Although traditionally only the role of vitamin D in bone health has been emphasized, its potential role in fertility is becoming increasingly important. This hormone has receptors throughout the body, including the ovary, endometrium, and placenta, and has been linked to reproductive and obstetric outcomes.
Studies have shown that optimal levels of vitamin D improve the chance of pregnancy. However, the mechanism by which the rate of gestation increases is not yet very clear.
In a study carried out on donor egg recipients, where it is assumed all the embryos will have a good quality, it was observed that those patients with correct vitamin D levels had a greater chance of becoming pregnant. However, in another study carried out with the transfer of euploid (chromosomally healthy) embryos, 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 may increase pregnancy rates is by improving egg quality. Blood levels of vitamin D have been shown to be proportional to levels in follicular fluid, and it is believed that vitamin D may palliate ovarian aging, although it has not been possible to study it directly in eggs.