Vit a,d l1, l2

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VITAMINS VITAMINS

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Vitamins These are potent organic compounds which

are not synthesized inside the body but are essential for the maintenance of metabolic processes at normal level, for the normal growth & health.

They required in very small amounts as they act as co-enzymes.

An absence of any of the vitamins in the diet may result in the development of a deficiency disease such as: beriberi, scurvy etc.

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Certain compounds which are converted to vitamins on hydrolysis or by activation with some physical factors such as radiation. They are called provitamins.

Examples: β-carotene – converted to vitamin A in the

liver. Cholesterol – converted to vitamin D by

sunlight.

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Vitamins with the same physiological action are called vitamers or isotels.

Examples: Different isotels of vitamin D are D2, D3 and vitamin A are A1, A2.

Some substances which have vitamin like actions & functions but they are not classified as vitamins, called smaller mites.

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Classification

Vitamins have been classified on the basis of their solubility. There are two common classes:

The fat soluble vitamins and water soluble vitamins.

Fat soluble vitamins – vitamin A, D, E & K. Water soluble vitamins – vitamin B-complex

& vitamin C.

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Classification of vitamins

Page 373 – figure 28.1

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Fat soluble vitamins Fat soluble vitamins Vitamin A (Retinol)Vitamin A (Retinol) The retinoids, a family of molecules that are

related to retinol (vitamin A), are essential for vision, reproduction, growth, and maintenance of epithelial tissues.

Retinoic acid, derived from oxidation of dietary retinol, mediates most of the actions of the retinoids, except for vision which depends on retinal, the aldehyde derivative of retinol.

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Structure of vitamin AStructure of vitamin A Vitamin A is often used as collective term for

several related biological active molecules. 1- Retinol (C20H29OH): A primary alcohol

containing a β-ionone ring with an unsaturated side chain, retinol is found in animal tissues as a retinyl ester with long-chain fatty acids.

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2- Retinal: This is the aldehyde derived from the oxidation of retinol. Retinal & retinol can readily be interconverted.

3- Retinoic acid: This is the acid derived from the oxidation of retinal. Retinoic acid cannot be reduced in the body, and, therefore, can not give rise to either retinal or retinol.

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4- β-carotene: Plant foods contain β-carotene, which can be oxidatively cleaved in the intestine to yield two molecules of retinal. In humans, the conversion is inefficient.

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Occurrence Occurrence Vitamin A naturally occurs in the animal

tissues. It is found in high conc in fish liver oils especially in cod liver oil, which is the most important source therapeutically.

Kidney, cream, butter, and egg yolk are good source of preformed vitamin A.

Another important source is the plants, which contain carotenoids, β-carotene is a yellow pigment contained in corn, sweet potatoes, carrots, tomatoes, apricots, yellow peaches etc.

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Requirements Requirements Per day vit A is required in international unit

of carotene from 5000 to 6000. In pregnancy this is required up to 8000 I.U.

Functions – deficiency of vit AFunctions – deficiency of vit A Night blindness is one of the earliest signs of

vit A deficiency. Prolonged deficiency leads to an irreversible loss in the number of visual cells.

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Severe vit A deficiency leads to xerophthalmia, a pathological dryness of the conjuctiva & cornea. If untreated, results in corneal ulceration &, ultimately blindness because of the formation of opaque scar tissue.

Acne & psoriasis: due to the deficiency of vit A causes changes in the skin, that leads to skin lesions & acne-vulgaris.

Reproduction: Vit A deficiency leads to the failure of reproduction. Males become sterile.

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Females although deficient are able to conceive, the babies are unable to survive due to placental defects.

Urolithiasis: A condition in which urinary calculous are present. Vit A and an acid ester diet are effective in dissolving calculi (calcium phosphate).

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Hypervitaminosis Hypervitaminosis

Excess of vitamin A intake may lead to skeletal decalcification (chronic cases), tenderness over long bones, headache, nausea, vomiting & drowsiness supposedly related to the increased spinal fluid pressure due to tendency of vit A to disrupt biological membrane.

A dose of 25,000 to 50,000 IU in children & over 100,000 in adults may cause severe hypervitaminosis.

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Pregnant women particularly should not ingest excessive quantities of vit A because of its potential for causing congenital malformation. .

Anorexia may also develop due to hypervitaminosis.

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Figure at 385

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Vitamin D

Vitamin D group belongs to steroids. They contain perhydrophenantherene cyclopentane ring as the basic frame work of the molecule.

They are sterols or activated sterols & are formed from certain sterols as a result of certain irradiations with sunlight.

Also called anti-Ricket factor, because, it prevents & cure Ricket.

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Chemistry of vit D Two types of vitamin D. 1- Vitamin D2 2- Viamin D3

1 – Vitamin D2

Vitamin D2 is the activated product of Ergosterol (provitamin) which is found only in lower plants.

The UV rays act on ergosterol & open the ring “B” to produce vitamin D2.

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A B

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B

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2 – Vitamin D3

The provitamin of D3 is the 7-Dehydrocholesterol which is present at the surface of skin.

It is activated by ultraviolet radiation of sun to form vitamin D3 by opening the ring “B”.

Sun light

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Occurrence Vitamin D is present in cows milk & other

milk in very small amount. It is also present in small amount in butter. The sterols (provitamin) are present in milk &

vegetable oils and are irradiated to the vit D by sunlight.

Richest source of vit D are fish liver oil. Cod liver oil, halibut liver oil & tuna liver oil are prescribed as a remedy for deficiency disease.

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Occurence of vit D

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Physiological actions & functions Vitamin D is essential for the normal growth

of mammals. This is related to the absorption & utilization of calcium & phosphorus in the body.

Vit D increases calcium & phosphorus absorption from small intestine.

It helps in the development & proper growth of bones & teeth.

It also has a general effect on the metabolism of citric acid.

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It has been observed that vit D increases the activity of the enzyme phytase. The enzyme hydrolyses the food phytic acid yielding inorganic phosphate.

It also influence the activity of parathyroid h. Requirement: Adults normally have little or no requirements

of vit D. They need vit D during calcium deficiency & in certain other disorders-200 IU (5μg).

The infants require 400 IU & the same is needed during pregnancy & lactation.

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Deficiency (hypovitaminosis) of vit D Nutritional rickets: Vit D deficiency causes a

net demineralization of bone resulting in rickets in children & osteomalacia in adults.

Rickets is characterized by the continued formation of the collagen matrix of bone, but incomplete mineralization, resulting in soft, pliable bones.

In osteomalacia, demineralization of pre-existing bones increases their susceptibility to fracture.

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Hypoparathyroidism: Lack of parathyroid hormones causes hypocalcemia. These patients may be treated with calcitriol and calcium supplementation.

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Toxicity of vitamin D (hypervitaminosis)

Like all fat-soluble vitamins, vitamin D can be stored in the body and is slowly metabolized. High doses can cause loss of appetite, nausea & thirst.

Enhanced calcium absorption & bone resorption results in hypercalcemia, which can leads to deposit calcium in many organs (arteries & kidneys).

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Beriberi = a degenerative disease of the nerves caused by a deficiency of the thiamine and marked by pain, inability to move, and swelling

Scurvy = a disease caused by insufficient vitamin C, the symptoms of which include spongy gums, loosening of the teeth, and bleeding into the skin and mucous membranes

Rickets = bone-softening disease: a disease, especially of children, caused by a deficiency in vitamin D