The aim of the present study was to investigate the association among lunar cycle, menstrual cycle onset, and subjective sleep quality. Menstrual cycle onset data from the six most recent menstrual cycles were obtained for 529 women (aged 25-39 years) using the smartphone app Luna Luna. We also collected questionnaire survey data on sleep quality from each participant. Overall, there was no association between the onset of menstrual cycle and lunar phase. Interestingly, the proportion of good sleepers with menstrual cycle beginning during the light period was significantly higher than that during the dark period, while the proportion of poor sleepers with menstrual cycle beginning during the dark period was significantly higher than that during the light period. When participants were categorized by the combination of lunar phases (light, dark, neutral periods) in the two most recent menstrual cycle onsets, the "both dark period" group and the "other (light and dark) period" group showed the lowest proportion of good sleepers. Menstrual cycle onset in the dark period was associated with a deterioration in subsequent subjective sleep quality, which was more apparent with consecutive onsets in the dark period or at a rapidly changing lunar phase.
Keywords: human; lunar rhythms; menstrual cycle; menstruation; moon; reproductive health; sleep quality.