The Microbe Connection: How Bacteria Create Vitamin K2
Unlike vitamin K1 (phylloquinone), which is found in leafy green plants, vitamin K2 (menaquinone) is largely a product of microbial synthesis. During the process of fermentation, specific strains of bacteria convert precursor compounds into menaquinones, a family of fat-soluble vitamins with varying side-chain lengths, denoted as MK-n. The concentration and specific types of menaquinones produced can differ dramatically based on the bacterial strains, the fermentation duration, and the substrate used. For instance, the bacteria responsible for fermenting soybeans to create natto produce exceptionally high levels of the MK-7 subtype, whereas the bacteria used for aging cheese produce different long-chain menaquinones like MK-8 and MK-9. This microbial activity is the core reason certain fermented foods are nutritional powerhouses for this particular vitamin.
Top Fermented Foods Rich in Vitamin K2
Natto: The Unrivaled Champion
Natto, a traditional Japanese food made from fermented soybeans, is in a league of its own when it comes to vitamin K2 content. Fermented using the bacterium Bacillus subtilis natto, it is the richest known dietary source, containing a particularly potent and long-lasting form of K2, menaquinone-7 (MK-7). A single serving can provide over 1,000 mcg of K2, vastly exceeding the content found in other foods. While its taste and sticky texture can be an acquired taste for some, its nutritional benefits, including potent K2 levels, make it a dietary superstar.
Aged Cheeses: A Western K2 Source
For those seeking a more familiar source of K2, certain types of cheese offer a valuable contribution. The bacterial cultures involved in cheese ripening produce menaquinones, with the specific MK subtypes and concentrations varying by cheese type and age. Generally, hard and semi-hard aged cheeses tend to have higher levels of K2. Notable examples include:
- Gouda: Known to be a good source, particularly for longer-chain menaquinones like MK-9.
- Edam: Another reliably rich source of K2.
- Swiss Cheeses: Varieties like Emmentaler and Raclette contain significant amounts of menaquinones.
- Other hard and blue cheeses: These can also contain moderate to high levels of various menaquinone subtypes.
Fermented Vegetables: Sauerkraut and Beyond
While not as concentrated as natto, fermented vegetables like sauerkraut also contain vitamin K2. The lactic acid bacteria involved in the fermentation process contribute to the production of menaquinones, including MK-4 and MK-7. Sauerkraut's K2 content can vary widely depending on fermentation methods and cultures. Other fermented vegetables like kimchi likely also contain K2, but research indicates their levels may be lower than those found in cheese or natto. The benefit of these foods also extends to their probiotic content, supporting overall gut health, which in turn can influence the body's own menaquinone production.
Fermented Dairy Drinks: Kefir
Kefir, a fermented milk drink, is a recognized source of vitamin K2. The kefir grains contain a mix of bacteria and yeasts that produce menaquinones during fermentation. Studies have found measurable levels of MK-7 in milk kefir, though the exact amount can depend on the fermentation process. Kefir is an excellent way to incorporate both probiotics and vitamin K2 into a daily routine, especially for those who tolerate dairy products.
Why Vitamin K2 is Important for Your Health
Vitamin K2's benefits go beyond blood clotting, a role traditionally associated with vitamin K1. K2 plays a critical role in two key physiological processes by activating specific proteins:
- Bone Health: K2 activates osteocalcin, a protein that directs calcium to bind with the bone matrix, which is vital for building and maintaining strong, dense bones. A deficiency can lead to improperly mineralized bones, increasing the risk of osteoporosis.
- Cardiovascular Health: K2 activates Matrix Gla Protein (MGP), which helps prevent the buildup of calcium in soft tissues, particularly the arteries. By preventing arterial calcification, K2 helps maintain arterial flexibility and reduces the risk of cardiovascular disease.
Comparing Vitamin K1 and Vitamin K2
| Feature | Vitamin K1 (Phylloquinone) | Vitamin K2 (Menaquinone) |
|---|---|---|
| Primary Source | Leafy green vegetables (e.g., spinach, kale) | Bacterial fermentation (e.g., natto, cheese), some animal products |
| Subtypes | One main form (K1) | Various subtypes (MK-4 to MK-13) based on chain length |
| Primary Role | Liver activation for blood clotting factors | Extrahepatic tissue activation for bone and cardiovascular health proteins |
| Absorption | Poorly absorbed from plants compared to K2 | Better absorbed, especially long-chain MK-7 |
| Half-Life | Short half-life, clears from the body quickly | Longer half-life, remains active in circulation longer (especially MK-7) |
How to Incorporate K2-Rich Fermented Foods into Your Diet
Integrating fermented foods into your meals can be a delicious way to boost your K2 intake. Here are a few practical tips:
- Natto: If you are adventurous, try natto. It's often served with rice and soy sauce, and its powerful taste can be moderated by adding mustard or chives.
- Cheese: Incorporate aged Gouda, Edam, or Swiss cheeses into sandwiches, salads, or as a snack. Be mindful of portion sizes due to their fat and sodium content.
- Sauerkraut: Add a spoonful of raw, unpasteurized sauerkraut to salads, sandwiches, or alongside meat dishes. Ensure it's not heat-treated, as that can destroy beneficial bacteria and enzymes.
- Kefir: Blend kefir into smoothies with fruits and a healthy fat source like avocado or nut butter to enhance absorption of the fat-soluble vitamin. You can also pour it over cereal or drink it plain.
The Verdict: Does Fermented Food Have K2?
The answer is a definitive yes, though the amount varies significantly across different products. Fermented foods are a primary dietary source of menaquinones (vitamin K2) due to the action of specific bacteria during the fermentation process. While natto provides an extraordinary concentration of K2, a diverse array of fermented dairy products like aged cheeses and kefir, and fermented vegetables like sauerkraut, can all contribute to meeting your body's needs. Consuming a variety of these foods, particularly those known for high K2 content, is an excellent strategy for supporting long-term bone and cardiovascular health. It is always wise to consult a healthcare professional or registered dietitian regarding specific dietary needs or before starting any new supplement regimen.
Menaquinones, Bacteria, and Foods: Vitamin K2 in the Diet - IntechOpen
