Vitamin B1 (Thiamine)

Vitamin B1 (thiamine) has a property that sets it apart: the body stores only a particularly small amount of it — on the order of 25-30 mg in total, enough for just 2-3 weeks.

By comparison, the liver’s stores of vitamin B12 last for years. This means thiamine deficiency can develop quickly, which is why it shows up in acute situations — after prolonged vomiting, after bariatric surgery, in intensive care and during alcohol withdrawal.

Thiamine also has a unique place in emergency medicine: in Wernicke’s syndrome, giving glucose before thiamine can make the condition worse — so the rule is thiamine first.

Dosage and sources

The last two rows are a history lesson: refining removes the bran and germ, where the thiamine is found. That is how beriberi broke out in 19th-century Asia, when rice-polishing machines became widespread.

Benefits (Pros)

1. Producing energy from carbohydrates

The active form, thiamine pyrophosphate (TPP), is a cofactor for key metabolic enzymes: pyruvate dehydrogenase (which feeds glucose into the Krebs cycle) and alpha-ketoglutarate dehydrogenase. Without thiamine, the cell cannot efficiently produce energy from glucose.

2. Nerve function

The nerves and brain depend almost entirely on glucose for energy, so they are the first to suffer in thiamine deficiency. The vitamin is also needed for myelin production and synaptic function.

3. Heart function

“Wet” beriberi is a cardiomyopathy caused by thiamine deficiency, with heart failure and edema. It is reversible with impressive speed once thiamine is given — one of the most dramatic pictures in medicine.

4. The pentose phosphate pathway

Thiamine is needed for transketolase, an enzyme that produces NADPH and ribose — raw materials for synthesizing fatty acids and nucleotides.

Downsides and side effects (Cons)

1. Alcohol — the main cause in the Western world

This is the biggest clinical risk. Alcohol damages thiamine status in three ways at once: it reduces absorption in the gut, reduces conversion to the active form in the liver, and increases excretion in the urine — and on top of that, heavy drinking usually comes with a poor diet.

The result:

• Wernicke’s encephalopathy — confusion, paralysis of the eye muscles (ophthalmoplegia) and ataxia. A medical emergency.
• Korsakoff syndrome — severe, irreversible memory damage, if Wernicke’s is not treated in time.

2. Glucose before thiamine — a clinical trap

Giving intravenous glucose to a patient with thiamine deficiency increases the metabolic use of the meager thiamine that remains, and can hasten the onset of Wernicke’s. The clinical rule: thiamine first, glucose after.

3. Refeeding syndrome

When feeding of a malnourished patient begins, the sudden switch to carbohydrate metabolism rapidly depletes thiamine stores and can cause Wernicke’s — alongside a sharp drop in phosphorus, potassium and magnesium.

4. Drugs and conditions that deplete it

• Furosemide and loop diuretics — increase thiamine excretion in the urine. Heart failure patients are at risk, and somewhat ironically, the deficiency worsens the heart condition.
• Bariatric surgery — a known complication, especially in the first months and when there is vomiting.
• Dialysis, pregnancy with hyperemesis, and prolonged stays in intensive care units.

5. What destroys thiamine in food

• Heat — thiamine is sensitive to cooking, especially prolonged cooking in water.
• Sulfites — preservatives in processed food and wine break down thiamine.
• Thiaminases — enzymes in raw fish and raw seafood break down thiamine. Cooking inactivates them.

6. No toxicity

No Tolerable Upper Intake Level has been set. Excess thiamine is excreted in the urine, and supplements are considered safe.

Summary

Thiamine is the vitamin that lets the cell produce energy from glucose — and its stores last only 2-3 weeks, a far shorter period than any other vitamin. On a varied Western diet it is very easy to get enough, so primary dietary deficiency is rare. The real risk is in specific situations: heavy alcohol use, prolonged vomiting, bariatric surgery, treatment with loop diuretics, and refeeding. In each of these, thiamine deficiency can turn into irreversible brain damage within days — which is why the rule in emergency medicine is thiamine before glucose.