Vitamin B1 (thiamine)

Vitamin B1, also called thiamine, is a water-soluble vitamin. The body cannot make it itself and stores only small amounts, mainly in muscle, heart, liver, kidneys and brain. Because the reserves are small and used up continuously, a low intake or impaired absorption becomes noticeable after just a few weeks. Vitamin B1 is measured in whole blood (EDTA blood) in its active form, thiamine pyrophosphate (TPP). This form is found mainly in the red blood cells and reflects the supply to the tissues better than free thiamine in serum.

What vitamin B1 does in the body

Thiamine pyrophosphate is a coenzyme for several key enzymes of energy metabolism. Pyruvate dehydrogenase needs it to convert pyruvate from sugar breakdown into acetyl-CoA, which enters the citric acid cycle in the mitochondria. α-ketoglutarate dehydrogenase in the citric acid cycle and the breakdown of the branched-chain amino acids also depend on TPP. In the pentose phosphate pathway it helps the enzyme transketolase provide ribose for genetic material and NADPH for antioxidant defence. Nerve cells and heart muscle draw their energy particularly heavily from glucose – which is why they react sensitively when vitamin B1 is lacking.

Low vitamin B1 – what happens in the body?

When thiamine pyrophosphate is lacking, pyruvate can no longer enter the citric acid cycle sufficiently. More of it is converted into lactate, and the cells gain less energy from sugar. This shows first in nerves and heart: tingling and numbness in hands and feet, muscle weakness, rapid exhaustion, palpitations and fluid retention. A pronounced deficiency is known as beriberi; in the brain it can lead to Wernicke's encephalopathy with confusion, unsteady gait and eye movement disorders. Causes include high alcohol consumption, impaired absorption in the gut, persistent vomiting, surgery on the digestive tract or increased loss via the kidneys, for example with diuretic medicines.

High vitamin B1 – what happens in the body?

As a water-soluble vitamin, excess thiamine is quickly excreted via the kidneys; absorption in the gut is also limited at higher amounts. High blood levels therefore almost always result from a generous intake via vitamin preparations or infusions in the weeks before the blood sample. No harmful effects from vitamin B1 in food are known. A high value mainly shows that the stores in the red blood cells are well filled. Because thiamine pyrophosphate leaves the blood cells only slowly, the value reflects the supply over the past weeks and not just the last meal.

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