Understanding Vitamin K2: The Two Key Forms
Vitamin K is a fat-soluble vitamin crucial for several physiological processes, most notably blood clotting and calcium metabolism. While vitamin K1 (phylloquinone) is found primarily in leafy green vegetables, vitamin K2 (menaquinone) is a family of compounds (designated MK-4 to MK-13) with two forms dominating the supplement and discussion space: MK-4 and MK-7. A key role of vitamin K2 is activating specific proteins, like osteocalcin for bone health and Matrix Gla Protein (MGP) for cardiovascular health. These proteins direct calcium to bones and teeth while preventing its harmful accumulation in soft tissues like arteries. The choice between MK-4 and MK-7 is not straightforward and depends heavily on their respective properties and the intended health goal.
The Case for MK-4: The Body's Primary Form
MK-4 is a short-chain menaquinone found in animal products such as butter, eggs, and organ meats. While it is the form predominantly found in human tissues, it is not well absorbed at standard nutritional supplement doses and has a very short half-life in the bloodstream, often less than eight hours. Some studies, predominantly in Japan, have shown benefits for bone density and fracture reduction using extremely high, pharmacological doses of MK-4, sometimes as high as 45 mg per day, administered several times throughout the day. This dosing schedule is necessary to compensate for MK-4's rapid clearance from the body.
Sources of MK-4:
- Eggs (especially pastured eggs)
- Dairy products, like grass-fed butter and certain cheeses
- Meat, particularly organ meats like liver
The Benefits of MK-7: The Long-Lasting Option
MK-7 is a long-chain menaquinone produced by bacteria and is found in fermented foods, most notably the Japanese dish natto, which is an exceptionally rich source. Unlike MK-4, MK-7 boasts a significantly longer half-life, circulating in the blood for approximately 72 hours, or about three days. This long duration allows for consistent levels of vitamin K2 in the body with once-daily dosing. Its superior bioavailability at nutritional doses means it effectively raises serum levels and efficiently activates the extrahepatic proteins critical for bone and cardiovascular health. Moreover, some evidence suggests the body can convert MK-7 into MK-4 in extrahepatic tissues, making it a better supplier for specific tissue needs than taking MK-4 directly at nutritional levels.
Sources of MK-7:
- Natto (fermented soybeans)
- Certain cheeses, curd, and sauerkraut
A Comparative Look: MK-4 vs. MK-7
To summarize the key differences, the following table provides a clear comparison:
| Feature | Vitamin K2 MK-4 | Vitamin K2 MK-7 |
|---|---|---|
| Dietary Sources | Animal products (eggs, meat, liver, butter) | Fermented foods (natto, cheese) |
| Biological Half-Life | Very short (< 8 hours) | Long (~72 hours or 3 days) |
| Bioavailability at Nutritional Doses | Poor; does not effectively increase serum levels | Excellent; increases serum levels significantly |
| Required Dose for Efficacy | High pharmacological doses (up to 45 mg/day), often divided | Much lower, nutritional doses (as low as 100 mcg/day) |
| Dosing Frequency | Multiple times per day due to short half-life | Once daily due to long half-life |
| Primary Clinical Evidence | High-dose trials, primarily in Japan, showing benefit for bone strength | Lower-dose trials demonstrating effectiveness for bone and cardiovascular health |
Which Form is Right for You?
The decision between MK-4 and MK-7 largely depends on whether you are seeking a nutritional supplement or are under the guidance of a physician for high-dose therapy. For the average person seeking to support their bone and cardiovascular health with a daily supplement, MK-7 is generally considered the superior option due to its high bioavailability and long half-life. Its ability to maintain consistent vitamin K levels in the blood is crucial for the continuous activation of extrahepatic proteins like MGP, which helps prevent arterial calcification.
For those on anticoagulant medication like warfarin, the longer-acting MK-7 can significantly influence anticoagulation sensitivity, and extreme caution and medical supervision are necessary. The shorter-acting MK-4 might be considered in some clinical scenarios, but the high doses required and the need for frequent dosing make it less practical for general wellness. Ultimately, consulting a healthcare provider is the best approach to determine the appropriate form and dosage for your specific health needs.
Conclusion
In conclusion, while MK-4 is the form of vitamin K2 that accumulates in the body's tissues, its poor bioavailability and very short half-life at nutritional doses make it less effective than MK-7 for consistent supplementation. The long-chain menaquinone MK-7 is well-absorbed, has a much longer half-life, and is effective at lower, once-daily doses for activating the key proteins involved in bone and cardiovascular health. For general dietary supplementation to support healthy aging and mineral metabolism, MK-7 stands out as the more efficient and practical choice. For a more detailed look at the science, the National Institutes of Health provides a comprehensive fact sheet on Vitamin K, including both K1 and K2.
