Vitamin K2, or menaquinone, is an essential fat-soluble vitamin critical for proper calcium metabolism, regulating bone health, and protecting against arterial calcification. While there are various subtypes of K2, the most commonly discussed are menaquinone-4 (MK-4) and menaquinone-7 (MK-7). When considering supplementation, understanding the key differences between these two forms is paramount to choosing the most effective option.
The Fundamental Difference: Bioavailability and Half-Life
The primary reason MK-7 is widely considered the best form of vitamin K2 is its superior bioavailability and significantly longer half-life in the body. Research has demonstrated that after ingestion, MK-7 can remain active in the bloodstream for up to 72 hours, whereas MK-4 is cleared rapidly, with a half-life of just 6 to 8 hours. This difference has profound implications for efficacy.
MK-4 is primarily transported via triglycerides, which are quickly used for energy or stored as fat. This short circulation time means MK-4 must be taken in very large, frequent doses throughout the day to achieve a constant therapeutic effect. MK-7, by contrast, is absorbed and transported via LDL-cholesterol, allowing it to circulate for days and accumulate in extrahepatic tissues like bones and blood vessels. This prolonged presence ensures consistent activation of vitamin K-dependent proteins where they are most needed.
MK-4 vs. MK-7: A Comparison
| Feature | Menaquinone-4 (MK-4) | Menaquinone-7 (MK-7) |
|---|---|---|
| Half-Life | Very short (~6-8 hours) | Long (~72 hours) |
| Bioavailability | Low at nutritional doses | High |
| Dosage | Requires high doses (mg level) and frequent intake | Effective at low doses (mcg level), once daily |
| Transportation | Transported by triglycerides, cleared quickly | Transported by cholesterol, circulates longer |
| Primary Function | Acts in specific tissues like brain and testes; high-dose therapeutic use | Provides widespread, consistent action for bone and heart health |
| Main Source | Animal-based foods (eggs, meat, liver); produced via conversion | Fermented foods like natto; bacterial fermentation |
| Overall Efficacy | Limited for general health supplementation due to poor absorption and short half-life | Superior for supplementing bone and cardiovascular health due to longer circulation |
Benefits of MK-7 for Bone and Heart Health
The prolonged circulation of MK-7 allows it to be more readily available to activate critical vitamin K-dependent proteins (VKDPs) outside the liver. The two most notable are osteocalcin (OC) and matrix Gla protein (MGP).
Bone Health
Osteocalcin is a protein produced by osteoblasts that helps integrate calcium into the bone matrix. In its inactive, uncarboxylated state, it cannot bind calcium effectively. MK-7 activates (carboxylates) osteocalcin, ensuring calcium is directed to where it belongs: strengthening bones and teeth. A steady supply of MK-7 is critical for maintaining robust bone mineral density, especially in postmenopausal women, and has been linked to a reduced risk of fractures.
Cardiovascular Health
Matrix Gla protein is a powerful inhibitor of arterial calcification. Inactive MGP allows calcium to deposit in soft tissues like artery walls, which increases arterial stiffness and is a major risk factor for heart disease. MK-7 activates MGP, effectively removing excess calcium from the bloodstream and preventing it from accumulating in arteries and heart valves.
How to Choose a Quality MK-7 Supplement
When selecting a vitamin K2 supplement, the form is important, but so is the quality of that form. For MK-7, one key indicator of a high-quality product is the all-trans designation.
- All-trans MK-7: The vitamin K2 MK-7 molecule exists in two forms: cis and trans isomers. Only the trans isomer is biologically active and can be used by the body. Quality supplements will specify that they contain at least 98% or higher
all-transMK-7, ensuring maximum efficacy. - Source: MK-7 can be naturally derived from fermented soybeans (natto) or other fermented foods. It can also be produced synthetically. Both forms, if all-trans, are effective, but some prefer a natto-based source. Always check the product label.
- Pairing with Vitamin D3: Vitamin K2 and Vitamin D3 work synergistically. Vitamin D3 facilitates the absorption of calcium, while Vitamin K2 directs that calcium to the correct places (bones) and away from the wrong places (arteries). Many high-quality supplements combine these two vitamins for optimal benefit.
The Role of Food Sources
While supplementation is an efficient way to ensure adequate vitamin K2 intake, especially MK-7, certain foods are also good sources.
- MK-7 Rich Foods: The most concentrated source of MK-7 is natto, a traditional Japanese fermented soybean dish. Other fermented foods like some types of cheese (Gouda, Edam) and sauerkraut contain varying amounts.
- MK-4 Rich Foods: Small amounts of MK-4 are found in animal products because the animal's body converts K1 from its feed. Sources include egg yolks, organ meats (like chicken liver), and meat. However, the levels are generally low, and the poor bioavailability of MK-4 means large quantities are needed to have a similar effect as a small MK-7 dose.
Conclusion: MK-7 is the Recommended Form
For anyone seeking to supplement their diet with vitamin K2 for bone or cardiovascular benefits, MK-7 is the clear choice. Its superior bioavailability and longer residence time in the bloodstream allow for once-daily dosing and more consistent activation of the vital proteins responsible for calcium regulation. While MK-4 has specific roles in the body, it is poorly absorbed at nutritional doses, requiring significantly higher, less convenient dosing schedules. When choosing a supplement, look for one that guarantees a high percentage of all-trans MK-7 to ensure you are getting the most potent and effective form of this crucial nutrient.
