To date, the key role of
vitamin D in male reproductive system has been suggested, since the expression of
vitamin D receptors and metabolizing
enzymes was demonstrated in the testis and spermatozoa. Nevertheless, a general consensus about the role of
vitamin D in male fertility is still debated. The aim of this review is to provide an updated systematic revision of the current available literature, discussing the experimental and clinical evidence on the role of
vitamin D in the regulation of testis
hormone production, seminal parameters and male fertility. The consequences of
vitamin D deficiency on serum levels of
testicular hormones have been analysed by several observational and interventional studies, with controversial results. Equally, the experimental researches not were able to state a certain relationship between
vitamin D status and testis
hormone production. Possible bias, including age, body mass index, and baseline
vitamin D status justified the differences among studies. As well as concerning the effect of
vitamin D on semen parameters, most of the studies agreed in the possibility that
vitamin D might have a positive effect on human male fertility potential, particularly through better sperm motility. Regarding pregnancy outcomes, normal level of
vitamin D seems to be related to better pregnancies. However, all the previous studies displayed a wide heterogeneity in study design, population, methodology, and cut off values used for the evaluation of
vitamin D status. Future studies are needed to better clarify the exact role of
vitamin D on hormonal and seminal panel in both fertile and infertile men.