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Vitamin K &amp; Warfarin

June 2007

By Laurie Barclay, MD

Dosage and Safety

Currently, the recommended daily allowance (RDA) of vitamin K is 70-80 mcg/day for men and 60-65 mcg/day for women.23 Recent studies of vitamins K1 and K2 suggest that the present RDA is too low to fully protect against atherosclerosis and heart disease.17,35 Some experts now suggest that low-dose vitamin K supplementation (50-150 mcg/day) may help stabilize fluctuations in INR in individuals who use warfarin.5 If you use warfarin, discuss the possible benefits of vitamin K supplementation with your physician. Certain medications, including cholestyramine, colestipol, mineral oil, and orlistat may decrease the absorption of vitamin K. Large doses of salicylates such as aspirin may result in vitamin K deficiency. Cephalosporin antibiotics can cause vitamin K deficiency.23


Recent evidence clearly indicates that vitamin K is crucial not only for proper regulation of blood clotting, but also for optimal bone and cardiovascular health. In patients on long-term treatment with the anticoagulant warfarin, vitamin K may also facilitate control of anticoagulation therapy, so that the INR remains in ideal range, without frequent changes in the warfarin dose. The result may be more consistent benefits of therapy—such as decreased risk for heart attack and stroke, and fewer risks—such as hemorrhaging. If you use warfarin, discuss the benefits of modest vitamin K supplementation with your physician.


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