Vitamin K2
Tells calcium where to go — into bone and teeth, not into arteries. Essential partner to vitamin D3.
Rotterdam Study (2004) showed K2 intake inversely correlated with arterial calcification and cardiovascular mortality. RCTs support K2 for bone density preservation in postmenopausal women and for reducing arterial stiffness. Mechanism is well-established; clinical end-points are still accumulating evidence. Bone and arterial effects: 6–12 months of consistent intake.
Vitamin K2 (menaquinones) activates two proteins that control calcium routing: osteocalcin (which incorporates calcium into bone) and matrix Gla-protein (which keeps calcium out of arterial walls and soft tissue). Without adequate K2, the calcium your body absorbs — including the extra calcium mobilised by vitamin D3 supplementation — ends up calcifying the wrong places: blood vessels, kidneys, breast tissue. The combination of D3 without K2 has been linked to increased arterial calcification, which is why these two should always travel together.
- Form
- MK-7 (menaquinone-7) — the practical winner for most people. Long half-life (~3 days), once-daily dosing, steady blood levels. MK-4 works too but has a very short half-life (~1 hour) — needs multiple daily doses at much higher amounts. MK-7 from natto fermentation is the standard form.
- Dose
- 100–200 mcg/day of MK-7. Pair 100 mcg K2 per 1,000–2,000 IU vitamin D3 as a rough rule.
- Timing
- With the fat-containing meal you take your vitamin D with. Morning typical.
- Schedule
- Daily, ongoing.
- Side effects
- Very well-tolerated. No established upper limit for K2 in healthy adults.
- Interactions
- Warfarin — vitamin K of any kind antagonises warfarin's action. Patients on warfarin should keep K intake stable (consistent, not high or low) and ideally avoid K2 supplements. Newer DOACs (apixaban, rivaroxaban) don't have this issue.
- Contraindications
- On warfarin (relative — talk to anticoagulation clinic). Otherwise none significant.
- Lab markers
- No standard clinical test. Research-grade: undercarboxylated osteocalcin (ucOC) — high levels indicate K2 deficiency.
- Food sources
- Natto (fermented soy — by far the richest source, almost 1,000 mcg per serving), hard aged cheeses (gouda, edam), egg yolks from pasture-raised hens, goose liver, grass-fed butter, sauerkraut. Most modern diets are very low in K2 — supplementation is usually the easier route.
Pairs with
Vitamin D3 — non-negotiable pairing. Together they direct calcium to where you want it. Magnesium (also required for D activation and bone formation). Calcium from food (not as a supplement).
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