Vitamin K2 (MK-7)
Vitamin K2 is the version of vitamin K that directs calcium to bone instead of soft tissue. MK-7 (menaquinone-7) is the long-acting form that stays bioavailable in the body for days, not hours.
The longest-lasting form of vitamin K2. Activates proteins that move calcium from blood into bone, and away from soft-tissue deposits like arteries. Synergistic with D3 — D3 brings calcium into the body, K2 directs where it goes.
What is vitamin K2 (MK-7)?
Vitamin K2 (menaquinone) is one of two main forms of vitamin K, the other being K1 (phylloquinone). Within the K2 family, there are several subtypes — MK-4 through MK-13 — differentiated by their side-chain length.
MK-7 is the form sourced from natto (fermented soybeans) and is preferred in modern supplementation because of its long biological half-life (about 72 hours, versus a few hours for MK-4). One daily dose of MK-7 maintains stable blood levels.
K1 vs K2 vs MK-4 vs MK-7
- K1 (phylloquinone): from leafy greens. Primarily used by the liver for clotting-factor activation.
- K2 MK-4: from animal foods (eggs, butter, dairy). Short half-life (a few hours); requires multiple daily doses.
- K2 MK-7: from natto fermentation. Long half-life (~72 hours); single daily dose is sufficient.
For daily supplementation, MK-7 is the practical choice because of its stable plasma levels with once-daily dosing.
What K2 does in the body
K2 activates two specific calcium-regulating proteins:
- Osteocalcin: directs calcium into the bone matrix
- Matrix Gla Protein (MGP): inhibits calcium deposition in soft tissues like arteries
Without adequate K2, these proteins remain inactive. The result is that calcium absorbed from food or supplements isn’t reliably directed to where it should go.
Why K2 pairs with D3
Vitamin D3 increases calcium absorption from the gut. Without K2, that calcium can end up deposited in soft tissues (arteries, kidneys) rather than bone. The pairing of D3 + K2 is one of the most well-established synergies in modern supplementation:
- D3 brings calcium in.
- K2 directs it where it should go.
- Neither nutrient alone provides the full picture.
See our vitamin D3 (cholecalciferol) page for more on this synergy.
How common is K2 insufficiency?
Most adults consume enough K1 from leafy green vegetables but very little K2. The richest dietary sources of K2 MK-7 are fermented foods (especially natto), which are uncommon in Western diets. Animal-sourced MK-4 is more available but still consumed in modest amounts.
Research suggests subclinical K2 insufficiency may be more common than recognized, which is why MK-7 supplementation has become a standard inclusion alongside D3.
Frequently Asked Questions
Short answers to the most common questions.
How much K2 MK-7 should I take?
Common supplementation doses are 45–180 mcg/day. The amount included in gut-support formulas is typically in the 45–100 mcg range — supportive without exceeding the doses studied in research.
Can I take K2 with blood thinners?
If you're on warfarin (Coumadin) or any vitamin K antagonist, talk with your prescribing physician before adding K2. Vitamin K is the antagonist these medications counteract. Other anticoagulants (DOACs like apixaban, rivaroxaban) don't have the same interaction concern.
Why MK-7 instead of MK-4?
MK-7 has a much longer biological half-life (~72 hours vs a few hours for MK-4), meaning a single daily dose maintains stable blood levels. MK-4 requires multiple daily doses to maintain coverage.
Is K2 natural or synthetic in supplements?
MK-7 is typically derived from natto fermentation (a traditional Japanese food). Some manufacturers use synthetic MK-7 of identical molecular structure. The current Supplement Facts panel for Complete Gut Defense lists the source.
What's the upper limit for K2?
Unlike many other fat-soluble vitamins, K2 doesn't have an established upper tolerable limit in standard supplementation. Research has used doses up to 900 mcg/day without safety concerns. Doses in commercial supplements are typically far below that range.
Takeaway
K2 MK-7 is the daily-use form of vitamin K2 — long-acting, stable, and synergistic with D3. Including it in a gut-support formula ensures that the D3 in the same capsule has its complementary cofactor for proper calcium metabolism.
References & Further Reading
- NIH Office of Dietary Supplements – Vitamin K
- Schwalfenberg GK. Vitamins K1 and K2: the emerging group of vitamins required for human health (Journal of Nutrition and Metabolism, 2017)
- Maresz K. Proper calcium use: vitamin K2 as a promoter of bone and cardiovascular health (Integrative Medicine, 2015)