Thiamine (Vitamin B1)
Summary
Most people get enough thiamine from food (adult RDA 1.1–1.2 mg/day; no upper limit). Supplements correct deficiency, which is common with heavy drinking, after bariatric surgery and in some people with heart failure or diabetes. Beyond deficiency, pooled heart-failure trials found no benefit (grade C), and benfotiamine results for diabetic neuropathy and early Alzheimer's disease are mixed (C–D).
Key facts
- Water-soluble vitamin B1; supplements use thiamine hydrochloride or mononitrate, or the fat-soluble derivative benfotiamine[1]
- Heart failure: no effect on LVEF or 6-minute walk in pooled RCTs (C); diabetic neuropathy symptoms with benfotiamine: mixed (C); early Alzheimer's with benfotiamine: mixed (D)[2][6][5]
- 150–300 mg/day thiamine HCl and 300–900 mg/day benfotiamine in oral trials, far above the 1.1–1.2 mg RDA[6][7][8][9][10]
- RDA 1.2 mg/day (men) and 1.1 mg/day (women), 1.4 mg in pregnancy and lactation; no UL was set[1]
- Thiamine is not known to interact with medicines, but furosemide and fluorouracil can lower thiamine levels[1]
- 7 graded human outcomes on this page
- October 10, 2026
How it works
EstablishedThiamin diphosphate (TDP) is a cofactor for five enzymes in glucose, amino acid and lipid metabolism, including transketolase. Benfotiamine was developed to raise thiamine levels more than water-soluble salts, and in diabetes research it is used to target glucose-driven damage pathways; whether this changes clinical outcomes is unproven.[1][6]
What the human research says
Human trials only, one row per outcome. The form column shows what each trial actually tested. Grades follow our evidence-grading policy.
At a glance: strongest evidence per outcome
| Outcome | Grade | Effect | Strongest evidence | Rows |
|---|---|---|---|---|
| Heart failure | Grade C | No effect | Meta-analysis of 6 trials · n = 298 · 2023 | 2 rows |
| Diabetes complications | Grade C | Mixed | RCT · n = 133 · 2008 | 3 rows |
| Cognition | Grade D | Mixed | RCT · n = 70 · 2020 | 1 row |
| Blood sugar | Grade D | Improved | Crossover RCT · n = 12 · 2013 | 1 row |
Every graded row
| Outcome | Effect | Grade | Best evidence | PMID |
|---|---|---|---|---|
| Heart failure: mortality, hospitalization and symptoms | No effect | Grade C | Meta-analysis · n = 298 · 2023 Adults with symptomatic heart failure in 6 RCTs Form: thiamine · Dose: Varied across trials (not given in the abstract) · Duration: Varied across trials No significant differences in mortality (p=0.61), hospitalization (p=0.53), dyspnea, LVEF (p=0.08) or 6-minute walk; heart rate was the only outcome that changed (p=0.04). | 37126872 (opens PubMed)Source [3] |
| Heart failure: ejection fraction, walking distance and NT-proBNP | No effect | Grade C | Meta-analysis · n = 274 · 2024 Adults with chronic heart failure in 7 double-blind RCTs (5 parallel, 2 crossover) Form: thiamine (oral or IV across trials) · Dose: Varied across trials (not given in the abstract) · Duration: Varied across trials No significant effect versus placebo on LVEF (WMD 1.65%, 95% CI −1.10 to 4.41), end-diastolic volume, 6-minute walk, NT-proBNP or NYHA class. Thiamine did correct thiamine deficiency. | 38940395 (opens PubMed)Source [2] |
| Diabetic polyneuropathy symptoms | Mixed | Grade C | RCT · n = 133 · 2008 Adults with symmetrical distal diabetic polyneuropathy (Germany) Form: benfotiamine · Dose: 300 or 600 mg/day · Duration: 6 weeks The Neuropathy Symptom Score improved more with benfotiamine in the per-protocol analysis (p=0.033) but only borderline when all randomized patients were analysed (p=0.055); the Total Symptom Score did not differ. Effects were larger at 600 mg/day. Well tolerated. | 18473286 (opens PubMed)Source [6] |
| Urinary albumin excretion in diabetic kidney disease | No effect | Grade C | RCT · n = 82 · 2010 Adults with type 2 diabetes and albuminuria (15–300 mg/24 h) despite ACE inhibitors or ARBs (Netherlands) Form: benfotiamine · Dose: 900 mg/day · Duration: 12 weeks Thiamine status improved (p<0.001), but neither 24-hour urinary albumin nor the kidney-injury marker KIM-1 fell versus placebo. | 20413516 (opens PubMed)Source [7] |
