Nutrition 101: Vitamin K

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Vitamin K is a fat-soluble vitamin, meaning that your body stores it in fat tissue and the liver. It is best known for its role in helping blood clot, or coagulate, properly. In fact, the letter “K” in the name of this vitamin originally came from the German word koagulation.

Recomme​nded ​Intakes

The Dietary Reference Intakes (DRI) for Vitamin K are shown below:


Age Group Recommended Dietary Allowance (RDA) per Day Tolerable Upper Intake Level (UL) per Day
Adults
19 years and up 120 mcg men

90 mcg women

*No upper limit is established for this nutrient
Kids and Youth
1 to 3 years 30 mcg
4 to 8 years 55 mcg
9 to 13 years 60 mcg
14 to 18 years 75 mcg
Special Considerations
Pregnant women 14 to 18 years 75 mcg
Pregnant women 19 years and up 90 mcg
Lactating women 14 to 18 years 75 mcg
Lactating women 19 years and up 90 mcg

What Does​ Vitamin K Do?

Vitamin K is best known for its role in healthy blood clotting. It acts as a coenzyme that assists in the synthesis of a number of proteins involved in the coagulation of blood. It helps keep our blood clotting ability at exactly the right level so that our blood is not too thick or too thin. Without adequate Vitamin K, blood does not clot properly. This can include delayed clotting time or for clotting not to occur at all. The latter can lead to increased bleeding from even minor wounds as well as internal hemorrhaging.

Warfarin (also known as Coumadin) is a widely used anticoagulant drug that interrupts the clotting process. For individuals with an excessive tendency to form blood clots, anticoagulant drugs like Warfarin can be life saving.

Vitamin K is a critical nutrient in bone health because it protects bones from weakening or fracture. It does this through two mechanisms. First, it blocks the formation of too many osteoclasts, which are the bone cells  in charge of bone demineralization. Though the activity of these cells is very important for proper health, having too many osteoclasts leads to bone demineralization. The second mechanism is Vitamin K’s involvement in a process called carboxylation. For our bones to be optimally healthy, one of the proteins found in bone, called osteocalcin, needs to be chemically altered through the process of carboxylation. When too few of the osteocalcin proteins in bone are carboxylated, the bones have increased risk for fracture.

Vitamin K helps to prevent calcification of blood vessels or heart valves. Calcification is build-up of calcium inside a tissue that is normally soft, which causes the tissue to harden and stop functioning properly. This is a common problem in many forms of heart disease and is typically referred to as hardening of the arteries. Vitamin K helps to prevent this calcification process from happening. Researchers have determined that individuals with Vitamin K deficiency are at greater risk for hardening of the arteries than individuals with healthy Vitamin K intake.

Top Vitamin K–Rich Foods

Dark green leafy vegetables are the best sources of Vitamin K. Plant oils like canola and soybean oil are also good sources of Vitamin K. Our bodies are able to make a small amount of Vitamin K.


Food Vitamin K per serving
Parsley, raw, 1/2 cup 492 mcg
Kale, raw, 1 cup 472.2 mcg
Swiss chard, raw, 1 cup 298.8 mcg
Collard greens, raw, 1 cup 157.4 mcg
Spinach, raw, 1 cup 144.9 mcg
Turnip greens, raw, 1 cup 138.0 mcg
Broccoli, cooked, 1/2 cup 110.1 mcg
Brussels sprouts, cooked, 1/2 cup 109.4 mcg
Scallions, raw, 1/2 cup 103.5 mcg
Romaine lettuce, raw, 1 cup 48.2 mcg
Soybean oil, 1 tbsp 25 mcg
Canola oil, 1 tbsp 10 mcg

Nutrition Facts Label and the % Daily Value

In the United States: The daily value (DV) for Vitamin K is 80 mg, which is lower than the DRI for adults. The number you see on the Nutrition Facts label is a percentage calculated by dividing the amount of Vitamin K in one serving of the food by the DV. Using an example from the above chart, 1/2 cup of cooked broccoli, which contains 110.1 mcg of Vitamin K, would have 138% of the DV for Vitamin K. The FDA does not require food labels to list the DV or amount for Vitamin K.

In Canada: The daily value for Vitamin K in Canada is also 80 mg. The CFIA does not require food labels to list the DV or amount of Vitamin K on the Nutrition Facts label.

Nutrient Interactions

Vitamin E: Very high doses of Vitamin E can make Vitamin K less effective for clotting blood. In people who are taking Warfarin, or in people who have low Vitamin K intakes, high doses of Vitamin E can increase the risk of bleeding.

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