Vitamin K2 MK-7 vs MK-4: Which Form Is Best for Bone Health?

Vitamin K2 is not a single compound but a family of molecules called menaquinones, differing in the length of their side chains. MK-4 (menaquinone-4) and MK-7 (menaquinone-7) are the two forms you will find in supplements, and they have meaningfully different pharmacokinetics, tissue distribution, and research profiles. Understanding the differences helps you choose the right form—and the right dose—for bone protection.

The Core Difference: Half-Life

The most important pharmacological difference between MK-4 and MK-7 is their half-life in circulation. MK-4 has a half-life of just 1–4 hours. Within hours of a dose, blood levels return to near baseline. MK-7 has a half-life of approximately 72 hours (three days), meaning a single daily dose maintains steady-state tissue levels throughout the week.

This is not merely a theoretical difference. Studies measuring carboxylation of osteocalcin and matrix Gla protein—the two vitamin K-dependent proteins most important for bone health—consistently show that MK-7 produces superior and more sustained carboxylation with once-daily dosing compared to MK-4 at equivalent or even higher doses.

Sources and Bioavailability

MK-4 is found in animal products: egg yolks, butter, chicken, and some meats. The body can also convert vitamin K1 from plants to MK-4, though conversion efficiency is low. Supplemental MK-4 is typically synthetic (geranylgeraniol).

MK-7 is found in fermented foods, most notably natto (fermented soybeans)—a traditional Japanese food with extraordinarily high K2 content (around 800–1,000 mcg per 100 g serving). Supplemental MK-7 is typically derived from natto bacteria using a fermentation process, giving it a food-derived character that some argue improves tolerability.

Bioavailability studies show MK-7 is more bioavailable than MK-4 from a single-dose perspective, and its prolonged half-life makes it effective at much lower doses.

Doses Used in Research

Japanese research using MK-4 has employed pharmacological doses of 45 mg (45,000 mcg) three times daily. These are drug-level doses, not nutritional ones, and this work was conducted in the context of osteoporosis treatment using menatetrenone (synthetic MK-4) as a pharmaceutical agent. These doses are not typical of over-the-counter supplementation.

MK-7 research has used nutritional doses of 90–360 mcg daily and shown significant improvements in osteocalcin carboxylation, bone density, and even arterial calcification biomarkers at these low doses. A landmark 3-year RCT (the Knapen et al. study) found that 180 mcg of MK-7 daily significantly improved bone mineral density and reduced bone strength loss in postmenopausal women.

Which Form Should You Choose?

For most people supplementing for bone health and cardiovascular protection, MK-7 at 100–200 mcg daily is the evidence-supported choice. It is effective at low doses, maintains steady tissue levels with once-daily dosing, and has a robust research base at supplement-level quantities.

MK-4 may be appropriate if you are following a specific protocol designed by a practitioner using higher therapeutic doses, or if you prefer a form derived directly from food matrix sources.

FAQ

Q: Is there any benefit to combining MK-4 and MK-7? A: Some products combine both forms, reasoning that different tissue distributions may complement each other. MK-4 concentrates in certain tissues (brain, adrenals, pancreas) while MK-7 has broad systemic distribution. There is no definitive evidence that combinations outperform MK-7 alone, but no harm has been shown either.

Q: Can I get enough K2 from diet? A: Only if you regularly eat natto (for MK-7) or substantial amounts of high-fat animal products (for MK-4). Most Western diets are quite low in K2. Supplementation is the practical solution for most people.

Q: Does K2 interfere with warfarin? A: Yes. All forms of vitamin K—including K2—interfere with warfarin's anticoagulant mechanism. Anyone on warfarin or other vitamin K antagonists should not change their K2 intake without medical supervision and INR monitoring.

Q: What is the difference between K1 and K2 for bones? A: Vitamin K1 (phylloquinone) is used primarily by the liver for clotting factor production and has minimal effect on osteocalcin carboxylation. K2 is the form that activates bone and vascular proteins. Do not substitute K1 for K2 when supplementing for bone health.

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