Evidence-based·Last reviewed May 30, 2026·How we grade evidence

Vitamin B1

Vitamin

Useful mainly for preventing and treating thiamine deficiency, including in alcohol use and malabsorption.

Quick decision guide

May help most

Preventing and treating thiamine deficiency, including in alcohol use and malabsorption

Common dosing range

1.1–1.2 mg/day RDA; 50–300 mg therapeutically

When to expect effects

Hours to days in deficiency

Watch out for

Acute Wernicke's encephalopathy is a medical emergency needing supervised IV thiamine

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.

Is it worth it for you?

Use this as a quick fit check, not a diagnosis.

Worth considering if…

You are at risk of deficiency (alcohol use, malabsorption, bariatric surgery)
You need repletion for a deficiency state
You take long-term loop diuretics

Probably skip if…

You are well-nourished and expect an energy boost
You expect benefit for fatigue at adequate status
You think oral dosing replaces emergency IV care for Wernicke's

Evidence at a glance

beriberi prevention and treatment

Strong Evidence
Effect
Resolves deficiency disease
Best fit
People with or at risk of thiamine deficiency
Time
Hours to days

wernicke-korsakoff syndrome

Strong Evidence
Effect
Prevents and treats the syndrome
Best fit
People with chronic alcohol use or severe malnutrition at risk
Time
Hours to days with adequate dosing

cardiac function in thiamine deficiency

Limited Evidence
Effect
Improves cardiac function when deficiency is present
Best fit
People with heart failure plus thiamine deficiency (e.g., long-term diuretic use)
Time
Days to weeks

diabetic complications

Limited Evidence
Effect
Marker-level changes
Best fit
People with diabetes exploring thiamine or benfotiamine, often with low thiamine status
Time
Weeks

Evidence for 4 uses

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

beriberi prevention and treatment

Corrects deficiency
Strong Evidence

Thiamine is an essential cofactor for carbohydrate-metabolizing enzymes, and its deficiency causes beriberi affecting the nerves and heart. Repletion prevents and treats beriberi, often with rapid clinical improvement.

Effect size
Resolves deficiency disease
Time to effect
Hours to days
Best fit
People with or at risk of thiamine deficiency

Bottom line: Definitively prevents and treats beriberi from thiamine deficiency.

SourceSmith et al., 2021 — PMCOverton et al., 2025 — PMC

wernicke-korsakoff syndrome

Corrects deficiency
Strong Evidence

Thiamine deficiency, common in chronic alcohol use, causes Wernicke's encephalopathy, which can progress to Korsakoff syndrome. Prompt high-dose thiamine, given intravenously in the acute setting, prevents and treats it and is standard care.

Effect size
Prevents and treats the syndrome
Time to effect
Hours to days with adequate dosing
Best fit
People with chronic alcohol use or severe malnutrition at risk

Bottom line: Standard, effective treatment and prevention for Wernicke-Korsakoff; acute cases need IV dosing.

SourceChandrakumar et al., 2018 — PubMedLatt et al., 2014 — PubMed

cardiac function in thiamine deficiency

Corrects deficiency
Limited Evidence

In thiamine-deficient patients, including some on long-term loop diuretics, supplementation can improve cardiac function and symptoms of high-output (wet) beriberi. Benefit is tied to correcting deficiency rather than a general heart-failure therapy.

Effect size
Improves cardiac function when deficiency is present
Time to effect
Days to weeks
Best fit
People with heart failure plus thiamine deficiency (e.g., long-term diuretic use)
Less likely
Thiamine-replete people with heart failure

Bottom line: Improves cardiac function specifically when thiamine deficiency is present.

SourceSmithline et al., 2019 — PMCSchoenenberger et al., 2012 — PubMed

diabetic complications

Biomarker support
Limited Evidence

Thiamine and the lipid-soluble derivative benfotiamine have been studied for diabetic complications such as neuropathy and nephropathy, with some studies showing changes in biochemical markers. Clinical benefit is inconsistent and not established.

Effect size
Marker-level changes
Time to effect
Weeks
Best fit
People with diabetes exploring thiamine or benfotiamine, often with low thiamine status

Bottom line: Possible biomarker effects in diabetic complications, but clinical benefit is unproven.

