Benders'dictionary of nutrition and food technology

500synthesis of noradrenaline, and peptidyl glycine hydroxylase(EC 1.14.17.3) in the post-synthetic modification of a number ofpeptide hormones. It is a general (non-enzymic) antioxidant,including the reduction of oxidised vitamin e in cell membranes.Deficiency results in scurvy: seepage of blood from capillaries,subcutaneous bleeding, weakness of muscles, soft, spongygums and loss of dental cement, leading to loss of teeth and inadvanced cases deep bone pain. A lesser degree of deficiencyresults in impaired healing of wounds.The requirement to prevent scurvy is less than 10 mg/day; referenceintakes range between 30 and 85mg/day, depending onthe criteria of adequacy adopted and the assumptions made inthe interpretation of experimental data. At intakes above100 mg/day the vitamin is excreted in the urine; there is noevidence of any adverse effects at intakes up to 4000 mg/day.Fruits and vegetables are rich sources; also used in curing ham,and as an antioxidant and bread improver.See also dichlorophenol indophenol; erythorbic acid; iron;o-phenylene diamine; oxalic acid.vitamin D (see p. 501) Vitamin D 3 is calciol or cholecalciferol;formed in the skin by the action of ultraviolet light on 7-dehydrocholesterol,hence not strictly a vitamin. However, in northernlatitudes sunlight exposure may not be adequate to meetrequirements, and a dietary source becomes essential.Vitamin D 2 (ercalciol or ergocalciferol) is a synthetic vitamerproduced by irradiation of ergosterol. The name vitamin D 1 wasgiven originally to an impure mixture and is not used now.The main storage form of the vitamin is the 25-hydroxyderivative, calcidiol, in plasma; the active metabolite is the1,25-dihydroxy derivative, calcitriol. Formation of calcitriol isregulated by the state of calcium balance.The function of calcitriol is mainly in regulation of calciummetabolism; it acts via nuclear receptors, like a steroid hormone,and also via cell-surface receptors. Stimulates absorption ofdietary calcium from the small intestine and calcium turnover inbone, by activating osteoblasts to mobilise calcium, then laterrecruiting and stimulating differentiation of osteoblast precursorsfor bone formation. Acting to regulate intracellular calciumconcentrations, it is important in control of the secretion ofinsulin and other hormones. It also has a role (together withvitamin a) in regulation of cell differentiation and replication,and control of the cell cycle.Deficiency causes rickets in young children, osteomalacia inadults.Not widely distributed in foods; egg yolk, butter, oily fish andenriched margarine are the only significant sources. Reference