What is Vitamin B1 (thiamine) used for?

Vitamin B1 (thiamine) helps convert carbohydrates into energy and supports normal nerve and heart function. It is also used to prevent or treat thiamine deficiency.

What are common signs of thiamine deficiency?

Deficiency can cause fatigue, weakness, numbness or tingling, and problems with coordination. Severe deficiency may lead to beriberi or Wernicke-Korsakoff syndrome.

What foods are high in thiamine?

Good sources include whole grains and fortified cereals, legumes, pork, nuts, and seeds. Cooking and processing can reduce thiamine content in some foods.

How much thiamine should adults take daily?

Typical recommended intakes are about 1.1 mg/day for adult women and 1.2 mg/day for adult men. Needs can be higher in certain medical situations under clinician guidance.

Is thiamine safe to take as a supplement?

Thiamine is water-soluble and is generally well tolerated at common supplemental doses. People with medical conditions or those taking multiple medications should consult a clinician for personalized advice.

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Vitamin B1
(Thiamine)

Strong study situation·10/10

A higher score indicates better study conditions, but not necessarily effectiveness.

A water-soluble vitamin essential for energy metabolism, nerve, and heart function.

Cardiovascular Support Cognitive Enhancement Essential Nutrient Glucose Metabolism Neuroprotective Energy Support

dose range

1.1–1.2 mg

Once daily

Consumption

Take with food to enhance absorption.

Not fat-soluble.

Best time

Best taken with meals; special forms (benfotiamine) may be used for specific conditions under supervision.

Description

Vitamin B1 (thiamine) is a crucial B vitamin needed to convert food into cellular energy (ATP) and support nerve signaling and cardiovascular health. Deficiency can cause neurological and cardiac problems, but adequate intake is easily achieved via a balanced diet or supplementation.

benefits

Main effects with level of evidence

Strong

Note on evidence

Role in energy metabolism and neurological function is well-established; benefits for heart failure when deficient are supported by clinical studies.

Supports energy production

Strong

Acts as a cofactor for enzymes in glucose metabolism, allowing efficient conversion of carbohydrates into energy and helping prevent fatigue.

Particularly relevant for: Athletes · Vegetarians · Individuals with high carbohydrate intake

1 · NIH Office of Dietary Supplements: Thiamin Fact Sheet 3 · Examine.com: Thiamine 4 · Linus Pauling Institute: Thiamin

Promotes nerve and brain health

Strong

Essential for nerve impulse transmission and neurotransmitter synthesis; supports mental function and mood stability. Severe deficiency can cause serious neurological syndromes.

Particularly relevant for: Older adults · Alcohol users · At-risk populations

1 · NIH Office of Dietary Supplements: Thiamin Fact Sheet 2 · MedlinePlus: Thiamine (Vitamin B1)4 · Linus Pauling Institute: Thiamin

Supports cardiovascular function

Moderate

Key for normal heart function; supplementation may improve heart function in deficiency (e.g., heart failure or beriberi).

Particularly relevant for: Older adults · People with heart failure · Alcohol users

1 · NIH Office of Dietary Supplements: Thiamin Fact Sheet 4 · Linus Pauling Institute: Thiamin 8 · UpToDate: Overview of vitamin B1 (thiamine)

Assists glucose metabolism and may help in diabetic states

Limited

Helps control blood sugar metabolism and may reduce risk of complications related to hyperglycemia, mainly in deficiency or with special thiamine forms.

Particularly relevant for: People with diabetes or prediabetes

1 · NIH Office of Dietary Supplements: Thiamin Fact Sheet 3 · Examine.com: Thiamine 4 · Linus Pauling Institute: Thiamin

Safety & Information

Important safety information & known risks

For educational purposes only • not medical advice

Thiamine is very safe at nutritional and moderate supplemental doses; serious adverse effects are rare.

warning notices

No tolerable upper intake level established as excess is excreted in urine.
Mild reactions (rash or GI discomfort) are extremely rare at high oral doses.
Risk of allergic reaction exists mainly with injectable forms.
High-dose supplementation should be supervised for individuals with kidney failure or on dialysis.
Do not use high-dose thiamine supplements without physician supervision if you have end-stage kidney disease or are on dialysis.
Seek medical advice before use if you have a known allergy to thiamine or its injection components.

