B vitamins are a class of water-soluble vitamins that play important roles in cell metabolism. Though these vitamins share similar names, research shows that they are chemically distinct vitamins that often coexist in the same foods. In general, dietary supplements containing all eight are referred to as a vitamin B complex. Individual B vitamin supplements are referred to by the specific name of each vitamin (e.g. B1, B2, B3 etc.).
Each B vitamin is either a cofactor (generally a coenzyme) for key metabolic processes or is a precursor needed to make one.
Note: other substances once thought to be vitamins were given numbers in the B-vitamin numbering scheme, but were subsequently discovered to be either not essential for life or manufactured by the body, thus not meeting the two essential qualifiers for a vitamin. That is why those numbers (4, 8, 10, 11) no longer appear in the classification.
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.
Because water-soluble B vitamins are eliminated in the urine, taking large doses of certain 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 foodstuffs.
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 (e.g., there is no vitamin B4). 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 (AMP), also known as adenylic acid. Vitamin B8 may also refer to inositol.Vitamin B10: 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 UV-blocking sunscreen applied to the skin, and is sometimes taken orally for certain medical conditions.Vitamin B11: pteryl-hepta-glutamic acid (PHGA; chick growth factor). Vitamin Bc-conjugate was also found to be identical to PHGA.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 (later in blood), 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 (DMG) is synthesized by the human body from choline.Vitamin B17: 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 severe lack of scientific evidence.Vitamin B20: L-carnitine.Vitamin Bf: carnitine.Vitamin Bm: myo-inositol, also called “mouse antialopaecia factor”.Vitamin Bp: “antiperosis factor”, which prevents perosis, a leg disorder, in chicks; can be replaced by choline and manganese salts.Vitamin BT: carnitine.Vitamin Bv: a type of B6 other than pyridoxine.Vitamin BW: a type of biotin other than d-biotin.Vitamin Bx: an alternative name for both pABA (see vitamin B10) and pantothenic acid.