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 don’t get enough vitamin K?
When people don’t 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 (1).
Anticoagulant medications such as warfarin (Coumadin®) are prescribed to interfere with normal function of vitamin K in the body. Eating very large or very small amounts of vitamin K can change how these drugs work.
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 vitamin E supplements, or supplements such as ginkgo and garlic, as these may also affect blood clotting.
How much vitamin K do we need?
The table lists the recommended intakes for vitamin K (2).
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 (3).
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.
The Family and Consumer Sciences (FCS) agent at your county 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.
1. Gropper, S. & Smith, J. (2008). Advanced nutrition and human metabolism (5th ed). Mason, OH: Cengage Learning.
2. Food and Nutrition Board, Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc (2001).Washington, DC:
National Academy Press.
3. U.S. Department of Agriculture, Agricultural Research Service. 2009. National Nutrient Database for Standard Reference, Release 22. Nutrient Data Laboratory Home
1. This document is FCS8666, one of a series of the Department of Family, Youth and Community Sciences, UF/IFAS Extension. First published: June 2001.
Revised: April 2006, October 2010 and December 2013. Please visit the EDIS website at http://edis.ifas.ufl.edu/.
2. R. Elaine Turner, PhD, RD, professor, and Wendy J. Dahl, PhD, RD, assistant professor; Food Science and Human Nutrition Department, UF/IFAS
Extension, Gainesville 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. U.S. Department of Agriculture, Cooperative Extension Service, University of Florida, IFAS, Florida A&M University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Nick T. Place, Dean.