Vitamin D aids in the absorption of calcium and has central roles in bone formation and maintenance, hypertension, cancer, and immunity. In addition, the active form of vitamin D, 1,25-dihydroxy vitamin D3, decreases the proliferation and increases differentiation of keratinocytes. 1,24-dihydroxy Vitamin D3 is an analog of 1,25-dihydroxy vitamin D3 which, when used in a 4 μg/g ointment, safely and effectively suppresses psoriasis. It also is effective at increasing the time interval between phototherapy cycles when ultraviolet light is used for psoriasis. 1,24-dihydroxy Vitamin D3 inhibits the growth of both normal and psoriatic human keratinocytes (IC50 ~ 10 nM) via the vitamin D receptor. It also suppresses the production of RANTES and IL-8 by human dermal fibroblasts and reduces cutaneous lymphocyte-associated antigen on CD4+ T cells, impairing migration and skin infiltration.
