Strong Bones, Safe Arteries: The Traffic Cop

Think of bone building like a construction site. Vitamin D is the foreman who opens the gate and schedules more deliveries (you absorb more calcium). Calcium is the stack of bricks. Vitamin K2 hands out the blueprints to the crew—activating proteins that anchor calcium into bone and discourage it from piling up in arteries. In humans, D+Calcium reliably improves hip BMD a little (and may reduce hip fractures when people actually take it consistently), while adding K (K1 or K2) consistently improves 'traffic-control' biomarkers and in vitro mineralization. But extra, across-the-board gains in bone density or fracture reduction from adding K2 have been small or inconsistent so far.

The trio is a biologically sensible system: Vitamin D opens the gut's "calcium gate," calcium supplies the bricks, and Vitamin K2 acts like a traffic cop that signals proteins to park calcium in bone and keep it out of arteries. In clinical trials, D+Calcium modestly preserves hip BMD and may reduce fractures in adherent older adults but raises kidney stone risk; adding K (K1 or K2) reliably improves vitamin K–dependent proteins and in vitro bone mineralization, with human results ranging from no added BMD benefit to small site-specific gains (e.g., wrist), and no clear fracture advantage yet. Bottom line: useful when dietary calcium and/or vitamin D are low; K2 likely adds "safer calcium handling," but proven extra fracture prevention over D+Calcium is unconvincing so far. ^{[4][5][1][2][3]}