Vitamin B1

How strong is the research?

1 paper read, 1 supporting.

Who was studied: Studied in elderly adults, who absorb thiamine less well and are more likely to be short of it.

How much to take

daily

50–150 mg

Deficiency impairs cognitive function rapidly. Benfotiamine crosses blood-brain barrier more effectively.

Before you take it

• No Tolerable Upper Intake Level (UL) has been established by the IOM/NAS for thiamine; the IOM concluded there were insufficient adverse-effect data to set a UL for any age group.
• Oral thiamine at clinical trial doses (up to 600–1,800 mg/day) has not been associated with significant adverse effects; as a water-soluble vitamin, excess is excreted renally.
• Rare anaphylactic reactions have been reported with intravenous thiamine administration (e.g., in emergency/ICU settings); this risk is not established for oral supplementation.
• Chronic alcohol use depletes thiamine through impaired intestinal absorption and reduced hepatic storage; patients with alcohol use disorder are at high risk of deficiency.
• Loop diuretics (e.g., furosemide) increase renal thiamine excretion and may deplete body stores with long-term use.
• Metformin use is associated with lower thiamine status in some studies; patients on long-term metformin may warrant monitoring.
• Antacids and proton-pump inhibitors may reduce thiamine absorption by raising gastric pH.
• Dietary thiaminases present in raw fish and certain teas (e.g., bracken fern) can degrade dietary thiamine; heavy consumption may compromise thiamine status.

When to take it

Best taken: morning

What we make of it

The trial we cite could not be found, and any real benefit is probably correcting a deficiency.