Fluctuation of Serum 25(OH)D during the Menstrual Cycle in Young Japanese Women

Background and objectives: There is a growing interest in the importance of vitamin D in gynopathy, female reproductive function, and menstruation. However, the role of vitamin D function in the female reproductive health has not yet been elucidated. Therefore, this study aimed to determine whether serum 25(OH)D levels change during the menstrual cycle of young women. Methods: The participants included 39 healthy Japanese women aged 20–27 years. The survey period was from October to December 2018. Before the survey, the participants measured their basal body temperature for two months to estimate the follicular, ovulation, and luteal phases of their menstrual cycle. For the ovulation phase, a test kit for the prediction of ovulation day was also used, which made estimates based on the measurement of urinary LH. Blood sampling and sun exposure time surveys were conducted within the follicular, ovulatory, and luteal phases (three times in total), and physical measurements and semi-quantitative food frequency questionnaire were conducted once during the survey period. Results: Regarding hormonal fluctuations during the menstrual cycle, LH levels were significantly higher in the ovulation phase than in the follicular and luteal phases. FSH levels were significantly lower in the luteal phase than in the follicular and ovulation phases. The estradiol levels were significantly higher in the ovulation and luteal phases than in the follicular phase. Progesterone levels changed significantly across all three phases and were highest in the luteal phase. Serum 25(OH)D also changed; it was significantly lower in the luteal phase (15.8 ± 3.7 ng / mL) than in the follicular (16.9 ± 3.5 ng / mL) and ovulation (16.5 ± 3.3 ng / mL) phases. Conclusions: The results of this study suggest that serum 25(OH)D levels change during the menstrual cycle of young Japanese women.