Vitamin K, a vital fat-soluble nutrient, exists in several forms, with the most prominent being K1 (phylloquinone) and K2 (menaquinone). While K1 is abundant in leafy green vegetables, K2 is primarily found in fermented foods and some animal products, with MK-7 being a particularly well-researched subtype. Understanding what foods have vitamin K2 as MK-7 is key for those looking to support their bone density and cardiovascular wellness through diet. MK-7 is known for its high bioavailability and longer duration in the body compared to other vitamin K forms, making it highly effective for extrahepatic tissues, such as bones.
Natto: The Unrivaled Fermented Superfood
When discussing dietary sources of MK-7, natto stands alone as the highest-potency source by a significant margin. This traditional Japanese dish consists of soybeans fermented with Bacillus subtilis bacteria, a process that generates exceptional levels of MK-7. A 100-gram serving of natto can contain anywhere from 882 to 1,034 micrograms of MK-7, making it a concentrated powerhouse of the nutrient.
However, natto is widely known to be an acquired taste. Its slimy, sticky texture and pungent flavor can be a major deterrent for those unfamiliar with it. For those willing to incorporate it into their diet, even small amounts can provide a substantial boost in MK-7 intake. Some people improve its palatability by mixing it with condiments like soy sauce and mustard.
Aged Cheeses and Fermented Dairy
For those who find natto unappealing, certain aged cheeses and fermented dairy products serve as a more familiar and accessible source of MK-7. The bacteria used in the fermentation and aging process of cheese produce various menaquinones, including MK-7. Studies indicate that the menaquinone content can vary significantly depending on the type of cheese, the bacterial cultures used, and the fermentation time.
- Gouda: A hard, aged cheese that is often cited for its high menaquinone content. Some studies report moderate levels of MK-7, among other K2 types.
- Brie and Other Soft Cheeses: Soft, fermented cheeses can also contain notable amounts of MK-7.
- Blue Cheese: Varieties like Stilton and Roquefort contain smaller but still appreciable quantities of MK-7.
It's important to note that the menaquinone content in these foods correlates with their fat content, as vitamin K is fat-soluble. Full-fat, grass-fed dairy products generally provide higher levels of K2.
Other Fermented and Animal-Based Sources
Beyond natto and cheese, other fermented foods and certain animal products contribute to dietary MK-7 intake, though in much lower concentrations.
- Sauerkraut: This fermented cabbage contains smaller amounts of MK-7 from the bacterial fermentation process. While not a concentrated source, it can still contribute to overall intake.
- Meat and Organ Meats: Some animal products contain trace amounts of MK-7, though they are much better sources of the MK-4 form of vitamin K2. Chicken thigh and beef have been cited to contain modest levels of menaquinones.
Comparison of MK-7 Food Sources
To provide clarity on the concentration of MK-7, the following table compares typical values in common dietary sources.
| Food Source (per 100g) | Primary MK Form(s) | MK-7 Content (µg) | Notes |
|---|---|---|---|
| Natto | MK-7 (primarily) | 882–1034 | The richest known dietary source, but with a unique taste. |
| Gouda Cheese | MK-7, MK-9 | ~76.3 | A more accessible source with moderate levels of MK-7. |
| Sauerkraut | K1, small MK-7 | ~4.8 | Contains low levels of MK-7 from the fermentation process. |
| Chicken Thigh (with skin) | MK-4, some MK-7 | ~36 | Primarily a source of MK-4, but contributes to overall K2 intake. |
Enhancing Vitamin K2 Absorption
Because vitamin K2 is a fat-soluble vitamin, its absorption from dietary sources is significantly enhanced when consumed with fat. When planning a meal with MK-7-rich foods, pairing them with a healthy fat source, such as avocado or olive oil, can help maximize the benefits. Many natural sources, like cheese and fatty meats, already contain fat, which aids in their absorption.
The Importance of MK-7
Research into MK-7 has highlighted its crucial role in promoting bone and cardiovascular health. It works synergistically with vitamin D to ensure that calcium is properly utilized in the body, directing it to the bones and teeth where it is needed and preventing its buildup in soft tissues like arteries. Higher dietary intake of vitamin K2, and specifically MK-7, has been linked to a reduced risk of bone fractures and vascular calcification.
Conclusion
For those seeking to increase their intake of vitamin K2 as MK-7, the traditional Japanese dish natto offers the most concentrated source. However, its polarizing taste may limit its appeal. Fortunately, a variety of aged, fermented cheeses and other fermented foods provide more moderate and palatable options. For optimal absorption, these foods should be enjoyed as part of a meal that includes some healthy dietary fat. By diversifying your diet with these fermented and cultured foods, you can ensure a consistent supply of this critical nutrient for long-term bone and cardiovascular health. You can find more information about vitamin K and its benefits from authoritative sources like the Harvard T.H. Chan School of Public Health.
