Vitamin K is a fat-soluble vitamin. Vitamin K is best known for its role in helping blood clot properly, and in preventing excessive bleeding. It also plays an important role in bone health. The "K" is derived from the German word "koagulation". Coagulation refers to blood clotting, because vitamin K is essential for the functioning of several proteins involved in blood clotting.
There are two naturally occurring forms of vitamin K. Plants synthesize phylloquinone, also known as vitamin K1. Bacteria synthesize a range of vitamin K forms, using repeating 5-carbon units in the side chain of the molecule. These forms of vitamin K are designated menaquinone-n (MK-n), where n stands for the number of 5-carbon units. MK-n are collectively referred to as vitamin K2.
Health Benefit of Vitamin K
The only known biological role of vitamin K is that of the required coenzyme for a vitamin K-dependent carboxylase that catalyzes the carboxylation of the amino acid, glutamic acid, resulting in its conversion to gamma (g)-carboxyglutamic acid (Gla). Although vitamin K-dependent carboxylation occurs only on specific glutamic acid residues in a small number of proteins, it is critical to the calcium-binding function of those proteins.
The ability to bind calcium ions (Ca2+) is required for the activation of the seven "vitamin K-dependent" clotting factors in the coagulation cascade. The term, "coagulation cascade," refers to a series of events, each dependent on the other that stops bleeding through clot formation. Vitamin K-dependent gamma (g)-carboxylation of specific glutamic acid residues in those proteins makes it possible for them to bind calcium. Vitamin K dependent coagulation factors are synthesized in the liver. Consequently, severe liver disease results in lower blood levels of vitamin K-dependent clotting factors and an increased risk of uncontrolled bleeding (hemorrhage).
Although vitamin K is a fat-soluble vitamin, the body stores very little of it, and its stores are rapidly depleted without regular dietary intake. Perhaps, because of its limited ability to store vitamin K, the body recycles it through a process called "the vitamin K cycle." The vitamin K cycle allows a small amount of vitamin K to function in the g-carboxylation of proteins many times, decreasing the dietary requirement.
Food Sources Rich in Vitamin K
Vitamin K is most commonly found
in green leaf-like food like spinach, green tea, cabbage,
turnip greens, and brussels sprouts. Other foods high in Vitamin K include alfalfa,
soybeans, cheddar cheese, oats, and cauliflower. So if you’re a big salad
eater, chances are that you’re getting a very
healthy dose of Vitamin K.
Below are good sources of vitamin K and food containing vitamin K: