Thiamine (vitamin B1) !

Thiamine, as thiamine pyrophosphate, is essential for drawing energy from glucose, especially in the brain and heart.

Updated 2026-11-01

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Key facts

Active form: thiamine pyrophosphate (TPP), coenzyme of the oxidative decarboxylations of α-keto acids.
Four enzymes use it: pyruvate dehydrogenase, α-ketoglutarate dehydrogenase, branched-chain keto acid dehydrogenase and transketolase.
Stores last only a few weeks: alcoholism, prolonged vomiting and malnutrition deplete it fast.
Deficiency: dry beriberi (neuropathy), wet beriberi (high-output heart failure) and Wernicke-Korsakoff encephalopathy.

Sources: whole grains, legumes, pork, seeds. Polished rice and unfortified refined flour lose almost all the thiamine in the husk.
Activation: thiamine pyrophosphokinase adds a pyrophosphate taken from ATP; it needs magnesium.
Chemistry: carbon 2 of the thiazole ring forms a carbanion that attacks the carbonyl of the α-keto acid and helps CO₂ leave.
Without TPP: pyruvate cannot enter the Krebs cycle and is diverted to lactate; ATP falls in neurons and heart muscle; the pentose phosphate pathway (transketolase) fails.
Thiamine destroyers: alcohol (less absorption and activation), thiaminases in raw fish and diuretics (more loss in urine).
Excess: no toxicity from food is known; any surplus leaves in urine.
Lab: red-cell transketolase activity (it rises when TPP is added if there is a deficit) or whole-blood TPP; raised lactate.

A pyrimidine ring joined by a methylene bridge to a thiazole ring; the pyrophosphate is attached to the thiazole's hydroxyethyl chain.
Carbon 2 of the thiazole, between the nitrogen and the sulphur, is the reactive centre.

Giving intravenous glucose to a malnourished person or one with alcoholism, without thiamine, can trigger Wernicke encephalopathy.
Thiamine is used to treat thiamine-responsive maple syrup urine disease.
In refeeding syndrome thiamine is used up fast when carbohydrate intake restarts.

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Which four enzymes use thiamine pyrophosphate?

Pyruvate dehydrogenase, α-ketoglutarate dehydrogenase, branched-chain keto acid dehydrogenase and transketolase.

Why does thiamine deficiency raise lactate?

Without TPP pyruvate dehydrogenase stops: pyruvate cannot become acetyl-CoA and is reduced to lactate.

Which functional test assesses thiamine?

Red-cell transketolase activity: if it rises a lot when TPP is added, the coenzyme was missing.

Why should glucose not be given without thiamine to a person with alcoholism?

Glucose increases the demand for TPP at PDH and can use up the little left, precipitating Wernicke encephalopathy.

Molecules are shown in their neutral form, as the databases deposit them; in the cell the acids and phosphates are ionised.

Educational information, not medical advice. For any symptom, see a health professional.

Sources: Thiamine diphosphate (CID 1132) (PubChem, NCBI, 2026) · Public domain; Thiamin: MedlinePlus Medical Encyclopedia (MedlinePlus, US National Library of Medicine, 2026); Beriberi: MedlinePlus Medical Encyclopedia (MedlinePlus, US National Library of Medicine, 2026); SLC19A2 gene: MedlinePlus Genetics (MedlinePlus, US National Library of Medicine, 2026); Textbook of Biochemistry for Medical Students, 6th ed. (Jaypee Brothers Medical Publishers (Vasudevan DM, Sreekumari S, Vaidyanathan K), 2011).

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