Sleep Debt Must be Paid Off: Relationship Between Sleep Loss and Mental Health Among Japanese Workers

Background: Sleep loss and sleep debt are common in Japanese workers. Although cumulative sleep debt may be considered a cause of mental health problems, that relationship has not been empirically confirmed. Sleep loss is de- fined as either self-perceived insufficient sleep and/or insomnia. We calculated sleep debt by subtracting the average number of hours of weekday sleep from hours slept on weekends. Methods: This cross-sectional study was conducted from April 2005 through March 2007 at the Osaka Prefectural Mental Health Center. Participants were 873 workers. First, we investigated characteristics of individuals with awareness of sleep loss. Second, we examined whether reasons for sleep loss (insufficient sleep or insomnia) were associated with sleep hab- its and psychometric variables. Finally, we identified characteristics of subjects with insufficient sleep and examined the association between self-perception of insufficient sleep and mental health. Results: Of the subjects, 64.0% perceived their own sleep loss. Workers with sleep loss related to overwork had signifi- cantly larger sleep debt. Subjects with predictable symptoms of insufficient sleep (short sleep on weekdays, difficulty in awakening or sleep maintenance, large sleep debt, and daytime sleepiness) tended to have higher scores on the General Health Questionnaire-28. Conclusion: Short sleep duration (< 6 hours/weekday), insomnia, and insufficient sleep are different although they can overlap and must be considered separately. Sleep debt might be an essential and useful indicator of insufficient sleep es- pecially caused by overwork. Assessing sleep health, including sleep debt, is important for promoting mental health. We postulate that sleep debt must be paid off.