Vitamin K2
The traffic director for calcium. Helps make sure it ends up in bone, not arteries.
Vitamin K2's main job is activation: it switches on the proteins that pull calcium out of soft tissue and direct it into bone matrix. MK-7 (menaquinone-7) is the form with the longest half-life in the body, which means a once-daily dose stays active for roughly three days. It is found in small amounts in fermented foods like natto, but most people in Western diets get almost none from food alone. Taking K2 alongside D3 and calcium is the approach most consistent with the available evidence.
Reference values
Daily reference values from official nutrition authorities. These are population reference figures, not personal recommendations.
| RDA | Upper limit | Source |
|---|---|---|
| 90 mcg | No UL set | No SACN K2-specific RNI; reference based on Schurgers et al. 2007 adequate-intake pattern |
Forms and bioavailability
Not all forms are absorbed equally. The form on your supplement label affects how much your body can actually use.
| Form | Absorption | With food | Timing | Evidence |
|---|---|---|---|---|
| MK-4 (menaquinone-4) | Typical | With food | Split dose | Likely |
| MK-7 (menaquinone-7) | Higher | With food | Either | Strong |
How it pairs with other supplements
Works well with
Vitamin D3 and K2 work together for calcium handling: D3 raises calcium absorption, K2 activates osteocalcin and MGP to direct calcium to bone rather than soft tissue.
Stack Almanac pairs K2 with D3 and Calcium automatically and will flag any gaps in the trio, or unusually high calcium intake that might benefit from a K2 review.
Track your Vitamin K2 in Stack Almanac
Last reviewed: 2026-05-21. Reference values are adult-general RDAs from UK. Individual needs may vary. This page is for informational purposes only and is not a substitute for professional medical advice.