Thiamin (Vitamin B1): Roles, Food Sources, Deficiency and Safety
Thiamin (vitamin B1): what it does, food sources, official intake levels, who is at risk of deficiency such as beriberi and Wernicke disease, and what is known about supplements.
Content last updated . This page has not been medically reviewed.
What is Vitamin B1 (thiamin) good for?
What the body uses it for, and how strong the evidence is. A normal job in the body is not proof that extra supplements add benefit; each card says which.
Turning carbohydrates into energy
Established roleThiamin helps body cells turn carbohydrates from food into energy.
Supplements: Supplements correct deficiency; no good evidence of extra benefit when intake is adequate. We found no source showing that extra thiamin raises energy in people who are not deficient.
Keeping the nervous system healthy
Established roleThiamin helps keep the nervous system working normally.
Supplements: Supplements correct deficiency; no good evidence of extra benefit when intake is adequate.
Sending nerve signals
Established roleThiamin takes part in how nerves pass signals.
Supplements: Supplements correct deficiency; no good evidence of extra benefit when intake is adequate.
Energy supply to the brain
Established roleThiamin helps supply energy to the brain and nervous system.
Supplements: Supplements correct deficiency; no good evidence of extra benefit when intake is adequate. Evidence for memory or mood benefit in people who are not deficient was not found.
Muscle contraction
Established roleThiamin plays a part in muscles contracting.
Supplements: Supplements correct deficiency; no good evidence of extra benefit when intake is adequate.
Preventing beriberi and Wernicke disease
Established roleEnough thiamin prevents beriberi (affecting heart or nerves) and the brain conditions Wernicke disease and Korsakoff syndrome.
Supplements: This is deficiency treatment and prevention for at-risk people, not a benefit for people with adequate intake.
Connected topics
Open a group to see how each topic connects and how strong the evidence is.
Body systems (5)
- Nervous SystemEstablished role
Thiamin is needed for a healthy nervous system, and severe lack causes nerve damage. Extra supplements have not been shown to help when intake is adequate.
- Brain & FocusEstablished role
The brain relies on thiamin to get energy from carbohydrate, and severe lack can cause brain damage. No source shows better focus from extra thiamin in people who are not deficient.
- Cardiovascular SystemDeficiency link
Severe thiamin lack can cause wet beriberi, which affects the heart and circulation. Trials of thiamin in heart failure found no evidence of benefit.
- Energy & FatigueEstablished role
Thiamin is needed to turn food into energy, and deficiency causes weakness and fatigue. There is no good evidence it raises energy in people who are not deficient.
- Musculoskeletal SystemEstablished role
Thiamin plays a role in muscle contraction. No benefit from extra supplements is shown.
Body parts (4)
- BrainEstablished role
The brain depends on thiamin for energy; severe deficiency can cause Wernicke disease and Korsakoff syndrome.
- Nervous SystemEstablished role
Thiamin helps keep nerves healthy and passing signals; deficiency can cause nerve damage.
- HeartDeficiency link
Wet beriberi from severe thiamin lack affects the heart. Thiamin supplements did not improve heart function in trials in people with heart failure.
- MusclesEstablished role
Thiamin plays a role in muscle contraction.
Functional actions (2)
- Energy ProductionEstablished role
Thiamin helps cells convert carbohydrate into energy. This is its normal role; extra amounts have not been shown to add energy.
- Nervous System SupportEstablished role
Thiamin supports normal nerve function and signalling.
Root causes (2)
- Nutrient DeficiencyDeficiency link
Not getting or absorbing enough thiamin causes weakness, fatigue, confusion and nerve damage, and can lead to beriberi.
- Medication Side EffectsDeficiency link
High doses of water pills (diuretics) can raise the risk of thiamin deficiency.
Habits (1)
- Balanced NutritionEstablished role
The body cannot store thiamin, so it comes from daily food such as whole and fortified grains, legumes, nuts, seeds, pork and fish.
Conditions & symptoms (4)
- BeriberiDeficiency link
Beriberi is caused by thiamin lack: wet beriberi affects heart and circulation, dry beriberi affects nerves. Treated with thiamin.
- Thiamine DeficiencyDeficiency link
Too little thiamin causes weakness, fatigue, confusion and nerve damage. Most often seen in the US in people who drink heavily.
