The purpose of this study was to clarify the impact of sleep debt, social jetlag, and insomnia symptoms on presenteeism and psychological distress. The findings indicated that sleep debt had a more significant impact on presenteeism and psychological distress than social jetlag. Among sleep debt, social jetlag, and insomnia symptoms, insomnia symptoms had a more significant impact than the other two variables on presenteeism and psychological distress. Thus, insomnia symptoms had the more significant impact on both presenteeism and psychological distress, and sleep debt had a more substantial impact than social jetlag. The impact on presenteeism and psychological distress was most significant for insomnia symptoms, followed by sleep debt. Therefore, it is essential to address insomnia symptoms. On the other hand, for those with sleep debt and no insomnia symptoms, the sleep debt needs to be addressed. However, no treatment program has been designed to improve presenteeism by addressing sleep debt [30]. This study is meaningful because it highlights the importance of addressing insomnia symptoms and sleep debt and the need to develop a program for sleep debt.
The impact of sleep debt on presenteeism was more significant than that of social jetlag, a finding that is consistent with previous research [6]. In the National Health and Nutrition Survey conducted in 2019, 37.5% of men and 40.6% of women slept less than six hours [31]. Compared to those who sleep seven to eight hours, those who sleep six hours or less have a higher rate of presenteeism [32]. Moreover, Japan faced the world's worst economic loss due to sleep debt [2]. Therefore, it is likely that sleep debt has affected presenteeism. In an experiment using a psychomotor vigilance task after two weeks of sleep restriction, the response time to the task gradually increased in the group that was restricted to four to six hours of sleep [33]. Although performance on cognitive functioning tasks decreases with sleep restriction, individuals do not perceive subjective sleepiness and follow a subjective sense of adaptability, even in the presence of chronic sleep restriction [33]. Therefore, people with sleep debt underestimate presenteeism, which is considered a daytime dysfunction. In modern society, it has been observed that people sleep longer on weekends than on weekdays [8], and many workers have a sleep debt. Social jetlag affects productivity in the group with short sleep duration but does not affect productivity in the group with long sleep duration, even when the social jetlag is large [34]. The results indicate that longer sleep duration may be a protective factor against productivity loss due to social jetlag [34]. In other words, although sufficient sleep duration on workdays is vital to reduce the impact on presenteeism, when achieving this is challenging, it is essential to sleep longer on weekends, even if this causes social jetlag. The results of the present study indicate that focusing on improving sleep debt or ensuring that individuals get the amount of sleep they need is important for improving presenteeism.
Social jetlag is a discrepancy between social time and the individual's circadian rhythm and may be excluded as it cannot be accurately assessed in people who use alarm clocks on weekends [8]. On the other hand, this study did not exclude individuals who use alarm clocks on weekends. This is becsuse the study also assesses sleep debt. Social jetlag is calculated as the discrepancy between the midpoint of sleep on weekdays and weekends. In general, workers sleep longer on weekends than on weekdays [8]. This suggests that sleep debt is present. Excluding those who used alarm clocks on weekends might exclude those with sleep debt. Japan has the world's worst economic loss due to sleep debt [2], and both objective and subjective sleep duration is short [1, 31]. For this reason, the evaluation of sleep debt was prioritized over the evaluation of social jetlag. The social jetlag in the previous study was 0.91 h on average [8], and the social jetlag in the present study was similar at 1.18 h on average. Therefore, while there may be some concern in terms of accurately assessing social jetlag, it is unlikely to affect the findings.
Insomnia symptoms had a more significant impact on presenteeism than sleep debt and social jetlag. Insomnia symptoms can be an aggravating factor for presenteeism, and the OR for presenteeism was reported at 5.49 in those with insomnia symptoms compared to those without such symptoms [14], which is consistent with the results of the present study. Therefore, this study confirms that insomnia symptoms affect presenteeism. Insomnia symptoms might have had the most significant impact on presenteeism due to persistence; research has shown persistence of insomnia symptoms at one, three, and five years of follow-up [35]. When insomnia was present at baseline, its persistence was observed in 70.7% of participants at one year, 49.7% at three years, and 37.5% at five years. In another study, its persistence was found in 86.0% at one year, 72.4% at three years, and 59.1% at five years in the presence of sleep-related psychological distress or daytime dysfunction problems [35]. Some of those with insomnia symptoms additionally present daytime dysfunction. Therefore, those with insomnia symptoms may be more likely to experience presenteeism, which is considered a daytime dysfunction. Given the above, insomnia symptoms may have more significantly impacted presenteeism than sleep debt.
Insomnia symptoms had the most significant impact on psychological distress, while sleep debt had a more substantial impact on psychological distress than social jetlag. Because insomnia symptoms [17] and short sleep duration are both risk factors for depression [36], the results of the present study are valid. Although social jetlag has been reported to increase depressive symptoms [6], the results of the present study differed from those of previous studies. A previous study used the Center for Epidemiologic Studies Depression (CES-D) scale, but the mean score was very low, which may be insufficient to identify the presence of depressive symptoms [6]. However, this study did not show that social jetlag affects psychological distress equivalent to insomnia symptoms and sleep debt. This does not imply that social jetlag need not be addressed but that it is less critical than insomnia symptoms and sleep debt.
There are several limitations to this study. First, although the study found that sleep debt and insomnia affected presenteeism and psychological distress independently, it failed to take into account the possibility that some people would have both insomnia and sleep debt at the same time. One of the characteristics of those with insomnia is that they rate their subjective sleep duration as shorter than their actual sleep duration when their objective sleep duration is six hours or more. However, when their objective sleep duration is less than six hours, their subjective sleep duration is never shorter than their actual sleep duration [37]. In other words, people with an objective sleep duration of more than six hours and insomnia symptoms may overestimate their sleep debt. Future studies need to use objective and subjective sleep measures and to include those who have both insomnia and sleep debt. Second, this study was conducted using an Internet survey. The participants in this study were those sufficiently interested in sleep and healthy to complete the Internet survey. Because sleep debt and insomnia symptoms are concerns in Japan and worldwide, replication of the results of this study in other studies would enhance the reliability of the results. Third, the design of this study prioritized the evaluation of sleep debt over social jetlag. Hence, those who used alarm clocks on weekends were not excluded from the study. However, the evaluation of social jetlag may have been compromised because those who used an alarm clock on weekends were not excluded. It should be cautioned that, although this study found that sleep debt had a greater impact on presenteeism and psychological distress than social jetlag, this result may be because of the study design.