Vitamin C

Vitamin C is different from all other vitamins, the chemistry and biochemistry of this compound make it in many aspects simply unique. Vitamin C is found in both animal and plant life, and its role is often not completely clear. Synthetic vitamin is widely used as food additives and its antioxidant properties contribute to the preservation of food and, consequently, has an E number (K300). Even today, the controversy about the importance of vitamin C for human health, as well as the optimum doses of the vitamin, should not stop: recommendations of various authors range from 30 mg to 10 g per day.

General information about vitamin C

Vitamin C has other names - it's an anti-vitamin vitamin, an antiscorbutic vitamin, also called ascorbic acid. Soluble in water, vitamin C is considered the main vitamin of vegetables, berries and fruits.

The biochemistry of vitamin C in mammals is so far from understanding that even until now its biochemical role in such systems remains unclear. The chemical structure of L-ascorbic acid is uniquely determined by X-ray diffraction analysis, but the structure of the product of its two-electron oxidation, dehydroascorbic acid, has not been finally established, since it has not yet been possible to obtain this compound in pure form in crystalline or at least solid state.

Among the higher organisms, only very few are capable of biosynthesis of vitamin C. These include Homo sapiens, so it is not surprising that most of what is known about the biochemistry of L-ascorbic acid has to do with mammals.

St. Dieri in 1927 discovered vitamin C from the juice of cabbage, orange and red pepper. They were crystals with pronounced restoring properties. They were called hexuronic acid. Scientists have proved in 1932 the antiscorb properties of vitamin C, then it received the name - ascorbic acid (from Greek "scurvy" translates as "scurvy").

Absorbability of vitamin C

If you take vitamin C after eating, it will be better absorbed.

[1], [2], [3], [4], [5]

The beneficial effects of vitamin C on the body

Anti-vitreous vitamin helps the production of collagen and connective tissue, binds bone tissue, vessels, skin and joints. It stimulates metabolism.

One of the most important properties of vitamin C is its antioxidant properties. Thanks to them, it neutralizes the toxic radicals that arise in the body with great physical exertion, with diseases and with negative environmental effects on the body.

Vitamin C is able to neutralize many dangerous poisons in the body: it connects to them and makes them harmless, then these compounds are excreted in the urine. It also helps to increase resistance to unfavorable conditions, overheating, cooling, stress, infections and allergies.

Ascorbic acid prevents the oxidation of important fats and fat-soluble vitamins A and E, helps to heal wounds and burns. Increasing the elasticity and strength of the vessels, activating the glands of the endocrine system, improving liver function, utilizing cholesterol from the liver and the walls of the vessels, protecting the heart - all this is the work of vitamin C.

Oxidation and hydroxylation

It is known that ascorbic acid is involved in the metabolism of certain amino acids, promoting the formation of hydroxyproline, hydroxylizine, norepinephrine (norepinephrine), serotonin, homogentisic acid and carnitine.

Hydroxyproline and hydrosilicin are found in animal tissues practically only in the composition of collagen, which accounts for about one-third of all proteins of the mammalian organism. Collagen synthesized with a deficiency or lack of vitamin C, is not capable of forming full-fledged fibers, which is the cause of skin lesions, brittle vessels, etc.

Reducing properties

It is known that life on Earth depends entirely on the supply of oxygen. But, being in excess, in an unsuitable form or in an inadequate place, oxygen is a potential hell. Particularly harmful are its reactive forms and oxidation radicals, for example, superoxide anion and hydroxyl radical. These are commonly known active oxidants, which can cause serious damage to the lipid components of cell membranes due to oxidation with peroxides. The protective antioxidant role of vitamin E and essential fatty acids is established. However, they are fat-soluble compounds and, obviously, the function performed by them inside the membrane on its surface passes to ascorbic acid. Here, in the aquatic environment, vitamin C facilitates the trapping of potentially dangerous oxidants with another water-soluble antioxidant, tripeptide glutathione. Paradoxically, there is an assumption that one of the functions of glutathione is to maintain ascorbic acid in the restored state!

