Vitamin D metabolites across the menstrual cycle: a systematic review.

No conclusion can be drawn on the pattern of 1,25(OH)2D concentrations across the normal menstrual cycle due to inconsistencies in study findings. Evidence is currently insufficient to assess 25(OH)D concentrations across the cycle. Future studies should aim to measure 1,25(OH)2D and 25(OH)D longitudinally, to understand relationships with other hormones and the potential impact on estimates of vitamin D deficiency.