FUNDAMENTALS OF BIOCHEMISTRY AND MOLECULAR BIOLOGY - N. N. Skvortsova - 2016

Part I. Chemical Components of the Cell

4. VITAMINS AND MINERALS - ESSENTIAL NUTRITIONAL FACTORS

4.1. General characteristics of Vitamins

Vitamins (from Latin vita, meaning life) are a group of low-molecular-weight Organic compounds of diverse chemical structures that are vital for the normal functioning of the Organism.

The Development of vitamin science is associated with the name of the Russian physician Nikolai Ivanovich Lunin (1853–1937). He concluded that, In addition to Proteins, fats, milk sugar, salts, and Water, animals require additional substances that are essential for Nutrition. In his paper "On The Significance of Mineral Salts in Animal Nutrition," Lunin wrote: "...it is of great interest to investigate these substances and study their significance for nutrition."

However, the History of Vitamin discovery began long before that: in 1757, James Lind demonstrated the beneficial effects of fruit consumption in curing scurvy. In 1794, the British Royal Navy recognized the benefits of citrus juices and began supplying them to crews embarking on long voyages.

In the late nineteenth and early twentieth centuries, Christiaan Eijkman and Frederick Gowland Hopkins enriched the knowledge of nutrition with important observations and discoveries. In Asian countries, the disease beriberi (polyneuritis) was widespread. It posed as serious a problem for Japanese sailors as scurvy did for the British. In 1901, Ch. Eijkman suggested that beriberi was caused by a deficiency in the diet of a specific nutrient found in certain foods. Eijkman's research laid the foundation for discovering treatments for many DISEASES ASSOCIATED WITH dietary deficiencies. Independently of Ch. Eijkman, F. G. Hopkins described scurvy and Rickets as diseases linked to dietary factors, referring to these essential substances as "accessory food factors."

Building on the work of his predecessors, Kazimierz Funk in 1911 isolated thiamine from rice bran—a compound capable of curing pigeons of beriberi—along with another active compound now known as nicotinamide, or vitamin B₃. Funk proposed the name "vitamins" for both substances (from vita, meaning life, and amines, the group of chemical compounds to which these substances belonged).

In 1929, F. G. Hopkins shared the Nobel Prize in Physiology or Medicine with Ch. Eijkman "for their discovery of growth-stimulating vitamins." In his Nobel lecture, "The Earlier History of Vitamin Research," F. G. Hopkins reminded his audience that his 1912 paper had noted the existence of "indispensable dietary constituents not previously considered thoroughly as matters of physiological necessity." F. G. Hopkins acknowledged Kazimierz Funk's contribution to vitamin research while asserting his own priority in grasping the true Significance of the identified facts.

The daily requirement for vitamins is small, but insufficient or excessive intake leads to characteristic and dangerous pathological conditions. Avitaminosis is a complex of symptoms developing in the organism As a result of a sufficiently prolonged complete or nearly complete absence of one or several (polyavitaminosis) vitamins. Hypo- and hypervitaminoses are diseases caused, respectively, by the insufficient or excessive intake of one or multiple vitamins (polyhypo- and polyhypervitaminoses).

Vitamin deficiency leads to decreased working capacity, a sense of weakness, loss of appetite, rapid fatigue, and lowered resistance to diseases. The simultaneous absence of several vitamins is particularly harmful. The physiological requirement for vitamins is individual for each organism and depends on sex, age, health status, and The Nature of a person's labor activity.

In mammalian organisms, most vitamins are not synthesized, while some are synthesized by the intestinal microflora or Tissues in insufficient quantities; therefore, the majority of vitamins must be obtained through food.

Plant raw Materials serve as a highly valuable source of vitamins for The Human Body; their consumption virtually eliminates the risk of overdose and side effects, which are inevitable with prolonged and uncontrolled use of synthetic vitamin supplements. The Nutritional Value of vegetables, fruits, and berries is largely determined by their vitamin content.

4.2. Classification of Vitamins

Each vitamin is designated by a Latin letter (for example, B-group vitamins). Individual vitamins may be represented by a group of compounds that are closely related in chemical Structure and exhibit similar biological activity.

Classification based on physicochemical properties (solubility in water and hydrophobic Solvents) divides vitamins into two groups: water-soluble and fat-soluble.

However, the rapid development of biochemistry in the 1960s–1990s led to the elucidation of the metabolic role and MOLECULAR MECHANISMS OF action for virtually all known water- and Fat-soluble vitamins. This made it possible to propose a system of functional classification based on the nature of their specific roles in vital processes. According to this classification, Vitamins can be divided into three main groups.

The first and most numerous group includes vitamins that serve as precursors for Coenzymes and prosthetic groups of various Enzymes in the organism. These include vitamins B₁ (thiamine), B₂ (riboflavin), B₆ (pyridoxine), B₁₂ (cobalamin), PP (niacin), folic acid, pantothenic acid, biotin (vitamin H), and vitamin K.

