Vitamin D - Cholecalciferol

Vitamin D hormone is derived from vitamin D (cholecalciferol). Vitamin D can also be produced in the body it is formed in the skin from dehydrocholesterol during irradiation with UV light. When there is lack of solar radiation, dietary intake becomes essential, cod liver oil being a rich source. Metaboli-cally active vitamin D hormone results from two successive hydroxylations in the liver at position 25 ( calcifediol) and in the kidney at position 1 ( calci-triol = vit. D hormone). 1-Hydroxylation depends on the level of calcium homeostasis and is stimulated by parathormone and a fall in plasma levels of Ca or phosphate. Vit D hormone promotes enteral absorption and renal reabsorption of Ca and phosphate. As a result of the increased Ca + and phosphate concentration in blood, there is an increased tendency for these ions to be deposited in bone in the form of hydroxyapatite crystals. In vit D deficiency, bone mineralization is inadequate (rickets, osteomalacia). Therapeutic Liillmann, Color Atlas of Pharmacology... 

Vitamin D Cholecalciferol Ergocalciferol 1,25-Dihydroxy- cholecalciferol Calcium uptake 1 i... 

Vitamin D (cholecalciferol ergocalciferol) has its active form as 1,25-dihydroxylchole-calciferol. It is responsible for calcium uptake, and a deficiency of the vitamin results in rickets (in children) and osteomalacia (in adults). The symptoms of both syndromes are soft, pliable bones. High levels of vitamin D are toxic. 

They facilitate the intestinal absorption of fat-solnble vitamins (vitamin A, retinol vitamin D, cholecalciferol vitamin E, tocopherol and vitamin K). 

Jones G, Seamark DA, Trafford DJH, Makin HLJ. Vitamin D cholecalciferol, ergocaliferol and hydroxylated metabolites. Chromatogr Sci 1985 30 73-129. 

Calcium homeostasis is modulated by hormones (Fig. 2). Parathyroid hormone (PTH) is the most important calcium regulator. It is a hormone of 84 amino acids, and is secreted from the parathyroid glands in response to a low unbound plasma calcium. PTH causes bone resorption and promotes calcium reabsorption in the renal tubules, preventing loss in the urine. 1,25-dihydroxycholecalciferol (1.23 DHCC) maintains intestinal calcium absorption. This sterol hormone is formed from vitamin D (cholecalciferol). following hydroxylation in the liver (at carbon-25) and kidney (at carbon-1). However.hydroxylation in the kidney is PTH dependent.andsoeven (he absorption of calcium from the gut relies (albeit indirectly) on PTH. 

Figure 1 Chemical structure of (A) vitamin A, all-frans-retinol (B) /i-carotene (C) vitamin D, cholecalciferol (D) vitamin E, a-tocopherol and (E) vitamin Ki(20), phylloquinone.

Indyk H, Woollard DC. Determination of vitamin D [cholecalciferol] in fortified milk powders and infant formulae by HPLC. J Micronut Anal 1985 1(2) 121—41. 

MEASUREMENT/ASS AY. Vitamin D potency is expressed in International Units (lU) and United States Pharmacopeia Units (USP), which are equal. One lU, or one USP, of vitamin D is defined as the activity of 0.025 meg of pure crystalline vitamin D, (cholecalciferol). 

Vitamin D has several beneficial effects on the skin prevents photo damage, wrinkles and other morphologic alterations. Its topical application has been recommended for psoriasis (Kira et al, 2003a, 2003b). However, it has an associate effect on calcium metabolism and this limits its clinical and cosmetic use (Mitani et al, 2004). Vitamin D (cholecalciferol) is not approved for use in the cosmetic industry in Europe. 

---