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.
Nervous System Health
Thiamine is crucial for nerve function, supporting nerve signal transmission and myelin sheath maintenance. Tingling, numbness and nerve pain are classic signs of thiamine deficiency and improve when that deficiency is corrected. Nothing cited on this page shows that extra thiamine helps nerve function in people who already get enough B1.
Brain Function
Thiamine supports cognitive health by aiding energy supply to brain cells. Severe deficiency can cause Wernicke-Korsakoff syndrome, most often in people with alcohol use disorder. Wernicke encephalopathy is a medical emergency that is treated in hospital with injected thiamine; an oral supplement is not a treatment for it. No study cited here shows that thiamine improves memory or focus.
Heart Health
The heart muscle depends on thiamine for its energy metabolism, and severe deficiency can cause a form of beriberi that affects the heart. No heart failure trial is cited anywhere on this page, so this is background biology rather than a demonstrated benefit of taking a supplement.
Metabolic Disorders
The trial usually cited for this did not test thiamine. BENDIP tested benfotiamine, a different compound, at 300 mg or 600 mg a day for 6 weeks in 165 people who already had diabetic nerve damage. Its pre-planned main analysis of all randomized participants missed statistical significance (p = 0.055) and only reached it when limited to people who completed the protocol as intended (p = 0.033). The authors wrote that further studies should confirm the findings. This is not evidence that thiamine helps blood sugar or diabetic complications.
Digestive Health
Loss of appetite is one of the early signs of thiamine deficiency and can improve once the deficiency is corrected. Nothing cited on this page shows that thiamine increases stomach acid, boosts digestive enzymes or improves digestion in people who already get enough B1.
Mechanism of action
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.
Nerve Function
TPP is involved in nerve signal transmission and in the energy supply nerve cells need to stay healthy. This is why prolonged deficiency damages nerves. It does not mean extra thiamine protects the nerves of someone who already gets enough.
Glucose Regulation
Thiamine-dependent enzymes sit at the center of how the body burns glucose, which is why deficiency disrupts energy metabolism. Claims about reducing diabetic complications come from studies of benfotiamine, a different compound, and those results were mixed.
Clinical trials
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.
The trial did not show an overall survival benefit. Lactate clearance signals were modest, and lower mortality appeared only in the subgroup of patients who were already thiamine deficient. Important context: this was high-dose thiamine given through a vein to intensive care patients in septic shock, which is hospital medicine, not the same as taking a B1 tablet. Larger and more rigorous later trials of the thiamine plus vitamin C plus steroid protocol, including HYVCTTSSS, were negative.
Pooled analysis of 35 clinical trials (n=3,494, through) evaluating IV thiamine (100-200 mg) in critically ill patients. (Nakanishi 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 intensive care patients (heavy alcohol use, malnutrition, refeeding syndrome), which is why doctors often give it there. This is thiamine given through a vein in hospital, not an oral supplement taken at home.
Multicenter clinical trial (ACTRN12619000121167) in 90 critically ill enterally fed patients receiving high-dose thiamine vs control. (Clin Nutr)
90 critically ill ICU patients.
The trial reported only modest changes in blood markers, with no clear benefit to how patients actually did. The intensive care evidence for high-dose thiamine remains mixed, and this was drug-dose thiamine given in hospital rather than a supplement.
Phase 2a, single-site, randomized, double-blind, placebo-controlled pilot trial in mild-moderate AD patients receiving high-dose thiamine.
Pilot AD patients.
This was a small pilot study of drug-level thiamine doses in people who already had Alzheimer's disease, designed to test feasibility rather than to prove a benefit, and the changes on cognitive measures were modest. Thiamine has no established role in treating Alzheimer's disease, and none of this tells you what a B1 supplement does for someone without the condition.
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.
The trial reported only modest changes in lactate during the bypass procedure, with no clear benefit for how patients recovered afterwards. This was injected high-dose thiamine in 64 surgical patients and it is not standard care.