Vitamin K is a fat-soluble vitamin required in the body for blood coagulation and several other functions. Vitamin K is needed for the synthesis of proteins involved in blood coagulation and for calcium binding in the bones and several other tissues. Without vitamin K, bleeding may be uncontrolled and bones may become weak. Some of the functions of vitamin K are described in more detail below.

• New born babies are at risk of deficiency of vitamin K for several reasons. Vitamin K does not cross the placenta to reach the fetus; the sterile gut of the newborn means colonic bacterial synthesis of vitamin K2 is low and breast milk is low in vitamin K. A breast-fed baby can be low in vitamin K for several weeks, until their gut starts to develop the bacteria required to synthesize vitamin K2. These babies are at risk of a condition called hemorrhagic disease of the newborn, where severe bleeding can sometimes cause brain damage. As a preventative measure, babies are routinely given vitamin K injections after birth.
• The function of Vitamin K is achieved through its role in a carboxylation reaction that converts glutamate (Glu) residues in prothrombin to gamma-carboxylglutamate residues (Gla). These modified residues are often found in the Gla domains of certain proteins involved in calcium binding, which are referred to as Gla proteins. Currently, there are six known proteins in the human body that contain Gla domains and these play a role in key bodily processes. Examples of these proteins include prothrombin and factors VII, IX, and X involved in blood coagulation. Another example is osteocalcin, which is required for bone metabolism. Several studies have shown that vitamin K supplementation can help to protect against bone loss in post-menopausal women, as it slows the osteoclastic processes mediated by calcium bonding.
• Vitamin K is widely used to treat cases of warfarin overdose.
• Studies have indicated that the antioxidant properties of vitamin K may have beneficial effects on neural damage. Research is ongoing to find out whether vitamin K supplementation may be useful in the treatment of illnesses such as Alzheimer’s disease.
• When applied topically as a 5% cream, vitamin K can help to reduce post-operative bleeding after cosmetic surgery. It can also improve the appearance of burst capillaries, rosacea symptoms and dark circles under the eyes.