed mid-sleep time on school days when students attended university are consistent with a circadian phase shift due to changes in class schedules, other zeitgebers, and lifestyle preferences. Age-related changes may also have occurred, although some individuality of the sleep pattern was maintained during the 5 yr study span. These findings have important implications for optimizing school and work schedules in students of different age and level of education. (Author correspondence: pneubloc@usz.uzh.ch)     

CHRONOTYPE,SLEEP LENGTH,AND SCHOOL ACHIEVEMENT OF 11- TO 23-YEAR-OLD STUDENTS IN NORTHERN EUROPEAN RUSSIA

Residing at northern latitudes for long periods of time is associated with sleep disturbances and internal desynchronization, which are considered to be causes of chronic diseases in old age. In children and teenagers, they result in a poor school achievement, psychological problems, and increase in consumption of stimulants. In this paper, we analyze the relationship between both chronotype and sleep length and the variables of age, sex, place of residence, type of settlement (village/city), latitude and longitude of residence, and school achievement of young inhabitants of northern European Russia. We surveyed 1101 children and teenagers between 11 to 23 yrs of age living in four settlements located between 59° and 67° North latitude and 33° and 60° East longitude. The Munich chronotype questionnaire (MCTQ) was used in the study, and all participants were also required to answer a question about their school achievements. An analysis of covariance (ANCOVA) was used to assess the influence of the analyzed factors on sleep length and chronotype. Self-reported sleep length of teenagers depended moderately on age, whereas the place of residence, latitude, and type of settlement only had a weak effect. Chronotype strongly depended on place of residence and longitude; it moderately depended on latitude and age; and it weakly depended on sex and type of settlement. The sleep length of village teenagers was 46?min longer than that of urban teenagers. The authors found a 1?h and 18?min phase delay of the sleep-wake rhythm (as a marker of chronotype) in teenagers moving in the East-West direction and a 16-min delay moving in the South-North direction within one time zone. There was a weak, but significant, positive correlation between chronotype and time of sunrise. There was about a 2-fold stronger influence of chronotype than sleep length on achievement of school children and college students. We conclude that socioeconomic factors exert a significant influence on sleep length and that climatic conditions exert a significant influence on the chronotype of teenagers in the northern latitudes. (Author correspondence: borisenkov@physiol.komisc.ru)     

Photic Resetting in Night-Shift Work: Impact on Nurses' Sleep

The objective of this study was to quantify daytime sleep in night-shift workers with and without an intervention designed to recover the normal relationship between the endogenous circadian pacemaker and the sleep/wake cycle. Workers of the treatment group received intermittent exposure to full-spectrum bright light during night shifts and wore dark goggles during the morning commute home. All workers maintained stable 8-h daytime sleep/darkness schedules. The authors found that workers of the treatment group had daytime sleep episodes that lasted 7.1?±?.1?h (mean?±?SEM) versus 6.6?±?.2?h for workers in the control group (p?=?.04). The increase in total sleep time co-occurred with a larger proportion of the melatonin secretory episode during daytime sleep in workers of the treatment group. The results of this study showed reestablishment of a phase angle that is comparable to that observed on a day-oriented schedule favors longer daytime sleep episodes in night-shift workers. (Author correspondence: diane.boivin@douglas.mcgill.ca)     

Prevalence and Correlates of Poor Sleep Quality and Daytime Sleepiness in Belgian Truck Drivers

Sleepiness and sleep complaints are common among professional drivers. Sleepiness is a considerable problem not only because it affects the drivers' well-being, but also because of the consequences for performance and safety. Assessment of the (self-reported) prevalence and research into the risk factors are thus an important health issue and are also indispensable to prevent productivity loss and work-related accidents and injuries. Therefore, the aim of this study was to describe sleeping, driving, and health characteristics of Belgian truck drivers and to determine occupational and individual factors associated with poor sleep quality and daytime sleepiness. Cross-sectional data were collected using a self-administered questionnaire that included the Pittsburgh Sleep Quality Index (PSQI), Epworth Sleepiness Scale (ESS), and Berlin Questionnaire (BQ). The mean (SD) age of the 476 studied truck drivers was 42.7 (10.2) yrs and the mean (SD) body mass index was 27.3 (5.1) kg/m². Approximately 47% declared that they drove >50 h/wk and found their work schedule unrealistic. The mean (SD) PSQI score was 4.45 (2.7); poor quality of sleep (PSQI >5) was found in 27.2%. The mean (SD) ESS score was 6.79 (4.17); 18% had a score >10. The BQ indicated that 21.5% had a higher risk on obstructive sleep apnea. In multiple logistic regression analysis, low educational level (odds ratio [OR] 1.86), current smoking (OR 1.75), unrealistic work schedule (OR 1.75), and risk for obstructive sleep apnea (OR 2.97) were found to be independent correlates of daytime sleepiness. Poor sleep quality was significantly associated with poor self-perceived health (OR 1.95), unrealistic work schedule (OR 2.85), low job satisfaction (OR 1.91), and less driving experience (OR 1.73). These results show that poor sleep quality and daytime sleepiness were prevalent in Belgian truck drivers. Taking into account that several significant correlates with respect to these sleep problems were identified both at the individual and the occupational level, comprehensive countermeasures to improve working conditions and organization are needed, as well as health promotion interventions, to ensure the safety and well-being of truck drivers. (Author correspondence: lutgart.braeckman@ugent.be)     

