Vitamin K is not a blood thinner. In fact, it is involved in the normal clotting of blood. The blood thinner, warfarin, works by interfering with vitamin K. According to Mayo Clinic.com, warfarin is prescribed for people who have clots near the heart, in the lungs or veins or who are at risk of forming clots due to heart arrhythmias or mechanical heart valves. Warfarin dosage has to be adjusted very carefully so that it does not inhibit vitamin K too much and cause bleeding.
Blood Clotting and Vitamin K
Blood clotting works through a cascade involving several proteins. As each protein is activated, it acts on a subsequent protein in the cascade, amplifying the signal to produce a clot. Vitamin K reacts with four of these proteins, making them able to bind calcium and attain their active form.
Plant Sources of Vitamin K
Natural vitamin K comes in two forms, K-1 and K-2. Vitamin K-1 comes from plants. Leafy greens and cruciferous vegetables are plentiful in vitamin K-1. The United States Department of Agriculture National Nutrient Database provides a detailed list of the vitamin K contents of foods. The Institute of Medicine Food and Nutrition Board recommends a vitamin K intake of 90 mcg per day for adult women and 120 mcg per day for adult men.
Bacterial Vitamin K
Vitamin K-2 comes from bacterial synthesis. About half of the vitamin K in the human body comes from bacterial synthesis in the gut. Antibiotics can cause drops in this source of vitamin K.
Vitamin K Intake Affects Warfarin Dosage
Patients on warfarin are given blood tests to monitor their clotting time and adjust their dosage. Changes in vitamin K level can affect this blood test and change the correct dosage. Such patients should consult with their doctor about any use or change in use of vitamin supplements. It is also helpful to avoid drastic changes in intake of vitamin K-rich vegetables.
References
- USDA National Nutrient Database for Standard Reference, Release 23, Vitamin K Content of Selected Foods
- Dietary Reference Intakes (DRIs): Recommended Dietary Allowances and Adequate Intakes, Vitamins Food and Nutrition Board, Institute of Medicine, National Academies
- Mayo Clinic Information on Warfarin
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