[Changes in biological rhythm and sleep structure during the menstrual cycle in healthy women].
It is well known that clinical symptoms such as psychosis, epileptic seizures and sleep disturbances aggravate around the time of menstruation. In some healthy women, subjective sleep feelings or moods have been reported to change throughout the menstrual cycle, which suggests that sleep structure and sleep-wake rhythm may change during the menstrual cycle. We investigated a circadian pattern of plasma melatonin, sleep-wake rhythm and sleep characteristics in the different phases of the menstrual cycle in young healthy women under controlled environmental conditions. The subjects were seven healthy women, aged 18 to 19, with regular menstrual cycles. They stayed in an experimental facility, where temperature and humidity were kept within a narrow range, for three days in successive five weeks. They got up and went to bed at their preferable time. Polysomnography was performed using ambulatory cassette EEG system on the first and second night. Sleep stages were scored according to Rechtshaffen and Kales' criteria. Plasma melatonin was measured at 1-hour intervals for 24 hours on the third day. The menstrual cycle was divided into four phases (menstruation, follicular, early luteal and late luteal). Although the plasma melatonin level in the late luteal phase tended to be higher than in other phases, no significant difference was observed across four phases. The phase in plasma melatonin level did not change. As for sleep-wake rhythm, the time of getting up on the first day was significantly late in the late luteal phase (p < 0.05), although it showed no significant change on the second day. The time of going to bed did not change. Sleep characteristics changed during the menstrual cycle. There was a significant difference in the amount of stage 3 + 4, slow wave sleep (p < 0.05), which was more abundant in the follicular phase than in the luteal phase. TIB (time in bed), SPT (sleep period time), TST (total sleep time) seemed to increase in the menstrual and follicular phases, while stage W increased in the early and late luteal phases. However, there were no significant differences in these parameters. The other parameters did not show any changes. The changes in amount of stage 3 + 4 throughout the menstrual cycle seem to be due to endogenous factors, because environmental factors were controlled in this experiment. It is possible that the menstrual cycle also affect the plasma melatonin level and sleep-wake rhythm.