Vitamins & Supplements · Vitamin
Vitamin B1 (thiamin)
Thiamine · also called Thiamin, thiamine, vitamin B1
Thiamin is a B vitamin that helps your cells turn carbohydrate into energy and keeps nerves working. The best-supported use is treating or preventing a real lack, which can cause beriberi and brain damage. For people who already get enough, trials have not shown clear benefits. The key caution is that confusion, poor balance or breathlessness need urgent medical care.
General information, not medical advice. Last substantive update · Not medically reviewed. A named clinician has not signed off on this page. How this page is made
About Vitamin B1 (thiamin)
Thiamin (vitamin B1) is an essential B vitamin. It helps cells turn carbohydrate into energy and supports nerves and muscles. Most people get it from food. Real deficiency is treatable and serious. Extra thiamin has not been shown to help people who already get enough.
What it is
Thiamin, also called thiamine or vitamin B1, is a water-soluble B vitamin. MedlinePlus says it helps the body's cells change carbohydrates into energy, especially for the brain and nervous system, and plays a role in muscle contraction and in conducting nerve signals. The NHS says thiamin cannot be stored in the body, so you need it in your diet every day.
Benfotiamine is a fat-soluble derivative used in some trials. It is not the same as plain thiamin.
We read nothing on how thiamin was discovered, so this page does not cover its history.
Food sources
MedlinePlus names enriched, fortified and whole grain bread, cereals, rice, pasta and flour, wheat germ, beef and pork, trout and bluefin tuna, eggs, legumes and peas, and nuts and seeds. The NHS also lists some fresh fruits such as bananas and oranges, wholegrain breads and fortified breakfast cereals.
Saved USDA data (unenriched foods, USDA portions): 1 cup of dried sunflower seed kernels about 2.07 mg; 1 cup of wheat germ about 2.16 mg; 1 cup of cooked black beans about 0.42 mg; 1 cup of raw green peas about 0.39 mg; 1 cup of cooked long-grain brown rice about 0.36 mg; 1 cup of cooked lentils about 0.33 mg; 1 ounce of raw peanuts about 0.18 mg. We had no USDA numbers for meat or fish.
Reference intakes set by the National Academies, as given by MedlinePlus: adult women 1.1 mg and men 1.2 mg a day, 1.4 mg during pregnancy and breastfeeding. The NHS gives 1 mg (men) and 0.8 mg (women) for UK adults. These are the regulators' numbers, not advice for you. Food sources differ from pills, and enriched products and brands vary, so read labels.
What the research shows
Deficiency: thiamine is the accepted treatment for beriberi and Wernicke encephalopathy, and a 2010 guideline says it should be given before carbohydrate, preferably into a vein by a clinician. A Cochrane review found only two trials and called the evidence insufficient to guide dose or route.
Fatigue: in a 40-person crossover trial in quiet IBD, high-dose oral thiamine lowered fatigue by 4.5 points against a 0.75 point rise on placebo (P = 0.0003). It has not been tested the same way in healthy people.
Memory: a 70-person benfotiamine trial did not reach significance on its main memory test (p = 0.125). A secondary measure favoured benfotiamine (p = 0.034).
Heart failure: a review of 8 trials and 384 people found no benefit. Septic shock: the main outcome of an 88-person trial was not met (P = 0.07). Nerve damage in diabetes: Cochrane called the evidence insufficient. Painful periods: one trial of vitamin B1 alone found lower pain, within a review that rates all evidence low or very low.
Food versus supplements
Food gives thiamin alongside other nutrients. The trials on this page used thiamine pills or injections, or benfotiamine, so their results do not apply to food. Several used amounts many times higher than food provides. Ask a doctor or pharmacist before taking supplements.
At a glance
Traditional uses history, not proof
- Eaten in food for as long as people have eaten grains, seeds, beans and meat
- Long use in food is not proof that supplements treat any condition
Studied for research
- Correcting a deficiency (beriberi, Wernicke encephalopathy), low certainty in trials but accepted clinical practice
- Fatigue in quiet inflammatory bowel disease, low certainty (one small trial)
- Memory and thinking in mild Alzheimer disease (benfotiamine), very low certainty
- Heart failure and septic shock, not enough evidence
- Nerve damage in diabetes and painful periods, very low certainty
Main compounds
- Thiamin (thiamine)
- Thiamine diphosphate (blood form)
- Benfotiamine (a fat-soluble derivative used in some trials)
Common forms
- Food sources: whole and enriched grains, seeds, legumes, pork, fish
- Thiamine supplements (tablets, injections given by clinicians)
- Benfotiamine and B-complex products are different products and are not covered as plain thiamin
Research links: 2010 guideline: Wernicke encephalopathy · 2022 review: thiamine in heart failure (8 trials) · 2021 trial: high-dose thiamine for fatigue in IBD · Research Library · Genes & Biomarkers Library
What it is and its history
- Accepted scientific name
- Thiamin (thiamine), vitamin B1. A nutrient, not a species.
- Common names
- Thiamin (English (US)); Thiamine (English (UK)); Vitamin B1 (English)
- Family or group
- Water-soluble B vitamin
- Harvest and processing
- Not covered. MedlinePlus lists enriched, fortified and whole grain products among food sources.
- Look-alikes and adulterants
- Name: Benfotiamine; Note: A lipid-soluble thiamine derivative (the 1996 trial abstract calls it an allithiamine) used in the nerve and Alzheimer trials; not the same as plain thiamin.; Name: Other B vitamins; Note: Thiamin is one of the B vitamins; the NHS covers them on one page.
What is inside, and how it may work
What it contains and how those compounds act in cells and animals. Laboratory and animal mechanisms are not proven effects in people.
Main compounds
| Compound | Family | Where it is concentrated | Activity studied | Level of evidence |
|---|---|---|---|---|
| Thiamin (thiamine) | vitamin | See food amounts in the nutrition note. | Helps cells turn carbohydrate into energy and supports muscle contraction and nerve signals (MedlinePlus). 18 | Human data |
| Thiamine diphosphate | vitamin (active form) | Measured in whole blood in one heart failure study. | A blood form of thiamine that was measured by chromatography in the Mayo clinic study. 12 | Human data |
| Benfotiamine | thiamine derivative | Supplement only. | Described as a lipid-soluble derivative of vitamin B1 with high bioavailability; tested in nerve and Alzheimer trials. 11 5 | Human data |
Mechanisms, receptors and pathways
| Target or pathway | Gene or receptor | What was found | Level |
|---|---|---|---|
| Carbohydrate to energy (pyruvate metabolism) | Not specified in the sources read | MedlinePlus says thiamin helps cells change carbohydrates into energy and is essential for the metabolism of pyruvate. 18 | Human data |
| Nerve signals and muscle contraction | Not specified in the sources read | MedlinePlus names a role in muscle contraction and in conduction of nerve signals. 18 | Human data |
| Loss in urine with loop diuretics | Not specified | A review suggests increased urine flow and possible direct block of cellular uptake by furosemide. 6 | Human data |
Absorption, metabolism and elimination
- Absorption
- MedlinePlus says heavy alcohol use makes it hard for the body to absorb thiamin from food.
- Distribution
- Not found.
- Metabolism
- Not found beyond its role in pyruvate metabolism.
- Elimination
- A review links loop diuretics to more thiamin loss in urine.
- Bioavailability
- Benfotiamine is described as a lipid-soluble form with high bioavailability in one abstract; not compared with plain thiamin here.
Isolated compounds versus whole extracts
Food sources of thiamin (whole grains, seeds, legumes) come with other nutrients and are the main way most people get it. The trials here used thiamine pills or injections, or benfotiamine, so their results do not transfer to food. Thiamin cannot be stored in the body (NHS), so it comes from food every day.
Nutritional composition
Reference intakes (MedlinePlus): adults aged 19 and over, women 1.1 mg and men 1.2 mg a day, 1.4 mg a day during pregnancy and lactation; infants 0.2 mg (0 to 6 months, adequate intake) and 0.3 mg (7 to 12 months); children 0.5 mg (1 to 3 years), 0.6 mg (4 to 8), 0.9 mg (9 to 13). The NHS gives 1 mg (men) and 0.8 mg (women) for UK adults 19 to 64. Foods named by MedlinePlus: enriched, fortified and whole grain bread, cereals, rice, pasta and flour, wheat germ, beef steak and pork, trout and bluefin tuna, egg, legumes and peas, nuts and seeds. The NHS adds some fresh fruits (such as bananas and oranges), wholegrain breads and fortified breakfast cereals. Amounts from saved USDA FoodData Central data (SR Legacy, April 2018 release; USDA portions, worked out from per-100 g values): sunflower seed kernels, dried, 1 cup (140 g) about 2.07 mg (1.48 mg per 100 g); wheat germ, crude, 1 cup (115 g) about 2.16 mg (1.882 per 100 g); cooked black beans, 1 cup (172 g) about 0.42 mg (0.244 per 100 g); raw green peas, 1 cup (145 g) about 0.39 mg (0.27 per 100 g); long-grain brown rice, cooked, 1 cup (202 g) about 0.36 mg (0.178 per 100 g); cooked lentils, 1 cup (198 g) about 0.33 mg (0.169 per 100 g); raw peanuts, 1 oz (28.35 g) about 0.18 mg (0.64 per 100 g). These are unenriched foods as listed; enriched or fortified products differ and brands vary, so read labels. We did not have USDA numbers for meat or fish. These numbers describe foods and are not advice on how much to eat.
