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'''B vitamins''' are a class of water-soluble [[vitamin]]s that play important roles in [[Cell (biology)|cell]] [[metabolism]] and synthesis of [[red blood cell]]s. They are a [[chemical]]ly diverse class of compounds, but are associated in [[Diet (nutrition)|diet]], often occurring together in the same foods. [[Dietary supplement]]s containing all eight are referred to as a '''vitamin B complex'''. Individual B vitamins are referred to by B-number or by chemical name, such as B<sub>1</sub> for thiamine, B<sub>2</sub> for riboflavin, and B<sub>3</sub> for niacin, while some are more commonly recognized by name than by number, such as pantothenic acid (B<sub>5</sub>), biotin (B<sub>7</sub>), and folate (B<sub>9</sub>).

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Each B vitamin is either a [[cofactor (biochemistry)|cofactor]] (generally a [[cofactor (biochemistry)|coenzyme]]) for key [[metabolism|metabolic]] processes or is a [[precursor (chemistry)|precursor]] needed to make one.

==List of B vitamins== <!--T:3-->

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{| class="wikitable sortable"
|+ List of B vitamins
! scope="col" data-sort-type="number" | Vitamin
! scope="col" | Name 
! scope="col" | Description
|-
! scope="row" data-sort-value="1" |[[Vitamin B1|Vitamin B<sub>1</sub>]]
| [[Thiamine]]
| A [[Cofactor (biochemistry)|coenzyme]] in the [[catabolism]] of [[sugar]]s and [[amino acid]]s.
|- 
! scope="row" data-sort-value="2" |[[Vitamin B2|Vitamin B<sub>2</sub>]]
| [[Riboflavin]]
| A [[Precursor (chemistry)|precursor]] of [[cofactor (biochemistry)|coenzymes]] called [[flavin adenine dinucleotide|FAD]] and [[flavin mononucleotide|FMN]], which are needed for [[flavoprotein]] enzyme reactions, including activation of other vitamins
|-
! rowspan="3" scope="row" data-sort-value="3" |[[Vitamin B3|Vitamin B<sub>3</sub>]]
| [[Niacin]] (nicotinic acid)
| rowspan="3" | A precursor of [[coenzyme]]s called [[nicotinamide adenine dinucleotide|NAD]] and [[nicotinamide adenine dinucleotide phosphate|NADP]], which are needed in many [[metabolism|metabolic]] processes.
|-
|[[Niacinamide]]
|-
|[[Nicotinamide riboside]]
|-
! scope="row" data-sort-value="5" |[[Vitamin B5|Vitamin B<sub>5</sub>]]
| [[Pantothenic acid]]
| A precursor of [[coenzyme A]] and therefore needed to metabolize many molecules.
|-
! rowspan="3" scope="row" data-sort-value="6" |[[Vitamin B6|Vitamin B<sub>6</sub>]]
| [[Pyridoxine]]
| rowspan="3" | A coenzyme in many enzymatic reactions in metabolism.
|-
|[[Pyridoxal]]
|-
|[[Pyridoxamine]]
|-
! scope="row" data-sort-value="7" |[[Vitamin B7|Vitamin B<sub>7</sub>]]
| [[Biotin]]
| A coenzyme for [[carboxylase]] enzymes, needed for synthesis of [[fatty acid]]s and in [[gluconeogenesis]].
|-
! scope="row" data-sort-value="9" |[[Folate|Vitamin B<sub>9</sub>]]
| [[Folate]]
| A precursor needed to make, repair, and [[methylation|methylate]] DNA; a cofactor in various reactions; especially important in aiding rapid [[cell division]] and growth, such as in infancy and pregnancy.
|-
! scope="row" data-sort-value="12" |[[Vitamin B12|Vitamin B<sub>12</sub>]]
| [[Cobalamin]]s
| Commonly [[cyanocobalamin]] or [[methylcobalamin]] in vitamin supplements. A coenzyme involved in the metabolism of all animal cells, especially affecting DNA synthesis and regulation, but also [[fatty acid metabolism]] and [[amino acid metabolism]].
|}

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'''Note:''' Other substances once thought to be vitamins were given B-numbers, but were disqualified once discovered to be either manufactured by the body or not essential for life. See [[#Related compounds]] for numbers 4, [[Inositol|8]], [[4-Aminobenzoic acid|10]], 11, and others.

