The naturally occurring forms of Vitamin K include Vitamin K1 and Vitamin K2
Vitamin K1 (Phylloquinone, phytonadione) is regarded as the major dietary source of Vitamin K, occurring naturally in plants, algae, and photosynthetic bacteria, green leafy vegetables, and vegetable oils.
Vitamin K2 or Menaquinone includes a range of related forms generally designated as menaquinone-n (MK-n) where n is the number of isoprenyl groups. Vitamin K2 compounds are made by bacteria in the human gut, and provide a smaller amount of the human Vitamin K requirement.
Vitamin K2-4 (MK-4) which is a short chain menaquinone is found predominately in meat, but can also be found in fermented products, certain types of cheese, butter, chicken, egg yolk and natto.
Vitamin K2-7 (MK-7) is among the most popular long chain menaquinones and is primarily derived from our gut bacteria, in addition, it can be found in lesser amounts in certain types of cheese, butter. The best source of Vitamin K2 is the traditional Japanese dish food natto which is rich in Vitamin K2 as Vitamin K2-7.
Vitamin K3 or menadione is a synthetic version, not recommended for human use due to its toxicity. Menadione is not considered a natural Vitamin K, but a synthetic analogue that acts as a provitamin. Vitamin K3 cannot exert all the functions of natural Vitamin K because of limited transformation into the fat soluble Vitamin K forms.