2 low certainty3 very low certainty2 not enough evidence
What was looked at
The 7 benefits and uses checked for Vitamin B1 (thiamin), each with how strong the evidence is. Tap one to open it.
- Correcting thiamin deficiency (beriberi, Wernicke encephalopathy)Low certainty
- Memory and thinking in mild Alzheimer disease (benfotiamine)Very low certainty
- Chronic fatigue in quiet inflammatory bowel disease (high-dose thiamine)Low certainty
- Heart failureNot enough evidence
- Septic shock (hospital use)Not enough evidence
- Nerve damage in diabetes or alcohol use (benfotiamine and B vitamins)Very low certainty
- Painful periods (dysmenorrhoea)Very low certainty
Lab markers tracked in the studies
Blood thiamine (total thiamine)Fatigue score (IBD-Fatigue Questionnaire)Memory and thinking score (ADAS-Cog)Clinical Dementia Rating (CDR)Left ventricular ejection fraction (LVEF)Serum creatinine (kidney marker)Nerve conduction velocityPeriod pain score (0 to 10 scale)
What is Vitamin B1 (thiamin) good for?
What trials found for each studied use and how strong the evidence is. Most uses are for people who are lacking thiamin or have a specific illness, and several trials used very high doses or a different form, benfotiamine.
Benefits, one by one
Each card is a research question, not a promise. Tap a goal to filter. Open a card to see the studies, doses and limits.
Correcting thiamin deficiency (beriberi, Wernicke encephalopathy)
Low certaintyThiamin is the accepted treatment for thiamin deficiency, including beriberi and the brain condition Wernicke encephalopathy. Official pages and a guideline say so. But there are almost no good randomised trials, and the best review found them too few to say what amount, route or length of treatment works best. This is about people who are lacking thiamin, not people who eat well.
4 studiesThiamine given by injection or by mouth by clinicians. No amounts are…
Studies, doses and limits
What the trials found
The EFNS guideline (2010) says thiamine is indicated for suspected or manifest Wernicke encephalopathy, given before any carbohydrate and preferably into a vein, and rates the overall safety of thiamine as very good. MedlinePlus says beriberi is treated with thiamine by injection or by mouth, and that symptoms usually improve quickly, heart damage is usually reversible, and nerve damage is reversible if caught early. A Cochrane review found only two randomised trials; only one had usable data (107 people) and it could not settle dose, route or duration.
Results
A well-accepted use for people who are deficient, based on guidelines and long clinical practice rather than strong trial evidence. It does not show a benefit for people with enough thiamin.
Effect sizes as reported
Cochrane: in one 107-person trial, 200 mg a day beat 5 mg a day on one memory test (mean difference -17.90, 95% CI -35.4 to -0.40, P = 0.04); other comparisons were not significant.
Why this rating
Low as trial evidence. Clinical practice and a guideline support it (the guideline levels are mostly C), but randomised trials are almost absent. This rating is about the strength of trial evidence, not about whether deficiency needs treatment: it does, and a clinician should do it.
Form and dose studied
Thiamine given by injection or by mouth by clinicians. No amounts are advised here.
Who was studied
People who are deficient or at risk, mainly with heavy alcohol use, after bariatric surgery, or with severe vomiting.
Limits
Almost no randomised trials. The guideline is from 2010. Wernicke encephalopathy is an emergency and is not something to treat at home.
Why researchers looked
Severe lack of thiamin damages nerves, brain and heart. People who drink heavily, have had weight-loss surgery, are on dialysis, or have severe vomiting are most at risk.
Traditional use
Thiamin has been eaten as part of ordinary food forever. Food use is not proof that supplements treat any condition.
Proposed mechanism Authoritative guidance
Thiamin helps cells turn carbohydrate into energy (MedlinePlus). Without it the brain and nerves, which rely on that energy, are harmed first.
A proposed mechanism does not show that the effect happens in people.
Wernicke encephalopathy needs urgent medical care. See the Safety tab for warning signs.
Memory and thinking in mild Alzheimer disease (benfotiamine)
Very low certaintyOne small 12-month trial of 70 people with mild memory loss or mild Alzheimer disease tested benfotiamine, a fat-soluble form of thiamin. Worsening on the main memory test was 43% lower, but that was not statistically significant. A secondary measure (CDR) was lower by 77% (p = 0.034). It is early research and the form is not plain thiamin.
1 studiesBenfotiamine, taken by mouth for 12 months. The amount is not stated …
Studies, doses and limits
What the trials found
In a randomised placebo-controlled phase IIa trial, 34 people got benfotiamine and 36 placebo for 12 months. The primary measure, ADAS-Cog, rose (worsened) 43% less with benfotiamine (p = 0.125, not significant). CDR worsening was 77% lower (p = 0.034), blood AGE rises were smaller (p = 0.044), and a brain-scan pattern differed (p = 0.002, exploratory). The authors say it was safe.
Results
Preliminary and uncertain. The main result did not reach significance. No trial has shown that ordinary thiamin protects memory in people who are not deficient.
Effect sizes as reported
ADAS-Cog worsening 43% lower (p = 0.125); CDR worsening 77% lower (p = 0.034); AGE p = 0.044.
Why this rating
Very low. One small phase IIa trial, the primary outcome was not significant, the other findings were secondary or exploratory, and the product was benfotiamine, not thiamin.
Form and dose studied
Benfotiamine, taken by mouth for 12 months. The amount is not stated in the abstract.
Who was studied
People with amnestic mild cognitive impairment or mild dementia due to Alzheimer disease.
Limits
70 people. Benfotiamine is a derivative and may behave differently from thiamin. Research support from NIH is listed.
Why researchers looked
Lab studies in animals suggested benfotiamine could help the brain handle sugar and reduce Alzheimer-type changes, so a small human trial was run.
Traditional use
Thiamin has been eaten as part of ordinary food forever. Food use is not proof that supplements treat any condition.
Proposed mechanism Hypothesis
The trial authors cite animal and lab work on plaques, tangles, sugar use in the brain and advanced glycation end products (AGE). That is a hypothesis; the abstract does not prove it works this way in people.
A proposed mechanism does not show that the effect happens in people.
The authors report no safety concerns in this trial. Ask a doctor before using any supplement for memory loss.
Chronic fatigue in quiet inflammatory bowel disease (high-dose thiamine)
Low certaintyIn a 40-person crossover trial of people with inflammatory bowel disease (IBD) who were in remission but very tired, high-dose thiamine lowered fatigue scores more than placebo. The doses were far above food amounts. It has not been shown for fatigue in people without IBD.
1 studiesOral thiamine, 600 to 1800 mg a day set by sex and weight in the tria…
Studies, doses and limits
What the trials found
In a randomised, double-blind, placebo-controlled crossover trial, 40 adults took high-dose oral thiamine for 4 weeks and placebo for 4 weeks, with a washout between. Fatigue fell by a mean 4.5 points on thiamine and rose by 0.75 on placebo (P = 0.0003). A 3-point improvement or more was seen in 55% and 75% of the two groups on thiamine against 25% and 35% on placebo. Only mild side effects.
Results
A promising but small result in one condition. It does not show that thiamin raises energy in healthy people, and the thiamine-fatigue link is not tested in people without IBD.
Effect sizes as reported
Mean fatigue score change -4.5 (95% CI 2.6 to 6.2 reduction) on thiamine vs +0.75 (95% CI -1.3 to 2.8) on placebo; P = 0.0003.
Why this rating
Low. One randomised, double-blind trial, but only 40 people, 4 weeks per arm, a symptom questionnaire, and very high doses in one condition.
Form and dose studied
Oral thiamine, 600 to 1800 mg a day set by sex and weight in the trial (trial dose, not advice).
Who was studied
Adults with quiescent IBD and severe chronic fatigue with no other explanation.
Limits
Small, short, one condition. Needs repeating by independent teams.
Why researchers looked
An earlier open-label pilot suggested high-dose thiamine eased fatigue in IBD, so a placebo-controlled trial followed.
Traditional use
Thiamin has been eaten as part of ordinary food forever. Food use is not proof that supplements treat any condition.
