A small but essential requirement
Thiamin (vitamin B1) helps the body turn food into energy and supports nerve function. The NIH Office of Dietary Supplements sets the adult RDA at 1.2 mg/day for men and 1.1 mg/day for women (1.4 mg in pregnancy and lactation) [1]. Whole grains, fortified cereals, pork, and legumes supply it readily.
No upper limit — but that's not the story here
The Food and Nutrition Board did not set a Tolerable Upper Intake Level for thiamin, because high intakes from food and supplements have not been linked to harm; excess is excreted in urine [1]. So unlike many nutrients, the issue with thiamin is deficiency, not overdose.
Who is at higher risk of running low
NIH highlights several groups prone to thiamin inadequacy [1]:
- People with alcohol use disorder — reduced intake, absorption, and storage; this is the classic high-risk group.
- Older adults — up to 20–30% show indicators of deficiency in some studies.
- People after bariatric (weight-loss) surgery — reduced absorption.
- People on long-term loop diuretics (e.g., furosemide) — increased urinary losses.
- People with HIV/AIDS and some people with diabetes.
Why severe deficiency is serious
Severe, prolonged deficiency causes beriberi (nerve and heart problems) and Wernicke-Korsakoff syndrome, a serious neuropsychiatric condition most often seen with heavy alcohol use [1]. These are medical situations, not something to self-treat — the takeaway is to recognize the risk groups and seek care.
Practical guidance
- Most people meeting the RDA through a varied diet do not need a thiamin supplement.
- If you fall into a higher-risk group, ask a clinician whether your thiamin status should be checked or supplemented — don't guess at high doses on your own.