Vitamin K2

What It Is

Vitamin K2 is a fat-soluble vitamin in the vitamin K family (distinct from K1). K1 is mainly used for blood-clotting. K2 is involved in calcium handling and is found in animal foods (cheeses, egg yolks, liver) and fermented foods (natto is the richest). K2 exists in several forms called menaquinones (MK-4, MK-7 etc.). MK-7 (from natto/ferments) has the longest half-life in humans; MK-4 (animal-derived or synthetic) is shorter acting but widely used in trials.

How It Works

K2 serves as a co-factor for the enzyme γ-glutamyl carboxylase, which “activates” specific proteins by carboxylating them. Two key proteins depend on it:

1. Osteocalcin (bone compartment) — When activated, osteocalcin binds calcium into bone matrix, supporting bone mineralization and strength.
2. Matrix Gla Protein (vascular compartment) — When activated, this protein inhibits calcium deposition in arteries and soft tissues.

In short, K2 helps pull calcium into the right places (bone/teeth) and keep it out of the wrong places (arteries, kidneys, soft tissue).

Why It’s Important

• Bone health — Trials combining K2 with calcium/vitamin D have shown improved bone turnover markers and, in some settings, reduced fracture risk (esp. with MK-4 in Japanese studies and MK-7 for long-term biochemical endpoints).
• Cardiovascular protection — Observational cohorts associate higher K2 intake with less vascular calcification and lower cardiovascular events. Interventional trials show improvement in surrogate markers (e.g., arterial stiffness, calcification scores) though hard-outcome trials are still limited.
• Synergy with Vitamin D — D increases calcium absorption; K2 helps direct that calcium. Using high-dose D without adequate K2 may theoretically increase mis-placement risk (calcification) in susceptible individuals.

Considerations

• Safety — K2 is well tolerated at nutritional/supplemental doses. No known toxicity ceiling comparable to fat-soluble vitamins A or D. The main clinical caution is anticoagulation therapy.
• Drug interaction—Warfarin — Warfarin antagonizes vitamin K. K2 can counteract warfarin’s intended anticoagulation. Do not add K2 on warfarin without physician guidance. Direct oral anticoagulants (DOACs) do not share this mechanism.
• Form & dose — MK-7 is most studied for chronic, low-dose daily use due to long half-life. MK-4 has been used in high pharmacologic doses in Japanese osteoporosis trials. Dose choice depends on goal (nutritional adequacy vs. therapeutic intent).
• Repletion takes time — Since MK-7 accumulates, vascular and bone endpoints are slow biology. Plan in months-to-years, not weeks.
• Context matters — Effects are most meaningful when combined with diet/lifestyle fundamentals (adequate protein, mineral balance, D status, load-bearing exercise, metabolic health, glycemic control). K2 is not a substitute for these.