- Wernicke EncephalopathyDeficiency link
A brain condition from severe thiamin lack with eye movement, walking and thinking problems. Needs urgent medical care.
- Wernicke-Korsakoff SyndromeDeficiency link
Korsakoff syndrome can follow Wernicke disease and brings memory loss and confusion.
Overview
Thiamin, also spelled thiamine, is vitamin B1. The NHS says it helps the body break down and release energy from food and keeps the nervous system healthy. [1] MedlinePlus adds that it helps cells turn carbohydrates into energy and plays a role in muscle contraction and nerve signals. [2] It is water soluble and the body cannot store it, so it is needed from the diet every day. [1]If you or someone else has confusion, unsteady walking or unusual eye movements, especially with heavy alcohol use or long-term poor eating, get urgent medical care. These can be signs of severe thiamin deficiency, which doctors treat. It is not something to treat alone with a shop supplement. [2][3]
Evidence labels used on this page: established nutritional role / deficiency treatment, insufficient evidence, no good evidence of benefit and marketing claim. "Proper evidence not found" means we looked in the places named and found nothing usable.
Food sources
The NHS lists peas, some fresh fruits such as bananas and oranges, nuts, wholegrain bread, some fortified breakfast cereals, and liver (avoid liver if pregnant). [1] MedlinePlus lists enriched, fortified and whole grain products, wheat germ, beef steak and pork, trout and bluefin tuna, eggs, legumes and peas, and nuts and seeds. [2] For serving-by-serving lists see foods high in biotin, thiamin, riboflavin, niacin, B6 and pantothenic acid.Official intake levels
These are published reference levels for the groups named. They are not personal advice. For what the terms mean, see RDA, AI, DV and UL.| Body, country and year | Group | Level for thiamin |
|---|---|---|
| NHS, UK, page reviewed 2020 | Adults 19 to 64, men / women | 1 mg / 0.8 mg a day [1] |
| US Dietary Reference Intakes, as listed by MedlinePlus (review 2025) | Males 14 and older / females 19 and older | RDA 1.2 mg / 1.1 mg a day; 1.4 mg in pregnancy and lactation [2] |
| Health Canada, table dated 2025 | Adults 19 to 30, males / females | RDA 1.2 mg / 1.1 mg a day; no upper level set because data are insufficient [4] |
| EFSA, EU, overview version 2025 | All groups | No adequate data to derive a tolerable upper level [5] |
| Daily Value on US labels (FDA, 2024) | Label reference only | 1.2 mg [6] |
A missing upper level means a lack of data, not proof that any amount is safe. [4]
Deficiency: who is at risk
Established. MedlinePlus says a lack of thiamin can cause weakness, fatigue, confusion, psychosis and nerve damage. In the United States it is most often seen in people who drink a lot of alcohol, because alcohol makes it hard to absorb thiamin. [2] Severe deficiency can lead to beriberi (wet beriberi affects the heart and circulation, dry beriberi affects the nerves) and to the brain conditions Wernicke disease and Korsakoff syndrome. [2][3]MedlinePlus also names other situations that raise risk: a rare inherited problem absorbing thiamin, dialysis, high doses of water pills (diuretics), and breastfed or formula-fed infants whose milk lacks enough thiamin. [3] A 2010 European neurology guideline advised following thiamin status for at least 6 months after weight-loss (bariatric) surgery. [7] See vitamins after bariatric surgery.
What research shows for specific uses
| Question | What the source found | Label |
|---|---|---|
| Treating severe deficiency (beriberi, Wernicke disease) | MedlinePlus says treatment is thiamin by injection or by mouth, and symptoms usually improve quickly once treated. [3] | Established |
| Which hospital regimen is best for alcohol-related Wernicke encephalopathy | A review of six publications (138 patients) found a wide variety of regimens, all with symptom improvement and few side effects, so no single best regimen could be named. [8] | Insufficient evidence on regimen |
| Thiamin supplements in people with heart failure | A 2022 meta-analysis of 8 trials (384 patients) found no evidence to support an effect on heart function or symptoms. [9] | No good evidence of benefit |
| Energy, mood or memory in people who are not deficient | Proper evidence not found. We read the NHS and MedlinePlus pages and searched PubMed for thiamine supplementation reviews; results were trials in heart failure and intensive care, not healthy adults. | Marketing claim |
Trials in people who are deficient, in hospital or at risk do not transfer to people eating a varied diet.
