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Vitamin K
What is it? Overview Usage Side Effects and Warnings

What is Vitamin K?

Vitamin K plays a major role in the body's blood clotting system. There are three forms of vitamin K: K 1 (phylloquinone), found in plants; K 2 (menaquinone), produced by bacteria in your intestines; and K 3 (menadione), a synthetic form.

Vitamin K is used medically to reverse the effects of "blood-thinning" drugs, such as warfarin (Coumadin). Growing evidence suggests that it may also be helpful for osteoporosis.

Growing, but not yet definitive, evidence suggests that vitamin K should be added to the list of nutrients helpful for preventing osteoporosis . 1 Based on its ability to help blood clot normally, vitamin K has been proposed as a treatment for excessive menstrual bleeding. 2 However, the last actual study testing this idea was carried out more than 55 years ago. 3 Vitamin K has also been recommended for nausea , although there is as yet no meaningful evidence that it really works.

Preliminary evidence suggests that vitamin K supplementation may help prevent liver cancer . 4 Very high doses of intravenous vitamin K have also been used to treat advanced liver cancer, with, perhaps, marginal benefits. 5

Safety Issues

Vitamin K is quite safe at the recommended therapeutic dosages.

Note: Vitamin K directly counters the effects of the anticoagulant warfarin (Coumadin) . If you are taking warfarin, you should not take vitamin K supplements or alter your dietary intake of vitamin K without doctor supervision. 6 (One study suggests a novel way of using this effect deliberately. 7 Researchers gave people on warfarin a fixed daily dose of vitamin K in order to override the changes in warfarin action caused by the natural variation in day-to-day dietary vitamin K consumption. The results were positive: INR values—the standard measurement of warfarin’s blood thinning effect—became more stable. Needless to say, however, this method should not be used except under close physician...