Vitamin K2 is a fat-soluble vitamin recognized for its actions beyond blood clotting, the primary function of Vitamin K1 (phylloquinone). This nutrient plays an important role in directing calcium to the appropriate places in the body, supporting both bone and cardiovascular health. Vitamin K2, a group of compounds called menaquinones (MKs), is the form most commonly used in supplements. The two most frequently discussed forms are Menaquinone-4 (MK-4) and Menaquinone-7 (MK-7), which differ significantly in how the body handles them.
The Role and Metabolism of MK-4
Menaquinone-4 (MK-4) is the most common form of Vitamin K2 found in body tissues. Unlike other K2 forms, MK-4 is not typically produced by bacteria but is synthesized within the body from dietary Vitamin K1. This form is found naturally in animal products, such as egg yolks, liver, and high-fat dairy. MK-4 has a rapid metabolism and a short half-life, approximately one to six hours. Due to this quick clearance from the bloodstream, MK-4 is considered a localized form, primarily targeting the liver and specific tissues for immediate cellular functions.
The Role and Metabolism of MK-7
Menaquinone-7 (MK-7) is a longer-chain form of Vitamin K2, primarily produced by bacterial fermentation. The best-known dietary source of MK-7 is natto, a traditional Japanese food made from fermented soybeans. MK-7 has a longer half-life, which can be up to three days (approximately 68 to 72 hours). This extended stability allows MK-7 to remain in the bloodstream for a prolonged period, facilitating its systemic distribution throughout the body. Because it circulates longer, it can accumulate in the blood with consistent daily intake, ensuring a steady supply to non-hepatic tissues.
Comparing Bioavailability and Targeting
The choice between MK-4 and MK-7 largely depends on their contrasting pharmacokinetics (how the body absorbs, distributes, and eliminates the nutrient). MK-7 exhibits superior bioavailability at nutritional doses because its long side chain allows it to be packaged into cholesterol-carrying lipoproteins. This enables MK-7 to circulate widely and remain active in the blood for days. Studies comparing the two forms at standard nutritional doses show that MK-7 is well-absorbed and detectable in the serum, while MK-4 levels often remain undetectable.
This difference in circulation time directly impacts the activation of Vitamin K-dependent proteins in tissues outside the liver (extrahepatic tissues). MK-7 is effective at activating Matrix Gla Protein (MGP) in the arterial walls and osteocalcin in the bone matrix. MGP activation prevents calcium from depositing in soft tissues like arteries, while activated osteocalcin directs calcium into the bones, supporting cardiovascular and skeletal health. Because MK-4 is cleared quickly, it is considered less effective for these systemic targets at typical supplemental doses, though it may have specialized localized functions in specific organs.
Practical Considerations for Supplementation
The difference in half-lives translates into varied dosing requirements for the two forms. MK-7 is effective at low, once-daily doses, typically ranging from 100 to 200 micrograms, because its sustained presence allows for continuous activation of systemic proteins. This once-daily convenience is a practical advantage for general supplementation. Conversely, achieving systemic benefits with MK-4 requires a large daily dose, often 45 milligrams, which must be divided and taken multiple times per day to compensate for its rapid clearance. For most people seeking general support, MK-7 is the more practical and efficient choice due to its superior bioavailability and sustained action at nutritional doses.
Both forms are fat-soluble and should be consumed with a meal containing dietary fat for optimal absorption. Vitamin K2 is also frequently paired with Vitamin D supplements, as the two nutrients work together to regulate calcium metabolism.