As Components of the catalytic centers of enzymes, vitamins participate in many critical metabolic processes: METABOLISM/26.html">Energy Metabolism (thiamine and riboflavin), the Biosynthesis and Transformations of Amino acids (vitamins B₆ and B₁₂), Fatty acids (pantothenic acid), purine and pyrimidine bases (folic acid), The formation of various physiologically active compounds (acetylcholine, Steroids), and others.

The second group consists of vitamins whose active forms exhibit hormone-like activity. This includes vitamin D, whose active metabolite, 1,25-dihydroxyvitamin D, Functions as a bioregulator in calcium metabolism. This group also includes vitamin A, whose regulatory form is retinoic acid, which plays a vital role in the growth and differentiation of Epithelial Tissues.

The third group comprises antioxidant vitamins: ascorbic acid (Vitamin C) and vitamin E (tocopherols), which are part of the body's antioxidant defense system against the damaging effects of reactive, free-radical oxygen species. This group also includes numerous carotenoids—such as beta-carotene, lycopene, and lutein—which, regardless of whether or not they can be converted into vitamin A in the body, possess independent antioxidant activity essential for health. Many bioflavonoids also exhibit antioxidant properties.

In the subsequent Discussion, we will adhere to the traditional classification that divides vitamins into water-soluble and fat-soluble, while detailing their roles in vital processes.

4.3. Water-Soluble Vitamins

4.3.1. Vitamin C (Ascorbic Acid)

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Ascorbic acid plays a fundamental biochemical and physiological role in the body, promoting the normal development of Connective Tissue, tissue regeneration and wound healing, increased resistance to various types of stress, as well as supporting hematopoiesis and normal immune status.

Vitamin C is a powerful antioxidant. It plays a vital role in regulating redox processes, exerts a protective effect on pantothenic and nicotinic acids, and promotes the enzymatic conversion of folic acid into its active coenzyme forms.

Ascorbic acid also regulates Blood clotting, normalizes capillary permeability, is essential for hematopoiesis, and exhibits anti-inflammatory and anti-allergic effects. Vitamin C acts as a protective factor against the effects of stress and increases the body's resistance to infections. There are numerous theoretical and experimental premises for using vitamin C in Cancer Prevention.

Vitamin C is also essential for plants, acting as an antioxidant that helps them withstand drought, ozone, and high levels of ultraviolet radiation. Prolonged storage of vegetables, fruits, and berries reduces their vitamin value. The retention of vitamin C also depends on the method of culinary Processing.

The human body cannot store vitamin C, making a continuous additional intake necessary. Because it is water-soluble and heat-sensitive, cooking Methods involving thermal processing destroy it.

The daily requirement for ascorbic acid in adults under favorable living and climatic conditions is approximately 70-80 mg. Factors that increase the requirement for this vitamin include smoking, heavy physical exertion, psycho-emotional stress, Pregnancy, breastfeeding, rehabilitation after serious illnesses or surgeries, and the need to strengthen The Immune System.

Dietary sources of vitamin C include rose hips, black currants, sweet peppers, green peas, sea buckthorn, garden strawberries, and lemons. Vitamin C is also found in green onions, fresh herbs, fresh white cabbage, and potatoes.

Vitamin C is highly sensitive to technological processing conditions. Chopping, grinding vegetables, fruits, and berries, and other operations preceding heat Treatment result in significant losses of ascorbic acid.

4.3.2. Vitamin B₁ (thiamine)

The structure of the vitamin includes pyrimidine and thiazole rings connected by a methylene bridge:

The Biological Role of vitamin B₁ is manifested in its coenzyme form (Thiamine diphosphate, TDP):

TDP is a component of enzymes and enzyme complexes involved in Carbohydrate Metabolism.

Thiamine deficiency impairs carbohydrate metabolism as well as water balance (causing water retention and edema). The most significant pathological changes due to thiamine deficiency develop in the digestive, nervous, and cardiovascular systems.

Thiamine deficiency can occur on a monotonous diet of polished rice and refined flour products that are poor in thiamine.

Vitamin B1 deficiency belongs to the so-called diseases of civilization. Its main causes are, on the one hand, the increasing consumption of bread products made from high-grade wheat flour, which are low in thiamine, and, on the other hand, a high intake of sugar and confectionery products, which increases the rapidly absorbable carbohydrate fraction of the diet and thereby raises the body's demand for thiamine.

The requirement for thiamine depends on various environmental and internal factors, particularly the Nature of the diet. For example, proteins of high biological quality have a known thiamine-sparing effect. Conversely, an excess of dietary CARBOHYDRATES increases thiamine expenditure.

