Vitamin K is a fat-soluble vitamin. Fat-soluble vitamins are stored in the body in the liver and fatty tissues. Unlike the other fat-soluble vitamins, the body actually stores very little vitamin K. This makes regular dietary intake important. Bacteria in the large intestines help by making a range of vitamin K forms called menaquinones. Vitamin K is also produced by plants (phylloquinone) and is primarily found in green vegetables, brussels sprouts, cabbage, and plant oils. The man-made vitamin K found in supplements is called menadione.
Vitamin K’s functions include:
Adequate Intake (AI)
If you do not get enough vitamin K, your blood will not clot normally. Among healthy people, a deficiency is rare. Symptoms of vitamin K deficiency include:
As a fat-soluble vitamin, vitamin K is stored in the body in small amounts. No tolerable upper intake level (UL)—that is, the highest amount healthy people can consume without endangering their health—has been established for vitamin K. However, excess amounts can cause the breakdown of red blood cells and liver damage. To be safe, you should follow the intake guidelines based on your age and gender
Foods that are high in vitamin K include:
If you take a blood-thinning drug (anticoagulant), try to consume the recommended intake of vitamin K. Avoid exceeding this. Taking a vitamin K supplement can change the effectiveness of the drug. Talk to your doctor about your how much vitamin K is safe for you.
In addition to killing harmful bacteria, antibiotics also destroy the healthful bacteria that live in the intestines and produce vitamin K. You may need to add more foods rich in vitamin K to your diet. Ask your doctor.
The liver plays an important role in metabolism and storage of vitamin K. If you have severe liver disease, you may need to take a vitamin K supplement to avoid complications.
Because vitamin K deficiency can be life-threatening in infants, the American Academy of Pediatrics recommends that all newborns receive an injection of phylloquinone, a plant-based vitamin K. This is the standard of care in most hospitals.
Abbreviations: mcg = microgram; tbsp = tablespoon; tsp = teaspoon
Academy of Nutrition and Dietetics
Choose My Plate—US Department of Agriculture
Booth SL, Sadowski JA, Pennington JAT. Phylloquinone (vitamin K1) content of foods in the US Food and Drug Administration’s total diet study. J Agric Food Chem. 1995; 43:1574-1579.
Common foods and their vitamin K content. Anticoagulation Europe website. Available at: http://www.anticoagulationeurope.org/files/files/Some%20common%20foods%20and%20the%20vitamin%20K%20content%20Jan%202013%20(1).pdf. Accessed January 25, 2016.
Fat-soluable vitamins: A, D, E, and K. Colorado State University website. Available at: http://extension.colostate.edu/topic-areas/nutrition-food-safety-health/fat-soluble-vitamins-a-d-e-and-k-9-315/. Updated November 2012. Accessed January 25, 2016.
Phytonadione. EBSCO DynaMed website. Available at: http://www.ebscohost.com/dynamed. Updated January 18, 2013. Accessed January 25, 2016.
Vitamin K. EBSCO Natural and Alternative Treatments website. Available at: http://www.ebscohost.com/academic/natural-alternative-treatments. Updated September 18, 2014. Accessed Januarty 25 ,2016.
Vitamin K. The Linus Pauling Institute website. Available at: http://lpi.oregonstate.edu/mic/vitamins/vitamin-K. Accessed January 25, 2016.
Last reviewed January 2016 by Michael Woods, MD Last Updated: 3/10/2014