Vitamin K is a fat-soluble vitamin that plays a crucial role in blood-clot formation, also known as coagulation. In developed countries, vitamin K deficiencies are rare, because many different foods contain vitamin K and most adults take in enough vitamin K through a normal diet. However, two vitamins and several medications can lower the activity of vitamin K and increase the risk of deficiency.
Vitamin A
Taking high doses of vitamin A can inhibit the activity of vitamin K, reports the Linus Pauling Institute at Oregon State University. If you take too much vitamin A, the extra vitamin A can reduce absorption of vitamin K from the digestive tract into the bloodstream, resulting in a vitamin K deficiency.
Vitamin E
High doses of vitamin E can also inhibit vitamin K. Instead of reducing absorption of vitamin K, vitamin E blocks its activity in the body. Technically speaking, this does not cause a vitamin K deficiency, because the vitamin K is in the body. However this inhibitory effect of vitamin E causes symptoms similar to a vitamin K deficiency, including a reduction in blood clot formation.
Antibiotics
A portion of the vitamin K that your body uses is actually produced by bacteria living in your digestive tract. Certain types of antibiotic medications, known as broad spectrum antibiotics, can kill a wide range of bacteria, including those beneficial bacteria living in your digestive tract. Taking one of these broad spectrum antibiotics to treat a bacterial infection can have the unintended consequence of killing the helpful bacteria that produce vitamin K, which can contribute to a vitamin K deficiency, explains the Linus Pauling Institute at Oregon State University.
Fetal Vitamin K Synthesis
Care should be taken with potentially conflicting vitamin supplements in newborns, as they have not yet fully developed the bacterial population to manufacture vitamin K on their own. Certain medications, if taken by a pregnant mother, can inhibit vitamin K synthesis in the unborn fetus, which can also cause a vitamin K deficiency when the baby is born. These medications include warfarin, a common blood thinner, several anticonvulsant medications, and two drugs used to treat tuberculosis, isoniazid and rifampin.
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