Enzymes like StAR, 17β-HSD, 3β-HSD, CYP11A1, and CYP17A1 are crucial for androgen synthesis in Leydig cells, with calcitriol shown to up-regulate CYP11A1 and CYP17A1 and increase 3β-HSD levels; conversely, vitamin D deficiency can decrease StAR, 3β-HSD, CYP11A1, and CYP17A1 expression in the testes [64, 81–83]. This evidence concerns the gene STAR and vitamin D deficiency.