Vitamin K is not a single vitamin but a group of very similar molecules that interact with a wide range of different proteins in the body. This vitamin group is involved in blood coagulation and the metabolism of several tissue types, including bone. Vitamin K deficiency is an extremely rare condition, particularly in adults, but it can occur in people affected by malnutrition and certain diseases.
There are currently five known forms of vitamin K, two of which are natural, and three of which are synthetic. The first is K1, which is found mainly in leafy green plants and serves as a dietary source of the vitamin. The second natural source is K2, which is produced by several species of gut bacteria. The three synthetic forms, denoted K3, K4, and K5, are used for a variety of industrial purposes.
Although vitamin K1 can be obtained from many edible plants as well as meat, eggs and dairy products, dietary sources are not always the most significant source of the vitamin for adults. This is because K2, produced by gut bacteria, also can provide for a significant amount of the body’s vitamin K requirements. In comparison to other types of vitamin deficiency, vitamin K deficiency is rare, largely because gut bacteria are capable of meeting most of the body’s needs. Even so, certain groups of people are at risk of vitamin K deficiency.
Newborn babies have a much increased risk of vitamin K deficiency in comparison to adults. This is because the gut of an infant contains no bacterial population, and it takes time for bacteria to colonize the gut. In addition, babies are born with little or no stored vitamin K, and this vitamin is present in only low levels in breast milk. Also at increased risk of deficiency are people who have suffered liver damage, people with digestive disorders such as inflammatory bowel disease and people with cystic fibrosis. People who are anorexic or bulimic or who are on very strict or sparse diets also are more likely to be deficient in vitamin K.
This type of vitamin deficiency often is asymptomatic. In fact, it often is only when blood coagulation is affected that symptoms become apparent. Symptoms of vitamin K deficiency include bleeding gums, unexplained bruising or bleeding, gastrointestinal bleeding and wound sites that continue to bleed. Women also might experience unusually heavy menstruation or menstrual periods of unusually long duration. In children and adolescents, deficiency can cause bone malformation.
Children who are deficient in vitamin K at or shortly after birth are at risk of a condition called hemorrhagic disease of the newborn. This disease is caused by reduced production of blood clotting factors as a result of insufficient vitamin K. Hemorrhagic disease is treated with vitamin K supplementation, and in many countries, vitamin K is administered as a prophylactic measure to all newborn babies.