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The Effect of Vitamin K on the INR: International Normalized Ratio

By Matthew Fox, MD ; Updated April 18, 2017

Vitamin K is a fat-soluble vitamin found in high concentrations in green leafy vegetables and obtained from synthesis by bacteria in the colon. Vitamin K helps certain enzymes to work correctly. An enzyme is a protein that speeds up chemical reactions. Proteins utilizing vitamin K are used to modify other proteins. If this modification is not made, it will have certain effects on the body, including an elevated INR, or international normalized ratio, a measure of blood clotting. The treatment and diagnosis of diseases should be done with the consultation of a licensed health care professional.

Vitamin K Functions and Mechanism

Vitamin K binds to specific enzymes, allowing them to transfer chemicals called carboxy groups to other proteins for them to work correctly. The carboxy groups bind to an amino acid in the proteins called glutamate. Vitamin K is necessary for the proper functioning of proteins involved in blood coagulation, bone development and the health of blood vessels.

Blood Clotting

Blood maintains a fine balance between clotting excessively and not enough. If it clots too readily, it will clot in the blood vessels and obstruct the flow of blood into or out of the tissues. If it does not clot enough, it will not be able to stop bleeding and bruising. Blood forms clots, and inhibits clot formation, with the help of platelets and special proteins. Several of these proteins need vitamin K to be active.

The INR Measurements of Blood Clotting

INR and prothrombin time measure coagulation. The normal range for the INR is 0.8 to 1.2, according to "Harrison's Principles of Internal Medicine." Above this level, blood may not clot as effectively and bleeding time can be prolonged.

Conditions of Elevated INR and Vitamin K

If vitamin K-dependent proteins are not functional, bleeding time will increase and INR will rise. Rarely, low vitamin K intake can cause low blood levels of this vitamin. More often, a person with low blood levels of vitamin K have a gastrointestinal disease that interferes with the absorption of vitamin K. A common reason for malfunctioning vitamin K-dependent proteins is the drug warfarin. Warfarin is prescribed to prevent blood clotting and works by interfering with vitamin K. Vitamin K can lower the INR over time and therefore antagonize the effects of warfarin. If INR is already normal, vitamin K adminstration will not lower INR farther.

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