==Sources== <!--T:6-->
B vitamins are found in abundance in meat, eggs, and [[dairy product]]s. Processed carbohydrates such as sugar and white flour tend to have lower B vitamin than their unprocessed counterparts. For this reason, it is common in many countries (including the United States) that the B vitamins thiamine, riboflavin, niacin, and folic acid are added back to white flour after processing. This is referred to as "[[enriched flour]]" on food labels. B vitamins are particularly concentrated in meat such as turkey, tuna and liver.

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Sources for B vitamins also include [[spinach]], [[legume]]s ([[Pulse (legume)|pulses]] or beans), whole grains, [[asparagus]], potatoes, bananas, chili peppers, [[breakfast cereal]]s.
The B<sub>12</sub> vitamin is not abundantly available from [[Vitamin B12#Non-animal sources|plant products]] (although it has been found in moderate abundance in fermented vegetable products, certain seaweeds, and in certain mushrooms, with the [[bioavailability]] of the vitamin in these cases remaining uncertain), making B<sub>12</sub> deficiency a legitimate concern for those maintaining a [[vegan]] diet. Manufacturers of plant-based foods will sometimes report B<sub>12</sub> content, leading to confusion about what sources yield B<sub>12</sub>. The confusion arises because the standard [[US Pharmacopeia]] (USP) method for measuring the B<sub>12</sub> content does not measure the B<sub>12</sub> directly. Instead, it measures a bacterial response to the food. Chemical variants of the B<sub>12</sub> vitamin found in plant sources are active for bacteria, but cannot be used by the human body. This same phenomenon can cause significant over-reporting of B<sub>12</sub> content in other types of foods as well.

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A common way to increase vitamin B intake is by using [[dietary supplement]]s. B vitamins are commonly added to [[energy drink]]s, many of which have been marketed with large amounts of B vitamins.

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Because they are soluble in water, excess B vitamins are generally readily excreted, although individual absorption, use and metabolism may vary. The elderly and athletes may need to supplement their intake of B<sub>12</sub> and other B vitamins due to problems in absorption and increased needs for energy production. In cases of severe deficiency, B vitamins, especially B<sub>12</sub>, may also be delivered by injection to reverse deficiencies. Both type 1 and type 2 diabetics may also be advised to supplement thiamine based on high prevalence of low plasma thiamine concentration and increased thiamine clearance associated with diabetes. Also, folate deficiency in early embryo development has been linked to [[neural tube defects]]. Thus, women planning to become pregnant are usually encouraged to increase daily dietary folate intake or take a supplement.

