Are the MK-4 and MK-7 Forms of Vitamin K2 Equivalent?
The vitamin K found in food can be divided into two categories: phylloquinone (K1) and menaquinone (K2). K1 is concentrated in leafy greens and other green vegetables. K2 can be further subdivided into menaquinone-4 through -14. The number represents the length of the side chain attached to the napthoquinone ring. Menaquinone-"X" can be abbreviated MK-"X". MK-4 is the type synthesized by animals for their own use from K1 (and from MK-7 in rats). MK-5 through MK-14 are synthesized by bacteria. MK-7 in particular is made in large amounts by the bacterium Bacillus subtilis that ferments the infamous Japanese condiment natto. It's also sold as a supplement. Animals concentrate MK-4 in a number of organs, with smaller amounts of K1. Certain organs such as the brain, pancreas and salivary gland show an overwhelming preference for MK-4 over K1 in rodents and humans. The liver is a notable exception; in some animals, including humans, it concentrates longer menaquinones to a greater extent than MK-4 if they're present in the diet.