Vitamins, also known as vitamins, are a kind of organic substances necessary to maintain human life activities and important active substances to maintain human health. The content of vitamins in the body is very small, but it plays an important role in the process of human growth, metabolism and development. Although the chemical structures and properties of various vitamins are different, they are similar as follows: ① Vitamins exist in food in the form of provitamins (vitamin precursors); ② Vitamins are not components of tissues and cells, and do not produce energy. Their function is mainly to participate in the regulation of metabolism. ③ Most vitamins can't be synthesized or the synthetic amount is not enough to meet the body's needs. You must always get it from food. (4) The demand for vitamins is very small, and the daily demand is often calculated in milligrams (mg) or micrograms (ug). However, once it is lacking, it will cause the corresponding vitamin deficiency and cause harm to human health. Vitamins, unlike carbohydrates, fats and protein, account for only a small proportion in natural foods, but they are also necessary for human body. Most vitamins cannot be synthesized in the body and must be taken from food. Vitamins themselves do not provide heat energy. Some vitamins, such as B6 and K, can be synthesized by bacteria in the intestinal tract of animals, and the synthetic amount can meet the needs of animals. Animal cells can convert tryptophan into nicotinic acid (a B vitamin), but the yield is not enough. Vitamin C can be synthesized by animals other than primates (including humans) and guinea pigs. Plants and most microorganisms can synthesize vitamins by themselves without external supply. Many vitamins are components of helper groups or coenzymes.
The discovery of vitamins
The discovery of vitamins is one of the greatest discoveries of the 20th century. 1897, C. Aikman found that only eating finely ground white rice in Java can cause beriberi, and unpolished brown rice can cure this disease. It was also found that substances that can cure beriberi can be extracted with water or alcohol, which was called "water-soluble B" at that time. 1906 proves that food contains "auxiliary factors" other than protein, lipids, carbohydrates, inorganic salts and water, which are extremely small substances necessary for animal growth. 19 1 1 year C. Feng Ke identified that the substance in brown rice that can fight beriberi is amine (a nitrogen-containing compound), which is necessary for maintaining life. It is suggested to name it "vitamin". That is, active amine, which means "active amine" in Chinese. Later, many vitamins were discovered one after another, with different chemical properties and physiological functions. It is also found that many vitamins do not contain amine or nitrogen at all, but only use the name of Funk, and only remove the last letter "e". The first vitamin B was later proved to be a vitamin B complex. After purification and separation, several substances were found, but their properties and distribution in food were similar, and most of them were coenzymes. Some supplies must be balanced with each other, such as vitamin B 1, B2 and PP, otherwise physiological functions may be affected. Vitamin B complex includes pantothenic acid, nicotinic acid, biotin, folic acid, vitamin B 1 (thiamine), vitamin B2 (riboflavin), pyridoxine (vitamin B6) and cyanocobalamin (vitamin B 12). Some people also add choline, inositol, p-aminobenzoic acid (p-aminobenzoic acid), carnitine and lipoic acid to the B complex.
Overview and classification of vitamins
Vitamins are essential organic compounds in human metabolism. The human body is like an extremely complex chemical plant, constantly carrying out various biochemical reactions. This reaction is closely related to the catalysis of enzyme. Coenzymes must participate in the activities of enzymes. It is known that many vitamins are coenzymes of enzymes or constituent molecules of coenzymes. Therefore, vitamins are important substances to maintain and regulate the normal metabolism of the body. It can be considered that vitamins exist in human tissues in the form of "bioactive substances".
The vitamin content in food is less, and the human body needs little, but it is an indispensable substance. If there is a lack of vitamins in the diet, it will cause metabolic disorder and cause vitamin deficiency. If vitamin A is lacking, there will be night blindness, dry eyes and dry skin; Lack of vitamin d can cause rickets; Lack of vitamin B 1 can cause beriberi; Lack of vitamin B2 can lead to cheilitis, angular stomatitis, glossitis and bursitis; Lack of PP can cause boils; Lack of vitamin B 12 will lead to pernicious anemia; Lack of vitamin c can lead to scurvy.
