Menaquinone – Vitamin K2: Function, Sources & Intake
Menaquinone is the natural form of vitamin K2 and plays a key role in blood clotting, bone health, and vascular protection.
Things worth knowing about "Menaquinone"
Menaquinone is the natural form of vitamin K2 and plays a key role in blood clotting, bone health, and vascular protection.
What is Menaquinone?
Menaquinone is a group of fat-soluble compounds belonging to the vitamin K2 family. The different forms are named according to the length of their side chain, such as MK-4, MK-7, or MK-9. Menaquinone is found primarily in fermented foods and animal products, and is also produced by intestinal bacteria. It differs from phylloquinone (vitamin K1), which is mainly found in green leafy vegetables and belongs to the same vitamin K family.
Biological Functions
Menaquinone performs several vital functions in the human body:
- Blood clotting: Menaquinone acts as a cofactor for the carboxylation of specific clotting proteins (e.g., factors II, VII, IX, X). Without sufficient vitamin K2, these proteins cannot be fully activated.
- Bone health: Menaquinone activates osteocalcin, a protein responsible for incorporating calcium into the bone matrix. Adequate intake may help prevent bone loss (osteoporosis).
- Vascular protection: Menaquinone activates Matrix Gla Protein (MGP), which inhibits calcium deposits in blood vessel walls and thereby helps maintain vascular elasticity.
- Cellular metabolism: Emerging evidence suggests menaquinone may also play a role in mitochondrial energy metabolism.
Dietary Sources
Foods particularly rich in menaquinone include fermented products such as natto (Japanese fermented soybeans, especially high in MK-7), cheese, curd, meat, and organ meats. The MK-7 form is considered especially bioavailable and has a longer half-life in the blood compared to MK-4.
Recommended Intake
The European Food Safety Authority (EFSA) has set an Adequate Intake (AI) for total vitamin K of 70 µg per day for adults. Specific reference values exclusively for menaquinone have not yet been fully established in official guidelines, as research in this area continues to evolve.
Deficiency Symptoms
A deficiency in menaquinone may lead to:
- Increased bleeding tendency and prolonged clotting time
- Elevated risk of osteoporosis and bone fractures
- Possible contribution to arterial calcification (arteriosclerosis)
Groups at risk of deficiency include individuals with malabsorption disorders (e.g., Crohn's disease, celiac disease), newborns, people on long-term antibiotic therapy, and patients with chronic liver disease.
Toxicity and Safety
Menaquinone is considered well tolerated at currently studied doses and shows no known toxicity even at higher supplementation levels. Unlike vitamin K1, no official Tolerable Upper Intake Level (UL) has been established for menaquinone. However, individuals taking vitamin K antagonists (e.g., warfarin, phenprocoumon) must consult a physician before supplementing, as menaquinone can reduce the effectiveness of these anticoagulants.
Interactions
- Vitamin K antagonists (e.g., warfarin, phenprocoumon): Menaquinone can diminish their anticoagulant effect.
- Vitamin D: Acts synergistically with menaquinone in calcium utilization and bone health.
- Calcium: Optimal bone formation requires coordinated intake of calcium, vitamin D, and menaquinone.
- Antibiotics: Long-term use can disrupt gut flora, thereby reducing the body's own menaquinone production.
References
- European Food Safety Authority (EFSA): Dietary Reference Values for Vitamin K. EFSA Journal, 2017; 15(5): 4780.
- Schurgers LJ, Vermeer C: Determination of phylloquinone and menaquinones in food. Haemostasis 2000; 30(6): 298–307.
- World Health Organization (WHO) / Food and Agriculture Organization (FAO): Vitamin and Mineral Requirements in Human Nutrition, 2nd edition. WHO Press, Geneva, 2004.
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