Vitamin K is found in two natural forms: phylloquinone and menaquinone.
Phylloquinone, also known as vitamin K1, is made by plants, so it makes up most of the vitamin K you get from your diet. Phylloquinone is found in green, leafy vegetables, okra, asparagus, prunes, avocado, canola, olive and soybean oils.
Menaquinone (vitamin K2) is made by probiotic bacteria in the digestive tracts of animals and is found in small amounts in meat, fish and fermented foods. A third form of vitamin K, menadione, is a synthetic form of vitamin K and is not used in humans.
Vitamin K is also available as a dietary supplement. It may interact with certain anticoagulant medications, so don't take vitamin K supplements before talking to your healthcare provider.
American Cancer Society. "Vitamin K." Accessed June 15, 2011. http://www.cancer.org/Treatment/TreatmentsandSideEffects/ComplementaryandAlternativeMedicine/HerbsVitaminsandMinerals/vitamin-k.
Food and Nutrition Board of the Institute of Medicine. "Dietary Reference Intakes - Vitamins." Accessed June 15, 2011. http://iom.edu/~/media/Files/Activity%20Files/Nutrition/DRIs/DRI_Vitamins.pdf
U.S. National Library of Medicine - MedlinePlus. "Vitamin K." Accessed June 15, 2011. http://www.nlm.nih.gov/medlineplus/druginfo/natural/983.html.