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Metabolic Health

Thiamine

Evidence Level
Strong
5 Clinical Trials
6 Documented Benefits
4/5 Evidence Score

Thiamine, also known as vitamin B1, is a water-soluble vitamin essential for converting carbohydrates into energy and supporting nervous system function. It plays a key role in glucose metabolism and is necessary for proper muscle and nerve activity. Natural food sources of thiamine include whole grains, pork, legumes, nuts, and seeds, as well as fortified cereals and bread. Thiamine is also available in supplement form, often as thiamine hydrochloride or benfotiamine, a fat-soluble derivative used for better absorption, especially in nerve health formulas.

Studied Dose 1.1–1.2 mg/day (RDA); Benfotiamine (fat-soluble form): 150–300 mg/day; therapeutic/neuropathy: 25–100 mg/day; IV in Wernicke encephalopathy
Active Compound Vitamin B1 (Thiamine HCl / Benfotiamine)
Deficiency information View details

Thiamine (vitamin B1) deficiency is rare in the US general population due to grain fortification, but it remains common in people with chronic alcohol use, certain GI conditions, and after bariatric surgery. Severe deficiency causes beriberi or Wernicke-Korsakoff syndrome — both can be life-threatening and may cause permanent neurological damage if not treated promptly.

Common symptoms

  • Fatigue and weakness
  • Loss of appetite, weight loss
  • Confusion or memory problems
  • Tingling or numbness in hands and feet (peripheral neuropathy)
  • Muscle weakness, especially in legs
  • Heart palpitations or shortness of breath (wet beriberi affects the heart)
  • Difficulty walking, balance problems (ataxia)
  • Eye movement abnormalities (ophthalmoplegia — Wernicke's)
  • Severe disorientation or confusion (Wernicke encephalopathy — medical emergency)

At-risk groups

  • People with alcohol use disorder (highest risk for Wernicke-Korsakoff syndrome)
  • People who've had bariatric surgery (especially gastric bypass)
  • People with severe or persistent vomiting (hyperemesis gravidarum, post-surgical)
  • People on long-term diuretic therapy (furosemide)
  • People with chronic kidney disease, especially on dialysis
  • Older adults with poor diets
  • People with chronic GI conditions causing malabsorption (Crohn's, celiac)
  • Populations relying on polished white rice as a staple
When to see a doctor: Sudden confusion, eye movement abnormalities, or balance problems — especially in someone with alcohol use disorder, recent bariatric surgery, or severe vomiting — should be treated as a MEDICAL EMERGENCY. Wernicke encephalopathy requires immediate IV thiamine; oral supplementation is too slow.
Explore related deficiencies →
Sources: NIH ODS — Thiamin Health Professional Fact Sheet · Vitamin B1 (Thiamine) Deficiency — StatPearls (NBK537204)

Benefits

Energy Production

Thiamine is a coenzyme in carbohydrate metabolism, helping convert food into energy (ATP). It supports cellular energy production, particularly in high-energy tissues like the brain and muscles.

Supported by Trial 1, Trial 2

Nervous System Health

Thiamine is crucial for nerve function, supporting nerve signal transmission and myelin sheath maintenance. It may help prevent or manage nerve-related conditions like neuropathy, especially in cases of deficiency.

Supported by Trial 2, Trial 1

Brain Function

Thiamine supports cognitive health by aiding energy supply to brain cells. Deficiency is linked to neurological issues like Wernicke-Korsakoff syndrome (common in alcohol use disorder), and supplementation may improve memory and focus in deficient individuals.

Supported by Trial 2, Trial 4

Heart Health

Thiamine supports heart muscle function and may improve outcomes in heart failure patients with deficiency. It helps maintain proper cardiac energy metabolism.

Supported by Trial 2, Trial 5

Metabolic Disorders

Thiamine may benefit individuals with diabetes by improving glucose metabolism and reducing complications like diabetic neuropathy, though evidence is preliminary.

Supported by Trial 1, Trial 2

Digestive Health

Thiamine aids in producing stomach acid and supporting digestive enzyme function, potentially improving digestion and appetite in deficient individuals.

Supported by Trial 1, Trial 2

Mechanism of action

1

Coenzyme in Energy Metabolism

Thiamine pyrophosphate (TPP), the active form of thiamine, is a coenzyme for enzymes like pyruvate dehydrogenase and alpha-ketoglutarate dehydrogenase in the citric acid cycle, facilitating carbohydrate metabolism and ATP production.

2

Nerve Function

TPP supports nerve signal transmission by aiding sodium-potassium ATPase activity and maintaining myelin integrity, preventing nerve damage.

3

Glucose Regulation

Thiamine modulates glucose metabolism pathways, reducing oxidative stress and complications in conditions like diabetes.

