A fat-soluble vitamin precursor, menadione is converted to menaquinone in the liver. The primary function of vitamin K in the body is to assist in normal blood clotting, but it also plays a role in bone calcification.

View a second image of menadione.

Natural sources of vitamin K are green leafy vegetables, such as spinach and kale, and some oils such as soybean oil, but it is found in lesser amounts in meats, eggs, fruits, and some dairy products. To help meet the United States Food and Drug Administration's recommended daily allowance (RDA) of 80 micrograms for adult males and 65 micrograms for adult females, enriched foods such as breakfast cereals, breads, rice, and pastas and dietary supplements are available. In the United States, many people do not meet their daily requirement, and from recent bone development research, even the RDA may be insufficient.

Phylloquinone (or phytylmenaquinone; vitamin K-1), the most common form of vitamin K, is used as a benchmark for dietary intake. The hydrogenation of vegetable oils for the grocery marketplace converts vitamin K to another formulation, dihydrophylloquinone. However, the hydrogenated version is much less biologically active than natural phylloquinone.

To a biochemist, menadione (vitamin K-3) is also known as kativ-G or 2-methyl-1,4-naphthoquinone. With a molecular weight of 172.18, a molecule features 11 carbons, 8 hydrogens, and two oxygen atoms. Vitamin K takes the form as K-2 or multiprenylmenaquinone in the intestinal flora.