The thiamine requirement in adults is influenced by their level of physical activity. The daily requirement for an adult is 0.6 mg per 1000 kcal of daily intake, ranging from 1.5 to 2.5 mg depending on Energy Expenditure. An increased need for thiamine has been observed in various types of heavy physical labor under conditions of high or low ambient temperatures. In addition to heavy physical exertion, psycho-emotional stress also affects the thiamine requirement, requiring a sufficiently high content of vitamins—primarily B-complex vitamins—in the diet even when energy expenditure is relatively low.

Among food products, vitamin B₁ is most abundant in whole-grain or fortified bread and bakery products; cereals, especially buckwheat, oatmeal, and millet; grains and legumes; Liver; and lean pork. Brewer's Yeast and wheat germ are also rich in thiamine.

This vitamin is particularly abundant in green peas, beans, carrots, cabbage, potatoes, tomatoes, apples, and the grains of wheat, rye, and oats—especially their germs and sprouts. The primary source of vitamin B₁ is bread made from rye or whole-wheat flour. Milk and dairy products are low in thiamine. Culinary processing causes only minor losses of vitamin B₁, but it is heavily destroyed in an alkaline environment (when baking soda is added). It is not stored in reserve in the body.

4.3.3. Vitamin B₂ (riboflavin)

Riboflavin consists of an isoalloxazine ring and the sugar alcohol ribitol:

Riboflavin exerts its biological role as a constituent of numerous essential oxidation-reduction enzymes (dehydrogenases).

Riboflavin derivatives are the coenzymes flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD) (Fig. 38).

Fig. 38. Structural diagram of the dehydrogenase coenzymes flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD)

These coenzymes function as intermediate carriers of electrons and protons cleaved from the oxidized substrate.

Riboflavin plays a crucial role in iron metabolism: it is essential for incorporating stored and dietary iron into Hemoglobin. Riboflavin deficiency leads to anemia. It is involved in light and Color Vision, showing a close metabolic relationship with vitamin A. It enhances dark adaptation and visual acuity, and is required for the proper functioning of retinal rod Cells. Furthermore, riboflavin protects the mucous membranes of the eye from the irritating effects of short-wave radiation. There is also a close functional interaction between riboflavin, other B-complex vitamins, and ascorbic acid.

External manifestations of vitamin B₂ deficiency include lesions of the labial mucosa accompanied by vertical fissures. Riboflavin deficiency also leads to ocular disorders, such as photophobia, Conjunctivitis, and keratitis.

The primary causes of riboflavin deficiency in humans include inadequate intake of milk and dairy products—which are the main dietary sources of this vitamin—and chronic gastrointestinal disorders. Riboflavin utilization in the body is also impaired by insufficient protein intake.

The requirement for riboflavin depends on total energy expenditure. The recommended daily allowances (RDAs) for men range from 1.5 to 2.4 mg (increasing with physical activity), and for women from 1.3 to 1.8 mg.

Dietary sources of riboflavin include eggs, milk and dairy products (especially cottage cheese), meat, liver, Kidneys, buckwheat groats, and yeast. Polished rice, pasta, and white bread are poor in riboflavin.

Riboflavin is relatively resistant to thermal culinary processing; however, it is sensitive to ultraviolet radiation, which converts it into an inactive substance. It is most effective when combined with vitamin B₁. The human body does not store it in reserve.

4.3.5. Vitamin B₃ (Vitamin PP, Niacin)

Niacin (vitamin PP, derived from the English term "pellagra-preventing") is a group of compounds whose most important representatives are nicotinic acid (pyridine-3-carboxylic acid) and nicotinamide, both possessing equivalent vitamin activity.

The primary biological function of vitamin PP is its participation in various cellular redox processes. In the body, nicotinic acid is a structural component of nicotinamide adenine dinucleotide (NAD⁺) (Fig. 39) and its phosphorylated analog NADP⁺, which serve as coenzymes for various dehydrogenases (oxidoreductases).

Fig. 39. Structural diagram of the dehydrogenase coenzyme nicotinamide adenine dinucleotide (NAD)

Vitamin deficiency occurs due to a combination of factors: low dietary intake, consumption of cereal products containing nicotinic acid in an unabsorbable form, or insufficient Tryptophan intake resulting from diets with an unbalanced amino acid profile.

Deficiency of vitamin B₃ in the diet leads to irritability, depressed mood, headaches, and other pathological symptoms. Individuals engaged in mental labor have an increased requirement for it. The primary manifestation of nicotinic acid deficiency in humans is pellagra. Acute pellagra is severe and accompanied by Central Nervous system and psychiatric symptoms (encephalopathy).

Nicotinic acid and nicotinamide are obtained not only from food but can also be synthesized endogenously from tryptophan, where 1 mg of nicotinic acid is produced from every 60 mg of L-tryptophan. Accordingly, human (and animal) requirements are typically expressed in niacin equivalents: 1 niacin equivalent is equal to 1 mg of nicotinic acid or 60 mg of L-tryptophan.