Known interactions with medications

Loop diuretics
5-fluorouracil

Contraindications / special precautions

Known allergy to thiamine or injection constituents
End-stage kidney disease or dialysis patients (without supervision)

interactions

Important interactions between active ingredient ↔ supplement / medication / food

Few clinically significant interactions, but some considerations for people with certain medications or health conditions.

Loop diuretics (e.g., furosemide) can increase thiamine loss.

drug · loop diuretics

MonitorModerate

Why

They increase urinary excretion of thiamine, potentially causing deficiency, especially in heart failure or kidney patients.

recommendation

Monitor thiamine status or supplement if at risk.

1 · NIH Office of Dietary Supplements: Thiamin Fact Sheet 8 · UpToDate: Overview of vitamin B1 (thiamine)

5-fluorouracil may inhibit thiamine phosphorylation.

drug · 5-fluorouracil

CautionLimited

Why

May impair conversion of thiamine to its active form, increasing deficiency risk.

recommendation

Clinician should monitor for deficiency.

1 · NIH Office of Dietary Supplements: Thiamin Fact Sheet 4 · Linus Pauling Institute: Thiamin

mechanisms of action

Brief explanations of how it works

Enzyme cofactor for carbohydrate metabolism

Thiamine acts as a coenzyme for pyruvate dehydrogenase and other enzymes involved in glycogen and energy production.

1 · NIH Office of Dietary Supplements: Thiamin Fact Sheet 3 · Examine.com: Thiamine 4 · Linus Pauling Institute: Thiamin

Regulates nerve signaling

Required for synthesis of acetylcholine and conductance of nerve impulses, explaining its neurological importance.

1 · NIH Office of Dietary Supplements: Thiamin Fact Sheet 4 · Linus Pauling Institute: Thiamin

Supports heart muscle energy needs

Provides energy for cardiac muscle contraction and overall function.

1 · NIH Office of Dietary Supplements: Thiamin Fact Sheet 8 · UpToDate: Overview of vitamin B1 (thiamine)

Sources & References

Primary literature and reviews on which these statements are based

8 sources

NIH Office of Dietary Supplements: Thiamin Fact Sheet

MedlinePlus: Thiamine (Vitamin B1)

Examine.com: Thiamine

Linus Pauling Institute: Thiamin

NHS: Thiamine (Vitamin B1)

Mount Sinai: Vitamin B1 (Thiamine)

WebMD: Thiamine (Vitamin B1)

UpToDate: Overview of vitamin B1 (thiamine)

Last updated: August 16, 2026

This information is for educational purposes only and does not replace medical advice.

All nutrients

Vitamin B1
(Thiamine)

Description

benefits

Supports energy production

Promotes nerve and brain health

Supports cardiovascular function

Assists glucose metabolism and may help in diabetic states

Safety & Information

interactions

Loop diuretics (e.g., furosemide) can increase thiamine loss.

5-fluorouracil may inhibit thiamine phosphorylation.

mechanisms of action

Enzyme cofactor for carbohydrate metabolism

Regulates nerve signaling

Supports heart muscle energy needs

Sources & References

Vitamins & Vitaminoids

Other categories

Safety & Information

interactions

Loop diuretics (e.g., furosemide) can increase thiamine loss.

5-fluorouracil may inhibit thiamine phosphorylation.

mechanisms of action

Enzyme cofactor for carbohydrate metabolism

Regulates nerve signaling

Supports heart muscle energy needs

Sources & References

Vitamin B1(Thiamine)

Description

benefits

Supports energy production

Promotes nerve and brain health

Supports cardiovascular function

Assists glucose metabolism and may help in diabetic states

Safety & Information

interactions

Loop diuretics (e.g., furosemide) can increase thiamine loss.

5-fluorouracil may inhibit thiamine phosphorylation.

mechanisms of action

Enzyme cofactor for carbohydrate metabolism

Regulates nerve signaling

Supports heart muscle energy needs

Sources & References

Vitamins & Vitaminoids

Other categories

Safety & Information

interactions

Loop diuretics (e.g., furosemide) can increase thiamine loss.

5-fluorouracil may inhibit thiamine phosphorylation.

mechanisms of action

Enzyme cofactor for carbohydrate metabolism

Regulates nerve signaling

Supports heart muscle energy needs

Sources & References

Vitamin B1
(Thiamine)