Essential for the clotting of blood, vitamin K (phytomenadione or phylloquinone) is fat-soluble and is found in most vegetables, particularly those with green leaves. It is also manufactured by bacteria living in the gut. It is not commonly used clinically.
It is named vitamin K because it was originally called the “koagulation vitamin” by its Danish discoverer Henrik Dam because of the role it played in blood coagulation.
A lack of vitamin K is relatively common in newborn infants, or may rarely be due to diseases that prevent fat absorption from the gut, and long-term potent antibiotic use. Excessive bleeding and bruising are the symptoms, but it is easily and well treated by vitamin K injections, which rarely, may be given to infants. The excessive bleeding may lead to anaemia if left untreated.
Excess vitamin K may occur with taking too many vitamin K supplements. This stops anticoagulants (eg. warfarin) from working and may lead to strokes or heart attacks. In pregnancy, the baby may be born jaundiced (yellow skin due to liver damage) due to anaemia in infants from the break down of red blood cells.