Understanding Vitamin K and its Subtypes
Vitamin K is a fat-soluble nutrient, but it exists in two primary forms: vitamin K1 (phylloquinone) and vitamin K2 (menaquinone). While K1 is primarily found in leafy green vegetables and is essential for blood clotting, K2 plays a distinct and critical role in regulating where calcium is deposited in the body. It helps ensure calcium goes into your bones and teeth, rather than accumulating in soft tissues like arteries and kidneys.
Vitamin K2 itself is further divided into several subtypes, known as menaquinones (MKs). The most well-studied are MK-4, which is primarily found in animal products, and MK-7, which is synthesized by bacteria and abundant in fermented foods. MK-7 is noted for its longer half-life, meaning it stays in the body for a more extended period compared to MK-4, allowing it to have a more sustained effect.
The Highest K2 Source: Natto
Without a doubt, the food with the highest concentration of vitamin K2 is natto. This traditional Japanese dish is made from soybeans fermented with Bacillus subtilis bacteria. This fermentation process is responsible for producing the extremely high levels of MK-7.
- Exceptional Potency: Natto can contain hundreds of micrograms of K2 (MK-7) per 100-gram serving, far surpassing any other food source.
- Bioavailability: The MK-7 form is highly bioavailable and easily absorbed by the body.
- Unique Flavor and Texture: Natto is known for its strong flavor, pungent aroma, and sticky, slimy texture, which can be an acquired taste for those unfamiliar with it.
Other Excellent Dietary Sources of Vitamin K2
While natto holds the top spot, many other foods can contribute to your K2 intake. These sources typically contain the MK-4 variant or other forms like MK-8 and MK-9.
Dairy Products
Certain dairy products, especially fermented and high-fat options, are great sources of vitamin K2. The K2 content varies depending on the type of cheese, its fat content, and how long it has been aged.
- Hard and Aged Cheeses: Cheeses like Gouda, Edam, and Munster are among the best dairy sources.
- Soft Cheeses: Soft fermented cheeses like Brie and Roquefort also contain significant amounts.
- Grass-Fed Dairy: Dairy from grass-fed cows tends to have higher levels of K2 (MK-4) than that from grain-fed cows.
Animal Products
Fatty animal products are another key source of MK-4, especially from animals raised on a diet rich in vitamin K1, which their bodies then convert.
- Organ Meats: Liver is a particularly rich source of MK-4. Goose liver pate, for example, is exceptionally high in K2.
- Egg Yolks: The vitamin K2 content in egg yolks depends on the chicken's diet. Pasture-raised hens that consume grass and insects produce eggs with higher K2 levels than conventionally raised hens.
- Meat: Other meats, like chicken breast and thigh, also contain moderate amounts of K2.
Other Fermented Foods
Outside of natto and cheese, other fermented foods contribute smaller but still notable amounts of K2.
- Sauerkraut: This fermented cabbage is a source of K2, though it typically provides less than natto.
- Kefir: As a fermented dairy drink, kefir offers probiotics and varying amounts of K2.
Comparison of Top Vitamin K2 Food Sources
To help visualize the difference in concentration, here is a comparison of some of the top dietary sources of vitamin K2. Values are approximate and can vary based on production methods.
| Food Source | Main K2 Form | Approximate K2 Content (μg/100g) | Notes |
|---|---|---|---|
| Natto | MK-7 | 800–1100 | The richest source by a significant margin. |
| Goose Liver Pate | MK-4 | ~369 | A very high animal-based source. |
| Hard Cheeses (e.g., Gouda) | MK-8, MK-9 | 40–50+ | Content increases with age. |
| Soft Cheeses (e.g., Brie) | MK-8, MK-9 | ~57 | Significant source in fermented dairy. |
| Chicken Thigh (with skin) | MK-4 | ~53 | High among common meats. |
| Egg Yolk (pasture-raised) | MK-4 | ~37–60 | Content varies greatly based on hen's diet. |
| Sauerkraut | Various | ~5 | A good fermented vegetable source. |
The Health Benefits of a K2-Rich Diet
Beyond its role in blood clotting, vitamin K2 is a powerful player in several aspects of long-term health. Studies suggest that higher dietary intake of K2 is linked to important health outcomes.
- Bone Health: K2 helps activate osteocalcin, a protein that binds calcium to the bone matrix, improving bone mineral density and reducing the risk of fractures. This is particularly important for postmenopausal women and the elderly.
- Cardiovascular Health: K2 activates a protein called matrix Gla protein (MGP), which prevents calcium from accumulating in the arterial walls. This may significantly reduce the risk of heart disease and vascular calcification.
- Dental Health: By activating osteocalcin, K2 also contributes to the regulation of dental health, promoting new bone and dentin growth in teeth.
Conclusion
While many foods contain some amount of vitamin K2, the undisputed champion for concentration is natto. However, for those with palates not accustomed to this potent fermented food, there are plenty of other viable options. Incorporating a variety of sources like aged cheeses, grass-fed dairy products, and animal products like egg yolks and liver can help ensure a healthy intake of this vital nutrient. When planning your diet, remember that vitamin K2 is fat-soluble, so consuming these foods with some dietary fat will improve absorption. Regular, moderate consumption of these K2-rich foods is a practical strategy to support long-term bone and heart health. For a balanced approach, consider combining these sources with K1-rich leafy greens and ensuring adequate vitamin D intake, which works synergistically with K2.
Integrating K2-Rich Foods into Your Weekly Meals
Incorporating K2 sources into your diet doesn't have to be a major change. Here are some simple ideas:
- Breakfast: Add eggs from pasture-raised hens, either scrambled or fried in grass-fed butter, or a side of aged Gouda with your morning meal.
- Lunch: Make a salad with grilled chicken breast and a sprinkling of blue cheese. A sandwich with a slice of hard cheese can also add K2.
- Dinner: Include chicken thigh with skin as part of a meal. Small, well-thought-out portions of cured meats like salami can also contribute.
- Snacks: Enjoy small cubes of aged cheese, or for the adventurous, a small side of natto with rice. You can also mix kefir into a smoothie.
- Other options: Consider adding a small portion of goose or chicken liver pate to crackers or toast occasionally.
Following a balanced approach that includes both K1 (from vegetables) and K2 (from fermented and animal sources) is the best way to ensure optimal vitamin K status.
A Final Word on K2 and Diet
While some K2 sources like certain dairy products and processed meats can be higher in saturated fat or sodium, moderation is key. The focus should be on nutrient density. Choosing higher-quality options, like grass-fed and pasture-raised products, can also improve nutrient content. For those concerned about intake, a balanced approach is recommended over relying on a single, less-healthy source. As with any dietary change, especially if you have health concerns or are on medication like blood thinners, consult with a healthcare provider or a registered dietitian.
