The current study demonstrates a clear association between sleep/wake habits and academic performance among medical students. Certain sleep habits were associated with lower academic performance. A late bedtime on weekdays and weekends was associated with lower academic performance. These findings agree with those of a study conducted on first-year college students showing that students with later bedtimes during weekdays and weekends had lower performance. Moreover, the bedtime during weekends was delayed in both groups compared with the weekdays. Experimental studies have demonstrated that a shift in bedtime by two hours while maintaining the same sleep duration resulted in increased feelings of depression, difficulty in concentration and mood changes . Previous studies have demonstrated that a shift delay in the bedtime of college students can impair the students’ academic performance . Sleep duration (TST) during the weekdays was significantly longer (by around 20 minutes) in the “excellent” group. Although the difference in sleep duration may not appear remarkable, it may have physiological importance, particularly when the sleep deprivation accumulates over several days . These results agree with previous reports in adolescents that demonstrated a significant impact of increased nocturnal sleep duration on academic achievement. In a sample of 3,000 adolescent students, Wolfson and Craskadon reported a significantly longer total sleep time and earlier bedtimes in students with higher grades . Students reporting a “B” or better got 17–33 minutes more total sleep on average school nights and went to bed 10–50 minutes earlier than “C,” “D” and “F” students . Because the students in the present study were not obtaining sufficient sleep on weekdays, they increased their sleep duration during weekends. A recent study showed that increased weekend catch-up sleep (as an indicator of insufficient weekday sleep) is associated with poor performance on objective attention tasks where the number of omission and commission errors is measured in a computerized system .
Although sleep deprivation affects academic performance, students who are sleep-deprived and experience academic difficulties are usually not aware of the extent to which their sleep loss can impair their ability to complete cognitive tasks. Pilcher and Walters subjected 44 college students to total sleep deprivation for one night and found that the sleep-deprived students performed significantly worse on cognitive tasks compared with students who had normal sleep . Paradoxically, the sleep-deprived students who performed worse reported higher levels of estimated performance and inaccurately rated their performance as better than that of students who were not sleep-deprived .
Sleep deprivation may affect school performance at several levels. Daytime sleepiness and reduced levels of attention affect performance . Moreover, sleep deprivation may impair memory and decision making . Previous studies have linked the consolidation of higher-order implicitly learned information to the rapid eye movement (REM) stage of sleep (the dreaming stage of sleep) . Previous studies reported a significant correlation between language learning efficiency and increases in the fraction of REM sleep, which suggests that learning performance may be an important factor in the relationship between information processing and REM sleep . As REM sleep episodes tend to increase in the last third of the night, sleep deprivation may significantly reduce the percentage of REM sleep. In addition, poor sleep may indirectly affect performance by increasing depression, decreasing motivation and compromising health .
A higher proportion of the “excellent” group felt that they obtained sufficient nocturnal sleep. In addition, the subjective feeling of getting sufficient sleep was an independent predictor of “excellent” performance. Howell et al. conducted a study on college students and confirmed a correlation between poor sleep quality and academic performance . The increased ESS score and the subjective feeling of sleepiness were more common among the “average” group. Sleepiness may negatively impact academic performance . Daytime sleepiness has been shown to negatively affect the participation of students in extracurricular activities . Daytime sleepiness is likely to be a consequence of sleep deprivation. However, circadian rhythm disorders in the form of delayed sleep phase syndrome marked by significant delays in sleep/wake cycles are common among college students and may result in increased daytime sleepiness . Smoking was more common among the average group and was an independent predictor of a lower academic performance. Previous studies suggested that students who do well in school are less like to smoke. In a recent study, Morin et al in a four-year cohort study on a total of 741 adolescents reported that smoking among persistently high achievers (7.1%) was significantly lower than average achievers (15.1%) and low achievers (49.1%) .
The present study reports important findings; nevertheless, this type of study has inherent limitations that must be addressed. First, the self-reporting of sleep/wake habits relies on the students’ subjective accounts, which raises the possibility that the students may not have accurately reported their sleep habits. We therefore conducted a limited validation of the self-reported sleep duration data against objective actigraphy measurements. Moreover, we used sleep diaries and contacted the participants on a regular basis during the study period. Additionally, Wolfson and colleagues have demonstrated the validity of self-reported survey estimates of sleep patterns in adolescents . Moreover, there are many hidden confounding variables that may influence the measurement of academic performance, such as self-concept, motivational changes, mental stress and social class. Furthermore, colinearity between the studied variables is another problem that was obvious in our preliminary analysis. Nevertheless, we tried to ameliorate that by testing for multicollinearity among the univariate predictors. At this stage, a crude analysis is required to build a solid base for future studies, especially because this area of research has not been well explored in medical students. Finally, because the study was cross-sectional, no conclusions about the long-term effects of insufficient sleep can be drawn. Although it is sensible to assume that improving the quality and pattern of sleep will contribute to the improvement of academic performance, a cause-effect relationship has not been established.