Vitamin K: Review and Information

Vitamin K is a fat-soluble vitamin named for its role in the coagulation (in German, “koagulation”) of blood. Vitamin K participates in this critical process by altering the amino acid glutamic acid in such a way that it can attach calcium ions and proteins together so blood can clot.

Vitamin K is made in the gut and is also obtained from foods, particularly leafy green vegetables. Without Vitamin K, blood could not clot, and uncontrolled bleeding could lead to death.

In addition to its role in blood clotting, Vitamin K also helps to produce the protein that moves calcium into bone. Without enough Vitamin K, dietary calcium cannot be utilized.

Vitamin K helps to prevent conditions of aging, such as disabling hip fractures and “hardening of the arteries,” which occurs when calcium is deposited around cholesterol in the arteries. Vitamin K can also protect the cardiovascular system by helping to keep arteries flexible. Flexible arteries mean lower blood pressure as well as lower risk for heart attack and stroke.

The body needs about 1000 micrograms of Vitamin K per week. Leafy green vegetables are an excellent source of Vitamin K, with just two cups of raw kale (at 547 micrograms of Vitamin K per cup) sufficient to meet the body’s weekly requirement.

Other top sources of Vitamin K are cooked broccoli (420 micrograms per cup), raw chard (300 micrograms per cup), raw spinach (120 micrograms per cup), and leaf lettuce (118 micrograms per cup).

Other leafy greens as well as other vegetables also contain Vitamin K. Since it is a fat-soluble vitamin, Vitamin K is best absorbed when greens are cooked in a small amount of oil.

Vitamin K can also be synthesized in the intestines from naturally occurring bacteria, though bacterial synthesis is not sufficient to meet the body’s total requirement of Vitamin K.

Vitamin K deficiency is uncommon, particularly in people who eat green vegetables on a regular basis. However, if absorption of fat is impaired by conditions such as faulty bile production or diarrhea, Vitamin K status may be compromised. Infants, who are born with a sterile digestive tract, do not manufacturer Vitamin K for the first few weeks of life. Because infants also do not consume greens, a single dose of Vitamin K is given at birth to prevent hemorrhagic disease in newborns.

Vitamin K is also available in supplements, often as part of a multivitamin formula. People who are taking anticoagulant medications to prevent blood clotting should not take supplements containing Vitamin K without consulting a physician.

Similarly, people on anticoagulants are often advised to limit consumption of leafy green vegetables or to adjust the dosage of their medication accordingly. Taking high doses of Vitamin K for a long period of time can result in anemia.

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