Unpacking the Different Forms of Vitamin K2
Vitamin K is a fat-soluble vitamin essential for a variety of bodily functions, most notably blood coagulation, but also bone and cardiovascular health. It comes in two primary natural forms: vitamin K1 (phylloquinone), found in green leafy vegetables, and vitamin K2 (menaquinones), produced by bacteria and found in fermented foods. K2 is further subdivided into various subtypes, denoted as MK-n, with the most studied being MK-4 and MK-7.
MK-7 is particularly valued for its superior bioavailability and long half-life, which means it remains in the bloodstream for a longer period compared to other forms, including MK-4. This extended presence allows MK-7 to be more effectively utilized by extrahepatic tissues, such as bones and blood vessels, where it activates crucial proteins involved in calcium metabolism.
The Crucial Distinction: All-Trans vs. Cis Isomers
Within the MK-7 molecule, a critical structural feature dictates its biological efficacy: its geometric isomerism. MK-7 can exist in two main isomeric forms, all-trans and cis. The difference lies in the arrangement of the double bonds within its side chain. The all-trans isomer has a linear structure, which is the naturally occurring form found in fermented foods like natto. In contrast, cis isomers have a bent, non-linear structure.
Scientific research has definitively shown that only the all-trans form is biologically significant and efficacious. The linear shape of all-trans MK-7 is perfectly suited to interact with vitamin K-dependent enzymes, such as gamma-glutamyl carboxylase (GGCX), which activate proteins for bone and heart health. The non-linear structure of the cis form prevents it from effectively fitting into these enzymatic structures, leaving the beneficial proteins inactivated. Studies have found that cis MK-7 has only a fraction of the biological activity of the trans form—in some cases, as little as 1%.
Why all-trans MK-7 is superior
- Longer half-life: The extended presence in the bloodstream ensures a sustained benefit for the body.
- Higher bioavailability: It is more efficiently absorbed and utilized by tissues throughout the body, including bone and arteries.
- Optimal activation: It effectively activates vitamin K-dependent proteins like osteocalcin (for bone binding) and Matrix Gla Protein (MGP) (for arterial protection).
Sources and Production of MK-7
The isomer ratio in MK-7 supplements can vary significantly depending on the production method and purification process.
Fermentation-derived MK-7
- Source: Traditionally produced by fermenting soybeans with Bacillus subtilis natto bacteria, yielding natto, the richest dietary source of MK-7.
- Purity: Fermentation naturally produces the highly active all-trans form, but the final product may contain a mix of isomers if not properly purified. Optimizing fermentation conditions is crucial for maximizing the all-trans yield.
- Advantage: Considered a natural source, which some consumers prefer.
Synthetic MK-7
- Source: Chemically synthesized in a lab.
- Purity: Advanced synthetic processes can consistently produce a pure all-trans MK-7 product without the contamination of cis isomers that can sometimes occur in fermentation.
- Advantage: Offers high purity and consistency of the bioactive all-trans form.
Making an Informed Choice: How to Identify Quality MK-7
Since the isomeric composition is critical, simply seeing "MK-7" on a label isn't enough. Here's how to ensure you're getting the best form:
- Check for "All-Trans" or "100% All-Trans" on the label: Reputable brands will explicitly state the all-trans content. This transparency indicates a focus on product quality and efficacy.
- Look for third-party verification: Supplements are not strictly regulated by the FDA, so choosing products tested by independent third-party organizations (like USP or NSF) can confirm the ingredients and purity.
- Prefer oil-based softgels: As a fat-soluble vitamin, MK-7 is best absorbed when consumed with fat. An oil-based formula or taking it with a meal containing fat can significantly enhance absorption.
Comparison of all-trans and cis MK-7
| Feature | All-Trans MK-7 | Cis MK-7 |
|---|---|---|
| Biological Activity | High; activates vitamin K-dependent proteins. | Negligible; has very low activity (e.g., 1% of trans). |
| Molecular Structure | Linear, allowing for optimal enzyme interaction. | Non-linear, which compromises its ability to bind to enzymes. |
| Natural Occurrence | The form found in natural, fermented foods like natto. | Not naturally occurring; can result from improper processing or synthesis. |
| Supplement Source | Derived from natural fermentation (purified) or chemical synthesis. | Impurity that may be present in supplements if not properly filtered or processed. |
| Health Efficacy | Supports bone mineralization and cardiovascular health. | Provides little to no health benefit due to its inactive form. |
Conclusion
For those seeking the significant bone and cardiovascular benefits associated with vitamin K2 MK-7, the evidence is clear: the all-trans isomer is the best and only biologically active form. When selecting a supplement, prioritize products that guarantee a high or 100% all-trans content, preferably in an oil-based format for optimal absorption. This ensures you are not just purchasing MK-7, but the specific form that can deliver on its therapeutic promise. As with any new supplement, it's always wise to consult with a healthcare provider, especially if you are taking blood-thinning medication.
What to look for in a K2 MK-7 supplement:
- Isomeric Purity: Opt for products explicitly labeled with "all-trans" or indicating a high percentage of the biologically active form.
- Oil-Based Formula: Choose a supplement in an oil-based softgel to maximize the absorption of this fat-soluble vitamin.
- Third-Party Testing: Rely on products tested by independent organizations to verify ingredient claims and purity.
- Reputable Sourcing: Some sources, like Norwegian, American, or Japanese-made K2, may be preferable due to perceived higher quality standards.
- Avoid certain combinations: While not always unstable, some excipients like magnesium oxide have shown potential to degrade MK-7 over time.
Final Thoughts on Vitamin K2 MK-7
Ultimately, the efficacy of your vitamin K2 MK-7 supplement hinges on the specific isomer it contains. By understanding the critical difference between the biologically active all-trans form and its inactive cis counterpart, you can make a more informed choice and invest in a product that genuinely supports your bone and heart health goals. Don't be misled by generic product labels; look for quality markers that guarantee the pure, active ingredient your body can use. For further reading, authoritative resources like the NIH Office of Dietary Supplements offer comprehensive fact sheets on vitamin K.
