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[Biochemistry](https://durgical.com/en/biochemistry/) · Molecule

# 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.

## In detail

- 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.

**Also called**
Vitamin B1, Thiamine pyrophosphate (TPP), Aneurine

**Formula**
C₁₂H₁₉N₄O₇P₂S⁺

**PubChem**
[CID 1132](https://pubchem.ncbi.nlm.nih.gov/compound/1132)

## Structure

- 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.

## Clinical notes

- 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.

## Pathways

- [Krebs cycle (citric acid cycle)](https://durgical.com/en/biochemistry/pathways/krebs-cycle/)
- [Glycolysis](https://durgical.com/en/biochemistry/pathways/glycolysis/)

## Related conditions

- [Wernicke encephalopathy (thiamine deficiency)](https://durgical.com/en/conditions/wernicke-encephalopathy/)
- [Beriberi (thiamine deficiency)](https://durgical.com/en/conditions/beriberi/)
- [Lactic acidosis](https://durgical.com/en/conditions/lactic-acidosis/)
- [Heart failure](https://durgical.com/en/conditions/heart-failure/)

## Related

- [Pyruvate dehydrogenase complex (PDH)](https://durgical.com/en/biochemistry/enzymes/pyruvate-dehydrogenase-complex/)
- [α-Ketoglutarate dehydrogenase](https://durgical.com/en/biochemistry/enzymes/ketoglutarate-dehydrogenase/)
- [Magnesium](https://durgical.com/en/biochemistry/topics/magnesium/)
- [Riboflavin (vitamin B2)](https://durgical.com/en/biochemistry/molecules/riboflavin/)

## Test yourself

Think of the answer, then tap the question to see it.

## 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.

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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)](https://pubchem.ncbi.nlm.nih.gov/compound/1132) (PubChem, NCBI, 2026) · Public domain; [Thiamin: MedlinePlus Medical Encyclopedia](https://medlineplus.gov/ency/article/002401.htm) (MedlinePlus, US National Library of Medicine, 2026); [Beriberi: MedlinePlus Medical Encyclopedia](https://medlineplus.gov/ency/article/000339.htm) (MedlinePlus, US National Library of Medicine, 2026); [SLC19A2 gene: MedlinePlus Genetics](https://medlineplus.gov/genetics/gene/slc19a2/) (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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