Vitamin K2: The Calcium-Routing Vitamin That Directs Minerals to Bones
Vitamin K2 activates proteins that direct calcium into bones and teeth rather than arterial walls — available as MK-4 (animal sources) and MK-7 (natto, fermented foods).
Vitamin K2 (menaquinone) is a fat-soluble vitamin distinct from vitamin K1 (phylloquinone, found in leafy greens). Its primary forms are MK-4 (short-chain, found in animal products, fast-acting but shorter half-life) and MK-7 (long-chain, found in natto and hard cheeses, longer half-life). ## The Calcium-Routing Hypothesis K2 activates two key proteins: - **Matrix Gla protein** (MGP): When activated by K2, inhibits calcium deposition in arterial walls - **Osteocalcin**: When activated, facilitates calcium incorporation into bones and teeth This "calcium routing" role explains why K2 deficiency is associated with both arterial calcification and poor bone mineralization — calcium goes to the wrong places. ## Dietary Sources Best sources: natto (~1,000 μg/100g MK-7), hard cheeses like Gouda and Edam, egg yolk, chicken liver, and grass-fed butter. MK-7 from natto has the longest half-life (~72 hours vs ~1 hour for MK-4), making it more effective at sustained doses. ## Supplementation Often paired with vitamin D3, which increases calcium absorption from the gut — K2 then ensures that absorbed calcium reaches bone rather than soft tissues. This D3+K2 combination is common in Osteoporosis: When Bone Breakdown Outpaces Bone Building prevention protocols.