| Cognitive decline in amnestic MCI or mild Alzheimer's disease | Mixed | Grade D | RCT · n = 70 · 2020 Adults with amnestic MCI or mild dementia due to Alzheimer's disease (US) Form: benfotiamine · Dose: 600 mg/day (300 mg twice daily) · Duration: 12 months The primary outcome (ADAS-Cog) worsened 43% less with benfotiamine, but this was not significant (p=0.125); worsening on the Clinical Dementia Rating was 77% lower (p=0.034). Benfotiamine was safe. | 33074237 (opens PubMed)Source [5] |
| Urinary albumin excretion in type 2 diabetes | Improved | Grade D | RCT · n = 40 · 2009 Adults with type 2 diabetes and microalbuminuria (Pakistan) Form: thiamine · Dose: 300 mg/day (3 × 100 mg) · Duration: 3 months Urinary albumin fell from baseline with thiamine (median −17.7 mg/24 h) and was lower than placebo at 3 months (30.1 vs 35.5 mg/24 h, p<0.01). | 19057893 (opens PubMed)Source [8] |
| Blood glucose in type 2 diabetes or impaired glucose tolerance | Improved | Grade D | Crossover RCT · n = 12 · 2013 Adults with impaired glucose tolerance or new type 2 diabetes (Australia) Form: thiamine · Dose: 300 mg/day · Duration: 6 weeks per phase 2-hour glucose fell from baseline on thiamine (8.78 vs 9.89 mmol/L, p=0.004); fasting glucose and insulin rose on placebo but not on thiamine. | 23715873 (opens PubMed)Source [9] |
Forms
| Form | Elemental % | Absorption (human data) | GI tolerance | Studied for |
|---|---|---|---|---|
| Thiamine hydrochloride or thiamine mononitrate | Varies[1] | Absorbed by active transport at nutritional doses and by passive diffusion at high doses; absorption declines steeply above about 5 mg per dose.[1] | No adverse effects reported from high intakes, so no UL was set.[1] | Heart-failure and blood-sugar trials (150–300 mg/day) |
| Benfotiamine (synthetic fat-soluble thiamine derivative) | Varies[1][7] | Not water soluble; converted to thiamine in the body. In a 12-week trial 900 mg/day clearly raised thiamine status.[1][7] | Well tolerated at 300–600 mg/day for 6 weeks and 600 mg/day for 12 months.[6][5] | Diabetic neuropathy (300–600 mg/day), diabetic kidney disease (900 mg/day), early Alzheimer's (600 mg/day) |
| Intravenous or intramuscular thiamine (prescription) | Varies[1][11] | Bypasses the gut; guidelines prefer it for suspected Wernicke's encephalopathy because oral doses may not raise blood levels enough.[1] | No dose-related differences in neurological outcomes across 100–1500 mg/day regimens in two RCTs.[11] | Wernicke's encephalopathy prevention and treatment |
Studied doses
Doses studied in human trials ranged from 150 to 300 mg/day of thiamine HCl for 1–3 months and 300 to 900 mg/day of benfotiamine for 6 weeks to 12 months. The RDA is only 1.1–1.2 mg/day; the WHO regimen for mild deficiency is 10 mg/day for a week, then 3–5 mg/day.[1][5][6][7][8][9][10]
Intake reference: Adult RDA: 1.2 mg/day for men and 1.1 mg/day for women; 1.4 mg/day in pregnancy and lactation. No Tolerable Upper Intake Level has been set.[1] No UL was set because no adverse effects have been reported from high intakes from food or supplements. NIH ODS fact sheet (updated February 9, 2023).
Interactions
Published interactions only: each row cites a source. No row means none was found in our sources, not that a combination is safe.
Medicines that can lower levels
- Loop diureticsNIH fact sheetLinked to lower thiamine levels through urinary loss, possibly to deficient levels; whether supplements stop this is untested.[1]
- Fluorouracil chemotherapyNIH fact sheetCase reports of beriberi and Wernicke's encephalopathy, possibly from blocked formation of active thiamine.[1]
Who should be careful
- Suspected Wernicke's encephalopathy
- Confusion, unsteady walking or eye-movement problems in someone who drinks heavily is an emergency. Guidelines call for intravenous thiamine because oral doses may not raise blood levels enough.[1]
- Expecting a heart-failure treatment
- Pooled trials found no effect on ejection fraction, walking distance, hospitalization or mortality, beyond correcting deficiency.[2][3]
- Long-term furosemide users
- Loop diuretics can drain thiamine; ask your prescriber about checking thiamine status before adding a supplement on your own.[1]
Talk to your pharmacist or clinician before starting a supplement, especially if you take prescription medicines.
Safety
Thiamine has an unusually clean safety record, which is why no upper limit exists.
