Although traditionally importance has been given only to the role of vitamin D in bone health, its possible role in fertility is gaining increasing interest. This vitamin has receptors throughout the body, including the ovary, endometrium and placenta, and has been linked to reproductive and obstetric outcomes.
Optimal vitamin D levels have been shown in several studies to improve the likelihood of pregnancy. However, the mechanism by which it increases the rate of gestation is still not very clear.
In a study carried out in recipients of donor eggs, in which it is assumed that all the embryos will be of good quality, it was observed that those patients with correct vitamin D levels had a greater chance of becoming pregnant. However, in another study performed with euploid embryo transfer (chromosomally healthy), this effect was not observed. Thus, although the evidence seems to indicate that vitamin D does improve endometrial receptivity, its role is probably more complex than it appears at first glance.
Another possible mechanism by which vitamin D could increase pregnancy rates is by improving oocyte quality. It has been shown that blood levels of vitamin D are proportional to follicular fluid levels, and it is thought that vitamin D may alleviate ovarian aging, although it has not been studied directly in oocytes.