To say that vitamins E and C perform identical antioxidant functions in the lipid matrix and in the aquatic cellular environment, respectively, means overly simplifying the state of affairs. It is shown that these vitamins act together, and, possibly, at the lipid / aqueous phase, ascorbic acid provides protection of vitamin E or restores its oxidized form after the attack of free radicals.

The restorative capacity of ascorbic acid is "used" by another vitamin with folic acid. To perform its function, folic acid should be in the reduced tetrahydrofolate form, and this condition is provided and / or maintained in the presence of ascorbic acid.

A big problem is the propensity of an aggressive peroxide free radical to oxidize the iron atom in erythrocytes, which leads to the formation of a functionally inactive methemoglobin (metHb). This process is reversed by the enzyme metHb - reductase, which functions in the presence of cytochrome bs and ascorbic acid. The superoxide free radical is usually destroyed by vitamin C-dependent superoxide-ssmutase (SOD), so the SOD prevents the formation of a very aggressive hydroxyl radical.

It is well known that ascorbic acid promotes the absorption of iron through the walls of the intestine. Perhaps this is due to the fact that it supports the element in a restored form, in which it is more easily absorbed by the mucosa.

Electronic transport

Oxidation-reduction properties of ascorbic acid have long been used in the study of in vitro electron transport in mitochondrial membranes.

[6], [7], [8], [9], [10], [11], [12], [13],

Distribution in tissues

Vitamin C is involved in hydroxylation reactions in the biosynthesis of collagen, serotonin and norepinephrine in animals. The key to solving the problem of the role of ascorbic acid in the process of metabolism in animals can be found based on the results of an analysis of its tissue distribution. Analyzed animal tissues contain the following amounts of vitamin C (in descending order): adrenal glands (55 mg%) pituitary and leukocytes, brain, lens and pancreas, kidneys, spleen and liver, heart muscle, milk (female 3 mg%, cow 1 mg%), plasma (1 mg%). In most of these tissues, the function of vitamin C is to maintain structural integrity through participation in the biosynthesis of collagen. Elevated levels of ascorbic acid reflect more specialized functions, for example, participation in the synthesis of hormones and neurotransmitters of the adrenal and brain, as well as in the formation of an immune response in the spleen and leukocytes, stimulating the pentose phosphate cycle in the liver, maintaining the transparency of the lens and cornea.

[14], [15], [16], [17], [18], [19], [20], [21],

Consumption, excretion and metabolism

For the prevention of scurvy, the human body needs 10 mg of vitamin C per day, the daily recommended dose in the UK is 30 mg, and a laboratory rat can synthesize an amount equivalent to 2000 mg (2 g) per day! In medicine, there is a direction that is not currently popular, recommending megadoses (1-10 g per day). Perhaps this makes sense. But the argument against this is that the body of an adult organism (human) is able to accumulate only a limited amount of vitamin, usually 2-3 g, possibly 4 g. At the same time, the plasma level reaches 1.4 mg%.

Ascorbic acid is metabolized in the liver and kidneys, undergoing a series of sequential transformations, the end result of which is the formation of oxalic acid excreted in the urine.

The restorative properties of vitamin C make it an excellent co-substrate in monooxygenase hydroxylation reactions leading to the formation of amino acids and catecholamines. Thanks to these same properties, vitamin C provides protection not only for cells, eliminating free radicals, but also for other antioxidants such as vitamin E. Its chelating and (or) reducing properties promote the assimilation of iron compounds in the intestine. It is suggested that it can function as a circulating oxidation-reduction pair in electronic transport and when creating a membrane potential, and its status corresponds to the status of cytochrome c. Vitamin C is the optimal, but not the only, factor necessary to maintain numerous ferric and copper-containing enzymes in the reducing state, in which they are most functionally active.

M. Davis et al. (1999) believe that our understandable interest in various aspects of the chemistry and biochemistry of vitamin C, fueled by very tangible income from its production, is not the best incentive to solve the riddle about the existence of one basic biological function in this simple molecule or its absence. Our enthusiasm is caused simply by the absence of all of us gulonolactoxidase. And the one and only gene that our distant ancestors lost 25 million years ago is guilty of this, which condemned the human along with other primates, as well as some species of birds, bats, beetles and, of course, guinea pigs, to be partly "vegetarians involuntarily" .

