title: Comparison of oral 25-hydroxycholecalciferol, vitamin D, and ultraviolet light as determinants of circulating 25-hydroxyvitamin D.
abstract: Circulating concentrations of 25-hydroxyvitamin D (25-OHD) were measured during short-term and long-term oral treatment with 25-hydroxycholecalciferol (25-OHD3), 25-H.C.C.) or with vitamin D in over 200 subjects over a period of 5 years. Ten times more vitamin D than 25-OHD3 was required to produce equivalent plasma-25-OHD concentrations. Plasma-25-OHD was a power function of dosage with both compounds. These data indirectly measure the superior therapeutic potency of 25-OHD3, show that dose-response relations with both compounds may be useful in diagnosis, and indicate that there are pronounced constraints on 25-hydroxylation of vitamin D. Together with the effects of ultraviolet light, now shown to be equivalent to oral vitamin D in doses of 8000-10 000 I.U. daily, these constraints may protect against vitamin-D deficiency in winter.
mesh_terms: D000284:Administration, Oral; D002762:Cholecalciferol / Q000008:administration & dosage* / Q000627:therapeutic use; D004305:Dose-Response Relationship, Drug; D004341:Drug Evaluation; D004872:Ergocalciferols / Q000008:administration & dosage* / Q000627:therapeutic use; D006801:Humans; D006887:Hydroxycholecalciferols / Q000008:administration & dosage / Q000097:blood*; D014467:Ultraviolet Therapy; D014808:Vitamin D Deficiency / Q000517:prevention & control / Q000628:therapy*
chemical_list: D004872:Ergocalciferols; D006887:Hydroxycholecalciferols; D002762:Cholecalciferol