Vitamin K

Fat-soluble · clotting

What does Vitamin K do in your body?

Activates proteins needed for blood clotting and for building bone.

What does Vitamin K do?

Lets enzymes modify clotting factors and bone proteins (like osteocalcin) so they can bind calcium and work.

Where does Vitamin K act in the body?

Liver (clotting factors), bone, blood vessels.

Which foods contain Vitamin K?

K1: leafy greens (kale, spinach, collards), broccoli, vegetable oils. K2: natto, some cheeses, eggs; also made by gut bacteria.

How much Vitamin K do adults need?

Adequate Intake: 120 mcg (men), 90 mcg (women). No upper limit has been set.

What happens with too little Vitamin K?

Rare in adults; can cause bleeding. Newborns routinely get a vitamin K injection because they're born with low levels.

Can you get too much Vitamin K?

No known toxicity from food.

What does Vitamin K interact with?

For people taking warfarin, sudden changes in vitamin K intake can change how well the medicine works. NIH ODS notes that a consistent intake is usually what matters; individual advice comes from the prescriber.

What is known and unknown about Vitamin K?

Clotting role is established. Effects of K2 supplements on bone and heart are still being studied.

Evidence & sources

For people taking warfarin, sudden changes in vitamin K intake can change how well the medicine works, so clinicians usually advise a consistent intake rather than avoidance. Evidence: established. Known: Vitamin K directly counteracts warfarin's mechanism; sudden intake changes alter clotting time. Unknown: — Source: NIH Office of Dietary Supplements, Vitamin K — Health Professional Fact Sheet (Current revision).

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General education only, not medical advice. Drafted Oct 2026 · pending qualified expert review.