[22], [23], [24], [25], [26], [27], [28]

Interaction with other elements of the body

With the help of vitamin C, iron (Fe) is well absorbed, which affects hemopoiesis.

What affects the amount of vitamin C in foods?

Vitamin C is one of the most sensitive vitamins. It is known that culinary processing of vegetables and fruits often entails loss of ascorbic acid. Any heat treatment of products or exposure to direct sunlight quickly reduces the content of this vitamin. Thus, when the products are crushed, the enzymatic activity of ascorbate oxidase contained in plants rich in vitamin C increases significantly. This enzyme is present in all plant tissues. Another enzyme, responsible for the loss of ascorbic acid, phenolase, catalyzes the oxidation of polyphenol compounds with air oxygen, which causes the darkening of fruits such as apples. The process is accompanied by the formation of dehydroascorbic acid, which rapidly converts to 2,3-diketogulonic acid, and is catalyzed by Ca and other transition metal ions. That is why it is not recommended to prepare vegetables and fruits in copper and iron utensils.

And, of course, the main factor affecting the loss of vitamin C in the cooking process is simply its dissolution in water. It should be noted that vegetables cooked in a microwave oven retain more of the much more vitamin C than those prepared by conventional methods. Thus, the loss of vitamin C can be prevented, not only by avoiding prolonged boiling of vegetables in copper dishes, but if you cook them whole. In order to preserve vitamin C in foods, they are advised to freeze and keep in a cold, dark place, for example, in a cellar or basement.

The need for vitamin C per day

For an adult, 70-100 mg of vitamin C will reimburse all losses of this vitamin to the body.

Under what conditions does the need for vitamin C increase?

If you are doing sports, then a day you need to consume 150-500 mg of antiserum vitamin. Pregnant women need to consume about 120-150 mg of this vitamin. With catarrhal diseases, it is recommended to increase the daily dose of vitamin C to 2000 mg. Also, in an unfavorable climate, it is necessary to increase the content of this vitamin in the body.

Why there is a lack of vitamin C in the body?

Lack of ascorbic acid in the body can occur with improper heat treatment of fruits and vegetables (when cooking is lost up to 60% of vitamin C). Also, this can happen if the vegetable is not properly stored (if fresh potatoes in 100 g contain about 20 mg of antiscorbutic vitamin, then after half a year of storage - only 10 mg).

Lack of this vitamin also occurs when there is not enough fruit and vegetables in food.

There is a view that avitaminosis is no longer found in western countries. But this is by no means the case. It is recognized that chronic diseases, elderly and lonely people suffer from vitamin deficiency associated with vitamin C deficiency. The level of ascorbic acid in plasma is at an average rate of 1.2 mg% (permissible limits of 0.6-2.5 mg%), the content of ascorbate in leukocytes is normally 25 μg per 10 ⁸ cells.

Recommended dietary norms for daily intake of vitamin C

Recommended dietary norms	mg per day
Infants	35
Children	45
Teens	50
Adults	60
Pregnant women	80
Breastfeeding mothers	100
Old men	150

An increase in the level of ascorbic acid in the plasma occurs only upon admission up to 150 mg per day. An indicator of the level of vitamin C in the body is the level of ascorbic acid in the plasma. The condition of insufficiency is indicated by its fall below 0.5 mg%. It was found that the plasma level decreases in many pathological conditions, such as infectious diseases, congestive heart failure, liver and kidney diseases, gastroenterological and endocrine disorders, purpura (hemorrhagic rash), malignant formations. Patients in fever, who have undergone surgical intervention or trauma, need large amounts of vitamin C with food.

Signs of vitamin C deficiency in the body

If a person suffers from a lack of vitamin C, then he can not heal badly wounds, bleed gums, bruises on the body, may swell the face, the vessels of the eyes become weak, joint pain may manifest, there may be a weak reaction of the body to colds. These people often have hair loss, frequent nosebleeds and the development of scurvy. The signs include scurvy: severe bleeding gums, loss of teeth, depression, loss of appetite, fatigue, skin bleeding, hysteria and anemia.

Signs of an overabundance of vitamin C

Symptoms of an overdose of vitamin C can be frequent urination, nausea, headaches, vomiting and mild diarrhea. Sometimes people have an overabundance of ascorbic acid manifested by colic in the lower abdomen and redness of the facial skin.

