The Microbial Origin of Vitamin K2
Vitamin K exists in two primary forms: vitamin K1 (phylloquinone), found in leafy greens, and vitamin K2 (menaquinones), which is predominantly produced by bacteria. Unlike vitamin K1, which we get directly from plants, our bodies rely on microbial synthesis for much of our vitamin K2. This process occurs both during food fermentation and within our own gut microbiome. While not all probiotics will contain vitamin K2, the key takeaway is that certain strains have the enzymatic capability to produce it.
Bacteria Responsible for Vitamin K2 Production
Not all probiotics are created equal when it comes to vitamin K2 synthesis. The strains with the proven capability to produce menaquinones (vitamin K2) are often found in fermented foods or as specific proprietary strains developed for supplementation. The Bacillus subtilis strain, for example, is famously used to ferment soybeans into natto, a Japanese food exceptionally rich in menaquinone-7 (MK-7). Other bacteria, both part of the gut flora and used in food production, also play a role.
Fermented Foods: A Direct Source of Probiotic-Made K2
Fermented foods are the most direct way to get vitamin K2 that is synthesized by bacteria. The microbes used in the fermentation process create menaquinones as a byproduct of their metabolism. This makes foods like natto, certain cheeses, and sauerkraut valuable dietary sources. The amount of vitamin K2 in these foods varies widely depending on the bacterial strain, fermentation time, and other conditions.
The Role of Your Gut Microbiome
Your intestinal flora is a bustling ecosystem, and some of its inhabitants contribute to your body's overall vitamin K2 status. Studies have shown that gut bacteria, particularly those in the Bacteroides genus, produce different menaquinones, such as MK-10 and MK-11, in the distal colon. However, the bioavailability of this internally produced K2 is not fully understood, and relying solely on gut synthesis may not be enough to meet optimal levels. For this reason, dietary sources and targeted supplements are often recommended.
Are Probiotic Supplements a Good Source of K2?
It is a common misconception that all probiotic supplements contain vitamin K2. Most standard probiotic supplements, which often contain Lactobacillus and Bifidobacterium, do not contain the vitamin itself. The benefit is indirect: by promoting a healthy gut environment, they support the native bacteria that may produce K2. However, some specialty supplements are now formulated with specific K2-producing strains or with K2 added directly to the formula. These products can be a reliable and concentrated source of the vitamin.
K2 Production in Fermented Foods vs. Supplements
| Feature | Fermented Foods | Probiotic Supplements (Standard) | Probiotic Supplements (K2-Added) |
|---|---|---|---|
| Source of K2 | Made during fermentation by bacteria like B. subtilis. | Indirectly supports gut bacteria that produce K2. | K2 is added during manufacturing. |
| K2 Content | Varies widely based on food type and process. | Typically none, or a variable, unquantified amount. | Quantified and guaranteed amount per serving. |
| Form of K2 | Longer-chain menaquinones (e.g., MK-7, MK-8, MK-9). | N/A (produced by native gut bacteria). | Can include MK-4, MK-7, or both. |
| Additional Benefits | Whole-food nutrition, other vitamins, and diverse gut flora. | Supports general gut health and digestion. | Concentrated dose with specific health-supportive cofactors. |
| Example | Natto, Gouda cheese, kefir. | Standard capsules containing Lactobacillus species. | 3-in-1 formulas with Vitamin D3, K2, and bacteria. |
Maximizing Your K2 Intake
To ensure you are getting adequate vitamin K2, a multi-pronged approach is often most effective. For dietary sources, look to fermented foods like natto, which is a powerhouse of MK-7. Incorporating aged cheeses, kefir, and sauerkraut can also provide smaller, but still beneficial amounts. For those who prefer supplementation, consider a product specifically formulated with both probiotics and added vitamin K2 to ensure a consistent and known dosage. Consulting with a healthcare provider can help determine the best approach for your individual needs. This is especially important for those taking blood-thinning medication.
Conclusion: The Probiotic-K2 Synergy
While probiotics do not inherently contain vitamin K2, a powerful link exists between them. Specific probiotic strains and other fermenting bacteria have the remarkable ability to synthesize menaquinones, which we can obtain from fermented foods. Furthermore, a healthy and diverse gut microbiome, nurtured by probiotic consumption, plays an ongoing role in the endogenous production of vitamin K2. By understanding which bacteria produce this vital nutrient and where to find them—in both food and specialized supplements—you can take a more informed approach to supporting your bone, cardiovascular, and overall health.
References
- Walther, B., & Chollet, M. (2017). Menaquinones, bacteria, and foods: vitamin K2 in the diet. IntechOpen.
- Lai, Y., et al. (2022). Role of vitamin K in intestinal health. ScienceDirect.
- Health~Holland. (2018). Effect of vitamin K producing probiotics on vitamin K status in adults.
- Cleveland Clinic. (2023). 11 Foods High in Vitamin K2.
- ScienceDirect.com. (2024). Review: Bacterially produced vitamin K2 and its potential to generate health benefits.
- Nutritional Outlook. (2013). New Probiotic Strain Increases Vitamin K Production.
- IntechOpen. (2016). Biosynthesis of Vitamins by Probiotic Bacteria.
- Healthline. (2024). Everything You Need to Know About the Vitamin K2.
- Consensus. (2024). Fermented Foods Main Vitamin K2.
- The Good Bug. (2025). Vitamin K2 in Sauerkraut: Benefits and Dietary Incorporation.
