Understanding the Forms of Vitamin K
Vitamin K is a family of fat-soluble vitamins essential for blood clotting, bone health, and heart health. The two most significant forms are Vitamin K1 and Vitamin K2.
Vitamin K1 (Phylloquinone): Primarily found in leafy green vegetables, K1 is vital for activating the coagulation proteins synthesized in the liver. However, it has a shorter half-life and lower bioavailability, meaning it is not as effective for tissues outside the liver.
Vitamin K2 (Menaquinones): K2 encompasses a group of compounds synthesized by bacteria and found in fermented foods like natto, as well as some animal products. It has a longer half-life and better distribution to extrahepatic tissues, making it more impactful for bone and cardiovascular health. K2 is further divided into subtypes, most notably MK-4 and MK-7.
Diving Deeper: MK-4 vs. MK-7
The most critical distinction for supplement quality is between the MK-4 and MK-7 forms of Vitamin K2. Both play similar roles, but their different half-lives and bioavailability impact effectiveness.
Menaquinone-4 (MK-4): Found in animal products and converted from K1 in tissues, MK-4 has a very short half-life of only a few hours. It doesn't maintain stable blood levels and is not efficiently transported to extrahepatic tissues at low doses, requiring pharmacological doses for therapeutic effects.
Menaquinone-7 (MK-7): Produced from bacterial fermentation, like in natto, MK-7 has a significantly longer half-life, circulating for up to 72 hours. This leads to stable and consistent blood levels, making it highly bioavailable and effective at lower, nutritional doses (micrograms). It is more efficient at activating proteins for extrahepatic functions.
Why MK-7 is Generally the Better Choice
Scientific evidence indicates MK-7 is generally superior for supplementation due to its bioavailability and efficacy. Its longer half-life allows better distribution to bone and vascular tissues. Effective at smaller, once-daily doses, MK-7 is more practical and cost-effective than the high doses of MK-4 needed for similar effects. MK-7 also induces more complete carboxylation of key proteins for bone mineralization and inhibiting arterial calcification.
Key Factors for Choosing a High-Quality Supplement
Selecting the MK-7 form is key, but other factors also determine supplement quality.
Third-Party Testing and GMP Certification: Choose brands with third-party testing and GMP certification to verify purity, potency, and safety, ensuring the product contains what the label states and is free from contaminants.
Source and Purity: High-quality MK-7 is typically from natural sources like fermented chickpeas or natto. Purity is also indicated by the “all-trans” form of MK-7, which is the fully bioactive isomer. Inquire with companies about their sourcing, as lower-quality products may use synthetic forms.
Combination with Vitamin D3: Vitamin K2 works synergistically with Vitamin D3, which aids calcium absorption. High-quality supplements often include both, as K2 directs calcium to bones, preventing arterial accumulation.
Formulation and Ingredients: Check for unnecessary additives, fillers, and allergens. Ensure the softgel or capsule suits your dietary needs.
Comparison Table: Vitamin K Forms
| Feature | Vitamin K1 (Phylloquinone) | Vitamin K2 (MK-4) | Vitamin K2 (MK-7) |
|---|---|---|---|
| Primary Source | Leafy green vegetables | Animal products, converted from K1 | Fermented foods (natto), bacteria |
| Half-Life | Short (hours) | Very Short (hours) | Long (up to 72 hours) |
| Bioavailability | Lower, poor absorption | Poor at nutritional doses | Highest, excellent absorption |
| Primary Function | Blood clotting in the liver | Bone and cardiovascular health (requires high dose) | Bone and cardiovascular health |
| Required Dose | High intake needed for extrahepatic benefits | Pharmacological (milligram) doses needed for efficacy | Nutritional (microgram) doses are effective |
| Supplementation | Not ideal for bone/heart benefits | Less efficient for consistent extrahepatic effects | Most effective for extrahepatic benefits |
What to Consider When Buying
Consider your health goals and conditions when buying a vitamin K supplement.
- Assess Your Goals: For bone density and cardiovascular health, a high-quality MK-7 is most effective. If taking blood thinners like warfarin, consult your doctor due to potential interactions.
- Look for a Combination Product: Combining K2 with Vitamin D3 is recommended for synergistic calcium utilization.
- Choose a Reputable Brand: Select well-established brands with third-party testing and transparent sourcing for purity and potency.
- Check the Label for "MK-7" and "all-trans": Verify the product contains Vitamin K2 as MK-7 and preferably the all-trans isomer for maximum bioactivity.
Conclusion: Choosing the Best Quality Vitamin K Supplement
For benefits beyond blood clotting, such as bone density and cardiovascular health, a high-quality MK-7 supplement is the superior choice. Its long half-life and bioavailability ensure effective delivery to extrahepatic tissues at a practical dose. Choose a reputable brand with third-party testing and an MK-7 formulation, ideally with vitamin D3. Always consult a healthcare provider, especially if on anticoagulant medication. For more information, refer to the NIH Health Professional Fact Sheet.
