157 The Circadian Variation of Sleep in Postmenopausal Women

Abstract Introduction During menopause, 40-60% of women report sleep complaints. Despite the fact that menopause is associated with fluctuations in sex hormones that can affect circadian physiology, the role of circadian factors in sleep disturbances after menopause is not well understood. The present study aims to understand the circadian variation of sleep occurring after menopause. Methods Eight healthy postmenopausal women (PMW; 54.8±3.4 years, one taking hormones) without sleep complaints were enrolled and compared to previously-collected data from 12 healthy young women (YW; 25.8±3.4 years) in mid-follicular phase. Following an 8-h baseline sleep period aligned to their habitual sleep times, participants underwent a 48-h (PMW) or 72-h (YW) ultradian sleep-wake cycle procedure (USW) with 60-min wake episodes alternating with 60-min nap opportunities. Sleep was recorded with polysomnography. Circadian parameters (amplitude, phase) of core body temperature (CBT) and sleep were assessed and compared using mixed-effects linear models on the first 48 hours of USW. Sleep parameters, including total sleep time (TST), arousals, sleep onset latency (SOL), stages N1, N2, N3, REM, and wake, were compared between groups during baseline and USW. Results PMW presented earlier habitual bedtimes (23:07±00:11 vs 00:13±00:12) and rise-times (07:07±00:11 vs 08:13±00:12) compared to YW (p=0.005). There were no differences in amplitude, phase, or phase angle of CBT. An advanced acrophase of REM sleep (p=0.034) and lower amplitudes of TST, arousals, SOL, N3, and wake, were observed in PMW vs YW (p≤0.05). During baseline, PMW presented more stage N1 (p=0.030) and arousals (p<0.001) than YW. During USW, group effects were observed, with more stage N1 (p=0.007) and N2 (p=0.0007) in PMW vs YW. Significant interactions showed greater TST (p=0.009), shorter SOL (p=0.001), and more arousals (p=0.027) in PMW during the habitual day. Conclusion The primary finding in this small group of PMW with no sleep complaints was a general increase in light sleep and arousals across circadian phases. No differences in CBT rhythms were observed, whereas small differences in the circadian variation of TST, N3, and REM sleep were observed. Further studies are needed to clarify the role of circadian processes on sleep in PMW. Support (if any) Study supported by the Canadian Institutes of Health Research.