Vitamin K is part of a group of vitamins, which also includes vitamins A, D and E, that your body stores in fat tissues for use as necessary. It is available from food sources, as well as in multivitamin supplements. Some health food stores and online vitamin retailers also carry standalone vitamin K supplements; however, you may need a prescription for vitamin K doses sufficient to address deficiencies caused by malabsorption-related conditions such as Crohn's disease and Alagille's syndrome. The primary function of vitamin K is to promote blood clotting.
Coagulation
Vitamin K is necessary for the activation of several separate proteins, called clotting factors, that allow clots to form to prevent excessive bleeding from wounds, according to the Linus Pauling Institute at Oregon State University. It enables the gamma-carboxylation of glutamic acid residues in clotting factors and allows these proteins to bind to calcium ions for the production of platelets. Platelets are irregularly shaped particles in blood that form clots when exposed to oxygen.
Recommended Dose
The recommended daily intake of vitamin K for adults is 120 micrograms for men and 90 micrograms for women. Meeting the daily recommended intake of this vitamin is particularly important for bleeding prevention in people who take blood thinners such as warfarin, which act as vitamin K antagonists, according to the Linus Pauling Institute. Pediatric intake recommendations range from 2 micrograms for infants to 75 micrograms for adolescents.
Food Sources
Vitamin K is primarily found in plant-based foods. Kale is among the richest sources of this vitamin -- a 1-cup serving of fresh, boiled kale contains about 1,062 micrograms of vitamin K, according to the USDA National Nutrient Database. The same-sized serving of fresh, boiled spinach contains about 888 micrograms, and a 1-cup serving of boiled turnip greens contains about 851 micrograms. Other foods rich in vitamin K include dandelion greens, Brussels sprouts, collard greens, parsley and romaine lettuce.
Considerations
Vitamin K is well tolerated at levels above recommended daily intakes -- there is no upper tolerable limit for vitamins K-1 and K-2, the forms of vitamin K most commonly found in foods and vitamin supplements. Check with your doctor before taking any vitamin supplement containing vitamin K-3, which is a synthetic substance. Vitamin K-3 may promote cellular damage by inhibiting the activity of glutathione, an antioxidant produced by your body, according to the Linus Pauling Institute.
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