How does vitamin K help blood clot?

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Several translucent, oval-shaped vitamin E gel capsules are scattered on a white surface near a partially visible bottle. — vitamin Vitamin E in gel-cap form.

Vitamin K is essential for the synthesis of several proteins involved in blood coagulation, including prothrombin and factors VII, IX, and X.12

In the liver, vitamin K acts as a necessary cofactor for an enzyme-mediated process called $γ$ -carboxylation. During this reaction, specific glutamic acid residues within precursor proteins are converted into $γ$ -carboxyglutamic acid. This modified amino acid is critical because it creates calcium-binding sites on the proteins.1

Calcium stabilizes these vitamin K-dependent proteins, allowing them to bind to cell membranes and perform their role in the clotting process. Without adequate vitamin K, these proteins remain in an inactive form that cannot bind to calcium or interact with membrane surfaces, leading to impaired blood clotting and an increased risk of bleeding.12