In brief
A vitamin your body needs to make proteins for blood clotting and for bone, such as osteocalcin.
- A vitamin K injection at birth helps prevent serious bleeding in newborns.
- It is unclear whether vitamin K supplements reduce the risk of osteoporosis.
- Green leafy vegetables such as spinach, kale, broccoli and lettuce are good sources.
How it works
The main form in food is vitamin K1, found mostly in green leafy vegetables. Vitamin K2 is found in modest amounts in some animal and fermented foods, and gut bacteria make it too.
Warfarin and some other blood thinners work by opposing vitamin K, so people taking them need to keep their vitamin K intake consistent. A sudden change in how much vitamin K you get can upset how well these medicines work.
Food sources
- Spinach and kale
- Broccoli
- Lettuce
- Meat
- Cheese and eggs
- Soybeans
From the AskBioMap food guide:
Connections
2 connections on the map. Select a topic to read its page.
Vitamin K is needed for
Your body needs vitamin K to make proteins for blood clotting.
Sources: NIH Office of Dietary Supplements, Vitamin K: fact sheet for health professionals; NIH Office of Dietary Supplements, Vitamin K fact sheet for consumers
Vitamin K is linked with
- Muscles and bones Emerging
Vitamin K is needed for bone proteins such as osteocalcin, but it is unclear whether supplements prevent osteoporosis.
Source: NIH Office of Dietary Supplements, Vitamin K: fact sheet for health professionals
Medicines and supplements
General education only. Never start, stop or change a medicine without your prescriber.
Sources
Each connection above names its own source. See every source AskBioMap uses.
Summarised from the NIH Office of Dietary Supplements. Sources read on 13 October 2026. General education only, not medical advice. Spotted a mistake? Please tell us through the HuBu-Intel contact page.