Vitamins are a huge family, and there are dozens of known vitamins, which can be roughly divided into fat-soluble and water-soluble. (See the table below for details) Some substances are similar to some vitamins in chemical structure and can be converted into vitamins through simple metabolic reactions. Such substances are called provitamins. For example, beta-carotene can be converted into vitamin A; 7- dehydrocholesterol can be converted into vitamin d 3；; However, tryptophan has to undergo many complicated metabolic reactions to become nicotinic acid, which cannot be called provitamin. Water-soluble vitamins are absorbed from the intestine and circulated to the tissues needed by the body. Most of the excess vitamins are excreted through urine, and very little is stored in the body. Most fat-soluble vitamins are absorbed by bile salts and reach various organs in the body through the lymphatic system. The body can store a lot of fat-soluble vitamins. Vitamins A and D are mainly stored in the liver, vitamin E is mainly stored in adipose tissue in the body, and vitamin K is less stored. Water-soluble vitamins are easily soluble in water and insoluble in nonpolar organic solvents, so they are rarely stored in the body after absorption, and the excess is mostly excreted in urine; Fat-soluble vitamins are soluble in nonpolar organic solvents, but insoluble in water. They can be absorbed by the body with fat and stored in the body at a low excretion rate.
Discovery of taxonomic names and sources of other names (table 1)
Fat-soluble retinol (vitamin A) was found by Elmer McCollum and M. Davis between 19 12 and 19 14. It is not a single compound, but a series of derivatives of retinol (retinol is also translated into vitamin A alcohol and rosin oil), also known as anti-dry eye vitamin cod liver oil and green vegetables.
Water-soluble thiamine (vitamin B 1) was prepared by casimir? It was discovered by Feng Ke in 19 12 (for example 19 1 1). It usually exists in organisms in the form of thiamine pyrophosphate (TPP). Yeast, grain, liver, soybean, meat.
Water-soluble riboflavin (vitamin B2) was found in 1926 by D.T. Smith and Hendrick, for example. Vitamin G is also called yeast, liver, vegetables and eggs.
Water-soluble nicotinic acid (vitamin B3) was discovered by Conrad Elvehjem in 1937. Also known as vitamin P, vitamin PP, nicotinic acid, nicotinic acid yeast, grain, liver and rice bran.
Water-soluble pantothenic acid (calcium pantothenate) was discovered by roger williams in 1933. Also known as pantothenic acid yeast, grain, liver and vegetables.
The water-soluble pyridoxine (vitamin B6) was discovered by Paul Georgi in 1934. Include pyridoxine, pyridoxal and pyridoxamine yeast, grains, livers, eggs and dairy products.
Water-soluble biotin (vitamin B7) is also called vitamin h or coenzyme r yeast, liver, grain,
Water-soluble folic acid (vitamin B9) is also called pteroyl glutamic acid, pteroyl glutamic acid, vitamin M or leaf essence, vegetable leaf and liver.
Water-soluble cobalamin (vitamin B 12) was discovered by Karl Fox and Alexander Todd in 1948. Also known as cyanocobalamin or [[coenzyme B 12]] liver, fish, meat and eggs.
The water-soluble choline was discovered by Maurice Gobley in 1850. Liver, egg yolk, dairy products and soybeans, one of the B vitamins.
Water-soluble inositol cyclohexanol, vitamin B-h heart, meat
Water-soluble ascorbic acid (vitamin C) is prepared by James? Linde found it in 1747. Also known as reverse circulation acid fresh vegetables and fruits.
Fat-soluble calciferol (vitamin D) was discovered by Edward Mellanby in 1922. Also known as calciferol and anti-rickets vitamins, there are mainly vitamin D2, ergocalciferol and vitamin D3, and cholecalciferol. This is the only vitamin that can be synthesized in a small amount, such as cod liver oil, egg yolk, dairy products, yeast and so on.
Fat-soluble tocopherol (vitamin E) was discovered by Herbert Evans and Catherine Bishop in 1922. There are mainly four kinds of eggs, liver, fish and vegetable oil: α, β, γ and δ.
