Thiamine (American spelling: thiamin) is designated vitamin B1, and is a water soluble vitamin consisting of a pyrimidine ring and thiazole linked by a methylene bridge. Thiamin is absorbed from plants in the free thamine form and following absorption is activated by the liver through attachment of two phosphate groups to form thiamine pyrophosphate (TPP). Consumption of animal tissue containing thiamine pyrophosphate requires hydrolysis of the phosphates in the intestine, followed by rephosphorylation in the liver. Thiamine pyrophosphate (sometimes called thiamine diphosphate; TDP) is required as a co-factor by certain enzymes involved in the main energy producing pathways. The α-keto acid decarboxylation reactions converting pyruvate to acetyl CoA and α-ketoglutarate to succinyl CoA, both require thiamine pyrophosphate. Thiamine pyrophosphate is also required for the transketolase reactions in the pentose phosphate pathway, which ultimately allow production of NADPH for synthetic reactions.
Thiamine is also believed to have a non-enzymatic role in nerve conduction, possibly interacting with in sodium ion channels in neurones. In this regard thiamine may be in the thiamine triphosphate (TTP) form. However, the exact mechanism of action is not clear. The role of thiamine in nerve conduction explains the neurological problems seen in the thiamine deficiency disease beriberi. Beriberi was first discovered in individuals consuming mainly white rice, the thiamine having been removed with the bran to produce cattle feed. Dry beriberi can form in adults exposed to chronic low intakes of thiamine, and results in neurological problems, muscle weakness and wasting. Wet beriberi results in oedema from cardiac failure. Acute beriberi is found in infants and is sometimes called infant beriberi. Wernicke’s encephalopathy (Wernicke-Korsakoff syndrome) is an alcohol induced thiamine deficiency which results in wasting, loss of memory and confusion.