B vitamins

B vitamins are a class of water-soluble vitamins that play important roles in cell metabolism and synthesis of red blood cells. They are a chemically diverse class of compounds.
Dietary supplements 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 B₁ for thiamine, B₂ for riboflavin, and B₃ for niacin, while some are more commonly recognized by name than by number, such as pantothenic acid, biotin, and folate. B vitamins are present in protein-rich foods, such as fish, poultry, meat, dairy products, and eggs; they are also found in leafy green vegetables, beans, and peas. Fortified foods, such as breakfast cereals, baked products, and infant formulas, may contain B vitamins.
Each B vitamin is either a cofactor for key metabolic processes or is a precursor needed to make one.

List of B vitamins

Vitamin	Name	Description
Vitamin B₁	Thiamine	A coenzyme in the catabolism of sugars and amino acids.
Vitamin B₂	Riboflavin	A precursor of coenzymes called FAD and FMN, which are needed for flavoprotein enzyme reactions, including activation of other vitamins
Vitamin B₃	Niacin	A precursor of coenzymes called NAD and NADP, which are needed in many metabolic processes.
Vitamin B₃	Niacinamide	A precursor of coenzymes called NAD and NADP, which are needed in many metabolic processes.
Vitamin B₃	Nicotinamide riboside	A precursor of coenzymes called NAD and NADP, which are needed in many metabolic processes.
Vitamin B₅	Pantothenic acid	A precursor of coenzyme A and therefore needed to metabolize many molecules.
Vitamin B₆	Pyridoxine	A coenzyme in many enzymatic reactions in metabolism.
Vitamin B₆	Pyridoxal	A coenzyme in many enzymatic reactions in metabolism.
Vitamin B₆	Pyridoxamine	A coenzyme in many enzymatic reactions in metabolism.
Vitamin B₇	Biotin	A coenzyme for carboxylase enzymes, needed for synthesis of fatty acids and in gluconeogenesis.
Vitamin B₉	Folate	A precursor needed to make, repair, and methylate DNA; a cofactor in various reactions; especially important in aiding rapid cell division and growth, such as in infancy and pregnancy.
Vitamin B₁₂	Cobalamins	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.

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 for numbers 4, 8, 10, 11, and others.

Molecular functions

To the right, a diagram of some of the major B vitamins are shown as precursors for certain essential biochemical reactants. The structural similarities between them are highlighted, which illustrates the precursor nature of many B vitamins while also showing the functionality of the end product used by essential reactions to support human, animal, or cellular life.
FAD, NAD+, and coenzyme A are all essential for the catabolic release of free energy to power the activity of the cell and more complex life forms. See the article on Catabolism for more details on how these three essential biochemical reactants help support life.
Tetrahydrofolate is a necessary co-reactant for synthesizing some amino acids, such as glycine. Heme B is the porphyrin derivative macrocycle molecule that holds the iron atom in place in hemoglobin, allowing for the transportation of oxygen through blood.

Deficiencies

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.

Side effects

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

Discovery

Related compounds

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. 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 B₄: can refer to the distinct chemicals choline, adenine, or carnitine.
* Choline is 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 B₈: adenosine monophosphate, also known as adenylic acid. Vitamin B₈ may also refer to inositol.
Vitamin B₁₀: para-aminobenzoic acid, a chemical component of the folate molecule produced by plants and bacteria, and found in many foods. It is best known as a UV-blocking sunscreen applied to the skin, and is sometimes taken orally for certain medical conditions.
Vitamin B₁₁: pteroylheptaglutamic acid. Vitamin Bc-conjugate was also found to be identical to PHGA. Derivative of folate.
Vitamin B₁₃: orotic acid.
Vitamin B₁₄: cell proliferant, anti-anemia, rat growth factor, and antitumor pterin phosphate, named by Earl R. Norris. Isolated from human urine at 0.33ppm, but later abandoned by him as further evidence did not confirm this. He also claimed this was not xanthopterin.
Vitamin B₁₅: 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 B₁₆: dimethylglycine is synthesized by the human body from choline.
Vitamin B₁₇: pseudoscientific name for the poisonous compound amygdalin, also known as "laetrile" or by 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 B₂₀: L-carnitine.
Vitamin B_f: carnitine.
Vitamin B_m: myo-inositol, also called "mouse antialopaecia factor".
Vitamin B_p: "antiperosis factor", which prevents perosis, a leg disorder, in chicks; can be replaced by choline and manganese salts.
Vitamin B_T: carnitine.
Vitamin B_v: a type of B₆ other than pyridoxine.
Vitamin B_W: a type of biotin other than d-biotin.
Vitamin B_x: an alternative name for both pABA and pantothenic acid.