Vitamin K2 is a type of Vitamin K found in animals and fermented foods. Also called menaquinone, Vitamin K2 is associated with several health benefits.
Vitamin K2 has two major subtypes. MK4 is from animal sources like chicken legs, and MK7 is from bacterially fermented foods. They have the same effect in helping calcium deposit into bones and preventing heart disease. However, MK7 has a longer chain and lasts longer in the body than MK4, and is more effective. Therefore, 100 mg MK7 may be equivalent to 150 mg of MK4. Consequently, MK7 may cost about 50% more than MK4.
If you are vegan, you should choose MK7. Otherwise, either is okay, but for MK4, you may need to increase the amount of daily intake by about 50% to match up with MK7.