Effects of sleep and circadian rest-activity rhythms on daily pain severity in women with temporomandibular disorders.

Although a robust connection between sleep and pain is established, the extent to which circadian rest-activity rhythms contribute toward unique variations in pain, beyond what is elucidated by sleep, remains uncertain. Furthermore, it is largely unknown whether sleep and circadian rest-activity rhythms have interactive effects on daily pain severity. Using wrist actigraphy and daily pain diaries, data from 140 women with temporomandibular disorders and insomnia symptoms were analyzed over a 14-day period. Sleep duration and continuity were quantified by using total sleep time (TST) and wake after sleep onset (WASO), and circadian rest-activity rhythms were characterized with the Relative Amplitude (indicating strength/robustness of rest-activity rhythm) and Intradaily Variability metrics (representing rhythm fragmentation). Linear mixed-effects modeling revealed that both TST ( b = -0.11, P = 0.006) and WASO ( b = 0.18, P = 0.006) from the previous night, along with Relative Amplitude ( b = -2.56, P = 0.001) from the past 24 hours, predicted next-day pain severity. Among the 4 interaction effects tested, both Intradaily Variability ( b = 1.52, P = 0.034) and Relative Amplitude ( b = -1.52, P = 0.003) moderated the relationship between WASO and next-day pain severity; on days characterized by less robustness (lower Relative Amplitude) or greater fragmentation (higher Intradaily Variability) in the circadian rest-activity rhythm, the positive association between previous night WASO and next-day pain severity intensified. These findings highlight the complex interplay among sleep, circadian rest-activity rhythms, and pain. While preliminary, our findings indicate that interventions aimed at improving both sleep and restoring circadian rhythms may provide enhanced benefits for managing chronic pain.