Vitamin D metabolites across the menstrual cycle: a systematic review

Background: Accurate estimation of vitamin D status is important for health research and can impact prevention and treatment of deficiency in women of reproductive age. We aimed to assess if blood concentrations of 25-hydroxyvitamin D [25(OH) D] or 1,25-dihydroxyvitamin D [1,25(OH)(2)D] change across the menstrual cycle. Methods: We conducted a systematic search in PubMed, Web of Science, CAB and BIOSIS of literature published until December 2018 which reported concentrations of vitamin D metabolites at two or more identified points among women with regular menstrual cycles. Results: Ten longitudinal studies met the inclusion criteria; nine studies measured 1,25(OH)(2)D and five studies measured 25(OH) D. Study size ranged from 5 to 47 subjects, with an age range of 18-47 years. One study found a decrease in concentration of 25(OH) D in the periovulatory and luteal phase. Four studies found no changes in concentrations of 25(OH) D. Two studies found a rise in 1,25(OH)(2)D within the follicular phase, including a 128% increase from day 1 to 15 and a 56% increase from day 0 to 12. Two studies found rises in 1,25(OH)(2)D concentrations from the follicular to luteal phase of 13 and 26%. Five studies did not find any changes in concentrations of 1,25(OH)(2)D. Conclusions: No conclusion can be drawn on the pattern of 1,25(OH)(2)D 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)(2)D and 25(OH) D longitudinally, to understand relationships with other hormones and the potential impact on estimates of vitamin D deficiency .