Main product description Vitamin K is actually a group of fat-soluble vitamins. The most important are vitamins K1 and K2. Vitamin K1 (phylloquinone) is found in green leafy vegetables, but is poorly absorbed, has a short bioavailability and remains mostly in the liver. Vitamin K2 (menaquinone) is produced by bacteria in a healthy intestinal environment, but most of it is excreted in the stool. Among foods, the richest source of vitamin K2 is the traditional Japanese food natto, made from fermented boiled soybeans. Vitamin K2 is little present in foods typical of Western society. Warning: Consult your doctor before use if you are taking blood thinners.