Menstrual symptoms may have a significant impact on women's lives. Many women experience menses-related health problems, such as menstrual pain, heavy menstrual bleeding, and premenstrual syndrome, during their reproductively fertile years. Circadian misalignment in shift workers has been reported to contribute to menstrual cycle irregularity and/or painful menstruation. However, the relationship between social jetlag (SJL) and menstrual symptoms/menstrual cycle has not been elucidated. In this study, we aimed to elucidate this relationship among female university students. One-hundred and fifty female university students (mean [SD]: 18.8 [0.71]-years old) completed self-reported questionnaires consisting of menstrual symptoms and menstrual cycle, sleep quality and sleep habits, quality of life, and demographic variables. The average menstrual cycle was 32.0 [5.4] days. The percentage of students who showed menstrual cycle irregularity, having less than 25 days or more than 39 days of menstrual cycle during the previous four menstrual cycles, was 60.6%. SJL, the difference between mid-sleep time on free days and mid-sleep time on school days, was categorized into small (absolute SJL < 1 h) or large (≥1 h). Overall, 78.0% of participants had SJL ≥ 1 h. Among the menstrual symptoms, pain, behavioral change, and water retention subscale scores were significantly higher in the SJL ≥ 1 h group than in the SJL < 1 h group. However, no significant differences were found in concentration, autonomic reaction, or negative affect subscale scores between the two groups. The menstrual cycle was 31.2 [5.5] days in the SJL < 1 h group and 32.2 [5.4] days in the SJL ≥ 1 h group, without significant difference. Logistic regression analysis showed that more than 1 h of SJL was a significant associated factor with severe menstrual symptom, independently of sleep duration and late chronotype. This study indicated that SJL was a significant factor associated with severe menstrual symptoms, suggesting the possibilities of association between circadian system and reproductive function among humans.
