Vitamin K is a group of vitamins found in some green vegetables. Vitamins K1 (phytonadione) and K2 (menaquinone) are commonly available as supplements.

Vitamin K is an essential vitamin needed by the body for blood clotting, bone building, and other important processes. It's found in leafy green vegetables, broccoli, and Brussels sprouts. The name vitamin K comes from the German word "Koagulationsvitamin."

People commonly use vitamin K for blood clotting problems or for reversing the blood thinning effects of warfarin. It is also used for osteoporosis, athletic performance, breast cancer, diabetes, and many other conditions.