The niacin requirement ranges from 16 to 28 mg of niacin equivalents for men (depending on energy expenditure), and from 14 to 20 mg for women. In infants during their first year of life, the requirement increases from 5 to 7 mg, reaching 15 mg of niacin equivalents by the age of 10.

Nicotinic acid and its amide are widely distributed in foods of plant and, particularly, animal origin. In plant foods, a significant portion of niacin is present as free nicotinic acid; rice bran and wheat germ are especially rich in it. In corn and other cereals, nicotinic acid is bound in an unabsorbable form (niacytin) and is fully released only after alkaline Hydrolysis. Other sources of vitamin PP include legumes (green peas, lentils, beans, soybeans), peanuts, spinach, tomatoes, potatoes, mushrooms, and whole-grain bread.

Niacin is found in all wild berries, with blueberries, rose hips, sea buckthorn, and raspberries containing the highest amounts.

In animal-derived products, niacin occurs as nicotinamide, which is part of nicotinamide coenzymes. Meat products, liver, kidneys, and fish have a high niacin content. Milk is low in niacin, yet given its tryptophan content, it serves as a good source of niacin equivalents. This explains the protective effect of milk against pellagra in corn-based diets.

4.3.5. Vitamin B₅ (Pantothenic Acid)

Chemically, pantothenic acid is a dipeptide composed of pantoic acid and The amino acid β-Alanine residues.

The term "pantothenic acid" originates from a Greek word meaning "ubiquitous," as it was found in significant quantities in both PLANT AND ANIMAL tissues.

Upon entering the body, pantothenic acid is converted into pantetheine, a constituent of coenzyme A (CoA), which plays a crucial role in metabolic processes. Coenzyme A is one of the few substances in the body involved in the metabolism of proteins, fats, and carbohydrates alike.

The function of certain Endocrine glands depends on an adequate supply of pantothenic acid in the body. For instance, vitamin B₅ stimulates The production of Adrenal Hormones—glucocorticoids—making it a therapeutic agent for conditions such as Arthritis, colitis, allergies, and Heart disease. It plays a vital role in antibody formation, promotes the absorption of other vitamins, and participates in the synthesis of Neurotransmitters (BIOLOGICALLY ACTIVE SUBSTANCES through which impulses are transmitted between Neurons).

A deficiency of pantothenic acid in the diet leads to weakness, fatigue, depression, headaches, tachycardia, hypotension, anemia, and anorexia.

The approximate daily requirement of pantothenic acid for an adult is 10–15 mg, or 4–5 mg/1000 kcal. Human daily requirements for pantothenic acid are met through a normal mixed diet, as this vitamin is found in A wide variety of animal and plant products (yeast, fish roe, beef liver, egg yolk, green plant parts, milk, carrots, cabbage, etc.).

Pantothenic acid is synthesized in the human body by the intestinal microflora.

4.3.6. Vitamin B₆

Vitamin B₆ comprises a group of three related compounds with similar biological activity: pyridoxine, pyridoxal, and pyridoxamine (differing by the presence of an alcohol, aldehyde, or amine group).

In the body, these compounds exist predominantly in phosphorylated forms as pyridoxine phosphate, Pyridoxal phosphate, or pyridoxamine phosphate.

All the aforementioned forms of Vitamin B6 are converted in the human body into the coenzyme form—pyridoxal phosphate:

Pyridoxal phosphate is a component of numerous enzymes that regulate critical reactions of Nitrogen metabolism, particularly the decarboxylation and Transamination of Amino acids.

Vitamin B₆ takes an active part in Tryptophan Metabolism. It is involved in many aspects of macronutrient metabolism, neurotransmitter synthesis, hemoglobin synthesis and function, lipid synthesis, Gluconeogenesis, and Gene Expression.

Symptoms of vitamin B₆ deficiency in adults include: oral mucosal lesions (stomatitis), dermatitis, heightened nervous excitability, depression, insomnia, and nausea.

The recommended daily intake of vitamin B₆ is set at 2 mg for men and 1.8 mg for women. For infants under one year of age, the daily intake ranges from 0.4 to 0.6 mg; by age 17, it reaches 2 mg for young men and 1.6 mg for young women. The requirement for vitamin B₆ depends on dietary protein content.

Dietary sources of vitamin B₆ include meat, liver, fish, eggs (primarily the yolk), wheat flour, potatoes, carrots, and yeast.

Thermal processing destroys 20–35% of pyridoxine, whereas freezing preserves it better.

4.3.7. Vitamin B₉ (folic acid, folacin)

Folacin (from Latin folium meaning leaf and English acid) refers to a group of related compounds exhibiting the biological activity of folic acid. The most important representatives of this group are folic acid itself (chemical name: pteroyl-para-aminobenzoylglutamic acid), its numerous coenzyme forms, and their di- and polyglutamates.

