The human body needs vitamin K, a fat-soluble vitamin, to activate an enzyme needed to stimulate the calcium-binding function of certain proteins. This makes vitamin K vital for blood clotting to prevent excessive bleeding and bone formation. Although classified as a fat-soluble vitamin, your body stores very little vitamin K, making toxicity rare. You should only take vitamin K supplements under a doctor's supervision because if you take too much you may experience adverse effects including allergic reaction, nutrient interactions and adverse drug interactions.
Types
Three different types of vitamin K exist. Plants produce a chemical compound called phylloquinone, also known as vitamin K1. Bacteria produce another chemical compound known as menaquinone, which doctors refer to as vitamin K2. A synthetic, or manmade, chemical compound called menadione represents vitamin K3. In the United States, over-the-counter supplements only contain vitamin K1, but other countries such as Japan utilize vitamin K2 supplements. The Linus Pauling Institute reports that vitamin K1 and K2 have no known toxicity associated with high doses. Vitamin K3; however, can cause adverse effects.
Side Effects
Taking too much vitamin K supplements that contain vitamin K3 can interfere with natural antioxidants in the body. This can cause damage to the cell membranes that can lead to serious medical problems. Because many vegetables and vegetable oils contain vitamin K, adults rarely suffer from a deficiency and need supplementation. Those most likely to need vitamin K supplements include newborn babies because vitamin K cannot easily cross the placenta barrier, the infant lacks bacteria in the intestine that produce vitamin K and the vitamin K cycle that preserves vitamin K in the body is not fully functional at birth. Injections of vitamin K3 supplements can cause liver damage, jaundice and anemia. For this reason, doctors use low- dose vitamin K1 injections in infants to avoid a potentially dangerous bleeding disorder.
Nutrient Interactions
Even though taking high doses of vitamin K usually causes no long-term side effects, taking too much vitamin A or vitamin E can interfere with vitamin K. Excessive amounts of vitamin A can interfere with the absorption of vitamin K. Without enough vitamin K, blood cannot clot effectively, which can lead to nose bleeds, bruising, bleeding gums and blood in the stool or urine. High doses of vitamin E inhibit the activity of the vitamin K-dependent enzymes also leading to excessive bleeding.
Drug Interactions
Taking too much vitamin K is most dangerous for patients who take anticoagulant medications such as warfarin. Doctors classify warfarin as a vitamin K antagonist because it interferes with the ability of vitamin K to activate the enzymes necessary for blood clotting. By doing this, warfarin prevents the formation of blood clots in patients at high risk for a stroke or heart attack. Taking high doses of vitamin K decreases the effectiveness of the medication, which increases the risk for death due to a stroke or heart attack.
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