Evidence is mixed

Trials of thiamine and benfotiamine for diabetic neuropathy and nephropathy report mixed results, with marker changes not reliably matched by symptom improvement.

SourceAlkhalaf et al., 2010 — PMC· conflicting
SourceAlkhalaf et al., 2010 — PMC

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.

How to take it

1. Typical dose
1.1–1.2 mg/day RDA; 50–300 mg/day orally for deficiency or specific conditions
2. Timing
Any time of day
3. With food
With or without food; food may improve tolerance
4. How long to try
Ongoing for at-risk groups; per clinician for therapy

What to track

Neurological symptoms in deficiency
Energy and appetite during repletion
Adherence in at-risk states

4 commercial forms

Compare the main delivery options and what they’re best suited for.

Thiamine HCl

Most common form in multivitamins and B-complex supplements.

Standard, well-absorbed form; widely available.

Thiamine mononitrate

Common in fortified foods and supplements.

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

Benfotiamine

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

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

Allithiamine

Less common in supplements than benfotiamine.

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

Safety

Know the common side effects, key cautions, and who should avoid it.

Common side effects

Very rare with oral use

Serious risks

  • Rare anaphylaxis with high-dose IV thiamine

Who should avoid it

  • No specific contraindications for oral use

Pregnancy & breastfeeding

Needs are slightly higher in pregnancy and breastfeeding; adequate intake should be ensured.

Interactions

Loop diuretics (e.g., furosemide)Moderate

Increase thiamine excretion and can cause deficiency with long-term use

AlcoholModerate

Impairs thiamine absorption and metabolism, raising deficiency risk

LevodopaMinor

Levodopa absorption may be affected by high-dose thiamine

Documented interactions

Evidence-graded pair pages with sources, dosing notes, and timing guidance — a complement to the narrative section above.

Warnings (1)

+ coffee

low

Coffee and tea were historically labeled antithiamine beverages, but later biochemistry walked the claim back: chlorogenic and caffeic acids do not destroy thiamine under physiological conditions, and the real activity comes from polyphenol oxidation products and tannins, which are lower in coffee than tea. The net effect on thiamine status is modest and unlikely to matter for well-nourished people; it becomes relevant only on a marginal diet or in groups already prone to deficiency.

Beneficial pairs (1)

+ magnesium

synergy

Magnesium is the cofactor that converts thiamine (vitamin B1) into its active coenzyme form, thiamine pyrophosphate (TPP). When magnesium is low, thiamine cannot activate fully, so a thiamine supplement may produce little benefit until magnesium status is restored. The two work together rather than against each other.

See all 2 Vitamin B1 interactions →

Food sources

Fortified breakfast cereals

Amount
1 serving
%DV
100%

Pork (lean)

Amount
3 oz
%DV
56%

Black beans

Amount
1/2 cup cooked
%DV
35%

Yogurt (plain)

Amount
1 cup
%DV
9%

Brown rice

Amount
1 cup cooked
%DV
15%

Sunflower seeds

Amount
1 oz
%DV
35%

Tuna

Amount
3 oz
%DV
19%

Whole wheat bread

Amount
1 slice
%DV
8%

Choosing a product

What to look for on the label — and what to be skeptical of.

Look for…

Form stated (thiamine HCl, mononitrate, or benfotiamine)
Dose matched to goal (RDA vs therapeutic)

Be skeptical of…

Energy booster for healthy people
Cures neuropathy
Detoxifies the body

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 by claim

beriberi prevention and treatment

Smith et al., 2021 — PMC (2021) link

Overton et al., 2025 — PMC (2025) link

wernicke-korsakoff syndrome

Chandrakumar et al., 2018 — PubMed (2018) link

Latt et al., 2014 — PubMed (2014) link

cardiac function in thiamine deficiency

Smithline et al., 2019 — PMC (2019) link

Schoenenberger et al., 2012 — PubMed (2012) link

diabetic complications

Alkhalaf et al., 2010 — PMC (2010) link

Track Vitamin B1 with Pilora

Set up dose reminders, check interactions, and join the community in the Pilora iPhone app.

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Evidence-based·Last reviewed May 30, 2026·Evidence current as of May 30, 2026·How we grade evidence

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.