Proposed mechanism Hypothesis
Not shown in the abstract. The authors do not give a tested explanation.
A proposed mechanism does not show that the effect happens in people.
Only mild side effects in the trial. The doses are far above food amounts; ask your gastroenterologist before trying them.
Heart failure
Not enough evidenceA 2022 review of 8 trials (384 people) found no evidence that thiamine supplements help heart failure. Some measures looked promising in single trials, but pooled results did not show a benefit. Heart failure from severe thiamin lack (wet beriberi) is a different problem.
3 studiesThiamine supplements of varied amounts across the trials.
Studies, doses and limits
What the trials found
The meta-analysis of 8 randomised trials found no significant change in left ventricular ejection fraction in chronic heart failure (mean difference -0.19, 95% CI -2.78 to 0.96 as printed), and no improvement in NYHA class, BNP, thiamine status, symptoms or quality of life. Acute heart failure also showed no improvement. A Mayo clinic study of 30 stable outpatients estimated deficiency prevalence below 11.6% and found no link between diuretic dose and thiamine level.
Results
No benefit shown overall. The authors say larger, better trials are needed.
Effect sizes as reported
LVEF mean difference -0.19 (95% CI -2.78 to 0.96), not significant.
Why this rating
Insufficient. Small trials, mixed results and no pooled benefit, with the authors calling for larger trials. This is a gap in evidence, not proof of no effect.
Form and dose studied
Thiamine supplements of varied amounts across the trials.
Who was studied
People with chronic or acute heart failure, often on loop diuretics.
Limits
Small trials, I2 = 49%. The Mayo study was only 30 people.
Why researchers looked
Water pills (loop diuretics) used in heart failure may lower thiamin, and thiamin deficiency can itself affect the heart.
Traditional use
Thiamin has been eaten as part of ordinary food forever. Food use is not proof that supplements treat any condition.
Proposed mechanism Hypothesis
Reviews suggest loop diuretics increase thiamin loss in urine and may block its uptake into cells. Whether fixing that helps the heart is not shown.
A proposed mechanism does not show that the effect happens in people.
Do not stop or change heart medicines. Ask your cardiologist before taking thiamin.
Septic shock (hospital use)
Not enough evidenceIn an 88-person hospital trial of septic shock, thiamine did not significantly change the main kidney marker (creatinine) at 72 hours. Patients on thiamine had more ICU-free days, a secondary result. This is a hospital treatment question and not about everyday supplements.
1 studiesThiamine given by a hospital team; the abstract does not give the amo…
Studies, doses and limits
What the trials found
In the randomised, placebo-controlled TRPSS trial, 88 patients (42 thiamine, 46 placebo) showed no significant difference in creatinine change at 72 hours (mean difference -0.57 mg/dl; 95% CI -1.18 to 0.04; P = 0.07). Kidney replacement therapy, severe kidney injury and mortality also did not differ significantly. ICU-free days were higher with thiamine (median 22.5 vs 0.0, P < 0.01).
Results
The main outcome was not met. A secondary result favoured thiamine, so this is an open question.
Effect sizes as reported
Creatinine change -0.57 mg/dl (95% CI -1.18 to 0.04), P = 0.07; mortality 35.7% vs 54.3% (P = 0.14).
Why this rating
Insufficient. One 88-person trial missing its primary outcome, in a critical-illness setting.
Form and dose studied
Thiamine given by a hospital team; the abstract does not give the amount.
Who was studied
Adults with septic shock in hospital.
Limits
Small trial in critically ill patients. Not relevant to supplements for healthy people.
Why researchers looked
People with septic shock are often low in thiamine, and researchers wondered whether replacing it would protect the kidneys.
Traditional use
Thiamin has been eaten as part of ordinary food forever. Food use is not proof that supplements treat any condition.
Proposed mechanism Hypothesis
The trial authors propose that thiamine helps cell energy production (mitochondria). That is a hypothesis not tested in the abstract.
A proposed mechanism does not show that the effect happens in people.
Septic shock is an emergency treated in hospital.
Nerve damage in diabetes or alcohol use (benfotiamine and B vitamins)
Very low certaintyA Cochrane review of 13 small trials (741 people) found the evidence too limited to say whether vitamin B helps nerve damage. One small 24-person trial of benfotiamine combined with B6 and B12 found better nerve conduction after 12 weeks. Combination products and benfotiamine are not plain thiamin.
2 studiesBenfotiamine or vitamin B-complex products; the combination trial can…
Studies, doses and limits
What the trials found
Cochrane (13 studies, 741 people with alcoholic or diabetic neuropathy): two small trials of vitamin B versus placebo showed no significant short-term pain benefit; one showed a small benefit in vibration detection with oral benfotiamine for eight weeks. The authors conclude evidence is insufficient to say whether vitamin B helps or harms. A separate double-blind trial of 24 people with diabetic polyneuropathy used benfotiamine plus B6/B12 for 12 weeks and found peroneal nerve conduction velocity improved (p = 0.006); no therapy-specific side effects were seen.
Results
Unclear. Small, old trials of combination products.
Effect sizes as reported
Nerve conduction velocity (peroneal) improved, p = 0.006 (24 people, combination product).
Why this rating
Very low. Small, mixed trials, a 1996 combination-product trial, and a Cochrane conclusion of insufficient evidence.
Form and dose studied
Benfotiamine or vitamin B-complex products; the combination trial cannot separate thiamine from B6 and B12.
Who was studied
People with diabetic or alcoholic peripheral neuropathy.
Limits
Different products, small numbers, searches to 2005 in the review.
Why researchers looked
Thiamin deficiency damages nerves, and benfotiamine, a fat-soluble derivative, was tried in diabetic nerve damage.
Traditional use
Thiamin has been eaten as part of ordinary food forever. Food use is not proof that supplements treat any condition.
Proposed mechanism Hypothesis
Not shown in the abstracts read.
A proposed mechanism does not show that the effect happens in people.
Numbness or tingling should be checked by a doctor; do not self-treat.
Painful periods (dysmenorrhoea)
Very low certaintyA Cochrane review found one trial of vitamin B1 alone (120 women) that reported lower period pain than placebo. The review rates all the supplement evidence as low or very low quality and says there is no high-quality evidence for any supplement.
1 studiesVitamin B1 alone and fish oil plus vitamin B1, in various amounts.
Studies, doses and limits
What the trials found
In the Cochrane review of 27 trials (3,101 women), one trial of vitamin B1 alone showed lower pain scores than placebo or no treatment (MD -2.70 points on a 0 to 10 scale, 95% CI -3.32 to -2.08; 120 women). The authors graded all the evidence as low or very low quality and found evidence of safety lacking.
Results
One trial pointing to benefit; not enough to rely on.
Effect sizes as reported
Pain score MD -2.70 (95% CI -3.32 to -2.08), one trial of 120 women.
Why this rating
Very low. A single trial inside a review that rates all evidence low or very low.
Form and dose studied
Vitamin B1 alone and fish oil plus vitamin B1, in various amounts.
Who was studied
Mostly young students with primary dysmenorrhoea.
Limits
One trial; mostly Iranian students; safety poorly reported.
Why researchers looked
Vitamin B1 was tested as an alternative to painkillers for period pain, mostly in students in Iran.
Traditional use
Thiamin has been eaten as part of ordinary food forever. Food use is not proof that supplements treat any condition.
Proposed mechanism Hypothesis
Not shown in the abstract.
A proposed mechanism does not show that the effect happens in people.
Severe or worsening period pain needs a clinician.
Connections to the rest of health
How Vitamin B1 (thiamin) connects to the rest of our health knowledge graph. Every link says what kind of connection it is. A safety link (for example to the liver) is a warning, not a benefit. A study that merely mentions a topic never creates a benefit link.
