Vitamin K2 (MK-7)

Medically reviewed by Prof. Giorgi Pkhakadze, MD, MPH, PhD — GMJ Editorial Board

Scientific name: Menaquinone-7
Category: Vitamin (fat-soluble)
RDA: No established RDA for K2 specifically; total vitamin K AI is 90-120 mcg/day
UL: Not established

What is Vitamin K2 (MK-7)?

Vitamin K2 (MK-7) is a specific form of vitamin K2, one of the two main types of vitamin K alongside vitamin K1 (phylloquinone). The “MK-7” designation refers to menaquinone-7, which has seven isoprenoid units in its side chain. This structural difference gives MK-7 unique properties compared to other vitamin K forms, including better bioavailability and a longer half-life in the body.

While vitamin K1 is primarily involved in blood clotting, vitamin K2 plays distinct roles in bone and cardiovascular health. MK-7 is naturally produced by certain bacteria and is found in fermented foods, particularly the Japanese dish natto. Unlike vitamin K1, which is rapidly cleared from the body, MK-7 remains active in tissues for several days, making it particularly effective for activating vitamin K-dependent proteins throughout the body.

Submit Your Paper

Health benefits & uses

Bone health (Moderate evidence): Clinical studies suggest that MK-7 supplementation may help maintain bone density and reduce fracture risk, particularly in postmenopausal women. MK-7 activates osteocalcin, a protein essential for binding calcium to bone matrix.

Cardiovascular health (Limited evidence): Research indicates MK-7 may help prevent arterial calcification by activating matrix Gla protein (MGP), which inhibits calcium deposits in blood vessels. Some studies show improvements in arterial stiffness markers.

Blood clotting support (Strong evidence): Like other forms of vitamin K, MK-7 supports normal blood coagulation by activating clotting factors, though this effect is less pronounced than with vitamin K1.

How it works

Vitamin K2 (MK-7) functions as a cofactor for the enzyme gamma-glutamyl carboxylase, which activates vitamin K-dependent proteins through a process called carboxylation. This process adds carboxyl groups to specific glutamic acid residues, enabling these proteins to bind calcium effectively.

Key proteins activated by MK-7 include osteocalcin in bones, which helps incorporate calcium into bone matrix, and matrix Gla protein in blood vessels, which prevents calcium from depositing in arterial walls. The longer half-life of MK-7 compared to other vitamin K forms allows for more sustained activation of these proteins, particularly in extrahepatic tissues.

Dosage

Typical supplemental doses of MK-7 range from 45-200 mcg daily for adults. Most clinical studies showing bone and cardiovascular benefits have used doses between 90-180 mcg daily. Since no specific RDA exists for vitamin K2, and no upper limit has been established, dosing should be individualized based on health goals and medical history.

For general health maintenance, 45-90 mcg daily is commonly recommended. For targeted bone or cardiovascular support, higher doses up to 180 mcg may be used. Always consult with a healthcare provider before starting supplementation, especially if taking anticoagulant medications.

Food sources

Natural dietary sources of MK-7 are limited compared to vitamin K1. The richest source is natto, a fermented soybean dish containing approximately 775 mcg per 100 grams. Other fermented foods provide smaller amounts:

• Hard and soft cheeses: 5-75 mcg per 100g
• Sauerkraut: 5-15 mcg per 100g
• Egg yolks: 15-35 mcg per 100g (from pasture-raised hens)
• Chicken liver: 10-15 mcg per 100g
• Butter from grass-fed cows: 10-15 mcg per 100g

Most Western diets provide insufficient MK-7, making supplementation potentially beneficial for many individuals.

Safety & side effects

Vitamin K2 (MK-7) is generally well-tolerated with few reported side effects. Unlike some nutrients, vitamin K has not shown toxicity even at high doses, which is why no upper limit has been established. Rare side effects may include mild digestive upset when taken on an empty stomach.

The primary safety concern relates to its potential to affect blood clotting. While MK-7 has less impact on clotting factors than vitamin K1, it can still influence coagulation, particularly at higher doses or with prolonged use.

Interactions

Anticoagulant medications: MK-7 can potentially reduce the effectiveness of warfarin and other vitamin K antagonist medications by supporting blood clotting factor production. Close monitoring of INR levels is essential if combining these.

Antibiotics: Broad-spectrum antibiotics may reduce gut bacteria that produce vitamin K2, potentially increasing the need for supplementation.

Vitamin D and calcium: These nutrients work synergistically with vitamin K2 for bone health, and combined supplementation may be more effective than individual nutrients alone.

Vitamin A and E: High doses of these fat-soluble vitamins may interfere with vitamin K absorption and function.

Who should be cautious

Individuals taking anticoagulant medications, particularly warfarin, should consult their healthcare provider before using MK-7 supplements. Those with bleeding disorders or scheduled for surgery should also exercise caution.

Pregnant and breastfeeding women should avoid high-dose supplementation unless medically supervised, as safety data is limited. People with gallbladder disease or fat malabsorption disorders may have difficulty absorbing fat-soluble vitamins like K2 and may need specialized formulations or medical guidance.

Frequently asked questions

How does MK-7 differ from other forms of vitamin K2?

MK-7 has a longer half-life and better bioavailability than shorter-chain menaquinones like MK-4. This allows MK-7 to remain active in tissues longer and reach extrahepatic tissues more effectively, making it particularly useful for bone and cardiovascular applications.

Can I take MK-7 with vitamin D?

Yes, vitamin D and K2 work synergistically for bone health. Vitamin D increases calcium absorption, while K2 helps direct that calcium to bones rather than soft tissues. Many supplements now combine these nutrients.

How long does it take to see benefits from MK-7 supplementation?

Benefits vary by individual and health goal. Some biomarkers of vitamin K status can improve within days to weeks, but bone density changes typically require months to years of consistent supplementation to become apparent.

Should I take MK-7 with food?

Yes, as a fat-soluble vitamin, MK-7 is better absorbed when taken with dietary fat. Taking it with a meal containing some fat can significantly improve absorption.

Is synthetic MK-7 as effective as natural forms?

Research suggests that both natural (from fermentation) and synthetic MK-7 are bioactive, though some studies indicate natural forms may have slightly better bioavailability. Both forms appear effective in clinical studies.