Biochemistry

A number of products contain provitamins, i.e., compounds from which vitamins are formed in the body. They are carotenes, which break down in a number of tissues with the formation of retinol (vitamin A), some sterols (ergosterols, 7-dehydrocholesterol, etc.), which turn into vitamin D under the influence of ultraviolet rays. 12.2 WATER SOLUBLE VITAMINS A large group of water-soluble vitamins is represented by В vitamins (13 items). These vitamins are characterized by the following features: 1) almost all of them are contained in the liver, yeast, bran; 2) most of the vitamins of this group are necessary for the normal functioning of the nervous system, skin, and gastrointestinal tract. The main property of В vitamins is neurotropy. This property of vitamins is important to take into account in the nutrition of people who are constantly experiencing nervous overload in modem conditions (socio-economic problems, lower living standards, accelerated rhythm of life, a huge flow of information, etc.). In ordinary diets, including products of animal and vegetable origin, the most deficiency (most often in winter and early spring) are vitamins C, В Қ В 2 , A and D, since they can be destroyed during processing and storage. In addition, it is important to change the assortment of products (fruits, vegetables, berries), which in these seasons becomes much less diverse; a light starvation plays an important role, since in winter, ultraviolet rays do not reach the Earth's surface. Some vitamins (pantothenic, lipoic, folic acid, biotin, tocopherols, etc.) are widely distributed in foods, so a healthy person with proper nutrition does not feel deficiency for them. A colon microflora synthesizes a number of vitamins that are used by the body: phylloquinone, folic acid, and pyridoxine. When the microflora composition changes due to an unbalanced diet, various diseases of the colon or taking medications that inhibit the vital activity' of microorganisms, the corresponding hypovitaminosis develops. Partial biosynthesis of niacin is carried out in the tissues of the human body from tryptophan with the participation of pyridoxine. Like all vitamins, group В plays a protective role in the body. The mechanism of participation in these processes is specific for each vitamin. Almost all vitamins of this group have a lipotropic effect, i.e., they enhance the oxidation of fats, prevent the accumulation of cholesterol, and improve the neutralizing function of the liver. Most of them activate each other. Almost all В vitamins contain nitrogen. 245