Vitamin K is a fat soluble vitamin which was first named in Germany- Koagulation vitamin – because of its role in the clotting of blood.
It was first identified in 1929 by a Danish Scientist, Henrik Dam, who was experimenting with feeding hens a diet deficient in cholesterol. The hens began to haemorrhage so he added cholesterol back into their diet. This did not stop the bleeding and he realised that something else was missing from their food. This something was vitamin K1, phylloquinone and is found in leafy green vegetables, peas, beans and most other greens. Vitamin K1 is stored in the liver.
Four other types of vitamin K have since been identified; vitamins K2, K3, K4 and K5. Ks 3,4 and 5 are all synthetic and vitamin K3, menadione,is used as a supplement in human diets but is toxic in excess.
Vitamin K2, menaquinone, is synthesised from K1 in the gut by bacteria. It is then stored in blood vessel walls, bones and other tissues but not in the liver. K2 is responsible for building good bone density and green vegetables are more important in preventing osteoporosis than dairy products because the calcium in these foods are not particularly well absorbed by the body.
Vitamin K in both forms is better absorbed if you eat it with fat because it is fat soluble. A spot of olive oil on your greens is good for you.
It is unusual for someone to be deficient in the K vitamins but it is more common if you have a digestive disorder which prevents you absorbing nutrients from your food properly. People with coeliac disease are more likely to be deficient which leads to problems in blood clotting. The signs of vitamin K deficiency include bleeding gums, unexplained nosebleeds, easy bruising and heavy periods.
Newborn babies are also liable to vitamin K deficiency. This is because the vitamin does not cross the placenta and the baby does not have the necessary bacteria in its gut to start synthesising its own.
An interesting vitamin K fact is that for thirty years after it’s discovery, the only way we had to work out how much vitamin K a food stuff contained was to feed it to deficient hens and see how much was needed to stop the bleeding.
The Wikipedia entry for vitamin K is comprehensive and can be found here.
Dr Mercola has a useful 10 important facts summary here.