Clinical trials

1
Thiamine for Septic Shock — Clinical Trial

Two-center clinical trial (NCT01070810) in 88 patients with septic shock (lactate >3 mmol/L) receiving IV thiamine (200 mg twice daily) vs placebo. Outcomes: lactate clearance, mortality. (Crit Care Med)

88 septic shock patients.

Modest signals on lactate clearance; mortality benefit in pre-specified thiamine-deficient subgroup. Critical context: subsequent vitamins, ATESS trials of thiamine + vitamin C + steroids (HAT protocol —) — large rigorous trials including the HYVCTTSSS multi-center clinical trial — were negative for the metabolic resuscitation protocol. The Marik HAT protocol generated enthusiasm that did not survive rigorous validation.

2
IV Thiamine in Critically Ill Patients — Evidence Synthesis

Pooled analysis of 35 clinical trials (n=3,494, through) evaluating IV thiamine (100-200 mg) in critically ill patients. (Tao et al. 2024, Clin Nutr)

Pooled across 35 critical care clinical trials.

IV thiamine modestly improved lactate clearance and certain ICU outcomes. Mortality benefit not consistently observed. Note: thiamine deficiency is common in ICU populations (alcoholism, malnutrition, refeeding syndrome) — empiric thiamine in critically ill remains reasonable practice.

3
Pharmacological Vitamin B1 in Critically Ill Enterally Fed — Clinical Trial

Multicenter clinical trial (ACTRN12619000121167) in 90 critically ill enterally fed patients receiving high-dose thiamine vs control. (Clin Nutr)

90 critically ill ICU patients.

Modest signals on certain biomarkers. ICU thiamine evidence base remains mixed; high-dose pharmacological thiamine is generally safe.

4
Pharmacological Thiamine in Alzheimer's Disease — Phase 2a Pilot

Phase 2a, single-site, randomized, double-blind, placebo-controlled pilot trial in mild-moderate AD patients receiving high-dose thiamine.

Pilot AD patients.

Modest signals on cognitive measures. Critical context: AD treatment landscape now includes lecanemab/donanemab (anti-amyloid antibodies, FDA-approved 2023-2024). Pharmacological thiamine has no established AD treatment role; pilot only.

5
Sustained High-Dose Thiamine in Cardiac Surgery — Clinical Trial

Clinical trial in 64 high-risk cardiac surgery patients undergoing CPB receiving high-dose thiamine vs placebo. Outcomes: lactate, postoperative outcomes. (J Cardiothorac Vasc Anesth)

64 cardiac surgery patients.

Modest signals on lactate during CPB. Cardiac surgery thiamine evidence still developing; not standard care.

Side effects and drug interactions

Common Potential side effects

Gastrointestinal Issues: Mild side effects like nausea, stomach upset, or diarrhea may occur, especially with high oral doses (e.g., >100 mg/day) or when taken on an empty stomach.
Allergic Reactions: Rare allergic reactions, such as rash, itching, or swelling, may occur, particularly with high doses or intravenous/intramuscular administration (used medically for deficiency). Severe allergic reactions (e.g., anaphylaxis) are very rare but have been reported, mostly with injectable thiamine.
Skin Irritation: Some users report mild skin irritation or flushing, especially with high doses or topical thiamine products (less common).
Restlessness or Nervousness: High doses may cause feelings of restlessness, nervousness, or mild agitation in sensitive individuals, though this is uncommon.

Important Drug interactions

Diuretics (furosemide) — loop diuretics increase urinary thiamine excretion, potentially causing deficiency with long-term use; thiamine supplementation recommended
Alcohol — ethanol impairs thiamine absorption, storage, and utilization; all heavy drinkers should supplement thiamine
Digoxin — thiamine deficiency can impair cardiac function; correction of deficiency may affect digoxin requirements
No significant pharmacokinetic drug interactions at supplemental doses

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Frequently asked questions about Thiamine

How much thiamine (B1) should I take?

The RDA is about 1.1 to 1.2 mg per day. B-complex and supplement doses are often much higher (25 to 100 mg), which is safe because thiamine is water-soluble and excess is excreted. Some therapeutic uses involve higher amounts under medical care.

What is thiamine good for?

Thiamine (vitamin B1) is essential for converting carbohydrates into energy and for healthy nerve and brain function. Deficiency, though uncommon, can affect the nerves and heart.

Who is at risk of thiamine deficiency?

People with heavy alcohol use, certain gut or absorption problems, those on long-term diuretics, and people with very poor diets are most at risk. These groups may benefit from supplementation or testing.

What is benfotiamine?

