Vitamin K is an essential, fat-soluble nutrient, but it comes in two distinct forms: K1 and K2. Most people are familiar with vitamin K1, found in leafy green vegetables, which is primarily involved in blood clotting. However, the less common vitamin K2 (menaquinone) plays a critical role in directing calcium to where it’s needed, such as bones and teeth, and preventing it from accumulating in soft tissues like arteries. As a fermented food, yogurt is often cited as a source of K2, but the reality is more nuanced.
The Source of Vitamin K2 in Yogurt
The production of vitamin K2 is a microbial process, meaning it is synthesized by bacteria. In fermented dairy products like yogurt, the bacterial starter cultures are responsible for creating menaquinones (MKs), the various forms of vitamin K2. However, not all bacteria produce K2, or they produce it in differing amounts. Research has shown that the type of bacterial culture used is a crucial factor, which explains the wide variation in K2 content across different dairy products.
The Fat Factor: Full-Fat vs. Low-Fat
Vitamin K2 is a fat-soluble vitamin, so its content is directly linked to the fat percentage of the dairy product. Studies confirm that full-fat dairy products, including yogurt, contain significantly more vitamin K2 than their lower-fat or fat-free counterparts. This is because the K2 produced by the bacteria is stored within the fatty component of the yogurt. For example, a whole milk yogurt might contain around 0.9 µg of K2 per 100g, whereas a skimmed milk yogurt could have as little as 0.1 µg. Choosing whole-fat yogurt is the first step toward maximizing your K2 intake from this source.
The Role of Fermentation Cultures
Fermentation is central to how much K2 ends up in yogurt, but the specific bacterial strains used have a major impact. Certain mesophilic cultures, like those used to make traditional cheeses, are excellent K2 producers. Conversely, many modern yogurts use thermophilic cultures that produce minimal to no K2. This is why some fermented dairy products, especially specific types of cheeses, are far richer sources of K2 than standard yogurt. This is also why fortified yogurts exist, which contain added synthetic K2, often in the MK-7 form. The duration and conditions of fermentation also play a role, influencing the activity of the bacteria and the final concentration of menaquinones.
How Does Yogurt Compare to Other K2 Sources?
While yogurt offers some K2, it pales in comparison to the richest sources. For example, the Japanese fermented soybean product, natto, is famously the most potent source of K2, particularly the highly bioavailable MK-7 variety. Hard and soft cheeses also typically provide much higher levels of K2, especially the longer-chain menaquinones like MK-8 and MK-9. This stark contrast highlights that while yogurt can be a contributor, it should not be the sole focus for increasing K2 intake.
K2 Content Comparison of Fermented Foods
| Food Source | Primary K2 Form | Approximate K2 Content (μg/100g) |
|---|---|---|
| Natto (Fermented Soybeans) | MK-7 | 800–1000+ |
| Aged Hard Cheeses (e.g., Gouda) | MK-8, MK-9 | 30–110 |
| Soft Cheeses (e.g., Brie) | MK-8, MK-9 | 50–70 |
| Kefir (fermented milk) | MK-7, MK-9 | ~4.8 |
| Whole Milk Plain Yogurt | MK-4, MK-8 | 0.5–2.0 (varies) |
| Skim Milk Plain Yogurt | Very low or Trace | 0.1 or lower |
The Role of Gut Bacteria
It is true that the healthy bacteria in our large intestine can synthesize menaquinones. However, research suggests that the bioavailability of this bacterially-produced K2 is quite low, as it is primarily produced in a part of the colon where absorption is limited. Therefore, relying solely on your gut microbiome is not a reliable strategy for meeting your body's vitamin K2 needs. Dietary intake from food sources is the main contributor to your K2 levels.
The Health Benefits of Vitamin K2
The benefits of adequate K2 intake are significant, particularly for long-term health. It helps to regulate calcium metabolism, ensuring calcium is used to strengthen bones and teeth rather than causing dangerous calcification in arteries. In conjunction with vitamin D, it supports strong skeletal health and may reduce the risk of osteoporosis and fractures. A high intake of K2, but not K1, has been associated with a reduced risk of coronary heart disease. Additionally, a balanced diet with sufficient K2 may offer benefits for insulin sensitivity and neurological health, although more research is needed.
A Deeper Look into K2 Subtypes
Vitamin K2 exists in various forms called menaquinones (MK-n). Different food sources provide different subtypes. For instance, animal products like liver and eggs are rich in MK-4, while fermented foods like natto are a major source of MK-7. Aged cheeses and certain fermented dairy contain longer-chain menaquinones like MK-8 and MK-9. Each subtype has a different bioavailability and distribution in the body, with the longer-chain menaquinones like MK-7 having a longer half-life and greater impact on extra-hepatic tissues.
Conclusion: The Bottom Line on Yogurt and K2
In summary, yogurt can contain vitamin K2, but its effectiveness as a primary source is limited and depends heavily on the product. Full-fat and fortified yogurts are the best options, while low-fat or standard varieties contribute very little. The fat content and bacterial cultures are the main determining factors. For those serious about increasing their K2 intake, relying on richer sources like natto, hard cheeses, or supplements is a more effective strategy. While yogurt remains a great source of protein and probiotics, it should not be considered a powerhouse for vitamin K2. For anyone with cardiovascular or bone health concerns, consulting a dietitian to optimize K2 intake is recommended.
Learn more about the specific benefits of vitamin K2 for bone and heart wellness from this resource on Healthline.