- No UL
- The Food and Nutrition Board found no reports of harm from intakes of 50 mg/day or more and set no UL, though it noted that excessive intakes could still have effects.[1]
- Trial tolerability
- Benfotiamine was well tolerated at up to 600 mg/day for 6 weeks and safe at 600 mg/day for 12 months.[5][6]
- Deficiency is the real risk
- Up to 80% of people with chronic alcohol use disorder develop deficiency, and Wernicke's encephalopathy after bariatric surgery can leave lasting damage.[1]
Food sources
| Food | Serving | Amount |
|---|---|---|
| Breakfast cereal fortified with 100% DV | 1 serving | 1.2 mg[1] |
| Egg noodles, enriched, cooked | 1 cup | 0.5 mg[1] |
| Pork chop, broiled | 3 oz | 0.4 mg[1] |
| Trout, cooked | 3 oz | 0.4 mg[1] |
| Black beans, boiled | 1/2 cup | 0.4 mg[1] |
- Breakfast cereal fortified with 100% DV1.2 mg
- Egg noodles, enriched, cooked0.5 mg
- Pork chop, broiled0.4 mg
- Trout, cooked0.4 mg
- Black beans, boiled0.4 mg
How to read the label
- Label dose vs clinical doseMultivitamins usually carry about 1.5 mg, close to the 1.1–1.2 mg RDA. Trials beyond deficiency used 100–300 mg thiamine HCl or 300–900 mg benfotiamine, 100 to 750 times the RDA.[1][6][8]
- Benfotiamine is not plain thiamineBenfotiamine is a synthetic fat-soluble derivative; the neuropathy, kidney and Alzheimer's trials used it, not thiamine HCl, so their results do not transfer to ordinary B1 tablets.[1][5][6]
- Salt formThiamine HCl and mononitrate are the common, stable supplement forms; the label amount usually refers to the salt.[1]
Cost per studied dose, without the sales pitch
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Cost per studied dose
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Frequently asked questions
How much thiamine do I need a day?
Adults need 1.2 mg/day (men) or 1.1 mg/day (women), and 1.4 mg in pregnancy or breastfeeding. Most people in the US get this from fortified grains, pork, fish and beans.[1]
Can you take too much vitamin B1?
No upper limit has been set because no harm has been reported from high intakes; absorption falls off sharply above about 5 mg at a time.[1]
Does thiamine help heart failure?
Not beyond fixing a deficiency. Pooled trials of 274–298 patients found no effect on ejection fraction, walking distance, hospitalization or death.[2][3]
What is benfotiamine and is it better?
It is a synthetic fat-soluble derivative that the body converts to thiamine. It has been tested for diabetic neuropathy and early Alzheimer's with mixed results; there are no head-to-head trials showing it beats thiamine HCl for outcomes.[1][5][6]
Does benfotiamine help diabetic neuropathy?
Possibly a little. In a 6-week trial of 133 patients symptom scores improved in the per-protocol analysis, but not significantly when all randomized patients were counted.[6]
Who is most likely to be low in thiamine?
People with alcohol use disorder, older adults, people with HIV or diabetes, and anyone after bariatric surgery.[1]
Sources
- [1]Thiamin: Fact Sheet for Health Professionals (updated February 9, 2023). NIH Office of Dietary Supplements, 2023. fact-sheet
- [2]Role of Thiamine Supplementation in the Treatment of Chronic Heart Failure: An Updated Meta-Analysis of Randomized Controlled Trials.. Clin Cardiol, 2024. meta-analysis
- [3]Does thiamine supplementation affect heart failure? A systematic review and meta-analysis of randomized control trials.. Heart Lung, 2023. meta-analysis
- [4]Effects of thiamine on cardiac function in patients with systolic heart failure: systematic review and metaanalysis of randomized, double-blind, placebo-controlled trials.. Ochsner J, 2013. meta-analysis
- [5]Benfotiamine and Cognitive Decline in Alzheimer's Disease: Results of a Randomized Placebo-Controlled Phase IIa Clinical Trial.. J Alzheimers Dis, 2020. RCT
- [6]Benfotiamine in diabetic polyneuropathy (BENDIP): results of a randomised, double blind, placebo-controlled clinical study.. Exp Clin Endocrinol Diabetes, 2008. RCT
- [7]A double-blind, randomized, placebo-controlled clinical trial on benfotiamine treatment in patients with diabetic nephropathy.. Diabetes Care, 2010. RCT
- [8]High-dose thiamine therapy for patients with type 2 diabetes and microalbuminuria: a randomised, double-blind placebo-controlled pilot study.. Diabetologia, 2009. RCT
- [9]High-dose thiamine supplementation improves glucose tolerance in hyperglycemic individuals: a randomized, double-blind cross-over trial.. Eur J Nutr, 2013. crossover-RCT
- [10]Effect of thiamine administration on metabolic profile, cytokines and inflammatory markers in drug-naïve patients with type 2 diabetes.. Eur J Nutr, 2011. pilot-RCT
- [11]What is the optimum thiamine dose to treat or prevent Wernicke's encephalopathy or Wernicke-Korsakoff syndrome? Results of a randomized controlled trial.. Alcohol Clin Exp Res, 2022. RCT
What changed
- First draft. Every PMID checked against NCBI E-utilities esummary (title and year taken from the record) and abstracts read for the cited rows.
- Adversarial review pass: each evidence row re-read against its PubMed abstract; benfotiamine Alzheimer's dose taken from the full text (PMC7880246); Wörwag Pharma ties taken from the kidney trial's disclosures (PMC2890365). Retraction and expression-of-concern check run on all 10 PMIDs via PubMed records: none flagged. Page set indexable.