Folic acid is involved in metabolism and DNA production, plays a key role in the synthesis of immune Blood Cells, and normalizes digestive tract function. A deficiency of folacin primarily affects tissues characterized by intensive DNA Synthesis.

Recommended daily intake levels are (mcg/day): up to 6 months of age — 40, from 6 to 12 months — 60, up to 3 years — 100; for adult men and women — 200. Additional prophylactic supplementation of this vitamin is necessary for pregnant and lactating women.

Dietary sources of folic acid include green vegetables and fruits. Liver and kidneys are particularly rich in folic acid, whereas meat, eggs, and milk contain little. Bread serves as the primary dietary source of this vitamin, covering about 50% of the daily requirement for vitamin B₉. Certain berries hold the highest value as sources of folic acid: rowanberry, rose hip, wild strawberry, and raspberry. Wild strawberries and gooseberries are especially rich in vitamin B₉.

Folic Acid and its coenzyme forms are quite unstable compounds: they can easily be destroyed during food processing and culinary preparation. Folic acid is especially vulnerable in vegetables, where prolonged boiling can result in folacin losses of up to 80-95 %.

4.3.8. Vitamin B₁₂ (Cobalamin)

Vitamin B₁₂ (cobalamin) is a group of related corrin-derivative compounds that exhibit the biological (vitamin) activity of cyanocobalamin. The most important representatives of this group are cyanocobalamin, hydroxycobalamin, methylcobalamin, and S-deoxyadenosylcobalamin.

Hydroxycobalamin is one of the natural forms of vitamin B₁₂ in which it is transported by blood proteins and stored in the body. Methylcobalamin and 5-deoxyadenosylcobalamin are the Coenzyme forms of vitamin B₁₂.

Vitamin B₁₂ is not synthesized in the human or animal body. It is produced by Microorganisms in the digestive tract of any animal, bird, or fish whose meat is consumed by humans, as well as in the Human digestive tract itself. Dietary vitamin B₁₂ is absorbed in the Small Intestine after binding in The Stomach to the so-called Castle's intrinsic factor. This glycoprotein forms a complex with vitamin B₁₂ that facilitates its absorption. In the absence of Castle's intrinsic factor, vitamin B₁₂ absorption cannot take place. Upon entering the bloodstream, the complex dissociates, and free cobalamin forms complexes with α- and β-globulins, which transport it to the tissues. Within tissues, cobalamin is converted into its active forms—methylcobalamin and deoxyadenosylcobalamin—which act as coenzymes for A number of enzymes.

In its coenzyme forms, vitamin B₁₂ participates in the synthesis of Methionine and Nucleic Acids, accelerates red blood Cell Formation in synergy with folic acid, ensures the regeneration of nerve tissues (fibers), and normalizes liver function. Vitamin B₁₂ also plays a role in Lipid Metabolism as a CoA protector.

Vitamin B₁₂ deficiency leads to severe hematopoietic disorders, damage to The Nervous System, and gastrointestinal issues. Symptoms in the digestive tract include loss of appetite and impaired intestinal motility.

The primary cause of vitamin B₁₂ deficiency is often impaired absorption. Dietary deficiency occurs when animal products are excluded from the diet for a prolonged period, particularly in vegetarians, leading to the development of anemia.

Human liver reserves of this vitamin are generally sufficient to prevent B₁₂ avitaminosis for 1-2 years. The daily requirement is 2-3 µg for adults and 0.5-2 µg for children. Recommended intake levels should be adequate not only to prevent anemia but also to build up vitamin reserves in the liver.

The main dietary sources of cobalamin for humans are animal-derived foods: meat, liver, kidneys, cottage cheese, and cheese. Plant-based foods contain only trace amounts of this vitamin.

4.4. Fat-Soluble Vitamins

4.4.1. Vitamin A (Retinol)

The Vitamin A Group includes retinol, retinal, and retinoic acid:

In animal tissues, retinol is most commonly found as an ester with palmitic acid—retinyl palmitate. In plant tissues, it occurs primarily as a provitamin in the form of carotenoids:

These include alpha- and beta-carotenes, lycopene, lutein, and many others. The biological activity of beta-carotene is twice as high as that of the others. Carotenoids were first isolated from carrots, deriving their name from the Latin name of this ROOT vegetable (Carota).

The Role of vitamin A in the body is associated with reproduction, growth, differentiation of epithelial and Bone Tissues, maintenance of immunological status, and vision. The necessity of vitamin A for vision is determined by its Participation in the Synthesis of the visual pigment rhodopsin. The resynthesis of rhodopsin and the increase in its concentration within the retina ensure the eye's adaptation to low-light conditions (dark adaptation).

