Associations of meal timing and sleep timing with premenstrual syndrome and dysmenorrhea in Japanese women: a cross-sectional study.

Background: Premenstrual syndrome (PMS) and dysmenorrhea (menstrual pain) are common among women of reproductive age. Fluctuations in reproductive hormone levels during the late luteal phase have been linked to changes in eating and sleep patterns, which may contribute to PMS and dysmenorrhea. This study examined the associations of meal timing and sleep timing with PMS symptoms and dysmenorrhea. Methods: In this cross-sectional study, 426 Japanese women (mean age: 33 ± 5 years; body mass index: 22.2 ± 4.3 kg/m Results: On workdays, later first meal (β = 0.211) and earlier wake-up time (β = -0.184) were associated with higher eating-related PMS symptoms. On free days, earlier first meal (β = -0.191), later last meal (β = 0.162), longer eating window (β = 0.133), later wake-up time (β = 0.308), and longer sleep duration (β = 0.147) were associated with higher dysmenorrhea severity. Lower breakfast frequency (β = -0.13) was associated with higher eating-related PMS symptoms. Higher afternoon snacking was associated with higher total PMS symptoms (β = 0.13), higher eating-related PMS symptoms (β = 0.11), and higher sleep-related PMS symptoms (β = 0.11). More frequent nighttime snacking was associated with higher odds of moderate-to-severe PMS symptoms (OR = 1.11, 95% CI = 1.00-1.23). Conclusions: Meal and sleep timings were differentially associated with PMS symptoms and dysmenorrhea across workdays and free days. Workday behaviors were primarily associated with eating-related PMS symptoms, whereas free-day behaviors were primarily associated with dysmenorrhea severity. These findings suggest that menstrual symptoms may be differentially associated with behaviors shaped by socially imposed schedules and circadian preferences. Future longitudinal and interventional studies are needed to clarify causal relationships between meal timing, sleep timing, and menstrual health.