Midpoint of sleep on school days is associated with depression among adolescents

Depression is a serious and prevalent disease among adolescents. Identifying possible factors involved with its genesis and presentation is an important task for researchers and clinical practitioners. The individual’s chronotype and social jetlag have been associated with depression in different populations. However, information on this is lacking among adolescents. The objective of this cross-sectional study was to examine the relationship between chronotype (midpoint of sleep) and social jetlag with the presence of depression symptoms in young students. We assessed 351 students aged 12–21?years old. They answered a questionnaire on demographic characteristics, the Munich Chronotype Questionnaire (MCTQ) and the Beck Depression Inventory (BDI). Demographic characteristics (age, sex and classes’ schedule) and circadian rhythmic variables for school and free days (sunlight exposure, sleep duration, midpoint of sleep and social jetlag) were taken as factors and the presence of at least mild depression symptoms as outcome. In univariate analysis, girls (χ²?=?5.01, p?≤?0.05) and evening students (χ²?=?6.63, p?≤?0.05) were more frequently present among the depressed. Also, the depression group was significantly delayed for both midpoints of sleep during school (t?=?2.84, p?≤?0.01) and free days (t?=?2.20, p?≤?0.05). The two groups did not differ in relation to their social jetlag hours (t?=??0.68, p?=?0.501) neither subjects with two or more hours of social jetlag were more frequent among the depressed (χ²?=?1.00, p?=?0.317). In multivariate analysis, the model that best explained our outcome (R²?=?0.058, F?=?2.318, p?≤?0.05) included sex (β?=??0.12, p?≤?0.05) and the midpoint of sleep on school days (β?=??0.21, p?≤?0.001) as significant predictor variables. A sleep phase delay (later midpoints of sleep for school and free days) was associated with higher levels of depression. However, we were not able to detect similar relationship with the social jetlag hours. This could be attributed to the fact that our sample showed a smaller amount of social jetlag, possibly because even during free days a social routine, this time parents’ rules, limited the observation from what could be a natural tendency to sleep later and over. Yet, even when considering the group with more social jetlag, we did not find an association. Perhaps, this variable will only manifest its effect if it is maintained for longer periods throughout life. Additionally, when considering all the variables together, the midpoint of sleep on school days was pointed as the predictor of greatest weight for depression, together with the factor sex. Young girls, possibly earlier types, who are required to study in the evening have more chances of presenting depression symptoms. This study explicit some peculiar characteristics of the assessment of chronobiological variables in the young, such as the presence of an imposed social routine also during free days. Therefore, the expression of chronotype under the influence of the weekly social schedule (midpoint of sleep on school days) could be a more useful marker to measure the stress produced from the mismatch between external and inner rhythms rather than social jetlag. This also reinforces the importance of reconsidering the weekly routine imposed on young people.     

ASSOCIATIONS OF METABOLIC PARAMETERS AND ETHANOL CONSUMPTION WITH MESSENGER RNA EXPRESSION OF CLOCK GENES IN HEALTHY MEN

Recent studies suggest that the impairment of circadian clock function causes various pathological conditions, such as obesity, diabetes, and alcoholism, and an altered mRNA expression of clock genes was found under these conditions. However, it remains to be determined whether clock gene expression varies depending on metabolic conditions even in healthy people. To address this issue, we investigated the associations of metabolic parameters and alcohol consumption with mRNA expression of clock genes (CLOCK, BMAL1, PER1, PER2, and PER3) in peripheral blood cells obtained from 29 healthy non-obese elderly men (age 51–78 yrs) who adhered to a regular sleep-wake routine, through a single time-of-day venous blood sampling at ～09:00?h. There were significant correlations between (1) waist circumference and mRNA level of PER1 (r?=?0.43), (2) plasma glucose concentration and PER2 (r?=?0.50), (3) ethanol consumption and BMAL1 (r?=?0.43), and (4) serum γ-GTP concentration (a sensitive marker of alcohol consumption) and PER2 (r?=?0.40). These results suggest mRNA expression of clock genes is associated with obesity, glucose tolerance, and ethanol consumption even in healthy people. (Author correspondence: akiofuji@jichi.ac.jp)