Explore every connection: goals, body systems, organs, symptoms, genes
A. Wellness goals
| Connected to | Kind of connection | Evidence status | Context | Studies |
|---|---|---|---|---|
| Brain Health | Low certainty | Correcting thiamin deficiency (beriberi, Wernicke encephalopathy): Thiamin is the accepted treatment for thiamin deficiency, including beriberi and the brain condition Wernicke encephalopathy. Official pages and a guideline say so. But there are almost no good randomised trials, and the best review found them too few to say what amount, route or length of treatment works best. This is about people who are lacking thiamin, not people who eat well. | 4 3 17 18 | |
| Brain Health | Very low certainty | Memory and thinking in mild Alzheimer disease (benfotiamine): One small 12-month trial of 70 people with mild memory loss or mild Alzheimer disease tested benfotiamine, a fat-soluble form of thiamin. Worsening on the main memory test was 43% lower, but that was not statistically significant. A secondary measure (CDR) was lower by 77% (p = 0.034). It is early research and the form is not plain thiamin. | 5 | |
| Energy Boost | Low certainty | Chronic fatigue in quiet inflammatory bowel disease (high-dose thiamine): In a 40-person crossover trial of people with inflammatory bowel disease (IBD) who were in remission but very tired, high-dose thiamine lowered fatigue scores more than placebo. The doses were far above food amounts. It has not been shown for fatigue in people without IBD. | 2 | |
| Heart Health | Not enough evidence | Heart failure: A 2022 review of 8 trials (384 people) found no evidence that thiamine supplements help heart failure. Some measures looked promising in single trials, but pooled results did not show a benefit. Heart failure from severe thiamin lack (wet beriberi) is a different problem. | 14 12 6 |
B. Body systems
| Connected to | Kind of connection | Evidence status | Context | Studies |
|---|---|---|---|---|
| Nervous System | Biological association | Low certainty | Studied for: Correcting thiamin deficiency (beriberi, Wernicke encephalopathy) Studied for: Nerve damage in diabetes or alcohol use (benfotiamine and B vitamins) | 4 3 17 18 1 11 |
| Brain Focus | Biological association | Very low certainty | Studied for: Memory and thinking in mild Alzheimer disease (benfotiamine) | 5 |
| Energy Fatigue | Biological association | Low certainty | Studied for: Chronic fatigue in quiet inflammatory bowel disease (high-dose thiamine) | 2 |
| Cardiovascular System | Biological association | Not enough evidence | Studied for: Heart failure Studied for: Septic shock (hospital use) | 14 12 6 8 |
| Reproductive Health | Biological association | Very low certainty | Studied for: Painful periods (dysmenorrhoea) | 9 |
E. Health conditions
| Connected to | Kind of connection | Evidence status | Context | Studies |
|---|---|---|---|---|
| Wernicke encephalopathy | Documented | A brain condition from severe thiamin lack; treated urgently with thiamine by a clinician (EFNS guideline). A brain condition from severe thiamin lack; an emergency treated by a clinician. Preparation or compound: Thiamine (vitamin B1) deficiency |
4 17 13 | |
| Beriberi | Documented | Wet beriberi affects the heart and circulation; dry beriberi affects nerves. Treated with thiamine. Wet beriberi affects heart and circulation; dry beriberi affects nerves. Treated with thiamine. Preparation or compound: Thiamine (vitamin B1) deficiency |
17 | |
| Heart failure | Not enough evidence | A review of 8 trials found no evidence that thiamine helps; not a treatment. Preparation or compound: Thiamine supplements |
14 |
I. Biomarkers
| Connected to | Kind of connection | Evidence status | Context | Studies |
|---|---|---|---|---|
| Blood thiamine (total thiamine) | Biological association | Low certainty | Measured in trials: measured. A lab change is not the same as a health benefit. | 4 17 |
| Fatigue score (IBD-Fatigue Questionnaire) | Biological association | Low certainty | Measured in trials: lowered. A lab change is not the same as a health benefit. | 2 |
| Memory and thinking score (ADAS-Cog) | Biological association | Very low certainty | Measured in trials: lowered. A lab change is not the same as a health benefit. | 5 |
| Clinical Dementia Rating (CDR) | Biological association | Very low certainty | Measured in trials: lowered. A lab change is not the same as a health benefit. | 5 |
| Left ventricular ejection fraction (LVEF) | Biological association | Not enough evidence | Measured in trials: unchanged. A lab change is not the same as a health benefit. | 14 |
| Serum creatinine (kidney marker) | Biological association | Not enough evidence | Measured in trials: mixed. A lab change is not the same as a health benefit. | 8 |
| Nerve conduction velocity | Biological association | Very low certainty | Measured in trials: raised. A lab change is not the same as a health benefit. | 11 |
| Period pain score (0 to 10 scale) | Biological association | Very low certainty | Measured in trials: lowered. A lab change is not the same as a health benefit. | 9 |
K. Biological pathways
L. Active compounds
| Connected to | Kind of connection | Evidence status | Context | Studies |
|---|---|---|---|---|
| Thiamin (thiamine) | Biological association | Human | Helps cells turn carbohydrate into energy and supports muscle contraction and nerve signals (MedlinePlus). | 18 |
| Thiamine diphosphate | Biological association | Human | A blood form of thiamine that was measured by chromatography in the Mayo clinic study. | 12 |
| Benfotiamine | Biological association | Human | Described as a lipid-soluble derivative of vitamin B1 with high bioavailability; tested in nerve and Alzheimer trials. | 11 5 |
Each connection is stored with the ingredient, the connected record, the kind of connection, the evidence status, the supporting studies, the preparation or compound involved, and a review date (last reviewed October 26, 2026).
Evidence at a glance: what changed in 6 lab markers
Tap a number to show only those markers. Counts are markers, not people.
The evidence
The research centre for Vitamin B1 (thiamin). Every record here was checked against PubMed or the publisher's page; we never list a study we have not verified.
Evidence by outcome
Bars show how many studies we found for each outcome, not how well it works. People are added up across trials only (reviews are not added, to avoid double counting).
How we rate evidence
High certainty
Several well-run trials or reviews agree; further research is unlikely to change the picture much.
Moderate certainty
Good trials point the same way, but some doubt remains.
Low certainty
Small, short or inconsistent trials. The finding could change with better research.
Very low certainty
Very little or very weak human data. Treat as a possibility only.
Mixed findings
Trials or reviews disagree with each other.
Not enough evidence
Not enough human research to say either way.
Evidence against
Good research found no benefit, or found harm.
We take the reviewers' own risk-of-bias and GRADE statements where they exist, and otherwise judge from study size, design, consistency, directness and whether a product matches what is sold. Many publications do not make evidence high. Method note: We started from our existing thiamin summary, read the MedlinePlus and NHS pages in full, used saved USDA FoodData Central data for food amounts and re-read PubMed abstracts for each study. Only abstracts were read for studies. Items we could not verify are flagged in the research gaps.
Study library: every study we checked 21
| Study | Design | People | Product, dose, length | Result |
|---|---|---|---|---|
| Ang 2008 Vitamin B for treating peripheral neuropathy. Cochrane Database Syst Rev · PMID 18646107 · DOI |
Systematic review |
741 People with alcoholic or diabetic generalised peripheral neuropathy (13 studies) |
Vitamin B preparations including oral benfotiamine (a thiamine derivative) and B-complex Vitamin supplement Various 2 to 8 weeks · vs Placebo, other vitamin B doses, alpha-lipoic acid, cilostazol or cytidine triphosphate |
Two small trials of vitamin B versus placebo showed no significant short-term benefit in pain; one showed a small benefit in vibration detection with oral benfotiamine. A larger trial found higher B-complex doses reduced pain more than lower doses. Vitamin B looked less effective than alpha-lipoic acid, cilostazol or cytidine triphosphate in small trials. Few minor side effects. The authors say the evidence is insufficient to say whether vitamin B helps or harms. No pooled effect (Not given in the abstract) Methods, limits and fundingOutcomes: Pain, vibration detection, nerve conduction Limitations: Searched to 2005. Small trials; mixes thiamine derivative and B-complex products. Funding and conflicts: Not stated in the abstract. Read: abstract |
| Bager 2021 Randomised clinical trial: high-dose oral thiamine versus placebo for chronic fatigue in patients with quiescent inflammatory bowel disease. Aliment Pharmacol Ther · PMID 33210299 · DOI |
Randomized trial |
40 40 adults with quiescent inflammatory bowel disease (IBD) and severe chronic fatigue |
High-dose oral thiamine Vitamin supplement 600 to 1800 mg a day, set by sex and weight (trial dose, not advice) 4 weeks, 4-week washout, 4 weeks (crossover) · vs Oral placebo |
