What is thiamine, and what are its active coenzyme forms?
Thiamine (vitamin B1) is a water-soluble vitamin whose biological mechanism of action necessarily involves its intracellular phosphorylation into active coenzyme forms. It is essential for the energy metabolism of all cells and for nervous system function. The human body cannot synthesize or store it in significant quantities (reserves ≈ 25–30 mg, sufficient for about 18 days)—hence the importance of a regular daily intake. For information on the nutritional role and dietary sources of vitamin B1, visit our vitamin B1 page. Discover our B-vitamin formulas available at pharmacies, our anti-fatigue supplements, and our energy and vitality products.
- Coenzyme forms of thiamine: thiamine pyrophosphate (TPP / TDP—thiamine diphosphate)—the major coenzyme form (80% of cellular thiamine) — cofactor for 3 critical mitochondrial enzyme complexes — thiamine monophosphate (TMP) — transport form — thiamine triphosphate (TTP) — specific neurological role (likely involvement in neuromuscular transmission)
- TPP-dependent enzyme complexes: pyruvate dehydrogenase (PDH) — converts pyruvate (the end product of glycolysis) to acetyl-CoA → entry into the Krebs cycle → ATP production — alpha-ketoglutarate dehydrogenase (AKGDH) — step in the Krebs cycle → production of NADH + succinate → mitochondrial ATP — transketolase (pentose phosphate pathway) — biosynthesis of nucleotides (DNA/RNA) + production of NADPH (antioxidant defense)
- Consequences of a TPP deficiency: inhibition of aerobic glycolysis → cells switch to anaerobic metabolism → accumulation of pyruvate and lactate (lactic acidosis) — the most vulnerable cells: neurons (the brain consumes 20% of the body’s glucose) and cardiomyocytes → neurotoxicity + cardiomyopathy
- Storage and kinetics: total body pool ≈ 25–30 mg — plasma half-life ≈ 9–18 days — highest concentrations in the liver, heart, the kidneys, and skeletal muscle—rapidly excreted by the kidneys (urine) → daily intake essential—intestinal absorption is saturable: optimal at low doses (< 5 mg), carrier-dependent (THTR-1 and THTR-2)
- Factors that inactivate thiamine: thiaminases (enzymes found in certain raw fish—carp, herring, freshwater fish) destroy dietary thiamine → avoid excessive consumption of raw fish — tannins (strong tea, coffee) reduce absorption — excessive cooking (> 100 °C) destroys thiamine (heat-sensitive)
Deficiency disorders and at-risk populations
- Beriberi (historically severe deficiency): two main forms — wet (cardiac) beriberi: high-output heart failure — cardiomegaly — peripheral edema — tachycardia — described in Asian populations whose diet was based on polished white rice (deprived of its thiamine-containing bran) — dry beriberi (neurological): symmetrical peripheral neuropathy (tingling + pain + paresis of the lower limbs) — muscle atrophy — still present in developing countries and situations of malnutrition
- Wernicke-Korsakoff syndrome: a severe neurological complication caused by acute thiamine deficiency — Wernicke syndrome (acute phase): classic triad — mental confusion + ophthalmoplegia (oculomotor paralysis) + cerebellar ataxia (unsteady gait) — medical emergency: IV thiamine injection — without treatment → progression to Korsakoff’s syndrome — Korsakoff’s syndrome (chronic phase): severe anterograde and retrograde amnesia — confabulation — irreversible alcoholic dementia in 80% of cases without early intervention
- Chronic alcoholism — leading cause in France: alcohol interferes with intestinal absorption of thiamine (THTR-1/2 inhibition) + increases requirements (alcohol metabolism consumes TPP) + associated malnutrition — underdiagnosed Wernicke’s syndrome: 80% of cases do not present with the classic triad—routine preventive thiamine supplementation is recommended for all patients with alcoholism (HAS)
- Other populations at increased risk of deficiency: bariatric surgery (malabsorption + dumping syndrome) — severe anorexia nervosa + chronic vomiting (hyperemesis gravidarum) — chronic dialysis (urinary and dialysable losses) — total parenteral nutrition without supplementation — malnourished older adults — prolonged chemotherapy — chronic inflammatory bowel disease (IBD)
