FAT SOLUBLE VITAMINS

Vitamin A (retinol). Vitamin A has several vitamers.

Vitamer is a substance similar in chemical structure and having physiological effects characteristic of a particular vitamin.

Retinol is oxidized in the organism with the participation of the biocatalyst. It is converted to retinal, also having the activity of vitamin A.

Vitamin A affects the barrier function of skin, mucous membranes, the permeability of cell membranes and biosynthesis of glycoproteins, it is involved in light perception, being a part of the photosensitive pigment rhodopsin.

Vitamin A deficiency leads to inhibition of growth, weight loss, lesions of skin, mucous membranes and eyes (night blindness).

Vitamin A is found in liver, egg yolk, milk, oil; provitamin A (carotene) - in red pulp vegetables. Daily requirement is 2.7 mg. In humans body vitamin A is stored mostly in liver.

There are cases of A hypervitaminosis at eating polar bear, seal, walrus liver, which contains plenty of vitamin A. Hypervitaminosis may develop as a result of receiving large amounts of fish oil and preparations with vitamin A. The characteristics of hypervitaminosis are eye inflammation, hair loss, headaches, dyspepsia (nausea, vomiting) dermatitis.

Vitamin D (calciferol) in the human organism exists as a form of D₂ and D₃. Precursor of vitamin D₂ (ergocalciferol) is ergosterol, which is present in plants. Precursor of vitamin D₃ (cholecalciferol)is cholesterol, which is present in animals. Ergosterol and cholesterol are transformed into D₂ and D₃ under the influence of solar radiation.

Calciferols are involved in the regulation of calcium and phosphorus digestion in the intestine, in osteogenesis, in the synthesis of mRNA and Ca-binding proteins and hormones.

Vitamin D deficiency in children leads to rickets. The result is bone softening and deformation, thickening at the bone-cartilage boundary ribs, large head, enlarged abdomen due to the muscle hypotonia). D avitaminosis in adults leads to osteomalacia and osteoporosis. It is bone demineralisation, causing the bones become fragile.

D hypervitaminosis is observed at very high dosages of vitamin and can be fatal. Toxic effect includes resorption of bones and deposition of phosphates in soft tissues (kidney and arteries).

Vitamin D is found in animal products - butter, liver, egg yolk and oil. Daily requirement is 10 micrograms, for children - 20-25 microgramms. To prevent rickets in children UV irradiation is recommended.

Vitamin E (tocopherol) (from the Greek Tokos - descendants, Fero - bring) got its name because it was established that it regulates the process of reproduction in rats.

Vitamin E is one of the strongest natural antioxidants. It protects polyunsaturated fatty acids and lipids of cell membranes from oxidation, especially from peroxidation reactions.

In the absence or deficiency of vitamin E in humans and animals embryogenesis is disturbed and degenerative changes in the reproductive organs are observed. Degeneration of the spinal cord develops and there is paralysis of limbs, fatty liver, muscular dystrophy, biochemical changes in muscles.

Sources of Vitamin E are mainly vegetable oils, cabbage and grain products. It also contained in meat, milk, butter, eggs. Vitamin E is deposited in muscle, pancreas, so the development of avitaminosis is almost not observed. Daily requirement is 5 milligrams.

Vitamin K (phyllochinone).It regulates the process of blood clotting. Vitamin K deficiency can lead to spontaneous nosebleeds, bloody vomiting and internal bleeding. K avitaminosis is rare. A mixed diet is rich enough with it; the intestinal micro flora is capable of synthesizing vitamin K.

The drug "vikasol" is derived from vitamin К₃.