==Molecular functions== <!--T:10-->
{| class="wikitable"
! scope="col" | Vitamin
! scope="col" | Name
! scope="col" | Structure
! scope="col" | Molecular function
|-
! scope="row" | Vitamin&nbsp;B<sub>1</sub> 
| [[Thiamine]]
| style="background-color: white;" | [[File:Thiamin.svg|frameless|center|upright=0.5]]
| Thiamine plays a central role in the release of energy from carbohydrates. It is involved in [[RNA]] and [[DNA]] production, as well as nerve function. Its active form is a coenzyme called [[thiamine pyrophosphate]] (TPP), which takes part in the conversion of pyruvate to [[acetyl coenzyme A]] in metabolism.
|-
! scope="row" | Vitamin&nbsp;B<sub>2</sub> 
| [[Riboflavin]]
| style="background-color: white;" | [[File:Riboflavin.svg|frameless|center|upright=0.5]]
| Riboflavin is involved in release of energy in the [[electron transport chain]], the [[citric acid cycle]], as well as the catabolism of fatty acids ([[beta oxidation]]).
|-
!Vitamin&nbsp;B<sub>3</sub> 
| [[Niacin (nutrient)|Niacin]]
| style="background-color: white;" | [[File:Niacin structure.svg|frameless|center|upright=0.3]]
| Niacin is composed of two structures: nicotinic acid and [[nicotinamide]]. There are two co-enzyme forms of niacin: [[nicotinamide adenine dinucleotide]] (NAD) and [[nicotinamide adenine dinucleotide phosphate]] (NADP). Both play an important role in energy transfer reactions in the metabolism of glucose, fat and alcohol. NAD carries hydrogens and their electrons during metabolic reactions, including the pathway from the citric acid cycle to the electron transport chain. NADP is a coenzyme in lipid and nucleic acid synthesis.
|-
! scope="row" | Vitamin&nbsp;B<sub>5</sub> 
| [[Pantothenic acid]]
| style="background-color: white;" | [[File:(R)-Pantothenic acid Formula V.1.svg|frameless|center|upright=0.5]]
| Pantothenic acid is involved in the oxidation of fatty acids and carbohydrates. Coenzyme A, which can be synthesised from pantothenic acid, is involved in the synthesis of amino acids, fatty acids, [[ketone bodies]], [[cholesterol]], phospholipids, steroid hormones, neurotransmitters (such as [[acetylcholine]]), and [[antibodies]].
|-
! scope="row" | Vitamin&nbsp;B<sub>6</sub> 
| [[Pyridoxine]], [[pyridoxal]], [[pyridoxamine]]
| style="background-color: white;" | [[File:Pyridoxal-phosphate.svg|frameless|center|upright=0.5]]
| The active form [[pyridoxal 5'-phosphate]] (PLP) (depicted) serves as a cofactor in many enzyme reactions mainly in amino acid metabolism including biosynthesis of [[neurotransmitters]].
|-
! scope="row" | Vitamin&nbsp;B<sub>7</sub> 
| [[Biotin]]
| style="background-color: white;" | [[File:Biotin structure JA.png|frameless|center|upright=0.5]]
| Biotin plays a key role in the metabolism of lipids, proteins and carbohydrates. It is a critical co-enzyme of four carboxylases: acetyl CoA carboxylase, which is involved in the synthesis of fatty acids from acetate; pyruvate CoA carboxylase, involved in gluconeogenesis; β-methylcrotonyl CoA carboxylase, involved in the metabolism of [[leucine]]; and propionyl CoA carboxylase, which is involved in the metabolism of energy, amino acids and cholesterol.
|-
! scope="row" | Vitamin&nbsp;B<sub>9</sub> 
| [[Folate]]
| style="background-color: white;" | [[File:Folic acid.svg|frameless|center|upright=0.5]]
| Folate acts as a co-enzyme in the form of [[tetrahydrofolate]] (THF), which is involved in the transfer of single-carbon units in the metabolism of nucleic acids and amino acids. THF is involved in purine and pyrimidine nucleotide synthesis, so is needed for normal cell division, especially during pregnancy and infancy, which are times of rapid growth. Folate also aids in [[erythropoiesis]], the production of [[red blood cells]].
|-
! scope="row" | Vitamin&nbsp;B<sub>12</sub> 
| [[Cobalamin]]
| style="background-color: white;" | [[File:Cobalamin skeletal.svg|frameless|center|upright=0.5]]
| Vitamin B<sub>12</sub> is involved in the cellular metabolism of [[carbohydrates]], [[proteins]] and lipids. It is essential in the production of blood cells in bone marrow, and for nerve sheaths and proteins. Vitamin B<sub>12</sub> functions as a co-enzyme in intermediary metabolism for the methionine synthase reaction with [[methylcobalamin]], and the methylmalonyl CoA mutase reaction with [[adenosylcobalamin]].
|}

==Deficiencies== <!--T:11-->
{{See also|Vitamin deficiency#Water-soluble vitamins}}

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Several named vitamin deficiency diseases may result from the lack of sufficient B vitamins. Deficiencies of other B vitamins result in symptoms that are not part of a named deficiency disease.

