Vitamins

Thiamine (Vitamin B1)

By All The Nutrients Editorial Team Published: 7 min read

Thiamine (vitamin B1) was the first vitamin to be chemically isolated, discovered through the study of beriberi — a paralytic disease caused by polished rice diets that strip away the bran where thiamine is concentrated. As the coenzyme thiamine pyrophosphate (TPP), it is essential at three critical chokepoints in energy metabolism: the conversion of pyruvate to acetyl-CoA (linking glycolysis to the TCA cycle), the TCA cycle step catalysed by alpha-ketoglutarate dehydrogenase, and the pentose phosphate pathway enzyme transketolase. Without thiamine, cells cannot extract energy from glucose — making nerve and heart tissue, which run almost exclusively on glucose, extremely vulnerable. The richest dietary sources are pork, legumes, nuts, seeds, and fortified grains.

Daily Value

1.20 mg

FDA 2020

Top Source

Yeast extract spread

23.4 mg

What Does Thiamine (Vitamin B1) Do?

  • Glucose metabolism and ATP production: Thiamine pyrophosphate (TPP) is required for pyruvate dehydrogenase (PDH) — the enzyme complex that bridges glycolysis and the mitochondrial TCA cycle by converting pyruvate to acetyl-CoA. Without TPP, pyruvate accumulates as lactate rather than entering the TCA cycle, dramatically reducing ATP yield from carbohydrates. Because the brain and peripheral nerves depend almost exclusively on glucose for energy, thiamine deficiency disproportionately affects the nervous system.
  • Pentose phosphate pathway and nucleic acid synthesis: Transketolase — a TPP-dependent enzyme in the pentose phosphate pathway — generates ribose-5-phosphate (needed for RNA and DNA synthesis) and NADPH (needed for fatty acid synthesis and antioxidant regeneration). Erythrocyte transketolase activity is the most sensitive functional biomarker of thiamine status, used clinically to detect subclinical deficiency before symptoms appear.
  • Nervous system function and acetylcholine synthesis: Beyond its metabolic role, thiamine has direct membrane effects on nerve conduction independent of TPP. Thiamine is found at high concentrations in synaptic vesicle membranes and modulates sodium channel activity. It is also involved in acetylcholine synthesis — a neurotransmitter critical for neuromuscular junction function and memory consolidation. Deficiency causes peripheral neuropathy and, in severe cases, the confusion and memory impairment of Wernicke's encephalopathy.
  • Cardiac function: Heart muscle has among the highest thiamine turnover rates in the body. In wet beriberi (a form of thiamine deficiency), peripheral vasodilation from impaired energy metabolism in blood vessel walls causes high-output cardiac failure — the heart compensates for the drop in vascular resistance by increasing output, eventually dilating and failing. This form of heart failure resolves rapidly with thiamine repletion, making thiamine deficiency a rare but important reversible cause of acute cardiomyopathy (also seen in alcoholic cardiomyopathy).
Horizontal bar chart of thiamine per 100g: flaxseeds 1.64mg, sunflower seeds 1.48mg, pork tenderloin 0.99mg, pork loin 0.78mg, enriched white bread 0.53mg, edamame 0.27mg, lentils cooked 0.17mg. FDA DV reference line at 1.2mg.
Pork is the standout whole-food thiamine source. Fortified grains make a reliable everyday contribution for populations eating varied diets.
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Signs of Thiamine (Vitamin B1) Deficiency

Thiamine deficiency produces two distinct clinical syndromes depending on the severity and duration of depletion. The body stores only 30–50 mg (about 18 days' worth at RDA intake), making depletion rapid with inadequate intake:

  • Dry beriberi — peripheral neuropathy: ascending symmetrical sensory loss (numbness, tingling, burning in the feet before the hands), followed by motor weakness (foot drop, difficulty climbing stairs), muscle wasting, and loss of deep tendon reflexes; predominantly affects the longest peripheral nerves
  • Wet beriberi — cardiovascular: high-output heart failure from peripheral vasodilation; symptoms include oedema (swelling) in the legs, dyspnoea (breathlessness), tachycardia, and cardiomegaly (enlarged heart); responds dramatically to thiamine injection within hours
  • Wernicke's encephalopathy — acute neurological emergency (classic triad: confusion, ophthalmoplegia/eye movement abnormalities, ataxia/gait instability); seen in people with alcoholism due to reduced intake, absorption, and utilisation of thiamine; if untreated, progresses to Korsakoff syndrome (irreversible anterograde amnesia — inability to form new memories)
  • Infantile beriberi — occurs in breastfed infants of thiamine-deficient mothers; presents as cardiac failure with irritability, vomiting, and sudden death in severe cases
  • Wernicke's in non-alcoholic populations — also occurs in hyperemesis gravidarum (severe pregnancy vomiting), bariatric surgery (especially gastric bypass), prolonged IV nutrition without thiamine, refeeding syndrome in malnutrition

Consider supplementing

B-Complex supplement

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How to Get the Most from Thiamine (Vitamin B1)

Thiamine absorption is carrier-mediated at low concentrations and passive at high concentrations, with maximal absorption of about 4.5 mg per dose. Several factors significantly affect thiamine status:

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Avoid raw fish and shellfish if thiamine intake is marginal

Many raw freshwater and saltwater fish contain thiaminase — an enzyme that cleaves and inactivates dietary thiamine. Thiaminase is destroyed by cooking. Regular consumption of raw fish (carp, herring, clams, mussels) as a dietary staple without cooking has historically caused thiamine deficiency in Scandinavian and Japanese fishing communities. This is not a concern with cooked fish, and the fish's own thiamine content provides a nutritional contribution.