- Thiamine deficiency and diabetes: chronic hyperglycemia increases renal clearance of thiamine → frequent functional deficiency in people with diabetes (studies showing a deficiency in 75% of people with type 2 diabetes not receiving supplementation) → contributes to diabetic neuropathy and microvascular complications
Neurological, cardiovascular, and energy metabolism roles
- Neurology and nerve transmission: thiamine triphosphate (TTP) is specifically concentrated in nervous tissue — likely involved in the opening of Na+/K+ chloride channels (nerve impulse transmission) — TPP-dependent transketolase is essential for NADPH synthesis → antioxidant protection of neurons — deficiency → neuronal hyperexcitability + axonal degeneration (peripheral neuropathy) + neuronal death (Wernicke’s cerebral nuclei—mammillary bodies, thalamus)
- Cardiac function: the myocardium is a tissue with very high energy demands—70% of its ATP comes from fatty acids + 30% from glucose (thiamine-dependent pathway) — deficiency → metabolic cardiomyopathy + heart failure — patients with heart failure on diuretics (furosemide) are at increased risk of deficiency (thiamine loss in urine) — supplementation is recommended for these patients
- Energy Production and Fatigue: PDH is the key enzyme in the transition to aerobic metabolism—without sufficient TPP → accumulated pyruvate → lactate → lactic fatigue—subclinical thiamine deficiency → chronic fatigue + lack of energy + decreased physical performance without an identified cause — Check out our anti-fatigue supplements
- Brain health and cognition: Glucose is the brain’s sole fuel → the brain is entirely dependent on TPP-dependent enzymes — subclinical deficiency → impaired concentration, memory, and mental clarity + irritability — epidemiological studies linking thiamine deficiency to an increased risk of dementia and Alzheimer’s disease — vitamin B6, vitamin B12, and thiamine form an essential neuroprotective trio
- Synergistic B-complex: B vitamins act as part of a metabolic network — thiamine alone is less effective than when combined with other B vitamins — B-complex + magnesium (a cofactor for transketolase) — check out our fatigue and herbal medicine formulas and our vitamins page
Supplementation, Dosage, and Precautions
- RDA and requirements based on specific situations: RDA (ANSES) — adult men: 1.2 mg/day — adult women: 1.1 mg/day — pregnancy and breastfeeding: 1.4–1.5 mg/day — increased requirements: athletes (increased carbohydrate metabolism) — alcoholics — older adults — people with diabetes — diets high in refined sugars (increases TPP requirements for glucose metabolism)
- Preventive and therapeutic supplementation: preventive nutritional doses (B-complex): 1.5–10 mg/day — pharmacological doses (confirmed deficiency): 50–300 mg/day orally — Wernicke’s encephalopathy emergency: 200–500 mg IV × 3/day for at least 3–5 days (IV thiamine is a priority—administration of IV glucose without thiamine in a deficient patient can precipitate Wernicke’s syndrome) — routine supplementation in alcoholic patients: 100–300 mg/day orally
- Benfotiamine (fat-soluble form): a fat-soluble thiamine derivative — higher intestinal and tissue bioavailability than water-soluble thiamine — particularly effective in diabetic peripheral neuropathy and early-stage Wernicke’s syndrome — dosages: 150–600 mg/day depending on the indication
- Safety and tolerability: thiamine is among the safest vitamins—very low toxicity even at high oral doses (excess is excreted in the urine) — rare cases of hypersensitivity (anaphylaxis possible with high-dose injectable forms → caution required in medical settings) — no upper limit established by the EFSA for oral thiamine (insufficient toxicity data but excellent safety profile)
- Drug interactions: loop diuretics (furosemide) → increase urinary excretion of thiamine — estrogen-progestin oral contraceptives → reduce plasma thiamine concentrations — alcohol → blocks intestinal absorption and increases requirements — phenytoin (antiepileptic) → reduces absorption — routinely check thiamine status in patients on these treatments
