Vitamin K2 engages in a delicate dance with vitamin D; whereas vitamin D provides improved bone development by helping you absorb calcium, there is new evidence that vitamin K2 directs the calcium to your skeleton, while preventing it from being deposited where you don’t want it — i.e., your organs, joint spaces, and arteries. As mentioned, a large part of arterial plaque consists of calcium deposits (atherosclerosis), hence the term “hardening of the arteries.”
Vitamin K2 has also actually been found to decalcify certain tissues undergoing pathological (also known as ectopic) calcification. Vitamin K2 activates a protein hormone called osteocalcin, produced by osteoblasts, which is needed to bind calcium into the matrix of your bone. Osteocalcin also appears to help prevent calcium from depositing into your arteries.
In other words, without the help of vitamin K2, the calcium that your vitamin D so effectively lets in might be working AGAINST you — by building up your coronary arteries rather than your bones. This is why if you take calcium and vitamin D but are deficient in vitamin K, you could be worse off than if you were not taking those supplements at all.