Vitamin B 12 (Cobalamins) act as coenzymes for various metabolic functions such as protein synthesis and fat and carbohydrate metabolism.

Vitamin B1 (thiamine) combines with ATP to form a coenzyme, thiamine pyrophosphate, which is necessary for carbohydrate metabolism.

Vitamin B3 or Niacin (after being converted to niacinamide) is a component of Nicotinamide Adenine Dinucleotide (NAD) and Nicotinamide Adenine Dinucleotide Phosphate (NADP). These co-enzymes are necessary for tissue respiration, glycogenolysis, and lipid, amino acid, protein, and purine metabolism. Niacin lowers serum cholesterol and triglyceride concentrations by inhibiting the formation of very low-density lipoproteins (VLDL). Niacin also causes direct peripheral vasodilation.

Vitamin B6 (Pyridoxine) is converted (in erythrocytes) to pyridoxal phosphate and pyridoxamine phosphate. These act as coenzymes for various metabolic functions involving protein, carbohydrate, and lipid utilization. Its use as an antidote is due to the fact that it increases the excretion of certain drugs like cycloserine and isoniazid, which act as its antagonists.

Vitamin C is required for synthesis of collagen, lipids, proteins, and carnitine, for tissue repair, in oxidation-reduction reactions in the body, metabolism of phenylalanine, tyrosine, folic acid, norepinephrine, histamine, iron, and some drug enzyme systems, in utilization of carbohydrates, for immune function, hydroxylation of serotonin, and preservation of blood vessel integrity among others. Its deficiency causes scurvy (currently a rare condition).

Vitamin C is required for synthesis of collagen, lipids, proteins, and carnitine, for tissue repair, in oxidation-reduction reactions in the body, metabolism of phenylalanine, tyrosine, folic acid, norepinephrine, histamine, iron, and some drug enzyme systems, in utilization of carbohydrates, for immune function, hydroxylation of serotonin, and preservation of blood vessel integrity among others. Its deficiency causes scurvy (currently a rare condition).

Vitamin E is thought to act as an antioxidant as well as being a cofactor in some enzyme systems. It protects polyunsaturated fatty acids, in conjunction with dietary selenium, in membranes and other cellular structures from attack by free radicals. It also protects red blood cells against haemolysis.

Vitamin K promotes the hepatic synthesis synthesis of clotting factors II, VII, IX, and X. It promotes synthesis of proteins necessary for normal calcification of bones.It is normally formed by bacteria in the intestine as well as being present in the diet hence its deficiency can arise when there is no bacteria in the gut e.g. in the newborn and in-patients on antibiotics. As it needs bile salts to be absorbed, its absorption is reduced in obstructive jaundice.