Vitamin K



Vitamin K, a group of three related substances, is the last of the fat-soluble vitamins, completing the family that also includes vitamins A, D, E, and F. This nutrient, both found in nature and made in the body, helps Phylloquinone, the natural vitamin K found in alfalfa and other foods, was discovered in Denmark and labeled vitamin K for the Danish word Koagulation. Food-source phylloquinone is termed K1, while the menaquinone produced by our intestinal bacteria is labeled vitamin K2. A synthetic compound with the basic structure of the quinones is menadione, or vitamin K3. It has twice the activity of the natural Ks and is used therapeutically in people who may not use natural vitamin K well, such as those with decreased bile acid secretion.


All vitamin K variants are fat soluble and stable to heat. Alkalis, strong acids, radiation, and oxidizing agents can destroy vitamin K. It is absorbed from the upper small intestine with the help of bile or bile salts and pancreatic juices and then carried to the liver for the synthesis of prothrombin, a key blood-clotting factor. High intake (as with supplementation) of vitamin E or calcium may reduce vitamin K absorption. Vitamin K is stored in small amounts; most is excreted after therapeutic doses.


Yogurt, kefir, and acidophilus milk may help to increase the functioning of the intestinal bacterial flora and therefore contribute to vitamin K production. Antibiotics that reduce these bacteria will diminish vitamin K synthesis in the colon. Rancid oils and fats, X-rays, radiation, aspirin, air pollution, and freezing of foods all destroy vitamin K, and mineral oil binds with K and rapidly eliminates it from the intestines.


Sources: Vitamin K is found in both plant and animal sources in nature. Good supplies are found in the dark leafy greens, most green plants, alfalfa, and kelp. Blackstrap molasses and the polyunsaturated oils, such as safflower, also contain some vitamin K. In animal-source foods, K is found in liver, milk, yogurt, egg yolks, and fish liver oils. The best source for humans is that made by the intestinal bacteria. It is important for the production of many nutrients that we keep our “friendly” colon bacteria active and doing their job; to aid this process we should minimize our use of oral antibiotics, avoid excess sugars and processed foods, and occasionally evaluate and treat any abnormal organisms interfering in our colon, such as yeasts or parasites.


Functions: Vitamin K is necessary for normal blood clotting. It is required for the synthesis of prothrombin and other proteins (Factors IX, VII, and X) involved in blood coagulation. Vitamin K also helps prothrombin convert to thrombin with the aid of potassium and calcium; thrombin is the important factor needed for the conversion of fibrinogen to the active fibrin clot.


Coumarin, which comes from sweet clover, acts as an anticoagulant (decreases blood clotting) by competing with vitamin K at its active sites. Coumarin or synthetic dicumarol is used medically primarily as an oral anticoagulant to decrease prothrombin. The salicylates, such as aspirin, increase the need for vitamin K.


Uses: Vitamin K is used commonly by physicians in the treatment of clinical problems. It should not be taken routinely without the ability to monitor its effects on blood clotting. Currently, its most regular application in Western medicine is to inject newborns with vitamin K to prevent hemorrhage and other minor bleeding problems. Vitamin K is not transferred from the mother, nor are there colon bacteria to make it in newborns since the gastrointestinal tract is usually sterile for a few days after birth. The production of vitamin K and, therefore, prothrombin usually begins by the fourth day of life, giving babies their ability to clot blood when necessary.


Vitamin K is also sometimes given by injection to women prior to labor (a deficiency can occur during pregnancy) or to patients before or after surgery to prevent hemorrhage. Higher doses of vitamin K than are needed by the body do not cause excessive blood clotting, so this is not a concern. Additional K is given at times to women with heavy menstrual flow, to help relieve menstrual pain, or to reduce the nausea and vomiting of pregnancy. It is also used to promote blood clotting in people with liver disease, jaundice, or malabsorption problems. Those people who bruise easily or whose blood clots slowly after injury sometimes benefit from supplemental vitamin K, as do some sufferers of rheumatoid arthritis, where K may reduce irritation in the synovial linings of the joints.


An occasional use of vitamin K that can be lifesaving is the treatment of people who have taken too much of the anticoagulant Coumadin. People with strokes, heart attacks, thrombophlebitis, or pulmonary embolism or who are at risk of having problems related to abnormal blood clotting may receive this type of anticoagulant therapy. As I described previously, the coumarol medications reduce blood clotting by competing with vitamin K sites and reducing prothrombin formation. If bleeding problems occur in patients on Coumadin therapy, an injection of vitamin K may help correct it rapidly. Vitamin K is also used at times as a preservative in foods; it helps control fermentation. If vitamin K deficiency is suspected, it is usually wise to consume more foods high in this vitamin before using supplements.


Deficiency and toxicity: Toxicity rarely occurs from vitamin K from its natural sources—that is, from foods or from production by the intestinal bacteria—but toxic side effects are more likely from the synthetic vitamin K used in medical treatment. Natural vitamins K1 and K2 are easily stored or eliminated, whereas menadione, or K3, can build up in the blood and cause some toxicity. Hemolytic anemia, a reduction in red blood cells due to destruction, is a possible problem. This usually increases the bilirubin, one of the breakdown products of hemoglobin in the blood, more of a problem in infants, who have a harder time handling high levels of bilirubin. Symptoms of adult toxicity may include flushing, sweating, or a feeling of chest constriction; however, problems arising from vitamin K use are rare.


Deficiency of vitamin K is also uncommon. It is more likely with poor intestinal absorption, with low dietary intake or decreased production in the intestines, or when the liver is not able to use vitamin K (which may be caused by either a genetic condition or liver disease). Deficiency of vitamin K is also more common in sprue or celiac disease (intestinal malabsorption problems), in colitis, in ileitis, or after bowel surgery. I mentioned that for a few days the newborn baby is at risk of bleeding because of lack of vitamin K; vitamin K deficiency may also be a problem in the elderly, when the diet is poor or when antibiotic use or other factors decrease intestinal bacterial production.


The problems that may occur from vitamin K deficiency involve abnormal bleeding, as in nosebleeds and internal hemorrhage, which can be severe if it occurs in the brain or internal organs. Miscarriage may occur secondary to bleeding problems from vitamin K deficiency in pregnancy. Fortunately, this is uncommon.


Requirements: There is no official RDA for vitamin K (there may be one soon), as there is usually sufficient supply from foods and intestinal bacteria. An average diet will usually provide at least 75–150 mcg., which is the suggested minimum, though 300 mcg. daily may be optimal. Absorption may vary from person to person, estimated from 20–60 percent of intake. Overall, suggested needs are about 2 mcg. per kilogram (2.2 pounds) of body weight.


Newborns need about 1–5 mg. daily to prevent bleeding. Usually a 10 mg. injection is given at birth. Vitamin K is not available over the counter and must be given by prescription; for those who wish to consume more vitamin K, alfalfa tablets are a good source.

Elson M. Haas MD Written by Elson M. Haas MD

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