Products that contain vitamin C

Very many products contain vitamin C, and we do not even know about it!

Most living organisms can convert D-glucose to L-ascorbic acid. Homo sapiens is entirely dependent on the intake of vitamin C with food. The only animal product containing significant amounts of vitamin C is milk (1 - 5 mg / 100 g); it is also found in the liver. The richest sources of ascorbic acid are fresh vegetables and fruits (especially citrus fruits, tomatoes and green peppers), baked potatoes (17 mg / 100 g) and leafy vegetables. Very rich in vitamin C guava (300 mg / 100 g) and black currant (200 mg / 100 g), but they are not very common in Western countries.

So, dog rose contains up to 1000 mg of antiscorbutic vitamin, sweet pepper - 250 mg, kiwi - about 180 mg, and sea buckthorn contains about 200 mg of this vitamin. If you love cabbage, then you will not suffer from vitamin C deficiency, because it contains from 70 to 100 mg of vitamin. All the favorite strawberries are saturated with ascorbic acid by 60 mg, as well as the orange, and the sour lemon is saturated with it by 40 mg. Use these foods more often, and you will not know what a cold is. The table provides exhaustive data on the content of vitamin C in the most consumed vegetables and fruits.

The content of vitamin C in common fruits and vegetables

Vegetables fruits	The content of ascorbic acid, mg per 100 g
Dog-rose fruit	1000
Black currant	200
Cabbage head	186
Green pepper	128
Horseradish	120
Broccoli	OF
Brussels sprouts	109
Watercress	79
Cauliflower	78
Strawberry	59
Spinach	51
Oranges / lemons	50
Cabbage leaves	47
New potatoes	Thirty
Peas	25
Old potatoes	8
Carrot	6th
Apples	6th
Plums	3

Vitamin C in medicine

The widespread use of vitamin C provides the basis for a large international business, from chemical synthesis to the formation of tablets. Its physiological role in the body is not clear until the end, despite the successful use of vitamin C in the treatment of various pathological conditions, often seemingly unconnected with it. For hundreds of years it has been used to treat scurvy, and in recent years it has been shown that vitamin C causes a state of remission in some patients with autoimmune thrombocytopenia.

Therapeutic application

Vitamin C is usually prescribed in a daily dose of 3 x 100 mg. Vitamin C not only promotes healing of wounds, but also strengthens the body's immune system, which prevents the penetration of dangerous infections. That is why ascorbic acid is prescribed for infectious diseases, fever and diarrhea, and when there is a high risk of infection and inflammation. To acidify the urine with chronic infections of the urinary tract are prescribed 0.5 - 0.3 g per day. Vitamin C is known as an immunomodulator acting on various points of the immune system. For example, it inhibits histidine decarboxylase, thereby suppressing the formation of a histamine immunosuppressant; promotes neutrophilic leukocyte activity; neutralizes the excess level of reactive oxidants produced by phagocytes in a chronic infection.

Vitamin C treats some diseases of the blood and circulatory system. Vitamin C is also indicated for common anemia caused by a lack of iron in the body. However, simultaneously it is necessary to treat iron preparations. Ascorbic acid promotes digestibility of iron by the body due to the formation of soluble complexes with it and the reduction of iron, thus preventing the binding of iron in the intestines with phytates and tannins coming from food. The level of reduced iron in the blood can be maintained by selecting a suitable iron-containing diet with the addition of 25-50 mg of ascorbic acid to each meal.

In order for hemoglobin to participate in the transport of oxygen, the iron atom in the heme molecule must be in the reduced state of iron. As a rule, over 98% of hemoglobin is present in the body in this form and less than 2% in the form of a functionally inactive methemoglobin with oxidized iron. Usually, these small amounts of methemoglobin are reduced to hemoglobin under the action of the enzyme NADH (methemoglobin reductase also called cytochrome reductase of erythrocytes). There are several types of congenital methemoglobinemia due to the deficiency of the cytochrome reductase system. In this case, oral daily intake of 500 mg of ascorbic acid or 100 to 300 mg of methylene blue is prescribed. Obviously, ascorbic acid directly, albeit slowly, restores methhemoglobin, whereas methylene blue activates NADPH-dehydrogenase, which is usually in a latent state, thus ensuring the continuity of the transformation chain in the NADH system. This type of methemoglobinemia is an easy form of the disease, and treatment simply eliminates manifestations of cyanosis.

