Vitamin B12: what it does and how much you need
Vitamin B12 keeps nerve and blood cells healthy and helps make DNA. Adults need 2.4 micrograms a day, 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 1.5 micrograms a day, and the NHS says up to 2 milligrams (2,000 micrograms) a day from supplements is unlikely to cause harm.
How much you need and the upper limit
| US (NIH) | UK (NHS) | |
|---|---|---|
| Adults need | 2.4 micrograms a day | 1.5 micrograms a day |
| Upper limit | No upper limit has been set for vitamin B12, because harm from high intakes has not been shown. | Up to 2 milligrams (2,000 micrograms) a day from supplements |
The UK figure is the amount the NHS says is unlikely to cause harm. Figures are for adults.
Cautions
- People who eat no animal foods usually need a fortified food or a supplement to get enough.
Food sources
- Meat and fish
- Poultry
- Eggs
- Milk and cheese
- Fortified cereals
- Fortified nutritional yeast
Forms on the label
- Methylcobalamin and cyanocobalamin are both forms of vitamin B12, and the body turns cyanocobalamin, the most studied, into the active forms.
Dose questions
Quick answers
- What does vitamin B12 do?
- Vitamin B12 keeps nerve and blood cells healthy and helps make DNA.
- How much vitamin B12 do adults need?
- Adults need 2.4 micrograms a day (US, NIH). In the UK: 1.5 micrograms a day (NHS).
- What is the upper limit for vitamin B12?
- US: No upper limit has been set for vitamin B12, because harm from high intakes has not been shown. UK (NHS): up to 2 milligrams (2,000 micrograms) a day from supplements is unlikely to cause harm.
- Which foods have vitamin B12?
- Meat and fish, poultry, eggs, milk and cheese, fortified cereals, fortified nutritional yeast.
- What should I watch out for with vitamin B12?
- People who eat no animal foods usually need a fortified food or a supplement to get enough.
Sources
- NIH Office of Dietary Supplements fact sheet
https://ods.od.nih.gov/factsheets/VitaminB12-HealthProfessional/ - NHS vitamins and minerals guidance
https://www.nhs.uk/conditions/vitamins-and-minerals/vitamin-b/
Ask Supplement Check yourself
Type a vitamin, mineral or supplement, a dose, or a product name, and get the daily need, the upper limit and any cautions. Open Supplement Check, free, no sign-up.
In Claude or any app that takes MCP connectors, add https://goodturn-mcp.pages.dev/supplementcheck/mcp and ask: “Is 1000 mcg of B12 too much?”