Vitamin D and Reproductive Hormones Across the Menstrual Cycle

Area of Science:

• Endocrinology
• Reproductive Health
• Nutritional Science

Background:

• Vitamin D status is linked to fecundability, but the underlying mechanisms are unclear.
• Estrogen influences 25-hydroxyvitamin D (25(OH)D) levels, and 1,25-dihydroxyvitamin D may affect ovarian steroidogenesis.
• Limited data exist on calciotropic hormone fluctuations during the menstrual cycle and reproductive hormone patterns by vitamin D status.

Purpose of the Study:

• To investigate the variation of calciotropic hormones (25(OH)D, 1,25(OH)2D, iPTH) across the menstrual cycle.
• To determine if cyclic patterns of reproductive hormones (estradiol, progesterone, LH, FSH) differ based on vitamin D status.

Main Methods:

• A prospective cohort study involving 89 women over two menstrual cycles.
• Serum samples analyzed for 25(OH)D, 1,25(OH)2D, iPTH, estradiol, progesterone, LH, and FSH.
• Non-linear mixed models used to assess hormone variability and differences by vitamin D status categories, adjusted for age, BMI, and physical activity.

Main Results:

• Calciotropic hormones (25(OH)D, 1,25(OH)2D, iPTH) showed minimal variation across the menstrual cycle, with some fluctuations observed for 1,25(OH)2D and iPTH.
• Women with lower 25(OH)D (<30 ng/ml) had significantly lower mean estradiol levels (13.8% lower) compared to those with sufficient levels.
• Higher intact parathyroid hormone (iPTH) levels were associated with lower mean estradiol (12.7% lower) and progesterone (7.3% lower).

Conclusions:

• Calciotropic hormone levels exhibit minimal variability throughout the menstrual cycle.
• Lower vitamin D status (lower 25(OH)D or higher iPTH) is associated with reduced mean estradiol and progesterone levels.
• Findings support current practices of not timing vitamin D deficiency testing to the menstrual cycle phase.