Henrik Dam discovered fat-soluble naphthoquinone (vitamin K) in 1929. It is the floorboard of a series of naphthoquinone derivatives, mainly including natural vitamin K 1 from plants, vitamin K2 from animals, and synthetic vitamins K3 and K4. Also known as frozen vitamins spinach, alfalfa, cabbage, liver.
trait
The definition of vitamins requires that vitamins meet four characteristics before they can be called essential vitamins:
Exogenous: the human body can't synthesize it itself (vitamin D can be synthesized in a small amount, but it is still regarded as an essential vitamin because of its importance), so it needs to be supplemented by food;
Traces: the human body needs little, but it can play a huge role;
Regulatory: vitamins must be able to regulate human metabolism or energy conversion;
Specificity: Without certain vitamins, people will show a unique pathological state.
According to these four characteristics, the human body needs 13 vitamin, which is also commonly known as 13 essential vitamin.
(1) vitamin a
Unsaturated monohydric alcohols are fat-soluble vitamins. Because people or mammals are prone to dry eye when they lack vitamin A, it is also called anti-dry eye wine. There are two kinds of vitamin A, A 1 and A2. A 1 exists in animal liver, blood and retina of eyeball, also known as retinol. Natural vitamin A mainly exists in this form. A2 mainly exists in the liver of freshwater fish. Vitamin A 1 is a fat-soluble yellowish flaky crystal with a melting point of 64℃, and vitamin A2 has a melting point of 17 ~ 19℃, which is usually a golden yellow oil. Vitamin A is a kind of polyenol containing β-Los Angeles ketone ring. The chemical structure difference between vitamin A2 and A 1 is only that there is an extra double bond in the 3-position and 4-position of β-Los Angeles ketone ring. Vitamin A molecules have unsaturated bonds and are very active in chemistry. It is easy to be oxidized in the air, or destroyed by ultraviolet rays, losing its physiological function. Therefore, the preparation of vitamin A should be stored in a brown bottle to avoid light. A 1 and A2 can react with antimony trichloride, showing dark blue, which can be used as the basis for quantitative determination of vitamin A. Many plants such as carrots, tomatoes, green leafy vegetables and corn contain carotenoids, such as α, β, γ-carotene, cryptoxanthin and lutein. Some carotenoids have the same cyclic structure as vitamin A 1, and can be converted into vitamin A in vivo, so they are called provitamin A. β -carotene contains two cyclic structures of vitamin A 1, and the conversion rate is the highest. One molecule of beta carotene and two molecules of water can produce two molecules of vitamin A 1. In animals, this water oxidation process is catalyzed by β-carotene-15, 15'- oxygenase, which is mainly carried out in the intestinal mucosa of animals. Vitamin A in food, or produced by the cleavage of β-carotene, combines with fatty acids in intestinal mucosal cells to form esters, which are then mixed with chyle particles and absorbed into the body through lymph. Animal liver is the main place to store vitamin A, which will be released into the blood when the body needs it. In blood, retinol (R) combines with retinol binding protein (RBP) and plasma prealbumin (PA) to form R-RBP-PA complex, which is transported to various tissues.
It was extracted from cod liver by American chemist Davis in 19 13. It is yellow powder, insoluble in water, soluble in organic solvents such as fat and oil. The chemical properties are relatively stable, but it is easily destroyed by ultraviolet rays, so it should be kept in a brown bottle. Vitamin A is the raw material of rhodopsin in eyes, and it is also an essential substance for skin tissue. Without it, people will get dry eye and night blindness. Usually everyone should take vitamin A2 ~ 4.5 mg every day, but not too much. In recent years, related research shows that it also has anti-cancer effect. Animal liver contains a lot of vitamin A, followed by cream and eggs.
