Understanding Vitamin K: K1 vs. K2
To understand how vegans can get K2, it's essential to differentiate between the two main forms of Vitamin K. Vitamin K1 (phylloquinone) is abundant in plants, especially leafy green vegetables such as kale, spinach, and broccoli, and is primarily involved in blood clotting. Vitamin K2 (menaquinone) is mainly found in animal products and some fermented foods and plays a crucial role in bone and heart health by activating proteins that regulate calcium.
The Importance of K2 (Menaquinone)
Vitamin K2 activates two key proteins: osteocalcin, which binds calcium to the bone matrix, and matrix Gla protein (MGP), which prevents calcium from depositing in soft tissues like arteries. A deficiency in active K2 can lead to calcium buildup in arteries, contributing to heart disease, and weaker bones.
Vegan Dietary Sources of K2 (Menaquinone-7)
The most notable vegan source of K2 is a fermented soybean product from Japan called natto. The fermentation process, which uses Bacillus subtilis bacteria, produces a very high concentration of Menaquinone-7 (MK-7), a highly bioavailable form of K2.
Natto: The K2 Powerhouse
- Unmatched Concentration: Natto contains a significantly higher amount of MK-7 than any other vegan food source, with one 3.5-ounce serving providing over 1,000 micrograms.
- Challenges: The strong smell and sticky texture of natto can be unpalatable for some. However, its immense health benefits, including high K2 content, make it a valuable food source for committed vegans.
Other Fermented Foods
While natto is king, other fermented foods may contain smaller amounts of K2 produced by probiotic bacteria, though quantities can be unreliable and much lower.
- Sauerkraut: Fermented cabbage contains a small, but measurable, amount of K2.
- Kimchi and Tempeh: Similar to sauerkraut, these fermented products can contribute to K2 intake, but not significantly enough to rely on them as a primary source.
K1 to K2 Conversion
The human body can convert vitamin K1 into K2, specifically into the MK-4 subtype. This conversion is not always efficient enough to meet optimal K2 requirements, especially for extrahepatic tissues like bones and blood vessels. The bacteria in the gut also produce some K2, though absorption from this source is often limited.
Maximizing Absorption
Since Vitamin K is fat-soluble, consuming K-rich foods or supplements with a source of healthy fat significantly enhances absorption.
- Pairing: Drizzle olive oil on a kale salad or add avocado to a meal with fermented foods.
- Consistency: Regular intake is better than sporadic consumption, especially for K2, which has a longer half-life than K1.
K2 Supplementation for Vegans
For many vegans, relying solely on dietary sources, particularly natto, can be challenging. This makes supplementation a practical and reliable way to ensure adequate K2 intake, especially the more bioavailable MK-7 form.
MK-4 vs. MK-7: Choosing the Right Supplement
Supplements commonly contain either MK-4 or MK-7. Their efficacy differs due to their different half-lives and bioavailability. The MK-7 form, often derived from natto, has a longer half-life, meaning it stays active in the body longer.
| Feature | Menaquinone-4 (MK-4) | Menaquinone-7 (MK-7) |
|---|---|---|
| Source | Produced by mammals from K1; can be synthetic in supplements. | Produced by bacterial fermentation (e.g., natto); often vegan-friendly. |
| Half-Life | Very short (6-8 hours). | Long (approx. 72 hours). |
| Bioavailability | Poorly absorbed from food; requires larger doses. | Well absorbed and stays in the body longer. |
| Supplementation | May require multiple daily doses due to short half-life. | Can be taken once daily due to longer half-life. |
Important Considerations
Before starting any new supplement, vegans should consult a healthcare provider or a registered dietitian, especially those on blood-thinning medication like warfarin. Vitamin K can interfere with these medications due to its role in blood clotting. Choosing a high-quality, third-party-tested vegan K2 supplement (MK-7) is crucial for safety and efficacy.
Conclusion: Strategic Approach for Vegans
Vegans can meet their K2 needs through a combination of dietary sources and, for most, supplementation. Natto is the most potent food source, though its taste can be a barrier. For reliable and consistent intake, a high-quality, vegan-friendly MK-7 supplement is the most effective solution. By combining these strategies with K1-rich leafy greens and healthy fats, vegans can ensure they maintain optimal levels of this vital nutrient for robust bone and cardiovascular health. The Vegan Society provides excellent resources on balanced plant-based nutrition.
The Role of Synergy
Remember that vitamin K2 works synergistically with other fat-soluble vitamins, particularly vitamin D. Both are essential for calcium metabolism, with vitamin D facilitating absorption and vitamin K2 directing it to the right places. Ensuring adequate vitamin D intake through fortified foods, sun exposure, or supplements is a key part of a comprehensive bone health strategy. Many vegan supplement companies now offer combined D3 and K2 products for this very reason, streamlining the process for those following a plant-based lifestyle.
