The relationship between stress and sleep quality: An intensive longitudinal study

Both stress and poor sleep quality can undermine long-term physical and mental health. Further, heightened stress has been shown to disrupt sleep, while poor sleep may increase stress reactivity, together compounding their impact on health. So far, few studies have captured the bidirectional, day-to-day dynamics of stress and sleep in daily life using both subjective and objective measures. In this 7-day intensive longitudinal study, 106 participants provided daily and momentary self-reports of perceived stress and subjective sleep quality via smartphone diaries, while a wearable sensor continuously recorded heart rate variability as a measure of stress-related physiology and objective sleep indicators, including sleep onset latency, wake after sleep onset, sleep efficiency, and total sleep time (n = 742 days). The data were analyzed using cross-lagged mixed models. At the within-person level we found indication that after nights of better-than-usual subjective sleep quality participants reported lower next-day momentary stress. At the between-person level, higher perceived stress was associated with worse subjective sleep quality and longer sleep onset latency. Findings for objective sleep quality indicators depended on the operationalization of nocturnal timeframe (i.e., time that participants spent in bed trying to sleep) with longer sleep onset latency inconsistently associated with lower next-day momentary stress and participants with generally higher daily stress levels inconsistently showing longer sleep onset latency. The findings reveal that stress–sleep associations differ at the within- and between-person levels, for subjective and objective sleep quality indicators and based on operationalizations of nocturnal timeframes. Future studies should further carefully consider measurement decisions and explore underlying mechanisms to better understand the relationship between stress and sleep quality in daily life.