The most common in the human diet is the short-chain MK-4, which is usually produced by bacterial conversion of Vitamin K1, and is commonly found in animal products. Long-chain menaquinones include MK-7, MK-8 and MK-9 and are more predominant in fermented foods such as natto. Longer-chain menaquinones (MK-10 to MK-13) are produced by anaerobic bacteria in the colon, but they are not well absorbed and have little biological function.[1]