B vitamins

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.

List of B vitamins

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.

B vitamin molecular functions

B vitamin deficiency

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.

Vitamin B6

Vitamin B₆ refers to a group of chemically very similar compounds which can be interconverted in biological systems. Vitamin B₆ is part of the vitamin B group, and its active form, pyridoxal 5'-phosphate (PLP) serves as a coenzyme in many enzyme reactions in amino acid, glucose, and lipid metabolism.

Forms

Several forms (vitamers) of vitamin B₆ are known:

All forms except pyridoxic acid and pyritinol can be interconverted. Absorbed pyridoxamine is converted to PMP by pyridoxal kinase, which is further converted to PLP by pyridoxamine-phosphate transaminase or pyridoxine 5’-phosphate oxidase which also catalyzes the conversion of PNP to PLP. Pyridoxine 5’-phosphate oxidase is dependent on flavin mononucleotide (FMN) as a cofactor which is produced from riboflavin (vitamin B₂) i.e. in this biochemical pathway, dietary vitamin B₆ cannot be used without vitamin B₂.