Thiamin (vitamin B1): what it does and how much you need
Thiamin (vitamin B1) helps turn food into energy and keeps nerves working. Adults need 1.2 milligrams for men and 1.1 milligrams for women, and no upper limit has been set.
General information, not medical advice. Check with a doctor or pharmacist before taking a supplement, especially if you are pregnant or breastfeeding, take any medicine, or are under 18.
In the UK
In the UK, adults need 1 milligram a day for men and 0.8 milligrams for women, and the NHS says up to 100 milligrams a day from supplements is unlikely to cause harm.
How much you need and the upper limit
| US (NIH) | UK (NHS) | |
|---|---|---|
| Adults need | 1.2 milligrams for men and 1.1 milligrams for women | 1 milligram a day for men and 0.8 milligrams for women |
| Upper limit | No upper limit has been set for thiamin. | Up to 100 milligrams a day from supplements |
The UK figure is the amount the NHS says is unlikely to cause harm. Figures are for adults.
Food sources
- Whole grains
- Fortified bread and cereals
- Pork
- Fish
- Beans and lentils
- Seeds
Quick answers
- What does thiamin (vitamin B1) do?
- Thiamin (vitamin B1) helps turn food into energy and keeps nerves working.
- How much thiamin (vitamin B1) do adults need?
- Adults need 1.2 milligrams for men and 1.1 milligrams for women (US, NIH). In the UK: 1 milligram a day for men and 0.8 milligrams for women (NHS).
- What is the upper limit for thiamin (vitamin B1)?
- US: No upper limit has been set for thiamin. UK (NHS): up to 100 milligrams a day from supplements is unlikely to cause harm.
- Which foods have thiamin (vitamin B1)?
- Whole grains, fortified bread and cereals, pork, fish, beans and lentils, seeds.
Sources
- NIH Office of Dietary Supplements fact sheet
https://ods.od.nih.gov/factsheets/Thiamin-HealthProfessional/ - NHS vitamins and minerals guidance
https://www.nhs.uk/conditions/vitamins-and-minerals/vitamin-b/
Ask Supplement Check yourself
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In Claude or any app that takes MCP connectors, add https://goodturn-mcp.pages.dev/supplementcheck/mcp and ask: “How much thiamin (vitamin B1) do I need?”