The Two Forms of Vitamin K: K1 vs. K2
Vitamin K is a fat-soluble vitamin crucial for several physiological processes, but it exists in two primary natural forms: Vitamin K1 (phylloquinone) and Vitamin K2 (menaquinones). Both are important, but they have different roles and distribution in the body.
Vitamin K1: The Coagulation Factor
Vitamin K1 is predominantly found in leafy green vegetables like kale, spinach, and broccoli. Its primary function, and the one historically most well-known, is facilitating blood coagulation. It is rapidly cleared from the body and preferentially used by the liver to synthesize blood clotting factors. For most healthy adults, a regular diet is sufficient to meet K1 needs for blood clotting functions.
Vitamin K2: The Bone and Heart Champion
Vitamin K2 is a more complex group of compounds, known as menaquinones (MKs), produced by bacteria and found in fermented foods like natto, certain cheeses, and some animal products. Unlike K1, which is concentrated in the liver, K2 is distributed to extrahepatic tissues like bones and arteries, where it activates proteins that manage calcium. This is why K2 is highly regarded for its benefits to bone and cardiovascular health.
The Key Distinction: MK-4 vs. MK-7
Within the Vitamin K2 family, two subtypes, MK-4 and MK-7, are most commonly discussed in supplementation. Their difference in chemical structure significantly impacts their bioavailability and effectiveness.
MK-4 (Menaquinone-4)
MK-4 is a short-chain menaquinone found in animal products like meat, eggs, and liver. It has a very short half-life in the bloodstream, meaning it is cleared quickly from the body. While MK-4 is active in tissues, its short plasma half-life makes it less effective for supplementation compared to longer-chain forms, requiring multiple high doses daily to maintain consistent levels. Some MK-4 in the body is converted from K1, though this process is not always efficient.
MK-7 (Menaquinone-7)
MK-7 is a long-chain menaquinone found in fermented foods, especially natto. Its longer side chain allows it to circulate in the bloodstream for a much longer period—up to several days—which gives it superior bioavailability and efficacy at lower, once-daily doses. This longer half-life allows MK-7 to effectively activate extrahepatic proteins, ensuring calcium is directed to the bones and away from arteries. For this reason, MK-7 is widely considered the best vitamin K2 subtype for supplements aimed at supporting bone density and cardiovascular health.
Benefits of the Best Vitamin K Supplement (K2 MK-7)
- Promotes Bone Mineral Density: MK-7 helps activate osteocalcin, a protein that binds calcium to the bone matrix, promoting stronger and denser bones. Studies in postmenopausal women have shown MK-7 supplementation can improve bone mineral density and strength.
- Supports Cardiovascular Health: K2, and specifically MK-7, activates the matrix Gla protein (MGP), which helps prevent the buildup of calcium in soft tissues and arteries. Arterial calcification is a major risk factor for heart disease, and research suggests higher K2 intake is correlated with a lower risk of cardiovascular events.
- Synergistic with Vitamin D3: Many supplements combine K2 with vitamin D3 because they work together to manage calcium. Vitamin D3 improves calcium absorption, while K2 directs that calcium to where it is needed most (the bones) and keeps it out of the arteries.
- Enhances Calcium Utilization: By properly regulating calcium, MK-7 ensures the body uses this vital mineral efficiently, benefiting not only bones and arteries but also other bodily functions.
Choosing the Right Vitamin K Supplement
Selecting a high-quality supplement involves considering the form of vitamin K, combination with other nutrients, and the manufacturer's reputation.
- Opt for K2 as MK-7: Given its superior bioavailability and longer half-life, a supplement containing Vitamin K2 as MK-7 is the best choice for targeted bone and cardiovascular health benefits.
- Consider a D3 Combination: For those also taking Vitamin D, a combination supplement containing both D3 and K2 MK-7 can simplify your regimen and ensure these synergistic vitamins are taken together.
- Check the Dosage: Dosages can vary, so consult a healthcare professional, especially for specific conditions. Standard nutritional doses for MK-7 are often in the 90-180 mcg range per day.
- Source and Quality: The sourcing of MK-7 matters. High-quality supplements often use naturally derived MK-7, for instance, from fermented chickpeas, rather than synthetic versions. Inquire about the manufacturer's quality control standards.
Comparison of Vitamin K Forms
| Feature | Vitamin K1 (Phylloquinone) | Vitamin K2 (MK-4) | Vitamin K2 (MK-7) |
|---|---|---|---|
| Primary Source | Leafy green vegetables, plant oils | Animal products (meat, eggs, butter) | Fermented foods (natto, hard cheeses) |
| Primary Function | Blood clotting in the liver | Bone and extrahepatic tissue activation | Bone and extrahepatic tissue activation |
| Bioavailability | Poorly absorbed from plants (~10%). | Variable; low bioavailability at nutritional doses. | Very high; excellent absorption. |
| Half-Life | Short (hours). | Very short (6-8 hours). | Very long (several days). |
| Circulation | Primarily used by the liver. | Cleared quickly from the blood. | Stays in circulation much longer. |
| Supplement Efficacy | Limited for bone/heart health from supplements. | Requires very high, frequent dosing. | Highly effective with once-daily dosing. |
Maximizing Your Supplement's Effectiveness
Since Vitamin K is fat-soluble, it's best absorbed when taken with a meal that contains some dietary fat. Taking your supplement with breakfast or dinner is often the most convenient and effective way to ensure optimal absorption. For combination supplements, like K2 with D3, taking them together is best due to their synergistic relationship. However, those on blood-thinning medications should not change their vitamin K intake without consulting a doctor, as it can interfere with medication efficacy.
Conclusion
While Vitamin K1 is vital for blood clotting and readily obtained from a healthy diet, the evidence points to Vitamin K2, specifically the MK-7 subtype, as the superior choice for a vitamin K supplement targeting bone and cardiovascular health. Its high bioavailability and long half-life mean it effectively distributes to extrahepatic tissues, helping to mineralize bones and prevent arterial calcification. When choosing a supplement, look for one containing MK-7, possibly combined with D3, and always take it with a fatty meal to ensure you are getting the most from your investment in your long-term health.
For more detailed information on vitamin K and its functions, refer to the National Institutes of Health Office of Dietary Supplements.
