Dr. Kumar’s Take:
This study makes an important point: even small doses of vitamin K2 (as low as 10 mcg daily) can interfere with the stability of vitamin K antagonist blood thinners. While K2 is often promoted for bone and heart health, patients on vitamin K antagonists such as warfarin or acenocoumarol should avoid MK-7 supplements. I want to be clear that this was a study in healthy volunteers who were anticoagulated for the purpose of the experiment, not in patients managed long term on a blood thinner, but the direction of the effect is consistent and it showed up below the dose most retail products sell.
If you’re on a blood thinner, don’t assume low-dose supplements are safe, talk to your doctor first.
Key Takeaways:
✔ MK-7 supplementation influenced anticoagulation sensitivity at doses as low as 10 mcg per day.
✔ At 20 mcg per day, two hematologists independently judged the INR drop to be clinically relevant in at least 60% of subjects; at 10 mcg per day, in at least 40%.
✔ 45 mcg per day lowered group mean INR and uncarboxylated factor II by about 40%.
✔ MK-7 changed liver-based clotting markers while leaving bone and vascular vitamin K markers unchanged.
Actionable tip:
If you’re taking a vitamin K antagonist like warfarin or acenocoumarol, avoid any supplement containing vitamin K2 (MK-7) unless specifically advised by your healthcare provider.
Brief Summary:
This 2013 study tested how low doses of MK-7 (vitamin K2) affect anticoagulation stability in healthy volunteers. Eighteen healthy men and women were anticoagulated with acenocoumarol for four weeks, and 15 of them reached a target INR of 2.0. Over the following six weeks they took increasing daily doses of MK-7 at 10, 20, and 45 mcg while staying on their established acenocoumarol dose. MK-7 lowered the INR in a dose-dependent way, and it did so at intakes below the usual 45 mcg retail dose. The authors concluded that MK-7 supplements need to be avoided in patients receiving vitamin K antagonist therapy.
Study Design:
- Type: Dose-escalation study in healthy volunteers
- Participants: 18 healthy men and women anticoagulated with acenocoumarol; 15 reached the target INR of 2.0
- Duration: 10 weeks (4 weeks of anticoagulation, then 6 weeks of MK-7)
- Intervention: Increasing daily MK-7 doses of 10, 20, and 45 mcg during continued acenocoumarol treatment
- Primary Outcome: INR
- Secondary Outcomes: Endogenous thrombin potential, uncarboxylated factor II (ucFII), uncarboxylated osteocalcin, desphospho-uncarboxylated matrix Gla-protein
Results:
- Acenocoumarol raised uncarboxylated factor II, uncarboxylated osteocalcin, and desphospho-uncarboxylated matrix Gla-protein, and lowered endogenous thrombin generation.
- 45 mcg of MK-7 daily lowered group mean INR and ucFII by roughly 40%.
- 10 mcg daily produced a clinically relevant INR drop in at least 40% of subjects and raised endogenous thrombin potential by about 20%; 20 mcg daily did so in at least 60% of subjects and raised thrombin potential by about 30%.
- Circulating uncarboxylated osteocalcin and desphospho-uncarboxylated matrix Gla-protein were not affected by MK-7 intake.
How MK-7 Interferes with Blood Thinners
MK-7 supports vitamin K-dependent clotting proteins by helping them carboxylate properly. Vitamin K antagonists such as warfarin and acenocoumarol work by blocking that same activation step. Adding MK-7 restores part of what the drug is suppressing, which is exactly what the falling INR and the rising thrombin generation in this study reflect. The pattern in the blood markers fits that picture: the liver clotting protein responded, while the bone and vascular vitamin K proteins did not.
Related Studies and Research
Is Vitamin K2 a Blood Thinner? No, It Does the Opposite: Answers the most common question about K2 and anticoagulants, including where DOACs differ.
Explores how vitamin K2 may influence heart disease outcomes, focusing on arterial stiffness and calcification.: Foundational summary of K2’s cardiovascular benefits.
Reviews the connection between vitamin K2 and reduced arterial calcification, including clinical data.: Chronicles clinical trial data on calcification reduction.
Meta-analysis showing vitamin K’s effect on arterial calcification progression in different populations.: Aggregates outcomes on calcification changes with K supplementation.
Examines how warfarin use is linked with increased arterial calcification risk due to vitamin K inhibition.: Details warfarin’s unintended calcification effects.
Frequently Asked Questions
How much MK-7 caused problems in the study?
10 mcg per day, which is lower than the usual retail dose of 45 mcg, significantly influenced anticoagulation sensitivity in some individuals. At that dose, two hematologists independently judged the INR lowering to be clinically relevant in at least 40% of subjects.
Does the dose matter?
Yes. The effect scaled with dose. Endogenous thrombin potential rose by about 20% at 10 mcg per day and about 30% at 20 mcg per day, and 45 mcg per day cut group mean INR by roughly 40%.
Can people on blood thinners take K2 for their bones?
The authors’ conclusion is that MK-7 supplements need to be avoided in patients on vitamin K antagonist therapy. Worth noting from the same data: MK-7 at these doses did not change the bone marker (uncarboxylated osteocalcin) or the vascular marker (desphospho-uncarboxylated matrix Gla-protein), so the anticoagulation interference was not buying a measurable bone or vascular benefit at these intakes. If K2 is being considered, that decision belongs with the prescribing physician.
Is this relevant for warfarin, or only acenocoumarol?
This study used acenocoumarol. The authors framed their conclusion around vitamin K antagonists as a class, and warfarin is in that class, so the caution applies. I would not read the specific percentages as measured in warfarin patients.
Conclusion
This study shows that vitamin K2 (MK-7) supplements can interfere with vitamin K antagonist anticoagulation at doses well below what is commonly sold. The interference appeared at 10 mcg per day, a fifth of a typical retail capsule, and grew with dose. These findings matter as MK-7 gains popularity for heart and bone health. The authors’ position, and mine, is that patients on vitamin K antagonists should avoid K2 supplements unless a physician is managing the combination directly.
