Vitamin K refers collectively to a group of fat-soluble vitamins required for the complete synthesis of the particular proteins which are necessary for blood coagulation. The chemical action of vitamin K on these proteins allows them to bind calcium, so that the blood coagulates and can help to form strong bones and tissues.
Vitamin K can be found in many food sources, especially dark green leafy vegetables, of which kale has the richest source, followed by spinach and collard greens, and many other brassicas. Since vitamin K is a fat-soluble vitamin, it is better absorbed by the body when taken in conjunction with fats, so putting butter on broccoli makes more sense than you might think! Some fruit, including kiwis, grapes and avocados, also have a high vitamin K content.
Deficiency is rare, as quite a lot of vitamin K is synthesised by bacteria in the colon, but it can cause bruising, bleeding of the nose and gums, anaemia and heavy menstrual bleeding. Bones are weakened and arteries and soft tissues are prone to increased calcification. Supplementation is necessary for newborn infants, who have no such bacteria until they are provided in their mother’s milk.