The main functions of vitamin A are as follows: ① It is necessary to maintain the health of all epithelial tissues. When lacking, the epithelial tissue is dry, proliferated and hyperkeratinized, and the ability to resist microbial infection is reduced. For example, the secretion of lacrimal gland epithelium stops, which can make cornea and conjunctiva dry, inflame and even soften perforation. When sebaceous glands and sweat glands are keratinized, the skin is dry and prone to hair follicle papules and hair loss. ② Promote growth, development and reproduction. When vitamin A is lacking, children will suffer from stunted growth, skeletal dysplasia and decreased reproductive function. (3) The composition of photosensitive substances in visual cells. Vitamin A can be oxidized by dehydrogenase to produce retinol, which can combine with different opsins in photoreceptors (rod cells and cone cells) to produce various opsins with different absorption spectra, such as rhodopsin and rhodopsin. Pigment is a photosensitive substance, and its absorption of photons will cause a series of physical and chemical changes, resulting in receptor potential. This receptor potential is transformed into pulsed nerve impulses through various nerve cells in the retina, which are transmitted to the brain to produce vision. It is known that rhodopsin in retina can be continuously decomposed and regenerated and form a dynamic balance during the photosensitive process. When the retinin is in the dark, the retinoic acid in it exists in the form of 1 1- cis, which is called 1 1- cis, but it quickly turns into all-trans retinoic acid after illumination. With the change of configuration, retinol fades and decomposes into trans retinoic acid and retinol. Trans-retinoic acid can be transformed into 1 1- cis-retinoic acid again after low light irradiation, which combines with visual protein to form rhodopsin, thus ensuring that rod cells can continue to be sensitive to light and appear dark vision, that is, they can see the outline and shape of things clearly under low light. However, rhodopsin and retinaldehyde often undergo catabolism, so protein and vitamin A need to be supplemented continuously. If the supply of vitamin A is insufficient, the synthesis of rhodopsin in rod cells will decrease, which will lead to dark vision disorder-night blindness.
Daily demand:
Women need 0.8 mg. That is, 80g eel, 65g chicken liver, 75g carrot and125g wrinkled cabbage or tuna 200g.
Efficacy: Enhance the immune system, help cells regenerate, and protect cells from free radicals that can cause many diseases. It can protect the mucous membranes of respiratory tract, mouth, stomach and intestine from damage, and vitamin A can also improve eyesight.
Side effects: Taking 3 mg of vitamin A every day may lead to the risk of osteoporosis. Long-term intake of 33 mg of vitamin A every day will lead to loss of appetite, dry skin, hair loss, joint pain and even abortion.
(2) Vitamin B B is rich in animal liver, lean meat, eggs, milk, bean products, grains, carrots, fish, vegetables and other foods. It is a water-soluble vitamin, and most of the human body is coenzyme, which mainly includes the following categories.
[classification]
① vitamin B 1
B 1 is the earliest purified vitamin. 1896, hickmann, a scientist from the Kingdom of the Netherlands, first discovered that 19 10 was extracted and purified from rice bran by Polish chemist Fonk. White powder, easily soluble in water and easily decomposed in alkali. Its physiological function is to stimulate appetite and maintain normal nerve activity. Without it, it will cause beriberi and neurodermatitis. Adults need to take 2 milligrams a day. It is widely found in rice bran, egg yolk, milk, tomatoes and other foods, and has been artificially synthesized. Because its molecules contain sulfur and amino groups, it is called thiamine, also known as anti-beriberi vitamin. It mainly exists in seed skin and germ, and is the most abundant in rice bran, wheat bran, soybean, yeast, lean meat and other foods. In addition, Chinese cabbage, celery, Chinese medicine Saposhnikovia divaricata and plantain seed are also rich in vitamin B 1. The extracted vitamin B 1 hydrochloride is monoclinic platelets. Vitamin B 1 nitrate is a colorless triclinic crystal with no hygroscopicity. Vitamin B 1 is easily soluble in water and will be lost with water during food cleaning. After heating, B 1 mainly exists in soup. If vegetables are processed too finely, cooked improperly or canned, vitamins will be lost or destroyed in large quantities. Vitamin B 1 is easily destroyed when heated in alkaline solution, but it is thermally stable in acidic solution. Oxidants and reductants can also make it ineffective. Vitamin B 1 is converted into dehydrothiamine (also known as sulfur pigment) after oxidation, which can show blue fluorescence under ultraviolet irradiation. This characteristic can be used to detect and quantify vitamin B 1. Vitamin B 1 is converted into thiamine pyrophosphate (also known as cocarboxylase) in vivo, which participates in the metabolism of sugar in vivo. Therefore, when vitamin B 1 is deficient, the oxidation of sugar in tissues will be affected. It also inhibits cholinesterase activity. When vitamin B 1 is deficient, the activity of this enzyme is too high, and acetylcholine (one of neurotransmitters) is destroyed in large quantities, which affects nerve conduction and can cause gastrointestinal peristalsis, decreased secretion of digestive tract, loss of appetite, indigestion and other obstacles.
