The term vitamin K refers to a group of substances (Vitamin K1, K2 and K3) which contain 2-methyl-1 and 4-naphthoquinone and that exhibit hemostatic activity. In addition to its hemostatic activity, vitamin K also plays a role in bone metabolism and blood clotting and is used by doctors in connection with overdoses of certain drugs such as warfarin. It is believed that many of vitamin K's effects come from its ability to increase the body's ability to transport calcium.

While uncommon, vitamin K deficiency can occur under certain conditions. These include poor diet, malabsorption syndromes (cystic fibrosis, Crohn's disease, ulcerative colitis, Whipple's disease, celiac sprue, short bowel syndrome), and liver disease. Signs of vitamin K deficiency include bruising, epistaxis, gastrointestinal bleeding, menorrhagia, and hematuria. Severe cases of vitamin K deficiency can lead to osteoporosis.

There is some evidence that indicates that supplemental vitamin K may help when used in connection with celiac disease (when suffering from a vitamin K deficiency), cystic fibrosis, and osteoporosis.

Vitamin K supplementation may be beneficial for the following conditions:

• Vitamin K deficiency
  
  
• Hemorrhagic disease in newborns
  
  
• Malabsorption syndromes
  
  
• Protection against osteoporosis