Calciferol Vitamin D

Unlike other vitamins, cholecalciferol (vitamin Dj) can be formed from a steroid precursor, 7-dehydrocholesterol (6.7), by the skin when exposed to sunlight with sufficient exposure to the sun, no preformed vitamin D is required from the diet. 

UV light (280-320 nm) causes the photoconversion of 7-dehydrocholesterol to pre-vitamin Dj. This pre-vitamin can undergo further photoconversion to tachysterol and lumisterol or can undergo a temperature-dependent isomerization to cholecalciferol (vitamin D3, 6.8). At body temperature, this 

Vitamin D2 (ergocalciferol) is formed by the photoconversion of ergo-sterol, a sterol present in certin fungi and yeasts, and differs from cholecalciferol in having an extra methyl group at carbon 24 and an extra double bond between C22 and C23. Ergocalciferol was widely used for many years as a therapeutic agent. 

Relatively few foods contain significant amounts of vitamin D. In addition to conversion in situ by the body, the principal sources of vitamin D are foods derived from animal sources, including egg yolk, fatty fish and liver. Unfortified cows milk is not an important source of vitamin D. 

The major form of vitamin D in both cows and human milk is 25(OH)Dj. This compound is reported to be responsible for most of the vitamin D in the blood serum of exclusively breast-fed infants. Whole cows milk contains only about 0.03 ng vitamin D per 100 g and 1 litre of milk per day will supply only 10-20% of the RDA. Therefore, milk is often fortified (at the level of c. 1-10 /tg 1 ) with vitamin D. Fortified milk, dairy products or margarine are important dietary sources of vitamin D. The concentration of vitamin D in unfortified dairy products is usually quite low. Vitamin D levels in milk vary with exposure to sunlight. 

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An X-ray crystal structure determination of calciferol (vitamin D-2,71) showed that steric crowding in the s-cis diene system resulted in a twisted conformation with a dihedral angle of 53° [59], On irradiation with a mercury lamp, it was partially converted into ergosterol (72) and tachysterol (73) [60, 61]. When a solution of calciferol in light petroleum containing a trace of iodine was exposed to diffuse daylight, the vitamin was photoisomerized to (74) [62],... 

The term vitamin D is used for a range of compounds which possess the property of preventing or curing rickets. They include ergocalciferol (calciferol, vitamin D ), chole-calciferol (vitamin Dg), dihydrotachysterol, alfacalcidol (la-hydroxycholecalciferol) and calcitriol (1,25-dihydroxycholecalciferol). 

Only a very small r.moimt of vitamin D is necessary for health-approximately 0.01 mg per day. The vitamin is a fat soluble itamin, occurring in cod liver oil, egg yolks, milk, and in very small amounts in other foods. Cereals, yeast, and milk acquire an added vitamin D potency when irradiated with ultraviolet light. The radiation converts a fatty substance (a lipid) that is present in the food, a substance called ergosterolj into another substance, calciferol (vitamin D.), tv hich has vitamin D activity. The structure of calciferol is closely related to that of vitamin Dg. 

An elderly woman with atrial fibrillation, successfully treated for over a year with verapamil, developed atrial fibrillation within a week of starting to take an oral calcium compound 1.2 g with calciferol (vitamin D) 3000 units daily for difluse osteoporosis. Her serum calcium levels had risen from 2.45 to 2.7 mmol/L. Normal sinus rhythm was restored by giving 500 mL of saline and repeated doses of furosemide 20 mg and verapamil 5 mg by intravenous injection. ... 

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