Crossover analysis showed a mean 4.5 point reduction in fatigue after thiamine (95% CI 2.6 to 6.2) against a 0.75 point increase after placebo (P = 0.0003). 55% and 75% of the two groups improved by 3 points or more on thiamine against 25% and 35% on placebo. Only mild side effects were detected. Mean fatigue score -4.5 on thiamine vs +0.75 on placebo, P = 0.0003 (2.6 to 6.2 (thiamine); -1.3 to 2.8 (placebo)) Methods, limits and fundingOutcomes: Fatigue on the Inflammatory Bowel Disease-Fatigue Questionnaire; improvement of 3 points or more Limitations: Small crossover trial in one condition (quiescent IBD) with doses many times the usual dietary amount. Short, and not shown in people without IBD. Funding and conflicts: Research support from a non-US government source is listed on the record; no conflicts stated in the abstract. Read: abstract |
| Day 2013 Thiamine for prevention and treatment of Wernicke-Korsakoff Syndrome in people who abuse alcohol. Cochrane Database Syst Rev · PMID 23818100 · DOI |
Systematic review |
107 People who abuse alcohol, at risk of or with Wernicke-Korsakoff syndrome |
Thiamine by injection into muscle, different amounts compared Vitamin supplement 5 mg a day compared with four higher daily amounts, for 2 days (one trial, Ambrose 2001) 2 days · vs Lowest thiamine amount (5 mg a day) |
Only two trials met the review criteria and only one had enough data (107 people). A significant difference favoured 200 mg a day over 5 mg a day on one delayed-alternation test (mean difference -17.90, 95% CI -35.4 to -0.40, P = 0.04); other comparisons were not significant and there was no simple dose-response pattern. The authors conclude trial evidence is insufficient to guide the dose, frequency, route or length of thiamine treatment. MD -17.90 on a delayed alternation test (200 mg vs 5 mg a day) (-35.4 to -0.40) Methods, limits and fundingOutcomes: Memory and thinking test results; Wernicke-Korsakoff manifestations Limitations: Only one analysable trial with design shortcomings. Searched to September 2012. Funding and conflicts: Research support from a non-US government source is listed on the record; no conflicts stated in the abstract. Read: abstract |
| Galvin 2010 EFNS guidelines for diagnosis, therapy and prevention of Wernicke encephalopathy. Eur J Neurol · PMID 20642790 · DOI |
Guideline |
Guideline panel; people with suspected or proven Wernicke encephalopathy | Thiamine given by a clinician (best by vein) for suspected Wernicke encephalopathy Vitamin supplement Guideline gives a clinician-set amount; not repeated here as advice |
The guideline says thiamine is indicated for suspected or manifest Wernicke encephalopathy and should be given before any carbohydrate, preferably into a vein (Level C). It rates the overall safety of thiamine as very good (Level B), advises measuring total thiamine in blood before giving it, and advises following thiamine status for at least 6 months after bariatric surgery. Recommendation levels B and C (not trial results) (Not applicable) Methods, limits and fundingOutcomes: Diagnosis, treatment and prevention of Wernicke encephalopathy Limitations: A guideline built from searches of MEDLINE, EMBASE, LILACS and the Cochrane Library. The abstract gives only recommendation levels (mostly C), not trial numbers. Dated 2010. Funding and conflicts: No funding or conflicts stated in the abstract. Read: abstract |
| Gibson 2020 Benfotiamine and Cognitive Decline in Alzheimer's Disease: Results of a Randomized Placebo-Controlled Phase IIa Clinical Trial. J Alzheimers Dis · PMID 33074237 · DOI |
Randomized trial |
70 People with amnestic mild cognitive impairment or mild Alzheimer dementia |
Oral benfotiamine (a lipid-soluble thiamine derivative) Vitamin supplement 12 months · vs Placebo |
34 people got benfotiamine and 36 placebo. The ADAS-Cog rise (worsening) was 43% lower with benfotiamine but this was not statistically significant (p = 0.125). Worsening in CDR was 77% lower (p = 0.034). Blood AGE rises were reduced (p = 0.044). The authors call it safe and potentially efficacious. ADAS-Cog worsening 43% lower, p = 0.125 (primary outcome, not significant) (Not given in the abstract) Methods, limits and fundingOutcomes: ADAS-Cog (primary), CDR score, brain FDG-PET, blood AGE Limitations: Small phase IIa feasibility trial; primary outcome not significant; secondary and exploratory results are not proof. Benfotiamine is a derivative, not plain thiamin. Funding and conflicts: Research support from NIH (extramural) and non-US government sources is listed on the record; no conflicts stated in the abstract. Read: abstract |
| Katta 2016 Does Long-Term Furosemide Therapy Cause Thiamine Deficiency in Patients with Heart Failure? A Focused Review. Am J Med · PMID 26899752 · DOI |
Narrative review |
People with heart failure treated with loop diuretics such as furosemide | Furosemide (a loop diuretic) and thiamine status Vitamin supplement |
Most studies report varying degrees of thiamine deficiency in heart failure, particularly with chronic high-dose furosemide. It seems mostly due to more urine and faster urine flow, and furosemide may directly block thiamine uptake into cells. Limited data suggest thiamine might raise ejection fraction in this group. No pooled numbers (Not applicable) Methods, limits and fundingOutcomes: Thiamine deficiency risk Limitations: A focused narrative review of limited and variable data. Funding and conflicts: Not stated in the abstract. Read: abstract |
| McLaughlin 2020 Safety of intravenous push thiamine administration at a tertiary academic medical center. J Am Pharm Assoc · PMID 31932197 · DOI |
Observational study |
2595 2,595 adults given thiamine by quick injection into a vein at one hospital |
Thiamine by IV push Vitamin supplement 7,605 doses of 100 mg, 433 of 200 mg, 549 of 250 mg, 19 of 500 mg June 2015 to July 2017 |
Across 8,606 doses no anaphylactic or anaphylactoid reactions were seen. There were 26 injection-site reactions (0.30%) in 19 patients (phlebitis 12, infiltration 14). 0 anaphylaxis in 8,606 doses; injection-site reactions 0.30% (Not given) Methods, limits and fundingOutcomes: Anaphylaxis and injection-site reactions Limitations: Single-centre retrospective chart review of hospital injections; rare events can be missed. Funding and conflicts: Not stated in the abstract. Read: abstract |
| Moskowitz 2023 Thiamine for Renal Protection in Septic Shock (TRPSS): A Randomized, Placebo-controlled, Clinical Trial. Am J Respir Crit Care Med · PMID 37364280 · DOI |
Randomized trial |
88 88 adults with septic shock in hospital |
Thiamine given in hospital (route/amount not stated in the abstract) Vitamin supplement · vs Placebo |
No significant difference in creatinine at 72 hours (mean difference -0.57 mg/dl; 95% CI -1.18 to 0.04; P = 0.07). Kidney replacement therapy (14.3% vs 21.7%), severe acute kidney injury (54.7% vs 73.9%) and mortality (35.7% vs 54.3%) did not differ significantly. Thiamine patients had more ICU-free days (median 22.5 vs 0.0, P < 0.01). Creatinine change -0.57 mg/dl, P = 0.07 (not significant) (-1.18 to 0.04) Methods, limits and fundingOutcomes: Change in serum creatinine at 72 hours (primary); kidney replacement therapy; mortality; ICU-free days Limitations: 88 people with a life-threatening illness treated in hospital, so not relevant to everyday supplement use. Primary outcome not met; ICU-free days was a secondary result. Funding and conflicts: Research support from NIH (extramural) is listed on the record; no conflicts stated in the abstract. Read: abstract |
| Pattanittum 2016 Dietary supplements for dysmenorrhoea. Cochrane Database Syst Rev · PMID 27000311 · DOI |
Systematic review |
3101 Mostly students with primary dysmenorrhoea (painful periods); 27 trials |
Many supplements, including vitamin B1 alone and fish oil plus vitamin B1 Vitamin supplement Various · vs Placebo, no treatment, NSAIDs or other supplements |
Vitamin B1 alone versus placebo or no treatment had very limited evidence of effectiveness (MD -2.70 points on a 0 to 10 pain scale, 95% CI -3.32 to -2.08; one trial, 120 women). Vitamin B1 may be more effective than fish oil (MD -1.59, one trial). The authors judged all the evidence to be low or very low quality and say there is no high-quality evidence for any supplement and evidence of safety is lacking. Vitamin B1 vs placebo: MD -2.70 pain points (one trial, 120 women) (-3.32 to -2.08) Methods, limits and fundingOutcomes: Pain intensity and adverse effects Limitations: The vitamin B1 result comes from one trial; most trials were in Iran and in young students. Searched to March 2015. Funding and conflicts: Research support from a non-US government source is listed on the record; no conflicts stated in the abstract. Read: abstract |
| Stephen 1992 Anaphylaxis from administration of intravenous thiamine. Am J Emerg Med · PMID 1736919 · DOI |
Case report |
1 One emergency department patient, with a literature review |
Thiamine given into a vein Vitamin supplement |
Reports an anaphylactic reaction to intravenous thiamine and reviews the literature. The authors say anaphylaxis from intravenous thiamine is uncommon but can be life threatening, that cases have been reported with some regularity outside the US, and that given the many patients treated without side effects thiamine appears relatively safe. One case; no rate (Not applicable) Methods, limits and fundingOutcomes: Allergic reaction (anaphylaxis) Limitations: Case report from 1992, about injections in a hospital setting, not pills. Funding and conflicts: Not stated in the abstract. Read: abstract |
