1987/12/01 by Michael F. Holick · 13 citations
Medicine · Immunology and Microbiology · Biochemistry, Genetics and Molecular Biology · #Vitamin D Research Studies #Psoriasis: Treatment and Pathogenesis #Biotin and Related Studies
paper · doi:10.1001/archderm.1987.01660360108022
• Vitamin D is a hormone, not a vitamin. The skin is responsible for producing vitamin D. During exposure to sunlight, ultraviolet radiation penetrates into the epidermis and photolyzes provitamin D<sub>3</sub>to previtamin D<sub>3</sub>. Previtamin D<sub>3</sub>can either isomerize to vitamin D<sub>3</sub>or be photolyzed to lymisterol and tachysterol. Vitamin D is also sensitive to sunlight and is photolyzed to 5,6-transvitamin D<sub>3</sub>, suprasterol I, and suprasterol II. In Boston, solar irradiation only produces previtamin D<sub>3</sub>in the skin between the months of March and October. Aging, sunscreens, and melanin all diminish the capacity of the skin to produce previtamin D<sub>3</sub>. Once formed, vitamin D<sub>3</sub>enters the circulation and is sequentially metabolized to 25-hydroxyvitamin D<sub>3</sub>and 1,25-dihydroxyvitamin D<sub>3</sub>(1,25-[OH]<sub>2</sub>-D<sub>3</sub>). The epidermis possesses receptors for 1,25-(OH)<sub>2</sub>-D<sub>3</sub>.1,25-(OH)<sub>2</sub>-D<sub>3</sub>D<sub>3</sub>inhibits the proliferation of cultured keratinocytes and induces them to terminally differentiate. The topical or oral administration of 1,25-(OH)<sub>2</sub>-D<sub>3</sub>has proved to be effective for the treatment of psoriasis. Therefore, the skin is the site for the synthesis of vitamin D and a target tissue for its active metabolite. The successful use of 1,25-(OH)<sub>2</sub>-D<sub>3</sub>for the treatment of psoriasis heralds a new approach for the treatment of this enigmatic disorder. (<i>Arch Dermatol</i>1987;123:1677-1683a)