B vitamins are a class of water-soluble vitamins that play important roles in cell metabolism and synthesis of red blood cells.[1][2] They are a chemically diverse class of compounds.[1]
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,[1][2] while some are more commonly recognized by name than by number, such as pantothenic acid (B5), biotin (B7), and folate (B9).[1] 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.[1] Fortified foods, such as breakfast cereals, baked products, and infant formulas, may contain B vitamins.[1]
Each B vitamin is either a cofactor (generally a coenzyme) for key metabolic processes or is a precursor needed to make one.[1][2]