Vitamin B1 (Thiamine)
Also known as: thiamine, thiamin
Medically reviewed by Nano Health Insights Editorial Team · Last reviewed 2026-06-29
Vitamin B1 (thiamine) is a water-soluble vitamin needed for energy metabolism, with only about 25–30 mg stored in the adult body.
Vitamin B1 (thiamine) is a water-soluble vitamin needed for energy metabolism, with only about 25–30 mg stored in the adult body. Because body stores are small and turn over quickly, thiamine must be consumed regularly through food or, when needed, supplements or medical treatment. Its active form, thiamine diphosphate, helps enzymes convert carbohydrates and some amino acids into usable cellular energy and supports normal nerve function. Severe deficiency can cause beriberi and Wernicke encephalopathy, which are medical problems that need prompt treatment.
What it is
Thiamine, also called thiamin or vitamin B1, is one of the eight B-complex vitamins. It is naturally present in foods, added to some fortified foods, and sold in multivitamins and standalone supplements. It is water-soluble, so the body does not store large reserves the way it stores fat-soluble vitamins.
Most thiamine in the body is present as thiamine diphosphate, also called thiamine pyrophosphate, which is the main metabolically active form. According to NIH Office of Dietary Supplements data, about 80% of the body's thiamine is in this form. Small body stores are one reason deficiency can develop within weeks in people with very low intake, poor absorption, heavy alcohol use, prolonged vomiting, or high metabolic stress.
Common food sources include:
| Food group | Examples |
|---|---|
| Whole and fortified grains | whole wheat, fortified cereals, enriched bread, rice |
| Legumes and nuts | lentils, beans, peas, peanuts, seeds |
| Animal foods | pork, some fish, poultry |
| Other | yeast extracts and some fortified packaged foods |
In India, thiamine intake can vary with dietary pattern and food processing. Diets heavily based on polished white rice can provide less thiamine than diets that include whole grains, pulses, nuts, and fortified foods.
How it works
Thiamine acts mainly as a coenzyme in carbohydrate metabolism. In practical terms, it helps cells extract energy from food. This matters most in tissues with high energy needs, especially the brain, heart, and nerves.
Key roles include support for enzymes involved in:
- Pyruvate metabolism
- Alpha-ketoglutarate metabolism
- Branched-chain amino acid metabolism
- Transketolase reactions in the pentose phosphate pathway
These pathways are important for ATP production, nerve signaling, and handling oxidative stress. When thiamine is low, cells cannot efficiently process glucose. That is one reason deficiency can affect the nervous system and heart so strongly.
Thiamine is absorbed in the small intestine. At usual dietary intakes, absorption is mainly by active transport; at higher supplemental doses, passive diffusion also contributes. Because excess thiamine is excreted in urine and the vitamin has a short half-life, regular intake matters more than occasional large amounts for most healthy people.
Evidence and uses
Thiamine is essential for preventing and treating deficiency. That is its clearest, best-supported use.
Deficiency syndromes include:
| Condition | Main features |
|---|---|
| Dry beriberi | peripheral neuropathy, weakness, numbness, reduced reflexes |
| Wet beriberi | fast heart rate, enlarged heart, edema, heart failure signs |
| Wernicke encephalopathy | confusion, eye movement problems, poor coordination |
| Wernicke-Korsakoff syndrome | severe neurologic syndrome, often linked to alcohol use disorder |
People at higher risk include those with alcohol use disorder, malnutrition, eating disorders, prolonged vomiting, bariatric surgery, chronic diuretic use, dialysis, HIV, severe illness, or refeeding after starvation. Infants can also be affected if intake is inadequate.
For the general public, thiamine supplements are sometimes marketed for energy, mood, or brain health. Evidence for benefit in people who are not deficient is limited and not consistent. Some studies have explored thiamine or related forms in diabetes, heart failure, neurodegenerative disease, and fatigue, but these are not established routine uses for most people.
If deficiency is suspected, clinicians may treat before lab confirmation, especially when Wernicke encephalopathy is a concern. In those settings, delay can be dangerous. Treatment often uses oral thiamine for mild deficiency and intravenous or intramuscular thiamine for severe deficiency or neurologic symptoms.
