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Thiamine for Health & Longevity

Created on 11/01/2026 – Quick Reference based on Evidence Review created using AI4L / Opus 5.5 – Audit

Thiamine (vitamin B1) is an essential vitamin that cells need to turn food into energy, sold as an inexpensive supplement for brain, heart and metabolic health. Its clearest long-term benefit is preventing and correcting deficiency, mainly in heavy drinkers, people with diabetes, long-term users of fluid-removing medications, weight-loss surgery patients and frail older adults. Gains beyond adequate levels remain uncertain. Oral risks appear minimal; injections rarely cause severe allergic reactions. (Full Review)

Protocol

Conventional approach
100–200 mg/day oral
Only to correct or prevent deficiency in at-risk groups; higher end in heart failure, lower end for menstrual pain
High-dose approach
600–1,800 mg/day oral
Thiamine hydrochloride, set by sex and body weight; tested for fatigue; doses above about 100 mg commonly split two or three times daily
Benfotiamine approach
300–600 mg/day
For diabetic nerve symptoms; 300 mg twice daily in the dementia trial
Time to effect
Deficiency signs
Hours to days
Signs can improve once deficiency is treated
Fatigue
4 weeks
Point at which responses to high-dose thiamine were measured
Nerve symptoms
3–6 weeks
Point at which benfotiamine responses in diabetes were measured

Benefits

Contraindications
  • Known hypersensitivity to thiamine or any inactive ingredient (injectable products)
  • Prior anaphylactic reaction to injected thiamine (further injected doses outside a setting equipped for resuscitation)
  • Active cancer (doses far above requirements; no human data)
    •
Key Interactions
  • Loop diuretics (furosemide)
  • Fedratinib (JAK2 inhibitor)
  • Fluoropyrimidines and ifosfamide (5-fluorouracil, capecitabine)
  • Alcohol
  • Phenytoin (anti-seizure medication)
  • Tea, coffee, betel nut and raw fermented fish
  • Magnesium (supplement interaction)
  • Trimethoprim (antibiotic)
  • Sulfite-preserved foods and drinks
  • Metformin
  • Metronidazole (antibiotic)
    •
Theoretical (inferred from mechanism)
  • Over-the-counter and prescription transporter inhibitors (famotidine, verapamil)
  • Alpha-lipoic acid, riboflavin and niacin (additive)
    •

Risk & Side Effects

  • High:
  • Medium:
  • Low: Hypersensitivity reactions to injected thiamine; mild adverse effects at high oral doses; toxicity with long-term oral doses above 3,000 mg/day; faster cognitive decline at higher dietary intake
    •
  • Speculative: Stimulation of tumor growth
    •

Monitoring

Marker Target Why
Whole-blood thiamine diphosphate (TDP) 70–180 nmol/L Confirms repletion
Erythrocyte transketolase activity coefficient (ETKAC) No established target; track change from own baseline Shows functional thiamine status
Serum magnesium 0.70–1.00 mmol/L Safety check; low values make thiamine ineffective

Cadence: Baseline before high-dose or long-term use; repeat TDP at 4–8 weeks after starting or changing a high dose, then every 6–12 months while risk factors persist, and at any new symptoms such as confusion or tingling; fedratinib users follow the label schedule

Qualitative Assessment

  • Energy and fatigue, rated with a fatigue questionnaire at baseline and after four weeks
  • Menstrual pain intensity on a 0–10 scale across several cycles
  • Tingling, burning or numbness in the feet and hands
  • Memory, concentration and mental clarity
  • Appetite, mood and any palpitations or sleep disturbance at high doses
Not medical advice. Educational distillation of a single evidence review. Confirm any decision with a qualified clinician, especially in the presence of prescription drugs or chronic conditions.