Menstrual variations of sleep–wake rhythms in healthy women

The ovarian steroid hormones, estrogen and progesterone, the levels of which fluctuate dynamically with the estrous cycle, alter circadian behavioral rhythms in mammals. However, it remains unclear whether the sleep–wake rhythm fluctuates with the menstrual cycle in humans. To ascertain the relationship between the menstrual cycle and sleep–wake rhythms, we evaluated the objective and long-term sleep–wake rhythms of ten healthy women using a recently developed wearable device. The results showed a strong negative correlation between the sleep midpoint and the quasi-peak value (an indicator of rhythm robustness), and a positive correlation between the length of the menstrual cycle (days) and social jetlag (hours). These results suggest that healthy women with late sleeping habits have a disturbed sleep–wake rhythm and that irregular habits prolong the menstrual cycle. The sleep midpoint and quasi-peak values showed variations during the menstrual cycle. The quasi-peak values in the follicular phase were significantly higher than those in the menstrual and luteal phases. In rodents, the phase of locomotor activity rhythm advances, and activity increases at night during proestrus. The increase in quasi-peak values during the follicular phase, when estrogen is relatively high, may be due to the increased activity caused by estrogen. These results suggest that ovarian steroid hormones influence sleep–wake rhythms in women. Verifying the results of this study under various conditions is necessary; however, accurately predicting the day of ovulation using only the acquisition of sleep–wake rhythms with wearable devices will be possible.