Vitamin K: what it does and how much you need
Vitamin K helps blood clot and helps keep bones healthy. Adults need an adequate intake of 120 micrograms for men and 90 micrograms for women, and no upper limit has been set. If you take a blood thinner such as warfarin, talk to your doctor before changing how much vitamin K you get.
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 microgram a day for each kilogram of body weight, and the NHS says up to 1 milligram (1,000 micrograms) a day from supplements is unlikely to cause harm.
How much you need and the upper limit
| US (NIH) | UK (NHS) | |
|---|---|---|
| Adults need | An adequate intake of 120 micrograms for men and 90 micrograms for women | 1 microgram a day for each kilogram of body weight |
| Upper limit | No upper limit has been set for vitamin K. | Up to 1 milligram (1,000 micrograms) a day from supplements |
The UK figure is the amount the NHS says is unlikely to cause harm. Figures are for adults.
Cautions
- If you take a blood thinner such as warfarin, talk to your doctor before changing how much vitamin K you get.
Food sources
- Green leafy vegetables
- Vegetable oils
- Blueberries
- Figs
- Natto
Dose questions
Quick answers
- What does vitamin K do?
- Vitamin K helps blood clot and helps keep bones healthy.
- How much vitamin K do adults need?
- Adults need an adequate intake of 120 micrograms for men and 90 micrograms for women (US, NIH). In the UK: 1 microgram a day for each kilogram of body weight (NHS).
- What is the upper limit for vitamin K?
- US: No upper limit has been set for vitamin K. UK (NHS): up to 1 milligram (1,000 micrograms) a day from supplements is unlikely to cause harm.
- Which foods have vitamin K?
- Green leafy vegetables, vegetable oils, blueberries, figs, natto.
- What should I watch out for with vitamin K?
- If you take a blood thinner such as warfarin, talk to your doctor before changing how much vitamin K you get.
Sources
- NIH Office of Dietary Supplements fact sheet
https://ods.od.nih.gov/factsheets/VitaminK-HealthProfessional/ - NHS vitamins and minerals guidance
https://www.nhs.uk/conditions/vitamins-and-minerals/vitamin-k/
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: “Is 200 mcg of vitamin K2 too much?”