Vitamin K is an essential, fat-soluble nutrient that comes in two primary forms: Vitamin K1 (phylloquinone) and Vitamin K2 (menaquinone). While K1 is well-known for its role in blood clotting, K2 is increasingly recognized for its vital functions in regulating calcium metabolism beyond the liver, influencing both bone and cardiovascular health. Within the K2 family, two forms—MK-4 and MK-7—stand out as the most researched, but they have key differences that affect their efficacy and impact on the body.
Understanding Vitamin K2: The Essential Co-Factor
Vitamin K2 acts as a co-factor for the body’s vitamin K-dependent proteins, activating them to perform critical functions.
- Osteocalcin Activation: Found in bone, osteocalcin is a protein that binds calcium to the bone mineral matrix, promoting bone mineralization and density. K2 is necessary to activate osteocalcin so it can effectively direct calcium into the bones.
- Matrix Gla Protein (MGP) Activation: MGP is a potent inhibitor of arterial calcification. K2 activates MGP, which helps prevent calcium from accumulating in soft tissues like arteries and blood vessels, thereby protecting cardiovascular health.
MK-4 vs. MK-7: A Head-to-Head Comparison
While both MK-4 and MK-7 activate these critical proteins, their sources, absorption, and half-lives vary dramatically.
Bioavailability and Half-Life
Perhaps the most significant difference between the two forms is their bioavailability and how long they remain active in the body. Research has shown that nutritional doses of MK-7 are well-absorbed and lead to a significant increase in serum K2 levels, which can be detected in the bloodstream for up to 72 hours. This long half-life allows MK-7 to accumulate and be delivered to extra-hepatic tissues, such as bone and arteries, over a sustained period. In contrast, MK-4 is absorbed but has a very short half-life of only a few hours and does not significantly increase serum K2 levels at nutritional doses. It is quickly metabolized and used primarily by the liver.
Dosage and Supplementation
The difference in half-life directly impacts the required dosage for supplementation. Due to its short duration, studies show that MK-4 requires extremely high doses (up to 45 mg per day, often split into multiple daily doses) to be effective for systemic benefits like bone health. Conversely, thanks to its superior bioavailability and longer half-life, MK-7 is effective at much lower daily doses, typically ranging from 90 to 180 mcg.
Natural Food Sources
- MK-4: This form is found predominantly in animal-derived foods, such as egg yolks, liver, and grass-fed butter. The MK-4 content can vary greatly depending on the animal's diet, with grass-fed sources containing more than grain-fed. Humans can also convert some K1 to MK-4, but this process is inefficient.
- MK-7: This longer-chain form is synthesized by bacteria and is most famously found in natto, a traditional Japanese fermented soybean dish. Natto is by far the richest dietary source of MK-7, but smaller amounts can also be found in certain aged cheeses like Gouda and Edam.
The Importance of All-Trans MK-7
For those considering an MK-7 supplement, the source and isomeric purity are critical. Like most biological molecules, MK-7 can exist as geometric isomers. Only the all-trans form is biologically active and effective in the body. High-quality MK-7 derived from natural bacterial fermentation is primarily in the active all-trans form, while cheaper, synthetic versions may contain less effective cis isomers. This distinction is crucial for ensuring the supplement provides the intended health benefits.
Comparison Table: MK-4 vs. MK-7
| Feature | MK-4 | MK-7 |
|---|---|---|
| Primary Source | Animal products (grass-fed butter, egg yolks, liver) | Fermented foods (natto, certain cheeses) |
| Bioavailability | Poor at nutritional doses, not reliably absorbed into serum | High, well-absorbed and accumulates in bloodstream |
| Half-Life | Short (cleared in hours) | Long (up to 72 hours) |
| Typical Dose | High (45 mg/day), often split | Low (90-180 mcg/day), once daily |
| Key Benefit | Supports localized K2 functions; requires high dose for systemic effect | Provides sustained, systemic support for bone and cardiovascular health |
The Healthiest Form for You
Considering bioavailability, half-life, and effective dosage, MK-7 is generally considered the most effective and practical option for long-term, systemic benefits related to bone and cardiovascular health. Its longer half-life means a once-daily, lower dose can provide sustained support, ensuring calcium is directed to the bones and away from the arteries. While MK-4 has specific biological roles and is the predominant K2 form in certain tissues, achieving therapeutic levels typically requires impractically high, multi-dose supplementation. For most people, a high-quality, naturally fermented all-trans MK-7 supplement offers a reliable and efficient way to optimize Vitamin K2 status. However, a balanced diet that includes both MK-4 and MK-7 sources (animal products and fermented foods) can also be beneficial.
Conclusion: Making an Informed Choice
The question of what is the healthiest form of K2 ultimately depends on your nutritional goals and lifestyle. While both MK-4 and MK-7 are important subtypes, MK-7’s superior absorption and prolonged action make it the more effective and widely recommended choice for supplementation aimed at systemic bone and heart health. For those seeking dietary sources, incorporating foods rich in both forms offers a holistic approach. However, due to the low concentration of K2 in many Western diets, a high-quality MK-7 supplement may be a more reliable option. Before starting any new supplement regimen, especially if you take blood thinners like warfarin, always consult with a healthcare professional to ensure safety and effectiveness.