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{| class="wikitable"
!Vitamin!! Name !! Deficiency effects
 |-
 ! Vitamin&nbsp;B<sub>1</sub> 
| [[Thiamine]] || [[Thiamine deficiency]] causes [[thiamine deficiency#Beriberi|beriberi]]. Symptoms of this disease of the [[nervous system]] include weight loss, emotional disturbances, [[Wernicke encephalopathy]] (impaired sensory perception), weakness and pain in the limbs, periods of [[Heart arrhythmia|irregular heartbeat]], and [[edema]] (swelling of bodily tissues). [[Heart failure]] and [[death]] may occur in advanced cases. Chronic thiamine deficiency can also cause [[alcoholic Korsakoff syndrome]], an irreversible [[dementia]] characterized by [[amnesia]] and compensatory [[confabulation]]. 
 |-
 ! Vitamin&nbsp;B<sub>2</sub> 
| [[Riboflavin]] || [[Riboflavin deficiency]] can cause [[ariboflavinosis]], which may result in [[Angular cheilitis|cheilosis]] (cracks in the lips), high sensitivity to sunlight, [[angular cheilitis]], [[glossitis]] (inflammation of the tongue), [[seborrheic dermatitis]] or pseudo-[[syphilis]] (particularly affecting the [[scrotum]] or [[labia majora]] and the [[nasolabial folds|mouth]]), [[sore throat|pharyngitis]] (sore throat), [[hyperemia]], and edema of the [[Pharynx|pharyngeal]] and [[Wiktionary:oral|oral]] [[mucous membrane|mucosa]].
 |-
 ! Vitamin&nbsp;B<sub>3</sub> 
| [[Niacin (nutrient)|Niacin]] || [[Niacin deficiency]], along with a deficiency of [[tryptophan]], causes [[pellagra]]. Symptoms include aggression, [[dermatitis]], [[insomnia]], [[weakness]], mental confusion, and [[diarrhea]]. In advanced cases, pellagra may lead to [[dementia]] and death (the 3(+1) D's: dermatitis, diarrhea, dementia, and death).
 |-
 ! Vitamin&nbsp;B<sub>5</sub> 
| [[Pantothenic acid]] || [[Pantothenic acid deficiency]] can result in [[acne]] and [[paresthesia]], although it is uncommon.
 |-
 ! Vitamin&nbsp;B<sub>6</sub>
| [[Pyridoxine]], [[pyridoxal]], [[pyridoxamine]] || [[Vitamin B6#Deficiency|Vitamin B<sub>6</sub> deficiency]] causes seborrhoeic dermatitis-like eruptions, pink eye and neurological symptoms (e.g. [[epilepsy]]).
 |-
 ! Vitamin&nbsp;B<sub>7</sub>
| [[Biotin]] || [[Biotin deficiency]] does not typically cause symptoms in adults, other than cosmetic issues such as decreased hair and nail growth, but may lead to impaired growth and neurological disorders in infants. [[Multiple carboxylase deficiency]], an inborn error of metabolism, can lead to biotin deficiency even when dietary biotin intake is normal.
 |-
 ! Folate
| [[Folic acid]] || [[Folic acid deficiency]] results in a [[macrocytic anemia]], and elevated levels of [[homocysteine]]. Deficiency in pregnant women can lead to birth defects, particularly [[neural tube defect]]s such as [[spina bifida]] and [[anencephaly]].
 |-
 !Vitamin&nbsp;B<sub>12</sub> 
| [[Cobalamin]]s || [[Vitamin B12 deficiency|Vitamin B<sub>12</sub> deficiency]] results in a [[megaloblastic anemia|macrocytic anemia]], elevated [[methylmalonic acid]] and [[homocysteine]], [[peripheral neuropathy]], sense loss, change in mobility, memory loss and other cognitive deficits. It is most likely to occur among elderly people, as absorption through the gut declines with age; the autoimmune disease [[pernicious anemia]] is another common cause. It can also cause symptoms of [[mania]] and [[psychosis]]. Untreated, it is possible to cause irreversible damage to the brain and nerve system — In rare extreme cases, paralysis can result.
|}

==Side effects== <!--T:14-->
{{Anchor|B vitamin toxicity}}<!-- Former section title -->

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Because water-soluble B vitamins are eliminated in the urine, taking large doses of certain B vitamins usually only produces transient side effects (only exception is pyridoxine). General side effects may include restlessness, nausea and insomnia. These side effects are almost always caused by dietary supplements and not foodstuffs.

