The name vitamin K stands for Koagulation vitamin which was given by Dam, a Danish scientist, to a substance that prevented hemorrhagic tendency. Its chemical names are Phytomenadione, Menadione, Phylloquinone and Menaquinone. It is fat soluble and heat stable but is sensitive to light and oxidizing agents. It occurs in two major forms, vitamin k1 and vitamin k2. These all vitamin K have a basic ring structure which is 2 methyl 1,4 naphthoquinone. There is another vitamin the vitamin K3 also called menadione. It is prepared synthetically.
Vitamin k1 is present in most edible vegetables especially in fresh green leaves and in some fruits. Cow‘s milk is a richer sources.
Vitamin K2 is produced by the intestinal bacteria, which usually provides an adequate supply in man. Long term administration of antibiotic dose for more than a week may temporarily suppress the normal intestinal flora and may cause a deficiency of Vitamin K.
Bile salts are needed for vitamin k absorption when then enters the blood by ways of lymph. Vitamin K is stored in the liver.
The daily requirement for man appears to be 0.03 mg/kg for the adults. New born are tend to be deficient in it so soon after birth they should be given an intramuscular dose of vitamin K.
- The most important function of vitamin k is that it helps in the formation of blood clotting factors prothrombin, VII, IX, and X by the liver. It is also essential for the posttranslational conversion of glutamic acid residues of all these proteinous clotting factor to gamma carboxylic glutamic acid.
- It appears to have some role in electron transport system because its structure is similar to coenzyme Q. In plant kingdom, vitamin K1 is an essential component of the photosynthetic process.
Although vitamin k deficiency does not stop the liver from producing prothrombin, factors VII, IX and X but these factors lack physiological activity due to the inhibition of carboxylation of glutamic acid residues of molecules. There is an increase in the prothrombin time showing a deficiency of prothrombin. Clotting time is prolonged with a tendency to bleed profusely from minor wounds or even spontaneously. Bleeding occurs mostly from gastrointestinal tract, urinary tract and the uterus; ecchymoses and epistaxis are also observed.
There are many conditions which are associated with a deficiency of vitamin K and these may lead to bleeding tendencies. These include
- Faulty vitamin K absorption due to lack of bile as occurs in obstructive jaundice and biliary fistula.
- Diarrheal diseases e.g. sprue, celiac disease and ulcerative colitis interfere with this vitamin k absorption.
- Administration of multiple broad spectrum antibodies may lead to its deficiency
- In newborn babies especially premature ones since vitamin K does not easily cross the placental barrier.
- In patients of uremia who are on parenteral nutrition.
- Drugs administration having vitamin k activity.
The excessive use of vitamin K can block the effects of oral anticoagulants. When given to pregnant women, it can lead to jaundice in the newborn.