August 30, 2016
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Vitamins and Calcium Supplements (cont.)

Medical Editor:

Vitamin K

What is vitamin K, and what does it do?

Vitamin K is a fat-soluble vitamin known for its role in blood clotting. There are three main types of vitamin K: vitamin K1 (phytonadione) if the natural form found in plants; vitamin K2 (menaquinones) is made by the human gut; and vitamin K3 (menadione) is the water-soluble form that is made for use in supplements.

People taking the blood-thinning medication warfarin (Coumadin) are at an increased risk for blood clotting. Warfarin works by decreasing the activity of vitamin K, lengthening the time it takes for a clot to form. The goal for vitamin K intake while taking warfarin is to keep your intake constant. This does not mean that you can't consume any vitamin K-containing foods. Instead, you want to consume a consistent amount so that the dose of warfarin that you are taking is working on the same amount. Sudden increases and/or decreases in vitamin K while taking warfarin can cause problems.

How much vitamin K do I need to consume?

There is no data to establish RDAs for vitamin K. Therefore, Adequate Intakes (AI) have been established:

Age Males Females Pregnancy Lactation
0 to 6 months 2.0 mcg 2.0 mcg N/A N/A
7 to 12 months 2.5 mcg 2.5 mcg N/A N/A
1 to 3 years 30 mcg 30 mcg N/A N/A
4 to 8 years 55 mcg 55 mcg N/A N/A
9 to 13 years 60 mcg 60 mcg N/A N/A
14 to 18 years 75 mcg 75 mcg 75 mcg 75 mcg
19+ years 120 mcg 90 mcg 90 mcg 90 mcg

What are sources of vitamin K?

Vitamin K is found primarily in green leafy vegetables and fruit. It can also be found in some animal foods.

Food Amount Vitamin K Content
Banana 1 medium 0.6 mcg
Beans, kidney, red, cooked 1 cup 14.9 mcg
Blueberries, raw 1 cup 28 mcg
Broccoli, raw 1 cup 89.4 mcg
Brussels sprouts, frozen, cooked 1 cup 299.9 mcg
Cabbage, cooked, boiled 1 cup 163.1 mcg
Carrot juice, canned 1 cup 36.6 mcg
Collards, frozen, chopped, cooked 1 cup 1,059 mcg
Dandelion greens, cooked 1 cup 579.0 mcg
Endive, raw 1 cup 115.5 mcg
Kale, frozen, cooked 1 cup 1,146.6 mcg
Lettuce, green leaf, raw 1 cup 97.2 mcg
Mustard greens, cooked 1 cup 419.3 mcg
Onions, spring or scallion 1 cup 207.0 mcg
Spinach, frozen, cooked 1 cup 1,027.3 mcg
Turnip greens, frozen, cooked 1 cup 851.0 mcg

Do I need to take a vitamin K supplement?

A well-balanced diet can provide an adequate amount of vitamin K. There are conditions that can interfere with the absorption of vitamin K, including celiac disease, ulcerative colitis, cystic fibrosis, biliary obstruction, regional enteritis, or intestinal resection. Medications that alter your liver function or kill the intestinal flora can also negatively impact your vitamin K levels. These medications include antibiotics, antiseizure medications, salicylates, and some sulfa drugs.

What happens if I don't have enough vitamin K?

Vitamin K is needed by the liver to make factors that are necessary for blood to clot properly. A deficiency in vitamin K can lead to defective blood clotting and increased bleeding.

Is there such a thing as too much vitamin K?

The Tolerable Upper Limit (UL) for vitamin K has not been established. Amounts exceeding 1,000 times the AI can promote formation of blood clots (thrombogenesis), breakdown of red blood cells (hemolysis), and raise the risk of jaundice.

Medically reviewed by a Board Certified Family Practice Physician


"Vitamin D Deficiency (Beyond the Basics)"

"Vitamin supplementation in disease prevention"

"Dietary Supplement Fact Sheets
National Institutes of Health

Medically Reviewed by a Doctor on 5/20/2015


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