Vitamin K is a fat-soluble nutrient essential for activating proteins involved in blood clotting, bone metabolism, and vascular health. While most Western diets contain vitamin K1, the long-chain menaquinone-7 (MK-7) variant of vitamin K2 is a powerhouse for health functions beyond the liver due to its superior bioavailability and longer half-life. Its primary sources are not green leafy vegetables, but rather specific fermented products and certain animal-derived foods.
Understanding Vitamin K2: MK-7 vs. MK-4
There are several forms of vitamin K2, but the most studied are MK-4 and MK-7. A key difference lies in their half-life—how long they remain active in the body. MK-4 is an animal-derived form with a very short half-life, meaning it is cleared from the bloodstream within hours. It is found in animal products like eggs and butter. In contrast, MK-7 is produced by bacterial fermentation and has a significantly longer half-life, remaining active in the blood for days. This prolonged presence allows MK-7 to better accumulate in the body's tissues, providing more consistent support for bone and cardiovascular health.
The Richest Source: Natto
Natto, a traditional Japanese food made from fermented soybeans, is the single most concentrated food source of MK-7. The fermentation process, using the bacterium Bacillus subtilis natto, is what generates the high levels of this specific menaquinone. A single serving of natto can provide hundreds of micrograms of MK-7, far exceeding the content found in any other food source. Regular consumption of natto in some parts of Japan is linked to higher serum MK-7 levels and a lower risk of hip fractures. However, its strong, pungent taste and sticky texture are not for everyone, which is why other sources are also valuable.
Fermented Cheeses and Dairy
Certain cheeses, particularly aged and fermented varieties, are good sources of MK-7 and other menaquinones like MK-8 and MK-9. The type of bacteria used in cheesemaking and the duration of the ripening process significantly impact the final MK content.
Notable cheese sources include:
- Gouda and Edam: Aged varieties of these Dutch cheeses are known to contain good levels of vitamin K2.
- Brie and Camembert: These soft, fermented cheeses also provide MK-7.
- Munster and Gorgonzola: Studies have shown that these cheeses contain higher amounts of MK-7 compared to others.
Beyond cheese, other fermented dairy products can also contribute. Kefir, especially when made with natural kefir grains, has been shown to produce MK-7 during fermentation.
Other Fermented Vegetables and Meats
Fermented vegetables and cured meats offer additional dietary routes for consuming MK-7, though generally in lower concentrations than natto or specific aged cheeses.
- Sauerkraut: This fermented cabbage product contains smaller, but still meaningful, amounts of MK-7, produced by the bacteria involved in the fermentation.
- Cured and Fermented Meats: Some processed and cured meats, such as salami and prosciutto, can contain a mixture of MK-4 and MK-7 from the fermentation and curing process.
How to Maximize MK-7 Absorption
As a fat-soluble vitamin, MK-7 is best absorbed when consumed with dietary fat. This is a crucial consideration for maximizing the nutritional benefit. For example, enjoying aged cheese alongside other meal items or pairing fermented vegetables with a fat-containing dressing will aid absorption. Many of the foods that naturally contain MK-7, such as cheese and meats, already have fat, making their consumption highly efficient.
Comparison of MK-7 Food Sources
| Food Category | Example Foods | Primary MK Form | Typical K2 Content (μg/100g) | Notes |
|---|---|---|---|---|
| Fermented Soy | Natto | MK-7 | 800–1100 | The richest source, but with a unique taste. |
| Aged Cheese | Gouda, Edam, Munster, Brie | MK-7, MK-8, MK-9 | Varies (e.g., 50+ in Gouda) | Content depends on cheese type, fat, and aging. |
| Fermented Dairy | Kefir, Probiotic Yogurt | MK-7, MK-9 | Varies (e.g., ~4.8 in kefir) | Production depends on specific bacterial cultures. |
| Fermented Vegetables | Sauerkraut | MK-7, K1 | Low (e.g., 4.8 in sauerkraut) | Good source for those avoiding soy or dairy. |
| Cured Meats | Salami, Prosciutto | MK-4, MK-7 | Varies | Contribution depends on processing methods. |
Integrating MK-7 Rich Foods into Your Diet
Building a diet rich in MK-7 doesn't have to be complicated, even if you are not a fan of natto. The key is to incorporate a variety of fermented foods regularly. Try adding aged cheeses to salads, sandwiches, or pasta dishes. For those more adventurous, experimenting with different fermented foods can be beneficial. In regions where MK-7 intake is low, supplements are a viable and effective option to ensure adequate intake. For instance, a small daily dose of MK-7 is proven to be sufficient to increase the activation of vitamin K-dependent proteins for bone and heart health.
Conclusion
What foods have MK-7 in them? The answer lies predominantly in bacterial fermentation. Natto stands out as the champion, but a variety of aged cheeses, some fermented milk products, and a few cured meats offer valuable contributions as well. By understanding these sources and incorporating them into a balanced diet, ideally with dietary fat to enhance absorption, you can significantly boost your MK-7 intake. This effort supports critical bodily functions, from promoting strong bones to protecting cardiovascular health, making MK-7 a crucial part of your overall nutritional strategy. For specific dietary guidance, always consult a healthcare professional. You can read more about vitamin K2's wide-ranging benefits by exploring research on the topic.
