B vitamins are a class of water-soluble vitamins that play important roles in cell metabolism. Though these vitamins share similar names, they are chemically distinct compounds 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 number or name of each vitamin: B1 = thiamine, B2 = riboflavin, B3 = niacin, etc. Some are better known by name than number: niacin, pantothenic acid, biotin and folate. Each B vitamin is either a cofactor 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. See section #Related compounds for numbers 4, 8, 10, 11, and others.
Molecular functions
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 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.
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 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: pteryl-hepta-glutamic acid. Vitamin Bc-conjugate was also found to be identical to PHGA.
Vitamin B12: Vitamin B12 is also Cyanocobalamin. This vitaman is a necessary substance needed to maintain the health of your metabolism, blood cells, and nerves. Vitamin B12 deficiency may result in anemia, stomach/intestine problems, and permanent nerve damage.
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 B16: dimethylglycine 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" even though 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.
