What causes vitamin K deficiency?

Diet or Antibiotics. The vast majority of our vitamin k is actually produced by symbiotic bacteria in our intestines. So, if one has recently had a bout of heavy antibiotic use (which kills off both "good and "bad" bacteria in the body), then vitamin k deficiency can result. Poor diet can also lead to this deficiency. A deficiency in vit. K most often results in easy bleeding/hemorrhage susceptibility.
VITAMIN K DEFICIENCY. It is caused by inadequate intake, malabsorption of fat and use of coumarin anticoagulants. It causes hemorrhagic disease of the newborn, common among breastfed infants.