Sleep Regularity is Associated with Sleep-Wake and Circadian Timing, and Mediates Daytime Function in Delayed Sleep-Wake Phase Disorder

Abstract Background In healthy populations, irregular sleep patternsare associated with delayed sleep and poor functional/ moodoutcomes. It is unknown whether irregular sleep contributes to poor functional/ moodoutcomes in individuals with Delayed Sleep-Wake Phase Disorder (DSWPD). Methods In 170 patients with DSWPD, we collected sleep-wake patterns, dim light melatonin onset (DLMO), and functional/ moodoutcomes. The Sleep Regularity Index (SRI) and other sleep timing metrics were computed. Correlations of SRI were computed with phase angle(difference between DLMO and desired bedtime), sleep timing and quality variables, daytimefunction, sleep-related daytimeimpairment, mood, and insomnia symptom severity. Path analyses assessed whether SRI or total sleep time mediated the associations between sleep onsettime and phase anglewith daytimefunctioning, sleep-related impairment, and moodoutcomes. Results Higher SRI was associated with earlier sleep and longer total sleep time, but did not relate to sleep quality, daytimefunction, or moodoutcomes. Path analysis showed that phase anglewas directly associated with all outcome variables, whereas sleep onsettime was not directly associated with any. SRI mediated the effects of sleep onsettime and phase angleon daytimefunction. Total sleep time mediated the effects of sleep onsettime and phase angleon sleep-related impairment. Conclusion Individuals with DSWPD who have more delayed sleep and a greater phase anglealso have more irregular sleep. This suggests that it is not delayed sleep timing per se that drives poor functional outcomes in DSWPD, but rather the timing of sleep relative to circadian phase and resultant irregular sleep patterns.