Safety and precautions
- Upper limits: the NHS says there is not enough evidence on the effects of high-dose thiamin supplements, and that 100 mg or less a day is unlikely to cause harm (UK advice). [1] MedlinePlus says no poisoning linked to too much thiamin is known (US). [2]
- Medicines: high-dose diuretics can raise deficiency risk (see above). [3] Other interactions: Proper evidence not found in the pages we could read (NIH Office of Dietary Supplements pages were blocked). Check medication interactions and ask a pharmacist.
- Pregnancy and breastfeeding: the US RDA rises to 1.4 mg. [2] Ask your midwife, doctor or pharmacist before adding supplements.
- Kidney and liver conditions, and alcohol: dialysis and heavy drinking both raise risk. [3] A 2023 review says the need for water-soluble vitamins changes as kidney disease advances and should be managed by the care team. [10] See vitamins and kidney or liver disease.
- Before surgery: Proper evidence not found for thiamin specifically; tell your surgical team about every supplement (vitamins before surgery).
- Quality: supplements are not all alike; see quality testing and certifications.
Testing and its limits
MedlinePlus says doctors can measure thiamin in blood and check urine when beriberi is suspected, and may repeat blood tests during treatment. [3] A European guideline advised drawing blood for total thiamin before treatment starts in suspected Wernicke disease. [7] Symptoms alone cannot confirm a deficiency, and ranges vary by laboratory. See vitamin deficiency testing.Related
All vitamins · Understanding vitamins · B-complex products · Vitamins and alcoholFrequently asked questions
What foods are high in thiamin?
The NHS and MedlinePlus list whole and fortified grains, peas and legumes, nuts and seeds, pork and some fish. [1][2]
Who is most at risk of thiamin deficiency?
In the United States, mainly people with heavy alcohol use. Dialysis and high-dose diuretics are also named as risks. [2][3]
Is thiamin safe in high amounts?
No poisoning is known in the US source, but the NHS says the evidence on high-dose supplements is not enough. [2][1] Talk to a clinician or pharmacist before taking high-dose products.
Does thiamin give you energy?
It is needed to turn food into energy, but Proper evidence not found that extra thiamin gives more energy in people who are not deficient. [1]
Can thiamin deficiency be diagnosed from symptoms?
No. Symptoms such as tiredness overlap with many conditions, and a clinician decides on blood or urine tests. [3]
References
- NHS (UK). B vitamins and folic acid. Page last reviewed 3 August 2020. Read 2026-10-23.
- MedlinePlus Medical Encyclopedia (US National Library of Medicine). Thiamin. Review date 1/21/2025. Read 2026-10-23.
- MedlinePlus Medical Encyclopedia (US National Library of Medicine). Beriberi. Review date 7/23/2024. Read 2026-10-23.
- Health Canada. Dietary reference intakes tables: Reference values for vitamins. Page dated 2025-11-19. Read 2026-10-23 through a web-fetch tool, which returned the tables as a text summary; direct download was blocked.
- European Food Safety Authority. Overview on Tolerable Upper Intake Levels as derived by the Scientific Committee on Food (SCF) and the EFSA NDA Panel, version 1, August 2025. Read 2026-10-23 (text extracted from the PDF; table layout reconstructed).
- US Food and Drug Administration. Daily Value on the Nutrition and Supplement Facts Labels. Content current as of 03/05/2024. Read 2026-10-23.
- Galvin R, Bråthen G, Ivashynka A, et al. EFNS guidelines for diagnosis, therapy and prevention of Wernicke encephalopathy. Eur J Neurol 2010;17(12):1408-18. Read 2026-10-23.
- Smith H, McCoy M, Varughese K, Reinert JP. Thiamine dosing for the treatment of alcohol-induced Wernicke's encephalopathy: a review of the literature. J Pharm Technol 2021;37(2):107-113. Read 2026-10-23.
- Xu M, Ji J, Lu Q, 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;70:102853. Read 2026-10-23.
- Kędzierska-Kapuza K, Szczuko U, Stolińska H, et al. Demand for water-soluble vitamins in a group of patients with CKD versus interventions and supplementation: a systematic review. Nutrients 2023;15(4):860. Read 2026-10-23.