| Stracke 1996 A benfotiamine-vitamin B combination in treatment of diabetic polyneuropathy. Exp Clin Endocrinol Diabetes · PMID 8886748 · DOI |
Randomized trial |
24 24 people with diabetic polyneuropathy |
Benfotiamine (a lipid-soluble thiamine derivative) plus vitamin B6/B12 combination Vitamin supplement 12 weeks (9-month follow-up in 9 people) · vs Control (double-blind) |
Nerve conduction velocity in the peroneal nerve improved significantly (p = 0.006) and vibration perception showed a trend to improvement. No treatment-specific side effects were seen. Peroneal nerve conduction velocity improved (p = 0.006) (Not given in the abstract) Methods, limits and fundingOutcomes: Nerve conduction velocity; vibration perception threshold Limitations: Only 24 people. Tested a combination with B6 and B12, so the thiamine part cannot be separated. The abstract does not name the comparator or funder; dated 1996. Funding and conflicts: Not stated in the abstract. Read: abstract |
| Teigen 2016 Prevalence of thiamine deficiency in a stable heart failure outpatient cohort on standard loop diuretic therapy. Clin Nutr · PMID 26923517 · DOI |
Observational study |
30 30 stable heart failure outpatients on loop diuretics at the Mayo Heart Failure Clinic |
No intervention (blood thiamine diphosphate measured) Vitamin supplement |
Estimated thiamine deficiency prevalence was below 11.6%. There was no link between diuretic dose and thiamine levels (r = 0.02, P = 0.93) or between ejection fraction and thiamine levels. Deficiency prevalence < 11.6%; diuretic dose vs thiamine r = 0.02 (Not given) Methods, limits and fundingOutcomes: Whole-blood thiamine diphosphate Limitations: Only 30 people at one clinic. It disagrees with earlier reports of much higher rates. Funding and conflicts: Research support from a non-US government source is listed on the record; no conflicts stated in the abstract. Read: abstract |
| Wijnia 2022 A Clinician's View of Wernicke-Korsakoff Syndrome. J Clin Med · PMID 36431232 · DOI |
Narrative review |
Narrative review of Wernicke-Korsakoff syndrome | Thiamine treatment (discussed) Vitamin supplement |
Says Korsakoff syndrome is chronic amnesia from unrecognised or undertreated Wernicke encephalopathy caused by thiamine deficiency. Wernicke encephalopathy is mostly linked to alcohol addiction but also occurs after bariatric surgery, in hyperemesis gravidarum (severe pregnancy vomiting) and in anorexia nervosa. People with low magnesium may fail to respond to thiamine. No numbers (Not applicable) Methods, limits and fundingOutcomes: Recognition and treatment of Wernicke-Korsakoff syndrome Limitations: A single clinician's narrative review, not a systematic one. Funding and conflicts: Not stated in the abstract. Read: abstract |
| Xu 2022 The effects of thiamine supplementation on patients with heart failure: A systematic review and meta-analysis of randomized controlled trials. Complement Ther Med · PMID 35842069 · DOI |
Meta-analysis |
384 People with chronic or acute heart failure (8 randomised trials) |
Thiamine supplementation Vitamin supplement Varied by trial · vs Placebo |
Eight trials (384 people) showed no benefit. LVEF did not change in chronic heart failure (mean difference -0.19; 95% CI -2.78 to 0.96 as printed in the abstract; I2 = 49%). NYHA class, BNP or NT-proBNP, thiamine status, symptoms and quality of life were not improved either, and acute heart failure showed no improvement. The authors say there is no evidence to support thiamine in heart failure, though some results are promising and larger trials are needed. LVEF mean difference -0.19, not significant (-2.78 to 0.96 (as printed)) Methods, limits and fundingOutcomes: Left ventricular ejection fraction, NYHA class, BNP, thiamine status, symptoms, quality of life Limitations: Small trials with mixed results (I2 = 49%). Searched to June 2022. Funding and conflicts: Not stated in the abstract. Read: abstract |
| Yasu 2020 Potential thiamine deficiency in elderly patients with gastrointestinal cancer undergoing chemotherapy. Int J Clin Pharmacol Ther · PMID 31983387 · DOI |
Observational study |
12 12 elderly patients with gastrointestinal cancer having chemotherapy |
Fluorouracil-based chemotherapy (observed, not given as a test) Vitamin supplement |
Median serum thiamine was 22.5 ng/mL (range 17 to 42). Four of 12 patients (33.3%) had deficiency (below 20 ng/mL). The authors say monitoring is warranted because deficiency may not cause obvious symptoms. 4 of 12 below 20 ng/mL (Not given) Methods, limits and fundingOutcomes: Serum thiamine Limitations: Twelve people, retrospective, no comparison group, so it cannot separate chemotherapy from cancer or poor eating. Funding and conflicts: Not stated in the abstract. Read: abstract |
| da Silva 2020 ASPEN Consensus Recommendations for Refeeding Syndrome. Nutr Clin Pract · PMID 32115791 · DOI |
Consensus statement |
Hospitalised adults and children at risk of refeeding syndrome | Not an intervention study (definition and risk criteria) Vitamin supplement |
The task force proposes severity criteria in which severe refeeding syndrome includes organ dysfunction resulting from falls in phosphorus, potassium or magnesium and/or from thiamin deficiency within 5 days of restarting calories. No numbers on thiamin (Not applicable) Methods, limits and fundingOutcomes: Definition and risk stratification of refeeding syndrome Limitations: Consensus statement from a professional society; the abstract does not give thiamin amounts. Funding and conflicts: Not stated in the abstract. Read: abstract |
| s-medlineplus-beriberi MedlinePlus: Beriberi · Source |
Health agency n/a |
Methods, limits and fundingRead: full-text | ||
| s-medlineplus-thiamin MedlinePlus: Thiamin · Source |
Health agency n/a |
Methods, limits and fundingRead: full-text | ||
| s-nhs-vitamin-b NHS: B vitamins and folic acid · Source |
Health agency n/a |
Methods, limits and fundingRead: full-text | ||
| s-nih-ods NIH Office of Dietary Supplements: Thiamin fact sheet for health professionals · Source |
Health agency n/a |
Methods, limits and fundingRead: not-read | ||
| s-usda-saved USDA FoodData Central, SR Legacy (April 2018 release), saved copies · Source |
Government database n/a |
Methods, limits and fundingRead: saved-copy |
What we do not know yet
- No randomised trial shows that extra thiamin improves energy, mood or memory in people who are not deficient.
- Trial evidence for how best to treat Wernicke encephalopathy is almost absent (Cochrane).
- The Alzheimer trial used benfotiamine and missed its main result; the fatigue trial was one small trial in one condition.
- Heart failure and septic shock trials are small; the heart failure review calls for larger trials.
- NIH Office of Dietary Supplements data could not be read, so no US upper limit or NIH interaction list is given.
- History, supplement quality and contaminants, liver safety, LactMed and meat and fish amounts were not researched.
How new research is added
New studies are found by a saved PubMed search and placed in a review queue before the page changes.
Lab markers
What changed in blood or saliva tests during trials. A changed number is not the same as feeling or being healthier, and we give no "normal ranges".
Other 8
Blood thiamine (total thiamine)
Measured in trials
The amount of thiamine in a blood sample, used to check whether someone is deficient.
Low certaintyResults and what it means
Why it was measured
The EFNS guideline says total thiamine in blood should be measured immediately before thiamine is given for suspected Wernicke encephalopathy.
Statistical vs. clinical meaning
A test used to find deficiency, not a result of taking thiamin.
Safety implication
None.
| Study | Result | People | Product |
|---|---|---|---|
| 4 | Total thiamine in blood should be measured before thiamine is given (good practice point) | People with suspected Wernicke encephalopathy | Guideline advice |
Fatigue score (IBD-Fatigue Questionnaire)
Lowered in trials
A questionnaire in which people with IBD rate their tiredness; a drop means less fatigue.
Low certaintyResults and what it means
Why it was measured
It was the trial's main measure of how tired people felt.
Statistical vs. clinical meaning
Lower tiredness scores in a small trial of people with IBD.
Safety implication
Only mild side effects reported.
| Study | Result | People | Product |
|---|---|---|---|
| 2 | Mean 4.5 point reduction after thiamine vs 0.75 point increase after placebo (P = 0.0003) | 40 adults with quiescent IBD and severe fatigue | High-dose oral thiamine vs placebo, crossover |
Memory and thinking score (ADAS-Cog)
Lowered in trials
A test of memory and thinking; higher scores mean more decline.
Very low certaintyResults and what it means
Why it was measured
It was the primary outcome of the benfotiamine trial.
Statistical vs. clinical meaning
The main result was not statistically significant.
Safety implication
Reported safe in the trial.
| Study | Result | People | Product |
|---|---|---|---|
| 5 | Increase in ADAS-Cog 43% lower with benfotiamine than placebo (p = 0.125, not significant) | 70 people with amnestic MCI or mild Alzheimer dementia | Benfotiamine vs placebo for 12 months |
Clinical Dementia Rating (CDR)
Lowered in trials
A rating of how far dementia has progressed.
