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Vitamin KVitamin K is a fat-soluble vitamin needed to produce blood-clotting factors, such as prothrombin, that prevent unchecked bleeding or hemorrhaging throughout the body. It also helps strengthen the body’s bones and capillaries.
Vitamin K comes in three forms: phylloquinone, menaquinone, and menadione. Phylloquinone, or K1, is found in green leafy vegetables, and helps bones absorb and store calcium. One recent study showed that increased amounts of vitamin K in the diet might lower the risk of hip fracture; over time, a shortage of vitamin K could lead to osteoporosis. Menaquinone, or K2, is manufactured in the body by naturally occurring intestinal bacteria. People that regularly take antibiotics or have a medical condition that upsets the balance of bacteria in the intestine are at risk of developing a vitamin K deficiency. Menadione, or vitamin K3, is an artificial form of vitamin K, which is water-soluble and more easily absorbed by people who have problems with fat absorption.
Vitamin K is now being studied for its effectiveness as a cancer treatment. Initial laboratory studies showed that vitamin K might be as effective as some prescription drugs at slowing the growth of cancerous tumors. Vitamin K is also be studied to see if it increases the effectiveness of standard anticancer drugs.
The Recommended Dietary Allowance (RDA) for vitamin K is based on an individual’s weight—about 1 microgram for every 2 pounds. The RDA for the average male is about 80 micrograms, and the RDA for the average female is about 65 micrograms. Greens, such as kale, spinach, broccoli, lettuce, and cabbage are good choices; cauliflower, soybeans, and strawberries are also high in vitamin K. High-protein foods, such as meats and eggs, have some vitamin K, but vegetables are far superior sources of this nutrient. Vitamin K is also in green tea—this is the only type of tea that contains vitamin K. You can also improve the your body’s absorption of vitamin K by eating yogurt, which supports the bacteria in your intestine.
Vitamin K deficiency is rare—most people get enough from food and from their own intestinal bacteria. One notable sign of vitamin K deficiency is abnormal bleeding and bruising as a result of minor injuries. Nosebleeds, blood in your urine, and intestinal bleeding are also signs of vitamin K deficiency. If you suspect a vitamin K deficiency, you should see your doctor immediately—left unchecked, vitamin K deficiency could result in hemorrhaging.
Some people have a higher risk of developing vitamin K deficiency. Newborns don’t have a supply of vitamin K in their system, so they are usually given an injection of vitamin K at birth, to avoid hemorrhage. People that don’t eat enough green vegetables, regularly take oral antibiotics or cholesterol-lowering drugs, or have a medical condition that upsets the balance of bacteria in the intestine or interferes with fat absorption, such as Crohn’s disease, colitis, or liver disease, should ask their doctor about supplementation.
Most multivitamin supplements don’t contain vitamin K. Vitamin K supplements are available in 100-microgram capsules, although, depending upon where you live, a prescription may be required for them. Taking more than 100 micrograms of vitamin K each day could a day cause liver damage, and people taking blood-thinning drugs should avoid this supplement altogether—it decreases the drugs’ effectiveness.
Some people have reported allergic reactions to high doses of vitamin K, and pregnant or nursing women should not take vitamin K supplements--infants who receive an excessive amount may suffer brain damage.
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