② Vitamin B2
B2 is also called riboflavin. Whey was first discovered by Bruce, a chemist from the United Kingdom of Great Britain and Northern Ireland, in 1879. It was extracted from milk by Goldberg, a chemist from the United States of America, and synthesized by Cohen, a German chemist, in 1935. Vitamin B2 is orange-yellow needle-like crystal, slightly bitter in taste, yellow-green fluorescence in aqueous solution, and easy to decompose under alkaline or light conditions This is why you don't need alkali to cook porridge. Without it, the human body is prone to stomatitis, dermatitis, microvascular hyperplasia and so on. Adults should take 2 ~ 4 mg daily, which is rich in cereals, vegetables, milk and fish.
③ Calcium pantothenate.
B5 is also called pantothenic acid. Anti-stress, anti-cold, anti-infection, prevent the toxicity of some antibiotics, and eliminate postoperative abdominal distension.
④ vitamin B6
Has the effects of inhibiting vomiting and promoting development. Without it, it will cause vomiting, cramps and other symptoms. Include pyridoxine, pyridoxal and pyridoxamine. Pyridoxine is transformed into pyridoxal in vivo, and pyridoxal and pyridoxamine can be transformed into each other. Foods such as yeast, liver, lean meat, grains and cabbage are rich in vitamin B6. Vitamin B6 is easily soluble in water and alcohol and slightly soluble in fat solvents. It is easy to be destroyed when exposed to light and alkali, and it is not resistant to high temperature. Vitamin B6 combines with phosphoric acid in vivo to form pyridoxal phosphate or pyridoxamine phosphate. They are coenzymes of many amino acid metabolizing enzymes, so they are very important for amino acid metabolism.
Daily demand:
The daily requirement of human body is about 1.5 ~ 2 mg. Food is rich in vitamin B6, and intestinal bacteria can also be synthesized, so vitamin B6 deficiency rarely occurs in humans.
Side effects: Taking 100 mg daily will cause brain and nerve damage. Excessive intake may also lead to so-called neuropathy, that is, nervous system diseases with insensitive senses. In the worst case, the skin will lose consciousness.
⑤ Vitamin B 12
1947 American female scientist Xiao Bo found vitamin B 12 in bovine liver extract. According to the analysis of chemists, this is an organic compound containing cobalt. It has stable chemical properties and is an indispensable substance for human hematopoiesis. Without it, pernicious anemia will occur.
Vitamin B 12, an anti-pernicious anemia vitamin, also known as cobalamin, contains the metal element cobalt, which is the only one among vitamins, and can resist fatty liver and promote the storage of vitamin A in the liver; Promote cell development and maturation and body metabolism. Different from other B vitamins, it rarely exists in plants and is only produced by some bacteria and bacteria in the soil. Liver, lean meat, fish, milk and eggs are the sources of vitamin B 12. Commodities can be made from the production of certain antibiotics or by-products of special fermentation. Vitamin B 12 is pink crystal, and its aqueous solution is quite stable in weak acid, easily decomposed in strong acid and alkali, and easily destroyed by sunlight, oxidants and reductants. When it is absorbed by gastrointestinal tract, it must be combined with a glycoprotein secreted by gastric pylorus to be absorbed. Lack of B 12 caused by lack of "internal factors" should be treated by injection. Deoxyadenosine cobalamin is the main form of vitamin B 12 in the body. It is a coenzyme of some enzymes that catalyze the exchange of hydrogen atoms, alkyl groups, carbonyl groups or amino groups on two adjacent carbon atoms. Another form of coenzyme in the body is methylcobalamin, which participates in methyl transport and is usually related to folic acid. It can improve the utilization rate of folic acid, affect the biosynthesis of nucleic acid and protein, and thus promote the development and maturation of red blood cells.
When vitamin B 12 is deficient, pernicious anemia will occur, and the demand for B 12 is very small. The human body needs about 12 microgram (11000 mg) every day, and people will not lack it under normal circumstances.
