For instance, in addition to its well-established physiological role as a regulator of Ca++ metabolism and bone growth, vitamin D has emerged as a potent neurosteroid hormone (Table 3) whose deficiency and aberrant signaling via nuclear vitamin D receptors (VDRs) have been linked to both depression and psychoses clinically, as well as in animal models [247,248,249]. Here, VDR is linked to major depressive disorder.