Vitamin D in human reproduction: a narrative review

TLDR: Vitamin D supplementation improves fertility outcomes in both sexes in men and women and may have a positive effect on sperm count and motility.

Abstract: Summary Background: Special attention has been given to the effect of vitamin D supplementation on fertility outcomes in both sexes. Aims:  The purpose of this narrative review was to elucidate the role of vitamin D in male and female reproduction, providing current evidence from both animal and human studies. Materials and Methods:  Using PubMed and Medline, we searched for publications during the last 30 years regarding the role of vitamin D in human reproduction. Results:  Accumulating evidence from animal and human studies suggests that vitamin D is involved in many functions of the reproductive system in both genders. In women, vitamin D status has been associated with in vitro fertilization (IVF) outcome, features of polycystic ovarian syndrome (PCOS) and endometriosis. Although several data converge towards a beneficial effect of vitamin D supplementation in metabolic disturbances in women with PCOS, a significant knowledge gap precludes the establishment of a clear cause-effect relationship. In men, vitamin D status has been associated with semen quality and sperm count, motility and morphology. There is evidence for a favourable effect of vitamin D supplementation on semen quality, testosterone concentrations and fertility outcomes. Discussion:  Studies with superior methodological characteristics are needed in order to establish a role for vitamin D on the treatment of female and male infertility. Conclusions:  Recent data on vitamin D provide new insights in the complex pathogenesis and treatment of infertility.