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Publication #FCS8666

Facts about Vitamin K1

R. Elaine Turner and Wendy J. Dahl2

Figure 1. 

Vitamin K is mostly found in vegetables, especially green vegetables such as turnip greens.


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Why do we need vitamin K?

Vitamin K is one of the fat-soluble vitamins. It helps the body make proteins that are needed for normal blood clotting. Vitamin K is also needed for making important bone proteins.

What happens if we do not get enough vitamin K?

When people do not get enough vitamin K, blood takes a long time to clot. This can cause excessive blood loss and increased risk of death from injuries. Vitamin K deficiency is rare in healthy adults. However, people with severe digestive disorders or on chronic antibiotic therapy may be at risk (Nelms, Sucher, & Lacey, 2016).

Anticoagulant medications such as warfarin are prescribed to interfere with the normal function of vitamin K in the body. Eating very large amounts of foods containing vitamin K can change how these drugs work (Leite, Martins, & Castilho, 2016).

If you take an anticoagulant, you should pay close attention to your intake of foods such as spinach and turnip greens that are very high in vitamin K, and ensure that your vitamin K intake is about the same from day to day. You should also consult your doctor before taking high dose vitamin E supplements (Podszun & Frank, 2014), or herbal supplements such as ginkgo, ginger, St. John's wort, ginseng, and garlic, as these may also affect blood clotting (Leite, Martins, & Castilho, 2016).

How much vitamin K do we need?

The table below lists the recommended intakes for vitamin K (Food and Nutrition Board, 2001).

Table 1. 

Recommended intakes for vitamin K.

Life Stage



Men, ages 19+


Women, ages 19+






μg = micrograms of vitamin K

How can we get enough vitamin K?

Vitamin K is mostly found in vegetables, especially green vegetables. Kale, collards, spinach, broccoli, and cabbage contain high amounts of vitamin K. Other sources are soybean oil, strawberries, and whole milk. Below are some foods and the amount of vitamin K they contain (USDA-ARS, 2015).

Table 2. 

Sources of vitamin K.


Vitamin K


Kale, ½ cup


Spinach, raw, ½ cup


Turnip greens, ½ cup


Broccoli, ½ cup


Cabbage, ½ cup


Soybean oil, 1 Tbsp


Iceberg lettuce, 1 cup


Green beans, ½ cup


Strawberries, 1 cup


Whole milk, 1 cup


Egg, 1 large


μg = micrograms

Tbsp = tablespoons

We also get some vitamin K from the bacteria that normally live in our large intestine. Our resident bacteria make vitamin K and we are able to absorb some of it.

Newborns have very little vitamin K in their bodies. They usually receive a shot of vitamin K soon after birth. This shot of vitamin K allows normal blood clotting to occur during the first weeks of life.

What about supplements?

Most people get plenty of vitamin K in their diet, so supplements are usually not needed. Water-soluble forms of the vitamin are manufactured and may be beneficial for people with problems in fat digestion and absorption. Multivitamin supplements are available with or without vitamin K. If you take an anti-coagulant, avoid supplements that contain vitamin K.

It is not known how much vitamin K is too much. Research has not found problems from consuming high intakes of vitamin K from food or supplements, except for people who take anticoagulant medications.

Learn More

The Family and Consumer Sciences (FCS) agent at your local UF/IFAS Extension office may have more written information and nutrition classes for you to attend. Also, a registered dietitian (RD) can provide you with reliable information.

Reliable nutrition information can be found at:


Food and Nutrition Board. (2001). Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc. Washington, DC: National Academy Press.

Leite PM, Martins MA, & Castilho RO. (2016) Review on mechanisms and interactions in concomitant use of herbs and warfarin therapy. Biomedicine & pharmacotherapy. 83:14–21.

Nelms M, Sucher KP, & Lacey K. (2016). Nutrition Therapy and Pathophysiology 3rd Ed. Cengage Learning.

Podszun M & Frank J. Vitamin E-drug interactions: molecular basis and clinical relevance. Nutrition research reviews. 27(2):215–231.

U.S. Department of Agriculture, Agricultural Research Service USDA-ARS. (2015). National Nutrient Database for Standard Reference, Release 28. Nutrient Data Laboratory Home Page.



This document is FCS8666, one of a series of the Department of Family, Youth and Community Sciences, UF/IFAS Extension. Original publication date July 2001. Revised April 2006, October 2010, December 2013, and December 2016. Visit the EDIS website at


R. Elaine Turner, RD, professor; and Wendy J. Dahl, RD, assistant professor; Food Science and Human Nutrition Department, UF/IFAS Extension, Gainesville, FL 32611.

The Institute of Food and Agricultural Sciences (IFAS) is an Equal Opportunity Institution authorized to provide research, educational information and other services only to individuals and institutions that function with non-discrimination with respect to race, creed, color, religion, age, disability, sex, sexual orientation, marital status, national origin, political opinions or affiliations. For more information on obtaining other UF/IFAS Extension publications, contact your county's UF/IFAS Extension office.

U.S. Department of Agriculture, UF/IFAS Extension Service, University of Florida, IFAS, Florida A & M University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Nick T. Place, dean for UF/IFAS Extension.