Vitamin K



Vitamin K promotes the formation of prothrombin and other blood-clotting proteins in the liver. A deficiency in the vitamin leads both to a slow-down in the clotting process and the strong possibility of a hemorrhage (excessive bleeding).

Dam's Hens

Research into vitamins began in 1929. Danish biochemist Carl Dam (1895-1976) noticed that his laboratory hens developed small hemorrhages (areas of blood vessel breakage) under the skin and within the muscles. Because the hemorrhages resembled those seen in scurvy, Dam first treated the hens for that disease. He added vitamin C in the form of lemon juice to his hens' diet. When that failed to stop their bleeding, he tried other additives. He ended up trying all the food additives that other investigators had found useful in correcting vitamin deficiencies. None of them worked.

Dam concluded that an unknown vitamin must be involved. Since the mysterious vitamin appeared to be essential for normal coagulation (clotting) of the blood, Dam named it vitamin K, for "Koagulation" (the German spelling of "coagulation").

The Search Begins

Intrigued by the thought of a new and potentially useful vitamin, others took up the challenge of the search. Within a few years, several biochemists were able to isolate the vitamin from an extract of alfalfa. An American group led by Edward Doisy (1893-1986) discovered that the alfalfa extract consisted of two chemically similar yellowish oils. The oils became known as KI and K2. Doisy's group went on to work out the chemical constitution of both varieties. Because of this work, Doisy shared the 1943 Nobel Prize for medicine with Dam.

Vitamin K Deficiencies

Vitamin K deficiencies are relatively rare. The vitamin is widespread in plants and it is also synthesized by the bacteria in the human intestinal tract. Because antibiotics often destroy all types of bacteria in the body, patients on long-term drug therapy may need vitamin K supplements to prevent bleeding problems.

Newborn infants are particularly susceptible to vitamin K deficiency. This is because the vitamin does not pass easily from the mother to the fetus through the placenta (birth sac). In addition, all babies are born with a sterile digestive tract.

Because of this, newborns often receive an intramuscular injection of vitamin K at birth. The vitamin is also routinely added to infant formula. This helps prevent hemorrhages. Infants can only begin to synthesize their own vitamin K several days after birth. This is when the digestive tract has acquired the necessary bacteria.

[See also Antibiotic ]



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