Vitamin K2 is not a single compound but a family of related molecules called menaquinones (MK-n). Among these, MK-4 and MK-7 are the most well-known forms, particularly in the supplement market, but they differ significantly. While both are critical for activating proteins involved in calcium metabolism and blood clotting, their absorption, half-life, and effective dosage levels vary drastically, which is central to the debate over which is superior.
The Fundamental Differences Between MK-4 and MK-7
The debate over whether MK-7 is better than MK-4 primarily centers on their distinct pharmacological profiles. MK-4, or menaquinone-4, has a very short half-life and is rapidly cleared from the body, typically within a few hours. In contrast, MK-7 has a significantly longer side chain, which allows it to remain in the bloodstream for up to 72 hours, meaning it can accumulate and provide a more consistent supply to extrahepatic tissues like bones and arteries.
Bioavailability and Absorption
- MK-4: Studies show that MK-4 is poorly absorbed at the low microgram dosages typically used in nutritional supplements. To achieve a significant biological effect, pharmaceutical-level dosages (in milligrams) are often required, which are over 1,000 times higher than a standard MK-7 dose. At normal dietary levels, supplemental MK-4 is largely ineffective at raising serum vitamin K2 levels.
- MK-7: This form is highly bioavailable and effectively absorbed at much lower, nutritional microgram dosages. Its long half-life allows it to build up in the bloodstream with consistent daily intake, ensuring a steady supply of vitamin K2 throughout the body. This makes it a far more efficient supplement choice for influencing long-term vitamin K status.
Sources and Production
- MK-4 Sources: Found predominantly in animal products, including eggs, meat, and liver. However, the MK-4 content in many modern animal products is lower than historical levels due to modern farming practices. Supplemental MK-4 is often produced synthetically.
- MK-7 Sources: Primarily derived from bacterial fermentation. The Japanese fermented soybean dish natto is an exceptionally rich food source of MK-7. In supplements, MK-7 is typically extracted from natto or derived from bacterial synthesis.
MK-4 vs. MK-7 Comparison Table
| Feature | MK-4 (Menaquinone-4) | MK-7 (Menaquinone-7) |
|---|---|---|
| Half-Life | Very short (hours) | Long (up to 3 days) |
| Bioavailability | Poor at nutritional doses | High at nutritional doses |
| Effective Dose | High, pharmaceutical-level (mg) | Low, nutritional-level (µg) |
| Primary Sources | Animal products (e.g., meat, eggs) | Fermented foods (natto, some cheeses) |
| Systemic Effect | Poor at supplemental doses, requires frequent intake | Sustained and consistent systemic effect |
| Main Advantage | It is the biologically active form used by tissues. | High bioavailability and long duration of action. |
The Role in Bone and Cardiovascular Health
Both forms of Vitamin K2 are involved in activating key proteins that regulate where calcium goes in the body. However, the efficiency with which they achieve this, especially outside the liver, is where MK-7 demonstrates a clear advantage.
- Bone Health: Vitamin K2 activates osteocalcin, a protein that binds calcium to the bone matrix. A consistent supply of Vitamin K2 is crucial for bone mineralization. Given its long half-life and steady presence in the bloodstream, MK-7 provides continuous support for activating osteocalcin, whereas MK-4's short lifespan at nutritional doses makes it far less effective for this purpose.
- Cardiovascular Health: Vitamin K2 activates Matrix Gla Protein (MGP), which helps prevent the calcification of arteries by directing calcium away from soft tissues. The superior bioavailability and prolonged circulation of MK-7 ensure that sufficient amounts reach arterial walls to effectively activate MGP, offering more robust cardiovascular protection compared to low-dose MK-4 supplementation.
Is MK-4 Useless, Then?
Not at all. The body efficiently converts other forms of vitamin K, including MK-7, into MK-4 at the local tissue level, particularly in extrahepatic tissues. Think of MK-7 as a highly effective delivery vehicle. It travels through the bloodstream and is then converted to the active MK-4 form where it's needed most. Therefore, supplementing with MK-7 can be a more efficient strategy to increase MK-4 availability throughout the body than taking nutritional doses of MK-4 directly.
The Verdict: Why MK-7 Edges Out MK-4
For the average consumer seeking a supplement for bone and heart health, MK-7 is the more logical and effective choice. Its superior bioavailability and prolonged half-life ensure a consistent and sustained elevation of vitamin K2 levels in the body, which is critical for activating vitamin K-dependent proteins in both bone and cardiovascular tissues. While MK-4 is the biologically active form at the tissue level, nutritional doses from supplements are poorly absorbed. By delivering a steady supply of MK-7, you are, in effect, providing your body with the raw material it needs to produce MK-4 where and when it's required, without the need for excessively high dosages or multiple daily pills. However, patients on blood thinners like warfarin must consult a doctor before starting any Vitamin K2 protocol.
How to Choose the Right Supplement
- Read the label carefully: Look for a supplement that specifies "MK-7" and check the dosage, typically in micrograms (µg).
- Consider combination products: Many supplements now combine MK-7 with Vitamin D3, as the two nutrients work synergistically for calcium regulation.
- Prioritize long-term health: If your goal is to consistently support bone mineral density and cardiovascular health, MK-7 is the more reliable option.
- Talk to a healthcare professional: This is especially important if you have pre-existing conditions or take other medications.
For a deeper dive into the science behind MK-7's efficiency, see the research published in PubMed Central on bioavailability: Comparison of menaquinone-4 and menaquinone-7 bioavailability in healthy women.
