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Vitamin K

Why We Need It

Vitamin K, a fat-soluble vitamin, helps the body make proteins, especially those needed for normal clotting of blood when you bleed. It is needed for making important proteins for blood, bones, and kidneys, also.

Amounts Needed

Recommended daily intakes of vitamin K are listed in the following table.

Recommended Daily Intakes of Vitamin K

Age Vitamin K (μg/day)
Infants birth-6 months 2
6 months-1 year 2.5
Children 1-3 years 30
4-8 years 55
Males 9-13 years 60
14-18 years 75
19 years and over 120
Females 9-13 years 60
14-18 years 75
19 years and over 90
pregnant < 18 75
19-50 90
breastfeeding < 18 75
19-50 90
μg = micrograms

Source: adapted from the Dietary Reference Intakes series, National Academies Press. Copyright 1997, 1998, 2000, 2001, 2002, 2004, by the National Academies of Sciences.

No Tolerable Upper Intake Level (UL) has been established for vitamin K.

Sources

Food: Vitamin K is found mostly in green, leafy vegetables and some fruits. Vegetable sources include collards, spinach, broccoli, Brussels sprouts, and cabbage. Good fruit sources include kiwi, blackberries, and blueberries.

Here are some foods and the amount of vitamin K they contain.

Food Sources of Vitamin K

Food Vitamin K
(μg per serving)
turnip greens, cooked, ½ cup 70
spinach, raw, 1 cup 145
broccoli, cooked, ½ cup 45
cabbage, cooked, ½cup 30
Strawberries, 1 cup 4
blackberries, 1 cup 30
okra, cooked, ½ cup 30
blueberries, 1 cup 30
red grapes, 1 cup 25
μg = micrograms

Bacteria: Like vitamin D, vitamin K is produced by the body. Vitamin K is made by the bacteria that normally live in the large intestines, and some of it is absorbed by the body.

Shots: A shot of vitamin K is usually given to newborns soon after birth because they have very little of this vitamin in their bodies. This shot allows their blood to clot normally during the first weeks of life.

If We Don’t Get Enough

Blood takes a long time to clot if the body does not get enough vitamin K. This can result in excessive blood loss and an increased risk of death from injuries. A vitamin K deficiency is very unlikely unless a person has a rare health problem. However, prolonged use of antibiotics can destroy some of the bacteria that produce vitamin K in your intestines.

Interaction With Anticoagulants

Anticoagulants, or blood-thinning drugs, interfere with the normal use of vitamin K by the body. If you take anticoagulant medication such as warfarin (Coumadin®), you should keep your vitamin K intake consistent day-to-day. Consuming very large or very small amounts of this vitamin can change how these drugs work. For example, too much vitamin K can make your blood clot faster, so limit your intake of foods high in vitamin K like spinach and turnip greens.

In addition, check with your doctor before taking vitamin E supplements (e.g., herbs such as ginkgo and garlic) if you take anticoagulant medications. High doses of vitamin E can interfere with the action of vitamin K in the body.

Supplements

Multivitamin supplements may or may not contain vitamin K. Usually it is not necessary to take a vitamin K supplement since most people get plenty of this vitamin in food. With the exception of people who take anticoagulants, research has shown no problems from consuming too much vitamin K from food or supplements. Moderation is still the best approach.

If you take an anticoagulant medication, avoid supplements that contain vitamin K.

For More Information

The Health Extension Agent or Nutrition Educator at your county Extension office may have more written information and nutrition classes for you to attend. Also, your doctor, health care provider, or a registered dietitian (RD) can provide reliable information.

Reliable nutrition information may be found on the Internet at the following sites:

http://www.clemson.edu/extension/hgic/
http://www.eatright.org
http://www.nutrition.gov
http://www.nal.usda.gov/fnic

Sources:

  1. Turner, Elaine R. University of Florida Extension. Facts About Vitamin K. FCS8666. April 2006. https://edis.ifas.ufl.edu/publication/fy209
  2. Duyff, Roberta Larson. American Dietetic Association Complete Food and Nutrition Guide, 3rd Edition. 2006.
  3. National Academies of Sciences. National Academies Press. Dietary Reference Intakes series. 2004.
  4. “Office of Dietary Supplements – Vitamin K.” NIH Office of Dietary Supplements, U.S. Department of Health and Human Services, Mar. 2021, ods.od.nih.gov/factsheets/VitaminB12-HealthProfessional/#h2.

If this document didn’t answer your questions, please contact HGIC at hgic@clemson.edu or 1-888-656-9988.

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