How does vitamin K help your blood clot?
Vitamin K lets your blood clot: the liver needs it to activate clotting factors, including prothrombin. It comes from green vegetables (K1) and fermented foods (K2); the body stores very little and recycles it constantly.
Which foods provide the most vitamin K?
Leafy greens for K1, and natto (fermented soybeans from Japan) for K2. One serving of cooked collard greens provides more than 4 times an adult man's recommended intake (our calculation: 530 ÷ 120, ODS figures).
| Food | Serving | Vitamin K | Form |
|---|---|---|---|
| Natto | 85 g | 850 µg | K2 (MK-7) |
| Cooked collard greens | ½ cup | 530 µg | K1 |
| Cooked turnip greens | ½ cup | 426 µg | K1 |
| Raw spinach | 1 cup | 145 µg | K1 |
| Raw kale | 1 cup | 113 µg | K1 |
| Cooked broccoli | ½ cup | 110 µg | K1 |
| Soybean oil | 1 tbsp | 25 µg | K1 |
Where does it go, and why so little storage?
It follows the route of fats: gut, chylomicrons, lymph, blood, liver, then other tissues (brain, heart, pancreas, bones). The body keeps only 30 to 40% of a normal dose of K1; about 20% leaves in the urine and 40 to 50% in the stool through the bile. The remaining store is small compared with vitamins A and E.
How does the body manage with so little?
It recycles it. One enzyme uses it to activate a protein, then another enzyme (VKOR) restores it. The same molecule therefore serves several times. Warfarin works by blocking this step: that is why it reduces clotting.
What does vitamin K do?
The liver needs it to activate several clotting factors, including prothrombin. Bones use it to activate osteocalcin. The protein MGP, which also depends on it, might limit calcium deposits in the arteries: this is still a hypothesis.
Page updated on October 30, 2026. Recommended intakes are those of the ODS (United States).
Frequently asked questions
Why a vitamin K shot at birth?
Newborns have very little in store, and breast milk provides little. The shot is recommended for all babies to prevent rare but serious bleeding.
Can you eat leafy greens while on warfarin?
Yes, but consistently: a sudden change in vitamin K can throw off the treatment. Talk to your doctor before changing your habits or taking a supplement.
K1 or K2: which is better?
Both activate the same proteins. K1 is the most common form in the diet. MK-7 stays longer in the blood (half-life of about 3 days), but this does not prove it protects bones or arteries better.
Who is at risk of vitamin K deficiency?
Severe deficiency is very rare in healthy adults. It mainly affects untreated newborns and people who absorb fats poorly.
Are gut bacteria enough?
They make K2, but it is not clear how much the body actually uses. It's better to rely on your diet.
See also
The route of fats Bone that renews itself Vitamin A and vision Vitamin E and oxidation
Sources
- NIH Office of Dietary Supplements. Vitamin K, fact sheet for health professionals. ods.od.nih.gov
- Linus Pauling Institute, Oregon State University. Vitamin K. lpi.oregonstate.edu
- Sato T, Schurgers LJ, Uenishi K. Comparison of menaquinone-4 and menaquinone-7 bioavailability in healthy women. Nutr J. 2012;11:93. PMC3502319
True or false?
The body keeps large stores of vitamin K.
False. It keeps only 30 to 40% of a normal dose, and its stores stay small. That is why it recycles it (ODS).
Warfarin works by blocking the recycling of vitamin K.
True. It blocks the VKOR enzyme: used vitamin K is no longer restored, and fewer clotting factors become active (ODS).
Newborns often receive a vitamin K shot.
True. They have very little in store. The shot is recommended to prevent rare but serious bleeding (Linus Pauling Institute).
Cite this page
To cite this page in a paper, an article or a presentation:
Metabolive. "How does vitamin K help your blood clot?" Updated November 1, 2026. https://metabolive.com/en/everyday/vitamin-k.