Vitamin K2 (Menaquinone-7)

What Is Vitamin K2?

Vitamin K2 (menaquinone) is the less-famous half of the vitamin K family. K1 (phylloquinone), abundant in leafy greens, is used mainly by the liver for blood clotting. K2 — from fermented foods and produced by gut bacteria — is the form that reaches bone and blood vessels, where it does something clotting-focused K1 does not: it decides where calcium goes.

The best-studied supplemental form is MK-7 (menaquinone-7), prized for a long circulating half-life that lets a single daily dose reach tissues beyond the liver.

The Calcium Traffic Controller

K2 activates two calcium-handling proteins by carboxylating them:

• Osteocalcin, which binds calcium into the bone matrix.
• Matrix Gla protein (MGP), the body's strongest inhibitor of arterial calcification.

Without enough K2, both proteins stay partly inactive — calcium is less efficiently locked into bone and less effectively kept out of arterial walls. This is the mechanistic core of the "calcium paradox": the same calcium can strengthen bone or stiffen arteries, and K2 is part of what tips the balance.

What the Trials Show

• A 3-year RCT of 180 mcg/day MK-7 in healthy postmenopausal women slowed the age-related loss of bone mineral density at the spine and femoral neck versus placebo.
• A parallel 3-year MK-7 trial improved arterial stiffness (measured by pulse-wave velocity) in the same population — a rare demonstration of a supplement moving a hard vascular marker.
• Observational work, including a vitamin K supplementation trial tracking coronary artery calcium in older adults, supports the direction of effect, though the evidence for hard cardiovascular endpoints is still maturing (grade B, not A).

Dosage

Why It Pairs With Vitamin D3

Vitamin D3 increases how much calcium you absorb — but it does not determine the destination. K2 does. Supplementing high-dose D3 without adequate K2 is the theoretical basis for concern about routing absorbed calcium toward soft tissue. Taking them together is the logic of the Bone & Arterial Longevity protocol: D3 opens the door, K2 directs the traffic.

Safety — Read This If You Take Warfarin

K2 is otherwise among the safest supplements — no established toxicity threshold, no hypercalcaemia risk because it routes calcium rather than increasing absorption. The one hard contraindication is warfarin and other vitamin-K-antagonist anticoagulants: K2 directly counteracts how these drugs work and can destabilise INR. If you are on warfarin, do not add K2 without your prescriber managing it. (This does not apply to DOACs like apixaban or rivaroxaban.)

Related Research

• Vitamin K2 (MK-7): The Calcium Traffic Controller
• Vitamin D Dosing: Why Most People Get It Wrong
• The Bone & Arterial Health Stack: D3 + K2 + Magnesium + Boron