Vitamin K belongs to compounds called anphthoquinones and includes vitamins K1, K2 and K3. Vitamin K plays a strong role in normal bone growth and bone metabolism.† K2 also makes sure calcium gets to the right places—like bones and blood—and stays out of the wrong places, like soft tissues† It also activates at least three proteins in osteoblasts, the cells that generate bone, while inhibiting the breaking down of bone.
Vitamin K2 helps maintain bone mass by activating the bone protein osteocalcin, which anchors calcium inside the bone. Vitamin K2 occurs in several forms, but two primary types are menaquinine-4 (MK-4) and menaquinine-7 (MK-7). MK-4 is synthesized by animals for their own use via vitamin K1 intake. MK-7 is made in large amounts by the bacterium Bacillus subtilis, found in natto, a fermented Japanese soybean food with the highest amount of vitamin K2. Other foods high in K2 are fermented cheeses, grass-fed dairy and butter, and organ meats.
One study suggests that the MK-7 form of vitamin K2 fosters bone health and strength thereby reducing the risk of bone fractures.† Additionally, when MK-7 is combined with vitamin D, the production of osteocalcin in osteoblasts is increased, allowing calcium to adhere to bone for bone-building.†
Research indicates that MK-7 from natto may be the ideal form of vitamin K2.† Its biological activity is reportedly several times higher than vitamin K1 and significantly higher than MK-4. It also stays in the body longer — a major plus for bone health.†