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Avoid prolonged tea and coffee consumption with meals if intake is low

Tea and coffee contain thiamine-degrading polyphenols (tannic acid and chlorogenic acid) that can reduce thiamine absorption when consumed with or immediately after meals. The effect is small in people with adequate intake from diverse diets, but is relevant for populations with marginal thiamine intake (e.g., subsisting on polished rice) who also drink large quantities of tea with meals, as seen in parts of Southeast Asia.

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Fortified grains and legumes are reliable everyday sources

In the US and most developed countries, refined grain products (bread, pasta, rice, cereals) are mandated to be enriched with thiamine, making them a reliable and widely accessible source. Legumes (lentils, black beans, edamame, green peas) naturally provide 0.3–0.5 mg per 100 g cooked — a meaningful contribution from whole-food sources. A diet including any combination of fortified grains and legumes reliably meets the RDA.

Common Thiamine (Vitamin B1) Questions

How much thiamine do I need per day?

The FDA Daily Value for thiamine is 1.2 mg/day. The National Academies RDA is 1.2 mg/day for adult men and 1.1 mg/day for adult women 19+. During pregnancy and breastfeeding: 1.4 mg/day. Thiamine requirements increase with higher carbohydrate intake because more TPP is needed for pyruvate dehydrogenase activity. No Tolerable Upper Intake Level has been established — no adverse effects have been documented from high oral thiamine intake in humans, as absorption is self-limiting and excess is rapidly excreted by the kidneys.

What foods are highest in thiamine?

Per 100 g: pork loin cooked (0.78 mg), pork tenderloin (0.99 mg), sunflower seeds (1.48 mg), flaxseeds (1.64 mg), pine nuts (0.36 mg), black beans cooked (0.24 mg), edamame (0.27 mg), lentils cooked (0.17 mg), green peas cooked (0.26 mg), enriched white bread (0.53 mg), fortified breakfast cereals (up to 1.5 mg per serving), nutritional yeast (varies; often fortified to ~1–2 mg per tablespoon). Pork is the single richest whole-food thiamine source — a 100 g serving of pork tenderloin provides over 80% of the daily value.

What is Wernicke's encephalopathy and who is at risk?

Wernicke's encephalopathy is an acute neurological emergency caused by severe thiamine deficiency. The classic triad is confusion, eye movement abnormalities (nystagmus, lateral gaze palsy), and ataxia (unsteady gait). It is caused by thiamine-dependent neurons in the thalamus, mammillary bodies, and oculomotor nuclei dying when deprived of TPP. Risk groups include: people with alcohol use disorder (alcoholism impairs thiamine absorption, utilisation, and intake); patients with severe hyperemesis gravidarum (repeated vomiting throughout pregnancy); post-bariatric surgery patients; patients receiving prolonged IV nutrition without thiamine supplementation; elderly people with poor dietary intake; and people with malabsorption disorders. Treatment is IV thiamine (100–500 mg/day) — the response is often dramatic and rapid for eye movement abnormalities and gait. Untreated, Wernicke's progresses to Korsakoff syndrome (permanent anterograde amnesia).

Does thiamine help with energy levels?

Thiamine corrects energy metabolism only when deficiency is the cause of fatigue. When thiamine status is adequate, supplementation does not further increase energy or ATP production — cells already have sufficient TPP for all metabolic demands. However, in people with subclinical thiamine deficiency (common in alcohol use disorder, elderly individuals, and those with malabsorption), restoring adequate thiamine can produce marked improvements in energy, cognitive clarity, and muscle function. If fatigue is the concern, checking thiamine status (erythrocyte transketolase or whole blood thiamine) is more informative than empirically supplementing.

Why is thiamine especially important for people who drink alcohol?

Alcohol interferes with thiamine at multiple steps simultaneously: (1) it directly impairs intestinal thiamine absorption by reducing the active transport carrier capacity; (2) it impairs the liver's ability to phosphorylate thiamine to TPP (the active form); (3) chronic heavy drinking causes dietary neglect — alcohol provides empty calories and reduces appetite for nutrient-dense foods; (4) alcoholic liver disease further impairs thiamine storage. The combination means that people with heavy alcohol use disorder deplete thiamine stores within 2–3 weeks and are at high risk for Wernicke's encephalopathy. Many hospitals and emergency departments now give prophylactic IV thiamine (Pabrinex) to all patients admitted with alcohol-related presentations before any glucose-containing IV fluid, because giving glucose without thiamine to a borderline-deficient patient can precipitate acute Wernicke's by driving the remaining TPP stores for pyruvate metabolism.