Understanding Vitamin K2 and Its Importance
Vitamin K is not a single compound but a family of fat-soluble vitamins. The two primary forms found in the human diet are vitamin K1 (phylloquinone) and vitamin K2 (menaquinones). While K1 is abundant in leafy green vegetables and is crucial for blood clotting, K2 has a different, longer-lasting effect in the body. It is transported and used by various tissues beyond the liver, playing a central role in activating proteins that regulate calcium. Specifically, K2 helps direct calcium into bones and teeth, where it belongs, while preventing its buildup in soft tissues like arteries and kidneys. This function is why K2 is so critical for supporting bone density and cardiovascular health.
Top Dietary Sources of Vitamin K2
There are two primary categories of foods rich in vitamin K2: animal-based products (containing the MK-4 form) and fermented foods (rich in the MK-7, MK-8, and MK-9 forms).
Fermented Foods (Primarily MK-7)
- Natto: This traditional Japanese dish of fermented soybeans is, by far, the richest food source of K2, particularly the highly bioavailable MK-7 subtype. Its strong smell and slimy texture can be an acquired taste, but even a small daily serving provides a potent dose.
- Hard and Soft Cheeses: Many cheeses, especially aged and fermented varieties, are good sources of long-chain menaquinones (MK-8 and MK-9). Examples include Gouda, Brie, and blue cheese. The K2 content can vary based on the fermentation process and fat content.
- Sauerkraut: Fermented cabbage contains smaller but still notable amounts of vitamin K2. Its probiotic benefits also support the gut microbiome, which can synthesize some K2.
Animal-Based Foods (Primarily MK-4)
- Goose Liver Pâté: Goose liver is an exceptionally rich source of K2.
- Organ Meats: Other organ meats, such as beef and chicken liver, contain significant amounts of the MK-4 form of K2.
- Egg Yolks: Eggs, particularly from pasture-raised or grass-fed chickens, are a reliable source of MK-4.
- Grass-Fed Butter and Dairy: Dairy products from grass-fed animals contain higher levels of K2 because the animals convert K1 from greens into K2. Look for full-fat, grass-fed butter, whole milk, and aged dairy products.
- Chicken: Chicken meat, especially the dark meat like thighs, contains a good amount of K2.
- Fatty Fish: Fish such as eel, salmon, and mackerel contain small to moderate amounts of K2.
How to incorporate more K2 into your diet
Integrating more vitamin K2 into your diet involves a strategic mix of fermented foods and high-quality animal products. For those who find natto's taste challenging, focusing on aged cheeses and incorporating more grass-fed animal products can be effective. Pairing K2-rich foods with healthy fats, like extra virgin olive oil, can also enhance absorption since it is a fat-soluble vitamin. For example, a salad with spinach (for K1) and a vinaigrette dressing, topped with some aged cheese, can provide a great mix of both forms.
K1 vs. K2: A Quick Comparison
| Feature | Vitamin K1 (Phylloquinone) | Vitamin K2 (Menaquinone) |
|---|---|---|
| Primary Sources | Leafy green vegetables (kale, spinach, broccoli), some vegetable oils | Fermented foods (natto), organ meats, full-fat dairy, egg yolks |
| Function | Primarily involved in blood clotting in the liver | Regulates calcium deposition in bones and teeth, prevents arterial calcification |
| Bioavailability | Poorly absorbed from plants | Generally better absorbed, especially the long-chain forms like MK-7 |
| Half-Life | Short, cleared from the blood quickly | Longer, can remain in circulation for days |
Conclusion
While vitamin K1 is relatively easy to obtain through a diet rich in green vegetables, ensuring adequate intake of vitamin K2 requires more deliberate food choices. For most Western diets, where fermented foods and organ meats are less common, supplementation might be worth considering. However, by focusing on rich dietary sources like natto, hard cheeses, grass-fed dairy, and organ meats, individuals can effectively increase their K2 levels naturally. The evidence supporting K2's role in bone and cardiovascular health makes it an important nutrient not to overlook. For specific dietary guidance, especially for those on blood thinners, a healthcare professional or registered dietitian should be consulted.
A note on supplements
For many, especially those who find it difficult to regularly consume K2-rich foods, supplementation is a viable option. The MK-7 form, often derived from natto, is widely available in supplements due to its higher bioavailability and longer half-life compared to the MK-4 form. Supplements containing both vitamin D3 and K2 are popular, as these two vitamins work synergistically in the body for calcium metabolism. When considering a supplement, it's always best to consult with a healthcare provider to ensure it is the right choice for your individual needs.
Understanding the different subtypes of K2 can also provide a more in-depth perspective on their varying roles in the body.