Safety and interactions
Thiamine from food is considered safe. Supplements are also generally well tolerated, and the NIH notes that there is no established tolerable upper intake level because serious toxicity from oral thiamine is rare.
Still, "safe" does not mean always appropriate. Important points include:
- Self-treating severe symptoms with supplements can delay urgent care.
- People with confusion, unsteady walking, persistent vomiting, or heavy alcohol use may need emergency assessment and parenteral thiamine.
- Some products contain very high doses that are not necessary for most healthy adults.
- Rare allergic reactions can occur, especially with injectable thiamine.
Drug and clinical interactions to know about:
- Loop diuretics such as furosemide can increase urinary thiamine loss.
- Chronic alcohol use can reduce intake, absorption, and utilization.
- After bariatric surgery or during prolonged illness, deficiency risk rises.
- Refeeding after starvation or severe malnutrition can unmask or worsen deficiency, so clinicians often give thiamine before or with carbohydrates.
If you are considering a supplement because of fatigue, neuropathy, poor appetite, alcohol use, or a restrictive diet, it is sensible to talk to a clinician or pharmacist rather than guessing the cause.
When to see a clinician
See a clinician if you have symptoms or risk factors that could fit thiamine deficiency, especially if they are new or progressive. Warning signs include numbness or tingling in the feet, muscle weakness, unexplained fatigue, poor appetite, swelling, shortness of breath, persistent vomiting, or major weight loss.
Seek urgent care for confusion, trouble walking, abnormal eye movements, severe weakness, or symptoms after heavy alcohol use or prolonged poor intake. These can suggest Wernicke encephalopathy or severe deficiency, which should be treated quickly.
Pregnant people, older adults, people with chronic illness, and those recovering from surgery or hospitalization may need closer nutritional review. In India and elsewhere, clinicians may also look at overall diet quality, grain type, alcohol use, and access to fortified foods.
Limitations and open questions
Thiamine's role in preventing and treating deficiency is well established, but several other claims are less certain. Evidence in humans is limited or mixed for using thiamine supplements to improve energy, cognition, mood, athletic performance, or chronic disease outcomes in people without clear deficiency.
Testing is also imperfect. Blood thiamine measures and functional markers such as erythrocyte transketolase are not always readily available, and results may not fully reflect tissue status in urgent situations. That is why clinicians sometimes treat based on risk and symptoms rather than waiting for a lab result.
Researchers are also studying whether different thiamine forms, such as benfotiamine, have distinct clinical uses. Some early findings are promising in specific settings, but they do not yet justify broad routine use for the general population. For most people, the main evidence-based message remains simple: get regular thiamine from a balanced diet, and treat suspected deficiency promptly.
FAQs
What does vitamin B1 do in the body?
Vitamin B1 helps enzymes turn carbohydrates and some amino acids into usable energy. Its active form, thiamine diphosphate, is especially important for the brain, nerves, and heart. Because the body stores only about 25–30 mg, regular intake is needed.
What foods are high in thiamine?
Good sources include pork, legumes, peas, nuts, seeds, whole grains, and fortified or enriched grain products such as some breads and cereals. In diets centered on polished white rice, thiamine intake may be lower than in diets that include whole grains and pulses. Food variety matters because thiamine is not stored in large amounts.
What are the signs of thiamine deficiency?
Early signs can include fatigue, irritability, poor appetite, tingling, numbness, and muscle weakness. More severe deficiency can cause dry beriberi, wet beriberi, or Wernicke encephalopathy, which may involve confusion, eye movement problems, and difficulty walking. These severe symptoms need urgent medical care.
Should I take a thiamine supplement for low energy?
Not necessarily. Thiamine supplements clearly help if you are deficient, but evidence is limited that they improve energy in people with normal thiamine status. If fatigue is persistent, a clinician can check for other common causes such as anemia, thyroid disease, sleep problems, depression, or other nutrient deficiencies.
Is too much vitamin B1 harmful?
Thiamine from food and standard supplements is generally considered safe, and no upper intake level has been set by the NIH because serious toxicity is rare. Even so, very high-dose products are usually unnecessary unless a clinician recommends them. Injectable thiamine can rarely cause allergic reactions, so medical supervision matters in hospital treatment.