Editing Vitamin K (section)

==Definition==
Vitamin K refers to structurally similar, fat-soluble vitamers found in foods and marketed as dietary supplements. "Vitamin K" include several chemical compounds. These are similar in structure in that they share a quinone ring, but differ in the length and degree of saturation of the carbon tail and the number of repeating isoprene units in the side chain (see figures in Chemistry section). Plant-sourced forms are primarily vitamin K<sub>1</sub>. Animal-sourced foods are primarily vitamin K<sub>2</sub>.<ref name="ods" /><ref>{{cite web|url=http://www.nutritiondata.com/|title=Nutrition facts, calories in food, labels, nutritional information and analysis|website=Nutritiondata.com|date=13 February 2008|access-date=21 April 2013}}</ref><ref name=USDA-VitK /> Vitamin K has several roles: an essential nutrient absorbed from food, a product synthesized and marketed as part of a multi-vitamin or as a single-vitamin dietary supplement, and a prescription medication for specific purposes.<ref name="ods" />