Circadian Rhythm Timing and Associations With Sleep Symptoms in People With Insomnia.

Circadian rhythmicity plays a crucial role in regulating sleep timing and continuity, but it may be altered in people with insomnia. This study tested whether dim-light melatonin onset (DLMO) timing is associated with sleep difficulties in insomnia. In total, 128 people diagnosed with insomnia disorder were recruited. Participants completed daily sleep diaries and wore an actigraph for up to 14 days before the laboratory visit to estimate mean sleep continuity (e.g., sleep latency, sleep duration) and sleep timing (sleep onset time and wake time from diaries, bedtime from diaries and actigraphy). After a sleep study, participants underwent salivary melatonin collection to estimate DLMO on the following night. Regressions and analyses of variances on tertile groups tested associations between DLMO (clock times and phase angle differences between DLMO and sleep timing) and sleep continuity and timing. There were associations between DLMO and sleep timing, r(s) = 0.27-0.37, but not with sleep continuity. The phase angle between sleep onset time and DLMO was associated with sleep latency, sleep duration, and sleep efficiency, r(s) = -0.32 to 0.41. Participants with a longer phase angle between DLMO and sleep onset time (> 3 h; i.e., greater delays) had longer sleep latencies (Mean diff = 43.21 min, SE = 12.99, p = 0.004) and shorter sleep durations (Mean diff = -65.66 min, SE = 20.75, p = 0.006) than participants with a shorter phase angle (< 2 h). Other phase angles (DLMO and mid-sleep, wake time) were not consistently associated with sleep continuity. Melatonin onset timing is associated with sleep timing in insomnia disorder. Larger phase angle differences between sleep onset and DLMO are linked to poorer sleep continuity. These findings highlight the importance of considering circadian alignment and its impact on sleep in understanding the pathophysiology of insomnia and in developing targeted treatment interventions.