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{| class="wikitable"
! Vitamin !! Tolerable Upper Intake Level (UL) !! Harmful effects
 |-
 ! Vitamin&nbsp;B<sub>1</sub>
| None || No known toxicity from oral intake. There are some reports of [[anaphylaxis]] caused by high-dose thiamin injections into the vein or muscle. However, the doses were greater than the quantity humans can physically absorb from oral intake.
 |-
 ! Vitamin&nbsp;B<sub>2</sub> 
| None || No evidence of toxicity based on limited human and animal studies. The only evidence of adverse effects associated with riboflavin comes from ''[[in vitro]]'' studies showing the production of [[reactive oxygen species]] ([[free radicals]]) when riboflavin was exposed to intense visible and UV light.
 |-
 !Vitamin&nbsp;B<sub>3</sub> 
| US UL = 35&nbsp;mg as a dietary supplement || Intake of 3000&nbsp;mg/day of nicotinamide and 1500&nbsp;mg/day of nicotinic acid are associated with nausea, vomiting, and signs and symptoms of liver toxicity. Other effects may include glucose intolerance, and (reversible) ocular effects. Additionally, the nicotinic acid form may cause vasodilatory effects, also known as [[Flushing (physiology)|flushing]], including redness of the skin, often accompanied by an itching, tingling, or mild burning sensation, which is also often accompanied by [[pruritus]], headaches, and increased intracranial blood flow, and occasionally accompanied by pain. Medical practitioners prescribe recommended doses up to 2000&nbsp;mg per day of niacin in either immediate-release or slow-release formats, to lower plasma triglycerides and low-density lipiprotein cholesterol.
 |-
 ! Vitamin&nbsp;B<sub>5</sub> 
| None || No toxicity known.
 |-
 ! Vitamin&nbsp;B<sub>6</sub> 
| US&nbsp;UL&nbsp;=&nbsp;100&nbsp;mg/day; EU&nbsp;UL&nbsp;=&nbsp;25&nbsp;mg/day || See [[Megavitamin-B6 syndrome|Megavitamin-B<sub>6</sub> syndrome]] for more information.
 |-
 ! Vitamin&nbsp;B<sub>7</sub> 
| None || No toxicity known.
 |-
 ! Folate 
| 1&nbsp;mg/day || Masks B<sub>12</sub> deficiency, which can lead to permanent [[neurological]] damage.
 |-
 ! Vitamin&nbsp;B<sub>12</sub> 
| None established || Skin and spinal lesions. Acne-like rash [causality is not conclusively established].
 |}

==Discovery== <!--T:17-->
{| class="wikitable"
! Vitamin!! Name !! Discoverer!!Date!!Notes
|-
! rowspan="2" |Vitamin&nbsp;B<sub>1</sub> 
| rowspan="2" |[[Thiamine]] || [[Umetaro Suzuki]]||1910||Failed to gain publicity.
|-
| [[Casimir Funk]] || 1912||
|-
! Vitamin&nbsp;B<sub>2</sub>
| [[Riboflavin]] || D.T Smith and E.G Hendrick
| 1926|| [[Max Tishler]] invented methods for [[chemical synthesis|synthesizing]] it.
|-
! Vitamin&nbsp;B<sub>3</sub>
| [[Niacin (substance)|Niacin]] || [[Conrad Elvehjem]]|| 1937||
|-
! Vitamin&nbsp;B<sub>5</sub>
| [[Pantothenic acid]] || [[Roger J. Williams]]||1933||
|-
! Vitamin&nbsp;B<sub>6</sub> 
| [[Pyridoxine]] etc. || [[Paul Gyorgy]]||1934||
|-
! Vitamin&nbsp;B<sub>7</sub>
| [[Biotin]] || colspan=3|Research by multiple independent groups in the early 1900s; credits for discovery include [[Margaret Averil Boas]] (1927), and [[Dean Burk]].
|-
! Vitamin&nbsp;B<sub>9</sub> 
| [[Folic acid]] || [[Lucy Wills]]||1933||
|-
!Vitamin&nbsp;B<sub>12</sub>
| [[Cobalamin]]s || colspan=3|[[Vitamin B12#History|Five people]] have been awarded [[Nobel Prize]]s for direct and indirect studies of vitamin B<sub>12</sub>: [[George Whipple]], [[George Minot]] and [[William P. Murphy|William Murphy]] (1934), [[Alexander R. Todd]] (1957), and [[Dorothy Hodgkin]] (1964).
|}