Methemoglobinemia is ultimately due to the presence in the patient's body of peroxidic O2 radicals, which are normally under the control of the superoxide dismutase (SOD) enzyme, which requires the presence of vitamin C as a coenzyme. It is believed that the intake of ascorbic acid can remove the acute condition in patients with sickle cell anemia, when red blood cells are depleted in vitamin and are susceptible to the destructive effect of oxidants.

It is proved that in higher doses vitamin promotes improvement of lipid metabolism in the body. As a result, cholesterol deposition is prevented on the walls of the arteries and the risk of coronary insufficiency is reduced. In coronary insufficiency, the level of ascorbic acid in plasma and leukocytes decreases, and what is the cause, and what is the consequence, is not yet clear. Nevertheless, it is believed that vitamin C contributes to the prevention of atherosclerosis, as it maintains the integrity of the artery walls (due to the proper level of hydroxyproline required for the biosynthesis of collagen), lowers cholesterol levels (promoting bile acid biosynthesis) and triglycerides (activating plasma lipase).

Vitamin C is useful for healthy metabolism and also by decreasing platelet aggregation and increases fibrinolytic activity in the blood. Once vitamin C was dubbed even a "hearty vitamin." Although it is possible to trace the relationship between cases of coronary heart disease (CHD) and low levels of ascorbic acid in plasma, the latter is probably the consequence of the first, and not vice versa.

Nevertheless, in the opinion of some specialists, a risk factor for IHD is the presence of various aggressive forms of oxygen, for example, a superoxide radical, whose existence is under the control of vitamin C-dependent superoxide dismutase.

Thus, ascorbic acid takes part in many metabolic processes. Vitamin C is involved in the synthesis of collagen, oxidation of tyrosine, synthesis of catecholamines, mobilization of iron and copper, histamine degradation, modulation of prostaglandin production, detoxification, cholesterol metabolism, immune control, etc. With an average daily requirement of 100 mg vitamin C, a number of factors require increasing the intake of vitamin C. This is the intake of certain medicines (contraceptives, antibiotics, aspirin, anti-inflammatory drugs), smoking, alcohol consumption, stress, old age, diabetes, mb. Although there is still no clear indication for the clinical use of vitamin C, it is recommended that it be widely used in medical practice (to accelerate wound healing, reduce inflammatory reactions, increase immune functions, in the treatment of respiratory diseases, iron deficiency, atherosclerosis, arthritis).

Vitamin C is usually prescribed for the threat of miscarriage, with thyrotoxicosis, idiopathic thrombocytopenic purpura (2 g daily), with thalassemia (Mediterranean anemia).

The physiological basis of vitamin C therapy is not always completely clear, except for cases of achlorhydria and diarrhea, when there is a threat of anemia due to reduced absorption through the intestines of non-haem iron, which is rectified with the help of vitamin C.

The main content of ascorbic acid in the CNS is in the hippocampus-hypothalamus compared with other sections of the central nervous system.

The low status of vitamin C accompanies cataract and increased intraocular pressure, diabetes, tobacco smoking and alcohol abuse. Daily intake of 1 g of vitamin C stops the development of cataract in the initial stage.

It was found that the level of vitamin C in the body of patients with diabetes is 70 - 80% lower than in healthy people. This gives grounds to believe that this is the root of complications such as cardiac and renal insufficiency, blindness and gangrene. According to one hypothesis, chronic hyperglycemia can be associated with intracellular deficiency of ascorbic acid in leukocytes due to the fact that glucose and ascorbic acid are quite similar among themselves and can be transported inside the cell using the same membrane system. This leads to a weakening of the response of the organism in case of acute inflammation in diabetic patients who are not receiving treatment, an increased susceptibility to infection and a pathology in the healing of wounds. It is not yet clear whether in these patients the body is able to absorb less vitamin than in healthy people, or excrete it in large quantities. There is an assumption that their status should be positively influenced by doses of vitamin, increasing the tolerance to glucose. However, very large doses should also be avoided, as this leads to an increase in the level of dehydroascorbic acid in the blood, which in turn causes diabetes mellitus in rats!