Vitamin A and carotenoids play a crucial role in the prevention of malignant neoplasms, and when combined with vitamins C, P, and the B group, it is prescribed for the treatment and prevention of radiation injuries.

The absorption of vitamin A and carotene takes place in the small intestine with the participation of Bile, which ensures their emulsification. The main storage depot for vitamin A in the body is the liver, which contains significant amounts of this vitamin, predominantly in the form of retinyl palmitate.

Vitamin A deficiency leads to severe disorders across many Organs and systems. Particularly characteristic are Skin lesions (skin dryness), respiratory tract issues (susceptibility to rhinitis, Bronchitis, Pneumonia), gastrointestinal problems (impaired gastric secretion, predisposition to gastritis, colitis), and Urinary Tract abnormalities. Mild to moderate forms of vitamin A deficiency are accompanied by impaired dark adaptation, conjunctivitis, and corneal dryness. Severe deficiency can lead to blindness. Disruptions in the barrier function of the epithelium lead to a sharp decrease in resistance to infections.

Liver stores of vitamin A are capable of maintaining normal retinol concentrations in the body for a considerable period.

The recommended daily intake of vitamin A in retinol equivalents (1 µg of retinol equivalent equals 1 µg of retinol or 6 µg of beta-carotene) is as follows: 1000 µg for men aged 18 to 60, and 800-1000 µg for women. Intense physical exertion increases the demand for vitamin A to 2-2.5 mg of retinol equivalents per day.

Vitamin A is widely distributed in nature. In plant tissues, it occurs mainly as the provitamin carotenoids, the majority of which are converted into vitamin A in the body. Among carotenoids, β-carotene is the most prevalent, accounting for 40-90 % of all carotenoids. It is localized in the green parts of plants, orange fruits and vegetables, Algae, and mushrooms. The degree of carotene assimilation from plant foods depends on The breakdown of Plant Cell Walls. Carotene contained in carrot puree is absorbed better than that from whole cooked or raw carrots.

Carotene is most abundant in carrots, green onions, yellow-fleshed potato tubers, pea pods, garden beet leaves, celery, ripe tomatoes, red peppers, Brussels sprouts, plums, and apples. Wild berries with intense yellow pulp are rich in carotenoids, including β-carotene, which is most efficiently converted into vitamin A in the human body. The primary dietary sources of β-carotene are sea buckthorn, hawthorn, and rose hips.

Carotene and retinol are largely destroyed under The Influence of heat, light, air, and neutral or alkaline environments. Proper thermal processing of dietary fats is extremely important. Their overheating leads to the formation of peroxides and epoxides, which promote the destruction of vitamin A and, alongside this, exert toxic effects on the body, potentially even showing carcinogenic activity.

4.4.2. Vitamin D (Calciferols)

Calciferols are formed as a result of the photoisomerization of corresponding provitamins under the influence of ultraviolet radiation. The provitamin of cholecalciferol is 7-dehydrocholesterol, which is formed in the body from Cholesterol; the provitamin of ergocalciferol is ergosterol.

The Main Functions of calciferols in the body are related to maintaining Calcium and phosphorus Homeostasis, as well as carrying out mineralization and remodeling processes in Bone tissue.

A typical symptom of vitamin deficiency is rickets, which begins between the 2nd and 4th months of a child's life and lasts until 1.5–2 years of age. In temperate and, especially, northern climates, the main cause of rickets is insufficient sunlight exposure for the child. Another cause of rickets is a lack of vitamin D in the diet. Vitamin D deficiency in adults manifests as Changes in the diaphyses of the bones. Vitamin D is essential for ensuring the growth and mineralization of bones and Teeth in infancy and childhood, and for maintaining them in a healthy state throughout later life, taking into account the increased demand for this vitamin during pregnancy, breastfeeding, and infectious diseases.

Vitamin D deficiency is a very common phenomenon and can cause problems with the growth of organ cells, the largest of which is the skin.

The human requirement for vitamin D is 10 µg per day. Vitamin D is found primarily in animal-derived products. It is abundant in the liver oil of cod, tuna, and other fish. In plant foods, it is extremely rare and occurs in very small amounts, most often in the form of the provitamin ergosterol. It is well preserved during culinary processing.

Prevention of vitamin D deficiency is achieved through regular sun exposure, or in its absence, by taking vitamin supplements containing physiological doses of vitamin D.

Prolonged use of the vitamin often causes side effects: headaches, a feeling of fatigue, weakness, nausea, loss of appetite or increased appetite, and thirst; sometimes retinal hemorrhages, psychoses, and severe Kidney damage (calcium deposits within them) are observed. It must be remembered that vitamin D, when consumed in elevated amounts, can exhibit strong toxic effects.

4.4.3. Vitamin E (Tocopherols)

In nature, vitamin E exists in eight different isomeric forms, which differ in biological activity and functions within the body.

