Daily associations of subjective and objective sleep parameters with restorative sleep and morning sleepiness in Japanese working adults

Restorative sleep and morning sleepiness are essential factors associated with daytime functioning among workers, yet their variability and determinants remain unclear. Previous studies have primarily focused on either subjective or objective sleep measures, with many cross-sectional investigations, although fewer longitudinal studies have considered the interaction with psychological and chronobiological factors. The aim of this study was to investigate both subjective and objective sleep parameters, along with psychological and chronobiological factors, and examine their influence on daily restorative sleep and morning sleepiness in healthy workers. Thirty-seven participants wore portable sleep monitoring devices over multiple days and completed daily subjective sleep assessments. Using multilevel linear mixed-effects models, we examined associations between sleep parameters and next-morning outcomes. The results indicated that longer subjective and objective total sleep time were associated with greater restorative sleep, while longer subjective and objective sleep onset latency were negatively associated with restorative sleep. Regarding morning sleepiness, longer subjective and objective total sleep time, as well as a higher proportion of deep sleep, were associated with reduced morning sleepiness. In contrast, a greater severity of depressive symptoms was associated with increased morning sleepiness. These findings highlight the value of considering both subjective and objective sleep parameters when evaluating daily sleep outcomes. In occupational medicine, assessing workers' sleep using both subjective and objective measures, while also considering depressive symptoms, could be beneficial.