The answer so far
Vitamin K is a nutrient the body needs for normal blood clotting and healthy bones. Leafy green vegetables provide it. People taking warfarin should keep their vitamin K intake consistent and discuss significant dietary changes or supplements with their healthcare professional.1
What vitamin K does
Vitamin K helps the body make proteins needed for blood clotting and is involved in bone health. Vitamin K1 and K2 are related forms; a form or product should not be assumed to have a particular clinical benefit without appropriate evidence.1
Where it comes from
Green vegetables such as spinach, kale and broccoli provide vitamin K. It is also present in some other foods. The amount in a supplement varies by product, so check the label.1
Warfarin and other medicines
Vitamin K can affect the action of warfarin, an anticoagulant. The aim is not to avoid leafy vegetables: people taking warfarin should keep vitamin K intake consistent and discuss substantial dietary changes or supplements with their healthcare team. Other medicines may also interact.1
Sources
Selected supporting sources; this is not a complete literature review.
- Vitamin K: Fact Sheet for ConsumersNIH Office of Dietary Supplements · Public-health consumer fact sheet