What is vitamin K?
Vitamin K is a nutrient that the body requires in small, regular amounts. It is essential for the formation of several substances called coagulation factors that work together to clot the blood when injuries to blood vessels occur. Insufficient vitamin K can lead to excessive bleeding and easy bruising. Vitamin K is also thought to play an important role in the prevention of bone loss. Low blood levels of vitamin K have been associated with low bone density, and there is some evidence that adequate levels of vitamin K can improve bone health while reducing the risk of fractures.
There are three different types of vitamin K:
- Vitamin K1 (phylloquinone) is the type that comes from the diet, especially green leafy vegetables but also dairy products and vegetable oils. K1 is also produced commercially to use as an oral or injectable Treatment for some conditions associated with excess bleeding.
- Vitamin K2 (menaquinone) is made by bacteria, the normal flora in the intestines. It supplements K1, but there is not enough of it to meet the body's requirements.
- Vitamin K3 (menadione) is a synthetic water-soluble form of vitamin K that is used as a treatment for adults. It is no longer given to infants in the United States as it can cause hemolytic anemia.
Since the body is not able to produce a sufficient amount of vitamin K, a certain amount must be taken in through the diet. It is present in a wide variety of foods, and the normal diet in the U.S. typically supplies a sufficient amount. Examples of different foods that contain high amounts, often more than the Recommended Daily Allowance (RDA), include leafy green vegetables such as kale, collards, spinach, turnip greens, mustard greens, green leaf lettuce, and other vegetables such as broccoli, green onions, parsley, asparagus, Brussels sprouts, and cabbage. Other sources include dairy products, cereals, vegetable oils, and soybeans. K1 and K2, the types provided by the diet and produced by the body, are both fat-soluble and are stored in the body's fat tissue and in the liver. An adult typically stores about a week's worth of vitamin K.
People who are on the anticoagulant drug warfarin (COUMADIN®) must be careful of the amount of vitamin K present in the foods that they eat. Vitamin K is an antagonist to warfarin. This means that it counteracts the action of the drug and makes it less effective in treating the condition for which it is prescribed. Warfarin is given to people with a variety of conditions such as deep vein thrombosis (DVT) and cardiovascular disease (CVD) to "thin" their blood and prevent inappropriate clotting. The drug works by inhibiting production of vitamin K-dependent clotting factors. Warfarin affects people differently and must be carefully monitored, typically with a PT (prothrombin time) test that gives results as an INR (International Normalized Ratio) value. The INR must be kept within a narrow therapeutic range. Too little warfarin can result in dangerous blood clots, but too much can cause bleeding episodes. Rather than avoid foods rich in vitamin K, it is more important for people on this drug to consume a consistent amount of vitamin K each day. Significant increases or decreases in vitamin K can affect how warfarin works in their bodies.