Very low certaintyResults and what it means
Why it was measured
A secondary outcome in the benfotiamine trial.
Statistical vs. clinical meaning
A secondary result in a small trial; not proof.
Safety implication
Reported safe in the trial.
| Study | Result | People | Product |
|---|---|---|---|
| 5 | Worsening in CDR 77% lower with benfotiamine than placebo (p = 0.034) | 70 people with amnestic MCI or mild Alzheimer dementia | Benfotiamine vs placebo for 12 months |
Left ventricular ejection fraction (LVEF)
Unchanged in trials
The share of blood the heart's main pumping chamber pushes out with each beat.
Not enough evidenceResults and what it means
Why it was measured
A standard measure of how well the heart pumps in heart failure.
Statistical vs. clinical meaning
No change shown overall.
Safety implication
None specific.
| Study | Result | People | Product |
|---|---|---|---|
| 14 | Mean difference -0.19 (95% CI -2.78 to 0.96 as printed); no significant change in chronic heart failure | 8 trials, 384 people with heart failure | Thiamine supplementation vs placebo |
Serum creatinine (kidney marker)
Mixed results in trials
A blood waste product that rises when the kidneys are not working well.
Not enough evidenceResults and what it means
Why it was measured
It was the primary outcome of the septic shock trial.
Statistical vs. clinical meaning
Not significant.
Safety implication
Hospital setting only.
| Study | Result | People | Product |
|---|---|---|---|
| 8 | Mean difference -0.57 mg/dl at 72 hours (95% CI -1.18 to 0.04), P = 0.07 | 88 adults with septic shock | Thiamine vs placebo in hospital |
Nerve conduction velocity
Raised in trials
How fast an electrical signal travels along a nerve.
Very low certaintyResults and what it means
Why it was measured
A measurable sign of nerve health in diabetic neuropathy trials.
Statistical vs. clinical meaning
A combination product in a small, old trial.
Safety implication
No therapy-specific side effects seen.
| Study | Result | People | Product |
|---|---|---|---|
| 11 | Peroneal nerve conduction velocity improved significantly (p = 0.006) | 24 people with diabetic polyneuropathy | Benfotiamine plus B6/B12 for 12 weeks |
Period pain score (0 to 10 scale)
Lowered in trials
A rating of pain from period cramps on a 0 to 10 visual scale.
Very low certaintyResults and what it means
Why it was measured
The Cochrane review's primary outcome.
Statistical vs. clinical meaning
One trial; evidence graded low or very low.
Safety implication
Safety poorly reported.
| Study | Result | People | Product |
|---|---|---|---|
| 9 | Vitamin B1 vs placebo or no treatment: MD -2.70 points (95% CI -3.32 to -2.08), one trial of 120 women | Women with primary dysmenorrhoea | Vitamin B1 alone |
Safety
What studies and official sources say about side effects, medicines and who should check first. Each point shows what kind of evidence it comes from.
Main points to know 4
- Lack of thiamin is the bigger risk than too much. Severe thiamin deficiency can cause beriberi (heart or nerves) and the brain conditions Wernicke encephalopathy and Korsakoff syndrome. In the US it is most often seen in people who drink heavily (MedlinePlus). Other risks named in the sources: weight-loss (bariatric) surgery, dialysis, high-dose water pills, severe pregnancy vomiting, and breastfed babies of mothers lacking thiamin. Authoritative guidance 18 17 4 13
- No known poisoning from too much, but limits are not fully settled. MedlinePlus says there is no known poisoning linked to excessive intake of thiamin. The NHS says there is not enough evidence to know the effects of taking high doses of thiamin supplements each day, and that 100 mg or less a day of supplements is unlikely to cause harm (page last reviewed 3 August 2020). We could not read the NIH fact sheet (blocked), so we state no US upper limit. This is what the regulators say, not advice to take any amount. Authoritative guidance 18 19 20
- Rare allergic reaction to thiamine injections. Severe allergic reactions (anaphylaxis) have been reported after thiamine given into a vein, but they are uncommon. A hospital review of 8,606 quick injections found none, and injection-site reactions in 0.30%. This concerns injections given by clinicians, not food or pills. Case report 10 7
- Do not self-treat warning signs of Wernicke encephalopathy or beriberi. Confusion, unsteady walking, abnormal eye movements, or breathlessness with leg swelling can mean severe thiamin lack or another serious illness. These need urgent medical care; MedlinePlus says untreated beriberi can be fatal. Authoritative guidance 17 4
Side effects 2
| Effect | How often | Severity and recovery | Evidence |
|---|---|---|---|
| Allergic reaction to injected thiamine, from skin reaction to anaphylaxis About injections in hospital, not oral thiamin. | Rare. 0 anaphylaxis in 8,606 hospital IV-push doses (2,595 patients); injection-site reactions (phlebitis, infiltration) 26 events, 0.30%. | can be life threatening (anaphylaxis) Not described in the abstracts read. | Observational 10 7 |
| Mild side effects with very high oral doses in a trial 40 people with IBD, 4 weeks per arm. | Not given; the trial reports only mild side effects. | mild Not described. | Randomized trial 2 |
Liver
No liver injury linked to thiamin was found in the sources read. A liver-safety database such as LiverTox was not checked.
How often. No frequency was found.
Monitoring. No agency monitoring advice was found.
This is a safety connection. It is not evidence that Vitamin B1 (thiamin) supports liver health.
Medicines and supplements 5
| With | Why it matters | Importance | Evidence | What to do |
|---|---|---|---|---|
| Loop diuretics (water pills such as furosemide) prescription | Loop diuretics may increase thiamin loss in urine and may block thiamin uptake into cells. | A review reports varying degrees of thiamine deficiency in heart failure, particularly with chronic high-dose furosemide. A 30-person Mayo clinic study found deficiency below 11.6% and no link between diuretic dose and thiamine level, so the evidence is mixed. MedlinePlus lists high doses of diuretics as a risk for beriberi. | Observational Low certainty 6 12 17 | If you take a water pill, ask your doctor or pharmacist whether thiamin matters for you. Do not stop the medicine. |
| Fluorouracil-based chemotherapy prescription | Not established in the abstract read. | In 12 elderly patients with stomach or bowel cancer on chemotherapy, 4 (33.3%) had low serum thiamine, but with no comparison group the cause is unclear. | Observational Very low certainty 15 | Ask your cancer team about nutrition and thiamin levels. |
| Alcohol (heavy use) lifestyle | MedlinePlus says heavy alcohol use makes it hard for the body to absorb thiamin from food. | The main cause of deficiency in the US. Unless people with heavy alcohol use get higher-than-normal amounts of thiamin, they will not get enough, according to MedlinePlus. | Authoritative guidance Moderate certainty 18 17 | If you drink heavily, talk to a doctor about thiamin and alcohol support. |
| Low magnesium nutrient | Not explained in the abstract. | A clinician review says people with low magnesium may fail to respond to thiamine, especially around alcohol withdrawal or with proton pump inhibitors combined with diuretics. | Narrative review Very low certainty 13 | A clinician checks magnesium when treating deficiency. |
| Other medicines and supplements (NIH list) unknown | Not read. | The NIH Office of Dietary Supplements fact sheet normally lists medicine interactions, but it was blocked and not read, so we do not state any others. | Not read Not enough evidence 20 | Ask your pharmacist to check your medicines. |
Who should check first 5
| Situation | Advice | Evidence |
|---|---|---|
| Past allergic reaction to thiamine | Tell any clinician before an injection. The source only reports rare anaphylaxis cases. | Case report 10 |
| Pregnancy | MedlinePlus lists a higher reference intake in pregnancy and breastfeeding (1.4 mg a day). Severe vomiting in pregnancy (hyperemesis) has been linked to Wernicke encephalopathy. Ask your midwife or doctor before taking supplements. | Authoritative guidance 18 13 |
| Babies and children | MedlinePlus says infants can develop beriberi if breastfed by a mother lacking thiamin or fed formula without enough thiamine. Do not give supplements to children without a doctor's advice. | Authoritative guidance 17 18 |
| Kidney disease, dialysis or weight-loss surgery | MedlinePlus names dialysis as a risk for deficiency, and the EFNS guideline advises following thiamine status for at least 6 months after bariatric surgery. Your care team decides what you need. | Authoritative guidance 17 4 |
| Refeeding after starvation | Restarting food after long undernourishment can cause refeeding syndrome, which can include thiamin deficiency. This is managed in hospital. | Consensus statement 16 |
Overdose, product quality and regulators
Summary. MedlinePlus says there is no known poisoning from excessive thiamin intake, and the NHS says evidence on high-dose supplements is limited. The EFNS guideline rates the overall safety of thiamine as very good.
