Diurnal fluctuation of sleep propensity and hormonal secretion across the menstrual cycle

Background: The fact that most women experience sleep changes across the menstrual cycle is thought to be associated with changes in circadian rhythms; however, few studies have investigated this relationship. Methods: We applied an ultrashort sleep–wake schedule to eight healthy women and studied diurnal fluctuations in sleep propensity, sleepiness, rectal temperature, and se-rum concentrations of melatonin, thyroid-stimulating hor-mone, and cortisol in the follicular and luteal phases. Results: In the luteal phase, amplitude of core body temperature, total melatonin secretions, and amplitudes of TSH and cortisol rhythms were significantly decreased, whereas sleepiness and occurrence of slow-wave sleep during the daytime were significantly increased. Differ-ences in the amount of daytime slow-wave sleep across the menstrual cycle were positively correlated with differ-ences in the daily mean rectal temperature. Conclusions: The findings suggest that the amplitude of circadian oscillation may be dampened in the luteal phase. Increased daytime sleepiness in the luteal phase may be associated with increased daytime slow-wave sleep, due possibly to changes in thermoregulation in the lutea