The role of vitamin C as a cofactor in the main biological processes is well established. The mammalian brain contains relatively high concentrations of ascorbic acid. In rats, the concentration of ascorbic acid is maximal at birth and then decreases with growth and aging. The levels in the embryo are twice as large as in adults. As the aging of more than 50% of men, the concentration of ascorbic acid in the blood plasma is less than 0.3 mg / dl (at a rate of 1 mg / dL) and it is necessary to take 40 to 50 mg of vitamin C for men every day and 30 mg for women. Since 1953, when Willis showed that the deficiency of ascorbic acid causes atherosclerotic lesions, a relationship is established between the level of ascorbic acid and the level of cholesterol in the blood. Ascorbic acid increases the amount of metabolites of prostacyclin (6-keto-PGF1; 1) and thromboxane B2. AK is the main one in stimulating the synthesis of prostaglandins. Lightweight is represented by the volume of the surface as a football field and carries out up to 9000 liters per day gas exchange of air. Vitamin C and E act as antioxidants and, possibly, PG are involved in these mechanisms, since both vitamins exert a complex effect on the metabolism of arachidonic acid.

The well-known toxic effect of alcohol can be reduced if you take vitamin C, which in this case is connected to the process of detoxification in the liver, participating in the oxidation of the cytochrome P450 system.

• Vitamin C helps maintain the tone and reactivity of the respiratory system.

As a result of smoking, the level of vitamin in the plasma drops to 0.2 mg% and smokers need to additionally receive 60 to 70 mg per day to compensate for this decline. It is not clear whether the low rate of ascorbate in the smokers' plasma is due to an increased metabolic rate, reduced absorption, or simply a lack of intake of vitamin C from food due to their habit of excluding fruits from the diet.

• Vitamin C is also recommended for the treatment and prevention of colds, mental illnesses, infertility, cancer and AIDS.

Vitamin C can be a reliable protection against stomach cancer due to its ability (demonstrated in vitro) to inhibit the formation of nitrosamines. Nitrosamines can be formed by the interaction of nitrites with amines coming from food, and are considered the most important cause of cancer of the stomach and esophagus. Food usually receives a small amount of nitrites, but they can form as a result of the reduction of nitrates by intestinal bacteria, which is why such concern is caused by an increase in the level of nitrates in drinking water. A conclusion is drawn on the effectiveness of ascorbic acid in the prevention of uterine cancer.

• Vitamin C is effective for the prevention and treatment of at least forty pathological conditions.

Scientists have investigated in vitro the role of the human placenta in cellular transport and the metabolism of toxic oxidized form of ascorbic acid (AA) (dehydro-AC; DHAQ) and its useful reduced form. It was shown that the placenta tissue promotes the regulation of the oxidation-reduction potential of AK / DHAA in the mother and fetus and the purification of the toxic form of DHAC from the mother's blood, restoring and supplying the fetus with a useful form of AK. Ascorbic acid easily passes to the fetus by simple diffusion. Pregnancy reduces the level of AA in the blood serum. At the same time, smoking reduces the level of AA in the serum of pregnant women. In pregnancy and lactation, the need for vitamin C increases from 45 mg / day to 60 and 80 mg / day, respectively. There are no reports of an adverse effect of vitamin C on a human fetus, a pregnant woman, or the course of pregnancy when taking vitamin C. Vitamin C passes into breast milk. Experiments on animals (guinea pigs, mice and rats), carried out in 1960 - 1970 gg. Showed that ascorbic acid can be teratogenic and dangerous in pregnancy. In guinea pigs, hypervitaminosis C leads to a complicated course of pregnancy and fetal death with the subsequent development of infertility. However, there is no true embryothetotoxic effect. In mice intravenous administration of 20 mg of AK on the 8th day of pregnancy leads to a significant increase in brain and spinal cord malformations. In rats, the dose of AK 1 g / kg of body weight from the 6th to the 15th day or throughout the entire pregnancy did not adversely affect the fetus.