==Related compounds== <!--T:18-->
Many of the following substances have been referred to as vitamins as they were once believed to be vitamins. They are no longer considered as such, and the numbers that were assigned to them now form the "gaps" in the true series of B-complex vitamins described above (for example, there is no vitamin B<sub>4</sub>). Some of them, though not essential to humans, are essential in the diets of other organisms; others have no known nutritional value and may even be toxic under certain conditions.
* '''Vitamin B<sub>4</sub>''': can refer to the distinct chemicals [[choline]], [[adenine]], or [[carnitine]].
** Choline is [[biosynthesis|synthesized]] by the human body, but not sufficiently to maintain good health, and is now considered an essential dietary nutrient.
** Adenine is a [[nucleobase]] synthesized by the human body.
** Carnitine is an essential dietary nutrient for certain worms, but not for humans.
* '''Vitamin B<sub>8</sub>''': [[adenosine monophosphate]] (AMP), also known as adenylic acid. Vitamin B<sub>8</sub> may also refer to [[inositol]].
* '''Vitamin B<sub>10</sub>''': [[4-Aminobenzoic acid|''para''-aminobenzoic acid]] (pABA or PABA), a chemical component of the folate molecule produced by plants and bacteria, and found in many foods. It is best known as a [[ultraviolet light|UV]]-blocking [[sunscreen]] applied to the skin, and is sometimes taken orally for certain medical conditions.
* '''Vitamin B<sub>11</sub>''': pteroylheptaglutamic acid (PHGA; chick growth factor). Vitamin Bc-conjugate was also found to be identical to PHGA. Derivative of [[folate]] ("pteroylmonoglutamic acid" in this nomenclature).
* '''Vitamin B<sub>13</sub>''': [[orotic acid]].
* '''Vitamin B<sub>14</sub>''': cell proliferant, anti-[[anemia]], rat growth factor, and antitumor [[pterin]] phosphate, named by Earl R. Norris. Isolated from human urine at 0.33ppm (later in blood), but later abandoned by him as further evidence did not confirm this. He also claimed this was not [[xanthopterin]].
* '''Vitamin B<sub>15</sub>''': [[pangamic acid]], also known as pangamate. Promoted in various forms as a dietary supplement and drug; considered unsafe and subject to seizure by the US [[Food and Drug Administration]].
* '''Vitamin B<sub>16</sub>''': [[dimethylglycine]] (DMG) is synthesized by the human body from choline.
* '''Vitamin B<sub>17</sub>''': pseudoscientific name for the poisonous compound [[amygdalin]], also known as the equally pseudoscientific name "nitrilosides" despite the fact that it is a single compound. Amygdalin can be found in various plants, but is most commonly extracted from apricot pits and other similar fruit kernels. Amygdalin is hydrolyzed by various intestinal enzymes to form, among other things, hydrogen cyanide, which is toxic to human beings when exposed to a high enough dosage. Some proponents claim that amygdalin is effective in cancer treatment and prevention, despite its toxicity and a lack of scientific evidence.
* '''Vitamin B<sub>20</sub>''': <small>L</small>-carnitine.
* '''Vitamin B<sub>f</sub>''': carnitine.
* '''Vitamin B<sub>m</sub>''': [[inositol|''myo''-inositol]], also called "mouse antialopaecia factor".
* '''Vitamin B<sub>p</sub>''': "antiperosis factor", which prevents [[perosis]], a leg disorder, in [[chicken|chicks]]; can be replaced by choline and manganese salts.
* '''Vitamin B<sub>T</sub>''': carnitine.
* '''Vitamin B<sub>v</sub>''': a type of B<sub>6</sub> other than pyridoxine.
* '''Vitamin B<sub>W</sub>''': a type of biotin other than d-biotin.
* '''Vitamin B<sub>x</sub>''': an alternative name for both pABA (see vitamin B<sub>10</sub>) and [[pantothenic acid]].


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{{Vitamins}}
{{Nutritional pathology}}


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{{二次利用|date=14 December 2023}}
{{DEFAULTSORT:B Vitamins}}
[[Category:B vitamins| ]]
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