⑥ Vitamin B 13
(Lactic acid clear).
⑦ Vitamin B 15
(alanine) It is mainly used to resist fatty liver and improve the oxygen metabolism rate of tissues. Sometimes used to treat coronary heart disease and chronic alcoholism.
8 vitamin B 17
Highly toxic. Some people think it can control and prevent cancer.
In addition, choline and inositol are usually classified as essential vitamins, and they are members of vitamin B group.
(3) vitamin c
It can treat scurvy and is acidic, so it is called ascorbic acid. It is rich in lemon juice, green plants and tomatoes. Ascorbic acid is monoclinic or needle-like crystal, which is easy to be oxidized to produce dehydrogenated bad blood acid, and still has the function of vitamin C. In alkaline solution, the lactone ring in dehydrogenated bad blood acid molecule is easy to be hydrolyzed to diketone gulonic acid. This compound can't change into lactone structure in animals. Oxalic acid or sulfate is combined with sulfuric acid, which is finally produced in human body and excreted from urine. Therefore, diketone gulonic acid no longer has physiological activity.
Norwegian chemist holst found it in lemon juice on 1907. 1934 to obtain pure product, which can be synthesized artificially now. Vitamin C is the most unstable vitamin. Because vitamin C is easily oxidized, it will be destroyed during food storage or cooking, even when chopping fresh vegetables. Trace amounts of copper and iron ions can accelerate the destruction. Therefore, only fresh vegetables, fruits or raw vegetables are rich sources of vitamin C, which is colorless crystal with melting point of 190 ~ 192℃ and is easily soluble in water. The aqueous solution is acidic, has strong chemical activity and is easily decomposed by heat, alkali and heavy metal ions. Therefore, copper pots are not allowed, and the heating time is too long.
Plants and most animals can synthesize vitamin C in their own bodies. However, humans, primates and guinea pigs can't synthesize vitamin C, because they lack enzymes to convert L- gulonic acid into vitamin C, so they must take it from food. If vitamin C is lacking in food, scurvy will occur. At this time, there are symptoms such as bleeding, loose teeth, difficult wound healing and easy fracture due to interstitial generation disorder. Because vitamin C has a long half-life in human body (about 16 days), scurvy will only appear after eating food without vitamin C for 3 ~ 4 months. Because vitamin C is easy to be oxidized and reduced, it is generally believed that its natural function should be related to this characteristic. Vitamin C is directly related to the normal synthesis of collagen, tyrosine metabolism and iron absorption. The main function of vitamin C is to help the human body complete the oxidation-reduction reaction and improve the sterilization and detoxification ability of the human body. Long-term lack of vitamin C can lead to scurvy. Eating more fruits and vegetables can meet the human body's demand for vitamin C. Vitamin C plays an important role in promoting the firmness of brain cell structure, preventing the relaxation and contraction of brain cell structure, and preventing the nerve tubules that transport nutrients from being blocked, thinned and relaxed. Taking enough vitamin C can improve the permeability of neural tubules, make the brain get nutritional supplements in time and smoothly, and thus improve brain power and intelligence. According to Nobel Prize winner Pauling, taking large doses of vitamin C has a certain effect on preventing colds and fighting cancer. However, it has been suggested that vitamin C can promote the production of free radicals in the presence of iron ions (Fe2+), so it is not safe to use it in large quantities.
Daily requirement: Adults need to take 50 ~ 100 mg every day. That is, guava half, pepper 75g, cauliflower 90g, kiwi fruit 2, strawberry 150g, grapefruit 1 piece, papaya half, fennel 125g, cauliflower 150g and orange juice 200ml.
Efficacy: Vitamin C can capture free radicals and prevent diseases such as cancer, arteriosclerosis and rheumatism. In addition, it can enhance immunity and is good for skin, gums and nerves.
Side effects: So far, vitamin C is considered harmless, because the kidney can excrete excess vitamin C. A newly published research report in the United States pointed out that there is a large amount of vitamin C circulating in the body, which is not conducive to wound healing. Daily intake of vitamin C exceeding 1000 mg will lead to diarrhea, infertility in kidney calculi and even genetic defects.