Animal. Not reviewed.
Human doses studied. Doses up to 1800 mg a day by mouth were used for 4 weeks in a trial with only mild side effects; this is a trial fact, not a recommendation.
High dose or long term signals. No long-term harm signal was found in the sources read, but long-term safety at high doses was not studied in them.
Overdose response. Not found.
Genotoxicity. Not researched.
Product quality, label accuracy and contaminants of thiamin supplements were not researched.
| Body | Action | Date |
|---|---|---|
| MedlinePlus (US National Library of Medicine) (United States) | Thiamin page: lists food sources, says deficiency is most often seen in the US with heavy alcohol use, says there is no known poisoning linked to excessive intake, and lists Dietary Reference Intakes (adult women 1.1 mg, men 1.2 mg a day; 1.4 mg in pregnancy and lactation). source | 2025-01-21 |
| MedlinePlus (US National Library of Medicine) (United States) | Beriberi page: deficiency disease treated with thiamine by injection or by mouth; untreated beriberi can be fatal. source | 2024-07-23 |
| NHS (UK) (United Kingdom) | B vitamins page: adults aged 19 to 64 need 1 mg a day (men) and 0.8 mg a day (women); not enough evidence on high-dose supplements; 100 mg or less a day of supplements is unlikely to cause harm. source | 2020-08-03 |
When to get medical help
- Confusion, trouble walking or balancing, or unusual eye movements, especially with heavy drinking, recent weight-loss surgery or severe vomiting (possible Wernicke encephalopathy): seek emergency care now
- Breathlessness at night or with activity, fast heartbeat and swollen lower legs (possible wet beriberi): get urgent medical care
- Swelling of the lips, face, tongue or throat, trouble breathing, widespread hives or collapse after a thiamine injection or any product (possible anaphylaxis): call 911 or your local emergency number
Stop using the product and contact a clinician or emergency service. In the US, Poison Control is 1-800-222-1222.
General information only, not medical advice. Ask a clinician or pharmacist before use, especially with medicines, in pregnancy or with a health condition. See the Natural Remedy Safety guide.
Frequently asked questions
What is thiamin (vitamin B1)?
Is thiamin the same as thiamine?
Which foods contain thiamin?
What happens if you do not get enough thiamin?
Who is at risk of low thiamin?
Does thiamin give you more energy?
Can thiamin help memory or Alzheimer disease?
Not shown. A 70-person trial of benfotiamine, a thiamine derivative, did not reach significance on its main memory test (p = 0.125), though a secondary measure favoured it. It is early research.
Does thiamin help heart failure?
A review of 8 trials with 384 people found no evidence of benefit on heart function, symptoms or quality of life. Larger trials are needed. Do not change heart medicines without your doctor.
Is thiamin safe in high amounts?
MedlinePlus says there is no known poisoning linked to excessive intake. The NHS says evidence on high-dose supplements is limited and that 100 mg or less a day is unlikely to cause harm. Rare allergic reactions have been reported with thiamine injections. Ask a doctor or pharmacist about your own case.
Do water pills affect thiamin?
Is thiamin needed during pregnancy and breastfeeding?
Explore by health goal
Editorial transparency
- Written by
- AlternativeMed editorial team. Research compiled with AI assistance, then checked against the sources listed.
- Medical review
- None. This page has not been reviewed by a physician or pharmacist.
- First published
- 2026-10-26
- Last substantive update
- 2026-10-26
- How we research
- We started from our existing thiamin summary, read the MedlinePlus and NHS pages in full, used saved USDA FoodData Central data for food amounts and re-read PubMed abstracts for each study. Only abstracts were read for studies. Items we could not verify are flagged in the research gaps.
- How we rate evidence
- See "How we rate evidence" in the Evidence tab.
- Independence
- No product is promoted on this page. No affiliate links are shown. Funding is stated where the PubMed record lists it; most abstracts do not state it.
Sources 21
Each source was opened and checked. Where we read only the abstract, it says so. The small numbers in the text point here.
- Ang CD, Alviar MJ, et al. Vitamin B for treating peripheral neuropathy.. Cochrane Database Syst Rev. 2008. PMID 18646107. DOI 10.1002/14651858.CD004573.pub3. (abstract)
- Bager P, Hvas CL, et al. Randomised clinical trial: high-dose oral thiamine versus placebo for chronic fatigue in patients with quiescent inflammatory bowel disease.. Aliment Pharmacol Ther. 2021. PMID 33210299. DOI 10.1111/apt.16166. (abstract)
- Day E, Bentham PW, et al. Thiamine for prevention and treatment of Wernicke-Korsakoff Syndrome in people who abuse alcohol.. Cochrane Database Syst Rev. 2013. PMID 23818100. DOI 10.1002/14651858.CD004033.pub3. (abstract)
- Galvin R, Bråthen G, et al. EFNS guidelines for diagnosis, therapy and prevention of Wernicke encephalopathy.. Eur J Neurol. 2010. PMID 20642790. DOI 10.1111/j.1468-1331.2010.03153.x. (abstract)
- Gibson GE, Luchsinger JA, et al. Benfotiamine and Cognitive Decline in Alzheimer's Disease: Results of a Randomized Placebo-Controlled Phase IIa Clinical Trial.. J Alzheimers Dis. 2020. PMID 33074237. DOI 10.3233/JAD-200896. (abstract)
- Katta N, Balla S, et al. Does Long-Term Furosemide Therapy Cause Thiamine Deficiency in Patients with Heart Failure? A Focused Review.. Am J Med. 2016. PMID 26899752. DOI 10.1016/j.amjmed.2016.01.037. (abstract)
- McLaughlin K, Joyal K, et al. Safety of intravenous push thiamine administration at a tertiary academic medical center.. J Am Pharm Assoc. 2020. PMID 31932197. DOI 10.1016/j.japh.2019.12.005. (abstract)
- Moskowitz A, Berg KM, et al. Thiamine for Renal Protection in Septic Shock (TRPSS): A Randomized, Placebo-controlled, Clinical Trial.. Am J Respir Crit Care Med. 2023. PMID 37364280. DOI 10.1164/rccm.202301-0034OC. (abstract)
- Pattanittum P, Kunyanone N, et al. Dietary supplements for dysmenorrhoea.. Cochrane Database Syst Rev. 2016. PMID 27000311. DOI 10.1002/14651858.CD002124.pub2. (abstract)
- Stephen JM, Grant R. Anaphylaxis from administration of intravenous thiamine.. Am J Emerg Med. 1992. PMID 1736919. DOI 10.1016/0735-6757(92)90129-l. (abstract)
- Stracke H, Lindemann A, et al. A benfotiamine-vitamin B combination in treatment of diabetic polyneuropathy.. Exp Clin Endocrinol Diabetes. 1996. PMID 8886748. DOI 10.1055/s-0029-1211460. (abstract)
- Teigen LM, Twernbold DD, et al. Prevalence of thiamine deficiency in a stable heart failure outpatient cohort on standard loop diuretic therapy.. Clin Nutr. 2016. PMID 26923517. DOI 10.1016/j.clnu.2016.02.011. (abstract)
- Wijnia JW. A Clinician's View of Wernicke-Korsakoff Syndrome.. J Clin Med. 2022. PMID 36431232. DOI 10.3390/jcm11226755. (abstract)
- Xu M, Ji J, et al. The effects of thiamine supplementation on patients with heart failure: A systematic review and meta-analysis of randomized controlled trials.. Complement Ther Med. 2022. PMID 35842069. DOI 10.1016/j.ctim.2022.102853. (abstract)
- Yasu T, Iimura Y, et al. Potential thiamine deficiency in elderly patients with gastrointestinal cancer undergoing chemotherapy.. Int J Clin Pharmacol Ther. 2020. PMID 31983387. DOI 10.5414/CP203595. (abstract)
- da Silva JSV, Seres DS, et al. ASPEN Consensus Recommendations for Refeeding Syndrome.. Nutr Clin Pract. 2020. PMID 32115791. DOI 10.1002/ncp.10474. (abstract)
- . MedlinePlus: Beriberi. . . (full-text)
- . MedlinePlus: Thiamin. . . (full-text)
- . NHS: B vitamins and folic acid. . . (full-text)
- . NIH Office of Dietary Supplements: Thiamin fact sheet for health professionals. . . (not-read)
- . USDA FoodData Central, SR Legacy (April 2018 release), saved copies. . . (saved-copy)
Where to buy
Check the label first. Whatever you buy, look for these:
- The amount of the active ingredient per serving, not just the front-label claim
- A third-party testing mark (USP, NSF or ConsumerLab)
- Other ingredients and allergens
- Ask a pharmacist about interactions with your medicines
Talk to a pharmacist or doctor before you start any supplement, especially if you take medicines. See the Safety tab for interactions.
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