It participates in The biosynthesis of heme and proteins, tissue Respiration, and other metabolic processes within cells. It stimulates Muscle activity and gonadal function, and promotes the accumulation of all fat-soluble vitamins in Internal Organs. Vitamin E regulates lipolysis and Lipogenesis processes, possesses anti-inflammatory properties, acts as a universal stabilizer of cell membranes, inhibits The oxidation of vitamin A and carotene, and prevents the formation of harmful toxic oxidation products in tissues.

The daily requirement for an adult is 10–30 mg. Tocopherol deficiency in the body leads to degenerative changes in The Heart muscle, skeletal musculature, Nerve Cells, and liver cells, and increases the permeability of blood capillaries.

Tocopherol is synthesized exclusively by plants. Sea buckthorn is exceptionally rich in it—up to 18 mg/100 grams in the berries and dozens of times more in the oil. Rose hips, hawthorn, and rowan berries are also rich in tocopherols. It is mainly found in vegetable oils (sunflower, linseed, peanut, soybean, sesame, etc.) and the green parts of plants. Significant amounts of vitamin E are also found in sea buckthorn oil, cloudberries, and black chokeberries.

Tocopherols have high stability and are not destroyed when heated up to 170 °C.

4.4.4. Vitamin K (Phylloquinone, Menaquinone)

Vitamin K is a group name for a number of 2-methyl-1,4-naphthoquinone derivatives with similar structures and functions in the body. Phylloquinone (also referred to as vitamin K₁) contains 4 isoprenoid units, one of which is unsaturated. Vitamin K₂ (menaquinone) exists in several forms and is produced by Bacteria in the intestine, which is why its deficiency rarely occurs, mostly in cases of dysbiosis.

Its biological role is due to its participation in blood clotting. It promotes the formation of prothrombin in the liver, enhances the MOTOR FUNCTION OF the gastrointestinal tract, and exhibits antimicrobial and antibacterial activity. It participates in bone and connective tissue metabolism, as well as in normal kidney function, ensuring calcium absorption and the interaction of calcium with vitamin D.

Vitamin K deficiency leads to poor blood clotting. A deficiency of vitamin K can develop due to impaired food Absorption in the intestine.

Vitamin K is found in green leafy vegetables, cruciferous vegetables such as white cabbage, cauliflower, broccoli, and Brussels sprouts; in stinging nettles, wheat bran, grains, certain fruits, meat; in milk and dairy products; eggs; and in soybeans and soybean products. Olive oil also contains a significant amount of vitamin K.

The daily requirement for an adult is 2 mg. It enters the body with food and is partially produced by the intestinal microflora. The synthetic analog of vitamin K, Vikasol (Vikasolum), is used as a hemostatic agent for bleeding.

Vitamin K is most abundant in shepherd's purse, water pepper, pale persicaria, stinging nettle, common yarrow, carrots, spinach, tomatoes, rowan berries, horse chestnut leaves, pine and spruce needles, cranberries, black currants, and blueberries. In berries, it occurs in the form of K₁. Among berries, rowan, black currants, rosehips, and blueberries accumulate the highest amounts of vitamin K₁.

4.5. Mineral Substances

The human body consists of 60% water, 34% organic compounds, and 6% Inorganic Compounds. The primary components of organic substances are carbon, hydrogen, and oxygen, along with nitrogen, phosphorus, and sulfur. The human body's inorganic matter invariably contains 22 chemical elements: Ca, P, O, Na, Mg, S, B, Cl, K, V, Mn, Fe, Co, Ni, Cu, Zn, Mo, Cr, Si, I, F, Se. For example, if a person weighs 70 kg, their body contains (in grams): calcium – 1700, potassium – 250, sodium – 70, magnesium – 42, iron – 5, zinc – 3.

Minerals are vital for the normal physiological functioning of the human body; they form an integral part of tissues, participate in metabolism, and contribute to the synthesis of enzymes, hormones, and digestive juices. Like vitamins, minerals frequently act as coenzymes in catalyzing biochemical reactions within the body. They represent essential dietary components that ensure the normal functioning and Development of the organism. A deficiency or complete lack of specific elements leads to severe disorders.

Based on their quantitative content in the body, minerals are classified into macro- and microelements. If the mass fraction of an element in the body exceeds 10^-2%, it is classified as a macroelement. Microelements account for 10^-3–10^-5% of body mass. If an element's concentration is below 10^-5%, it is considered an ultramicroelement.

Macroelements include calcium, phosphorus, iron, potassium, sodium, magnesium, sulfur, chlorine, etc. Calcium, phosphorus, and magnesium are involved in bone tissue formation. Furthermore, phosphorus participates in respiration, motor activity, energy metabolism, and enzyme activation.

Dietary sources of phosphorus include meat, fish, eggs, and cheese. The recommended daily intake of phosphorus is approximately 1600 mg.