Benfotiamine is a fat-soluble form of thiamine that is better absorbed and is often used in studies on nerve comfort and blood-sugar-related nerve support. It is a popular alternative to regular thiamine for those specific goals.

What is Thiamine?

Thiamine, also known as vitamin B1, is a water-soluble vitamin essential for converting carbohydrates into energy and supporting nervous system function. It plays a key role in glucose metabolism and is necessary for proper muscle and nerve activity.

What is Thiamine used for?

Thiamine is researched primarily for Metabolic Health. Thiamine is a coenzyme in carbohydrate metabolism, helping convert food into energy (ATP). It supports cellular energy production, particularly in high-energy tissues like the brain and muscles.

What are the signs of Thiamine deficiency?

Thiamine (vitamin B1) deficiency is rare in the US general population due to grain fortification, but it remains common in people with chronic alcohol use, certain GI conditions, and after bariatric surgery.

What is the recommended dosage of Thiamine?

The clinically studied dose is 1.1–1.2 mg/day (RDA); Benfotiamine (fat-soluble form): 150–300 mg/day; therapeutic/neuropathy: 25–100 mg/day; IV in Wernicke encephalopathy Always follow the product label and check with a healthcare provider for personal advice.

Is Thiamine safe, and does it have side effects?

For most healthy adults, Thiamine is well tolerated at studied doses. Reported effects can include: Gastrointestinal Issues: Mild side effects like nausea, stomach upset, or diarrhea may occur, especially with high oral doses (e.g., >100 mg/day) or when taken on an empty stomach. It may also interact with some medications. Thiamine is not right for everyone, so check with a healthcare provider first if you are pregnant or breastfeeding, have a medical condition, or take prescription medication.

Does Thiamine interact with any medications?

Possible interactions include: Diuretics (furosemide) — loop diuretics increase urinary thiamine excretion, potentially causing deficiency with long-term use; thiamine supplementation recommended Alcohol — ethanol impairs thiamine absorption, storage, and utilization; all heavy drinkers should supplement thiam… If you take prescription medication, check with a pharmacist or doctor before using it.

How strong is the scientific evidence for Thiamine?

NutraSmarts rates the evidence for Thiamine as Strong (4 out of 5). It is backed by 5 clinical trials and 4 cited references summarized on this page. A higher rating reflects more, larger, and better-designed human studies.

References(4 citations)

Evidence ratings on NutraSmarts are based on the totality of human clinical research, with emphasis on randomized controlled trials, meta-analyses, and systematic reviews. The references below directly support claims made throughout this page.

  1. Galvin R, Brathen G, Ivashynka A, Hillbom M, Tanasescu R, Leone MA. EFNS guidelines for diagnosis, therapy and prevention of Wernicke encephalopathy. Eur J Neurol. 2010;17(12):1408-18. doi: 10.1111/j.1468-1331.2010.03153.x.PubMedUsed to support: Supports deficiency claim (solid): authoritative EFNS guideline establishing parenteral thiamine as the treatment and prophylaxis for Wernicke encephalopathy, including in alcohol-use disorder. Confirms thiamine correction of deficiency is essential and well established.
  2. Sechi G, Serra A. Wernicke's encephalopathy: new clinical settings and recent advances in diagnosis and management. Lancet Neurol. 2007;6(5):442-55. doi: 10.1016/S1474-4422(07)70104-7.PubMedUsed to support: Supports deficiency claim (solid): comprehensive review of thiamine-deficiency states (Wernicke-Korsakoff syndrome and beyond) showing prompt thiamine repletion prevents and treats the syndrome. Reinforces that deficiency correction is the core, evidence-based use.
  3. Stracke H, Gaus W, Achenbach U, Federlin K, Bretzel RG. Benfotiamine in diabetic polyneuropathy (BENDIP): results of a randomised, double blind, placebo-controlled clinical study. Exp Clin Endocrinol Diabetes. 2008;116(10):600-5. doi: 10.1055/s-2008-1065351.PubMedUsed to support: Diabetic neuropathy mixed: this RCT of benfotiamine (a thiamine derivative) showed only a modest improvement in a neuropathy symptom score that did not reach the primary significance threshold for most outcomes. Illustrates the inconsistent, mixed evidence for benfotiamine in diabetic neuropathy.
  4. Mancinelli R, Ceccanti M. Biomarkers in alcohol misuse: their role in the prevention and detection of thiamine deficiency. Alcohol Alcohol. 2009;44(2):177-82. doi: 10.1093/alcalc/agn117.PubMedUsed to support: Supports thiamine-in-alcohol-use-disorder claim: reviews why chronic alcohol misuse causes thiamine deficiency (poor intake, malabsorption, impaired utilization) and the role of thiamine repletion. Reinforces the well-established deficiency-correction benefit in this population.