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 (collards, spinach, salad green, broccoli), brussels sprouts, cabbage, and plant oils. The man-made vitamin K found in supplements is called menadione.
Vitamin K’s functions include:
Vitamin K Deficiency
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:
Vitamin K Toxicity
As a fat-soluble vitamin, vitamin K is stored in the body and not excreted in the urine, like most water-soluble vitamins. While allergic reactions could happen, no symptoms have been observed among people consuming excess amounts of the natural-form of vitamin K. There have been some problems associated with the man-made form of the vitamin (menadione), though. Some infants who were given injections of menadione had liver toxicity, jaundice, and rupture of the blood cells. 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. But, to be safe, you should follow the intake guidelines based on your age and gender.
Major Food Sources
If You Take a Blood-thinning Drug
If you take a blood-thinning drug (anticoagulant), try to consume the recommended intake of vitamin K (90 mcg). Avoid exceeding this. Taking a vitamin K supplement can cause drug interactions. Talk to your doctor about your how much vitamin K is safe for you.
If You Take Antibiotics
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.
If You Have Liver Disease
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 (eg, bleeding or bruising).
If You Have a Newborn Baby
Because vitamin K deficiency can be life-threatening in newborns, 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 many hospitals.
Tips For Increasing Your Vitamin K Intake
Abbreviations: mcg = microgram; tbsp = tablespoon; tsp = teaspoon
American Dietetic Association
Canada's Food Guide
Dietitians of Canada
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.
Duyff RL. The American Dietetic Association’s Complete Food and Nutrition Guide . Minneapolis, MN: Chronimed Publishing; 1998.
Micronutrient information center: vitamin K. The Linus Pauling Institute website. Available at: http://lpi.oregonstate.edu/infocenter/vitamins/vitaminK/. Accessed June 11, 2012.
Phytonadione. EBSCO DynaMed website. Available at: http://www.ebscohost.com/dynamed. Updated April 11, 2011. Accessed June 1, 2011.
Vitamin K. EBSCO Natural and Alternative Treatments website. Available at: http://www.ebscohost.com/healthLibrary/ . Updated August 2011. Accessed June 1, 2012.
Vitamin K deficiency. EBSCO DynaMed website. Available at: http://ebscohost.com/dynamed. Updated July 20, 2010. Accessed June 1, 2012.
Last reviewed June 2012 by Brian Randall, MD