Calcium is present in foods as compounds with acids and proteins. It is found in milk and dairy products, egg yolks, fish, lettuce, spinach, and parsley. The recommended daily intake of calcium is approximately 800 mg.

Calcium and phosphorus are most efficiently absorbed by the body when their dietary ratio is 1:1.2 or 1:1.5.

Magnesium normalizes nervous system excitability, stimulates intestinal peristalsis, and enhances bile secretion. It is found in grains, legumes, nuts, and fish. The recommended daily intake of magnesium is approximately 500 mg.

Iron plays a key role in hematopoiesis, with about 70% of total body iron being part of hemoglobin. Dietary sources of iron include meat, liver, kidneys, eggs, fish, grapes, strawberries, apples, cabbage, peas, potatoes, etc. The recommended daily intake of iron is 15 mg.

Potassium and sodium regulate water balance in the body. Blood Plasma contains approximately 16 mg% of potassium. The recommended daily intake of potassium is 2–3 g.

Sulfur is a constituent element of proteins.

Chlorine is essential for the production of gastric juice.

The body's requirement for sodium and chlorine is met primarily through the consumption of table salt.

The body's requirement for Trace Elements, as well as their content in food, is exceptionally small. At the same time, mineral deficiencies are associated with severe clinical symptoms (Table 10).

Trace elements include copper, cobalt, iodine, manganese, fluorine, etc. Copper and cobalt facilitate blood hemoglobin synthesis. The functions of copper are closely linked to those of iron. Cobalt participates in the catalytic function of vitamin B₁₂. The recommended daily intake of copper is 2–5 mg.

Iodine is essential for normal thyroid function. It is abundant in marine fish, seaweed, crustaceans, Mollusks, eggs, onions, persimmons, lettuce, and spinach. The recommended daily intake of iodine is 100–150 mcg.

Manganese and fluorine contribute to Bone Formation.

Trace elements are found in relatively high quantities in egg yolks, beef liver, meat, fish, potatoes, beets, and carrots.

Minerals are also referred to as ash elements because they remain as ash after a food product is incinerated. Plant and animal foods contain virtually all ash elements found in nature, although in varying amounts. The ash content serves as a quality indicator for grading flour and starch and also reflects the degree of product purity (e.g., sugar, cocoa powder).

Table 10. Typical symptoms of chemical element deficiencies in the human body

The daily requirement of an adult for minerals ranges from 13.6 to 21 g. An excess of trace elements leads to bodily poisoning. Copper, lead, and tin salts can enter food products during processing as a result of acids dissolving metal processing equipment or through equipment wear. Consequently, the levels of copper and tin in food products are strictly limited by standards, while lead, zinc, and arsenic are strictly prohibited.

Review Questions

1. Outline the BRIEF HISTORY OF the discovery of vitamins.

2. Provide the classification of vitamins based on their solubility.

3. Provide the classification of vitamins based on their biological functions.

4. Define hypovitaminosis, hypervitaminosis, and avitaminosis.

5. What are the causes of hypo- and avitaminoses, and what are their consequences?

6. Describe the structure of water-soluble vitamins (В₁, В2, В3, В5, Вб, В12).

7. Which vitamins possess coenzyme functions?

8. Describe the structure of fat-soluble vitamins (А, Е, D, К).

9. Name the vitamins whose deficiency causes the following conditions: a) beriberi; b) pellagra; c) scurvy; d) rickets; e) anemia.

10. What is the biological role of: a) vitamin C; b) pantothenic acid; c) vitamin K; d) vitamin PP; e) vitamin В₁₂?

11. What physiological disorders occur in the body due to a deficiency of: a) vitamin A; b) folic acid; c) vitamin E; d) vitamin B1; e) vitamin D?

12. List the vitamins that are synthesized within the human body.

13. Name the vitamins synthesized by the human intestinal microflora.

14. Name the vitamins that act as the most effective natural antioxidants.

15. List the mineral substances that make up biological tissues.

16. Describe the functions of minerals in the body.

17. How are minerals classified according to their quantitative content in the body?

18. Indicate dietary sources of macrominerals.

19. Indicate dietary sources of trace elements.

20. What is the human daily requirement for minerals?

21. Which mineral substances act as toxicants?

22. Describe the role of iron in the human body.

23. Which trace elements are essential for body growth?

24. A deficiency of which trace element causes weakness in The Cardiovascular system?

25. Which minerals are involved in the transmission of nerve impulses?

26. Which minerals are involved in the Regulation of Water-salt balance?

27. A deficiency of which trace elements leads to a predisposition to dental caries?

28. A deficiency of which trace element causes thyroid dysfunction and a slowdown in metabolism?

29. A deficiency of which trace element causes pernicious anemia?

30. What is the recommended ratio of calcium to phosphorus in the diet, and what are the consequences of their deficiency?