Vitamin B1

vitamin

What is it

Vitamin B1, also known as thiamine, is an essential water-soluble B vitamin that plays a critical role in energy metabolism. It is required for converting carbohydrates into usable energy and for normal function of nerves, muscles, and the heart. Severe deficiency causes beriberi and Wernicke-Korsakoff syndrome.

How it works

Thiamine is converted in the body to its active coenzyme form, thiamine diphosphate (TDP, also called TPP). TDP is a cofactor for several key enzymes in carbohydrate metabolism, including pyruvate dehydrogenase (linking glycolysis to the citric acid cycle), alpha-ketoglutarate dehydrogenase (in the citric acid cycle), and transketolase (in the pentose phosphate pathway). This central role in carbohydrate metabolism means thiamine requirements rise with carbohydrate intake. Tissues with high energy demands (brain, heart, skeletal muscle) are particularly dependent on adequate thiamine. The brain has minimal stores and is sensitive to even short-term deficiency, which can cause severe neurological symptoms. Thiamine absorption occurs in the small intestine through both active transport (at low intakes) and passive diffusion (at high intakes). Alcohol use significantly impairs thiamine absorption and increases requirements. The vitamin is poorly stored in the body (only several weeks of reserves), so regular dietary intake is needed.

Evidence for 5 uses

AI-assisted evidence assessment — talk to your doctor before relying on any single supplement.

Beriberi prevention and treatment

Grade A

Strong evidence

Thiamine reliably prevents and treats beriberi (the classic deficiency syndrome characterized by neuropathy, heart failure, and edema). This is a well-established medical use.

Wernicke-Korsakoff syndrome

Grade A

Strong evidence

High-dose thiamine is critical for prevention and treatment of Wernicke-Korsakoff syndrome (a serious neurological condition usually associated with chronic alcohol use). IV thiamine before glucose administration in suspected cases is standard medical practice.

Cardiovascular function (in deficiency)

Grade B

Good evidence

Thiamine deficiency causes wet beriberi with heart failure, which responds to thiamine replacement. Some research suggests thiamine supplementation may modestly improve heart function in non-deficient heart failure patients, but evidence is mixed.

Diabetic complications

Grade C

Moderate evidence

Some studies suggest thiamine (or its derivative benfotiamine) may support nerve function and reduce diabetic neuropathy symptoms. Benfotiamine has more evidence than basic thiamine for this use.

Fatigue and energy (in adequate-status adults)

Grade D

Mixed evidence

Supplementing thiamine in adults with adequate baseline status has not been shown to improve energy or fatigue. Effects are seen only in deficient individuals.

4 commercial forms

Thiamine HCl

Standard, well-absorbed form; widely available.

Most common form in multivitamins and B-complex supplements.

Thiamine mononitrate

More stable in food fortification and supplements; similar bioavailability to HCl.

Common in fortified foods and supplements.

Benfotiamine

Lipid-soluble derivative; substantially higher bioavailability than water-soluble forms.

Used for diabetic neuropathy and other applications where higher tissue thiamine levels are desired.

Allithiamine

Another lipid-soluble form found in garlic; better absorbed than basic thiamine.

Less common in supplements than benfotiamine.

Dosage

The RDA for thiamine is 1.2 mg/day for men and 1.1 mg/day for women, with slightly higher needs in pregnancy and breastfeeding (1.4 mg/day). There is no established Tolerable Upper Intake Level because thiamine has very low toxicity. Therapeutic doses for deficiency states or specific conditions can be much higher (50 to 300 mg per day orally; IV doses for acute Wernicke's encephalopathy reach 500 mg several times daily).

When and how to take it

WHEN: Take thiamine at any time of day. With or without food are both acceptable, though taking with food may improve tolerance. HOW: Take with water. Most B-complex supplements provide thiamine alongside other B vitamins. For carbohydrate-heavy diets or athletic training, taking with meals supports metabolic use. The active form benfotiamine has better lipid solubility for certain conditions.

Food sources

Food	Amount	%DV
Fortified breakfast cereals	1 serving	100%
Pork (lean)	3 oz	56%
Black beans	1/2 cup cooked	35%
Yogurt (plain)	1 cup	9%
Brown rice	1 cup cooked	15%
Sunflower seeds	1 oz	35%
Tuna	3 oz	19%
Whole wheat bread	1 slice	8%

Safety

Thiamine has an excellent safety record at typical doses. Side effects from oral supplementation are very rare. There is no established Tolerable Upper Intake Level. High-dose IV thiamine can rarely cause anaphylactic reactions. Long-term high-dose oral use is generally well tolerated.

Who should be cautious

Pregnant and breastfeeding women have increased needs and should ensure adequate intake. People with chronic alcohol use disorder are at high risk for thiamine deficiency and may need supplementation. Those on long-term loop diuretics should monitor thiamine status. People with malabsorption conditions, bariatric surgery, or chronic dialysis are at increased risk for deficiency.

Interactions

Loop diuretics (especially furosemide) increase thiamine excretion and may cause deficiency with long-term use. Alcohol significantly impairs thiamine absorption and metabolism. Some chemotherapy agents may interact with thiamine pathways. Levodopa absorption may be affected by high-dose thiamine.

Frequently asked questions

Who is at risk for thiamine deficiency?⌄

People with chronic alcohol use disorder, those on long-term loop diuretics, individuals with malabsorption (celiac, IBD, bariatric surgery), people with chronic kidney disease on dialysis, and those with HIV/AIDS are at increased risk.

Does taking extra thiamine boost energy?⌄

Only if you are deficient. In adults with adequate baseline status, supplementing thiamine does not improve energy or athletic performance.

What's the difference between thiamine and benfotiamine?⌄

Benfotiamine is a lipid-soluble derivative of thiamine with significantly better absorption. It is used in research for diabetic neuropathy and to achieve higher tissue thiamine levels.

Is high-dose thiamine safe?⌄

Yes. Thiamine has an excellent safety profile, with no established Upper Intake Level. Even high doses are generally well tolerated. Anaphylaxis from IV thiamine is very rare.

Can I get enough from food?⌄

Yes, easily, if you eat a varied diet including whole grains, pork, beans, and fortified cereals. Strict whole-food vegan diets, very low-carb diets without adequate variety, or alcohol use may increase risk.

References

NIH Office of Dietary Supplements - Thiamin — ODS link
Wikidata: Thiamine — Wikidata link
PubChem: Thiamine (CID 1130) — PubChem link

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Disclaimer: These statements have not been evaluated by the FDA. This page is educational, not a substitute for personalized medical advice. Evidence grades are AI-assisted assessments — talk to your doctor before starting any new supplement, especially if you're pregnant, breastfeeding, on medications, or managing a chronic condition.