Vitamin B1 (Thiamine)
Supplements · Vitamins · Supplement, Typed Supps
Essential for turning carbohydrates into usable energy.
Stage by stage
- Intake (Tablet): Absorbed via active transport at low doses and passive diffusion at higher ones.
- Small intestine (Dual absorption route): Both absorption routes operate in the small intestine, depending on dose.
- Bloodstream (Carried to cells): Carried in the blood to cells throughout the body.
- Nerve & heart cells (Energy cofactor): Used as a cofactor in enzymes converting carbohydrates into cellular energy, especially for nerve and heart function.
What the evidence supports
- Treating and preventing beriberi — strong evidence. Unambiguous, and historically important — thiamine deficiency was the first vitamin deficiency to be understood.
- Preventing Wernicke encephalopathy in at-risk people — strong evidence. Standard practice in alcohol dependence and after bariatric surgery. Untreated, it causes permanent neurological damage.
- Improving energy in people who are not deficient — insufficient evidence. The reason it appears in every B-complex and energy drink, and it does nothing there.
Typical dose
Multivitamins usually supply around 1.5 mg, and stand-alone or B-complex thiamine products commonly supply 50–250 mg, which is far above requirement; treatment doses for deficiency are set by a clinician and are much higher, often given intravenously in Wernicke encephalopathy
Upper limit: No UL has been set. The Food and Nutrition Board declined to set one because there are no reports of harm from high thiamine intakes — 50 mg a day or more — from food or supplements; excess is excreted in urine
Timing
With food, standard dosing.
Time to effect
- Weeks: Levels normalize if deficient.
Medication interactions
- Loop diuretics (furosemide): Increased urinary loss of thiamine has been linked to furosemide use and can lower thiamine concentrations, though whether supplementing prevents that is not settled. (moderate)
- Fluorouracil (5-FU): Thiamine deficiency has been reported in people receiving fluorouracil. Manage this through the oncology team rather than self-supplementing during chemotherapy. (moderate)
Common myth
“Thiamine deficiency is rare in developed countries.” In reality: Genuinely rare with a typical diet, but chronic heavy alcohol use significantly impairs absorption and is a well-documented cause of deficiency.
Food sources
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