Among patients with psoriasis, the BDI scores correlated positively with the serum IL-18 concentration (r = 0.27, p = 0.0100), PASI scores (r = 0.46, p < 0.0001), BSAs (r = 0.46, p < 0.0001), and psoriasis duration (r = 0.43, p < 0.0001); the BDI scores correlated negatively with serum 25(OH)D3 concentrations (r = -0.23, p = 0.0200; Table 2). Here, IL18 is linked to psoriasis.