Vitamin K2 (MK-7)
Directs calcium into bone and away from arteries
What is Vitamin K2 (MK-7)?
Vitamin K2 (menaquinone) is a fat-soluble vitamin distinct from vitamin K1 (phylloquinone), which is involved in blood clotting. K2 acts as a biological 'traffic controller' for calcium — it activates proteins that direct calcium into bone and teeth while simultaneously preventing calcium from depositing in arteries and soft tissues. The most bioavailable form, MK-7 (menaquinone-7), is produced by fermentation and found in natto (fermented soy). UK dietary intake is typically low.
How it works
K2 activates two key proteins via carboxylation: osteocalcin (a protein in bone matrix that binds calcium, produced by osteoblasts) and Matrix Gla Protein (MGP), which inhibits calcium crystallisation in blood vessel walls. Without K2, these proteins remain inactive: calcium absorbed (e.g., from vitamin D supplementation) is not efficiently directed to bone and can accumulate in arteries — contributing to arterial stiffness and cardiovascular risk. K2 essentially 'unlocks' the calcium system.
What the evidence shows
The Rotterdam Study (2004, 4,807 participants) found high K2 intake associated with 57% lower risk of coronary heart disease mortality and 26% lower all-cause mortality. The Prospect cohort study showed MK-7 specifically inversely associated with cardiovascular disease. Multiple RCTs show MK-7 supplementation increases carboxylated osteocalcin (active form) and reduces uncarboxylated MGP (a marker of vascular calcification). The MenaQ7 trial showed 180mcg MK-7 for 3 years significantly improved bone mineral density.
When to expect results
Carboxylation of osteocalcin and MGP beginning. No perceptible changes yet — these are biochemical processes.
Measurable changes in osteocalcin carboxylation status. Ongoing cardiovascular protection accumulating silently.
Bone density changes beginning to accumulate. MGP carboxylation inhibiting new arterial calcium deposits.
Full structural benefits to bone mineral density (measurable on DEXA scan). Sustained cardiovascular protection.
Dosing
Clinical trials use 90–360mcg MK-7 daily. The most commonly studied dose with significant effects is 180–200mcg MK-7 daily. MK-7 has a half-life of approximately 72 hours (vs 1–2 hours for K1 and MK-4), making once-daily dosing effective. Take with a fat-containing meal for best absorption.
Forms to choose
MK-7 is the preferred form for supplementation: long half-life, high bioavailability, derived from natto fermentation (Bacillus subtilis natto). MK-4 (found in meat and some supplements) has a very short half-life and requires much higher doses (1,500mcg+) to achieve comparable effects. K1 supplements do not provide the same cardiovascular and bone effects as K2. Always pair K2 with D3 for synergistic calcium metabolism.
Who benefits most
Everyone taking vitamin D3 supplements (K2 is the ideal pairing), people with cardiovascular risk factors or family history of arterial calcification, postmenopausal women (significant bone mineral density benefits in trials), people with osteoporosis or osteopenia, those with low dietary intake (not eating natto, cheese, or organ meats regularly).
Who should avoid / caution
People on vitamin K-antagonist anticoagulants (warfarin, acenocoumarol) must consult GP before taking K2 — it can undermine the medication's effect on INR. Not suitable for anyone told specifically to maintain low vitamin K intake.
Interactions & stacking
The essential pairing. D3 increases calcium absorption; K2 ensures that calcium goes to bone not arteries. Always combine these two.
K2 directly antagonises warfarin's mechanism. Do not supplement K2 without GP supervision if on anticoagulants.
K2 activates the proteins needed to direct supplemental calcium into bone. If taking calcium, K2 makes it more likely to end up where you want it.
Magnesium supports bone mineralisation alongside calcium and K2. A D3+K2+Mg stack is considered excellent for bone health.
Safety & side effects
Vitamin K2 is very safe. The primary concern is interaction with vitamin K-antagonist anticoagulants (warfarin) — these drugs work by blocking vitamin K activity. K2 can reduce warfarin effectiveness. For people on anticoagulants: consult GP before supplementing.
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This information is for educational purposes only and does not constitute medical advice. Always consult your GP or a qualified healthcare professional before starting any new supplement, particularly if you are pregnant, breastfeeding, have a medical condition, or are taking prescription medication.