0031 Sex-Specific Differences in the Relationship Between General Pain and the Circadian Timing of Sleep

Abstract Introduction Pain and disrupted sleep have a bidirectional relationship such that pain impairs sleep and disrupted sleep increases pain perception. In males, acute pain exhibits circadian rhythmicity with a maximum during the night, but the relationships between sex, sleep timing, circadian phase, and pain remain underexplored. Thus, in both females and males with general pain, we examined the relationships between pain and sleep timing and between pain and sleep relative to circadian phase (i.e., phase angle of entrainment). Methods General pain levels over the previous week were assessed utilizing a 10-point scale (1=no pain, 10=worst pain imaginable) in 34 participants (15F). Sleep timing (bedtime, waketime, and sleep duration) was measured using one-week sleep diaries. Dim-light melatonin onset (DLMO) was measured during an in-laboratory visit via saliva collection in dim light (lux< 5) between 1700 and 2300. Phase angle was calculated as the time duration between DLMO and average bedtime. Differences in pain, DLMO, and sleep timing between sexes were assessed using independent t-tests, and the relationships between sleep timing, phase angle, and pain were assessed with Pearson correlation analyses. Results There were no significant differences between females and males in pain levels (mean±SD, Female vs. Male; 3.50±1.77 vs. 3.97±1.97, p=0.47), bedtime (23.20±1.58 vs. 23.04±1.36h, p=0.74), waketime (06.75±1.50 vs. 06.26±1.28h, p=0.29), DLMO (20.11±1.27 vs. 19.61±1.18h, p=0.61), or phase angle (2.81±1.69 h vs. 3.43±1.69h, p=0.19). Among females, phase angles were positively correlated with pain (r=0.54, p=0.02), such that a wider phase angle was associated with higher pain. Among males, phase angles were not correlated with pain (r=0.19, p=0.50); however, in a subset of males with moderate/severe pain, phase angles were negatively correlated with pain (r=0.73, p=0.04), such that a wider phase angle was associated with lower pain. There were no significant correlations in either group between pain and sleep timing, DLMO, or sleep duration. Conclusion We found sex-specific differences in the associations between circadian phase angle of sleep and pain levels in females and males. It is unclear what mechanism(s) is driving these differences, but with the relationship between pain and phase angle moving in opposite directions between sexes, future work is warranted. Support (if any)