The circadian variation of sleep and alertness of postmenopausal women

Several factors may contribute to the high prevalence of sleep disturbances occurring in postmenopausal women. However, the contribution of the circadian timing system to their sleep disturbances remains unclear. In the present study, we aim to understand the impact of circadian factors on changes of sleep and alertness occurring after menopause.

Eight healthy postmenopausal women and 12 healthy young women in their mid-follicular phase participated in an ultradian sleep-wake cycle procedure (USW). This protocol consisted of alternating 60-min wake periods and nap opportunities for ≥ 48 h in controlled laboratory conditions. Core body temperature (CBT), salivary melatonin, self-reported alertness, and polysomnographically recorded sleep were measured across this procedure.

In both groups, all measures displayed a circadian variation throughout the USW procedure. Compared to young women, postmenopausal women presented lower CBT values, more stage N1 and N2 sleep, and number of arousals. They also showed a reduced amplitude of the circadian variation of melatonin, total sleep time (TST), sleep onset latency (SOL), stage N3 sleep, and alertness levels. Postmenopausal women fell asleep faster and slept more during the biological day and presented higher alertness levels during the biological night than young women.

These results support the hypothesis of a weakened circadian signal promoting sleep and wakefulness in older women. Aging processes including hormonal changes may be main contributors to the increased sleep-wake disturbances after menopause.