What is Vitamin K2? The Different Forms of Vitamin K
Vitamin K is a family of fat-soluble vitamins with two primary forms: vitamin K1 (phylloquinone) and vitamin K2 (menaquinones). While K1 is well-known for its role in blood clotting and is found predominantly in leafy green vegetables like spinach and kale, vitamin K2 is a lesser-known but equally important nutrient. Vitamin K2 is necessary for the proper functioning of proteins that regulate calcium, directing it to where it's needed, such as in the bones, and keeping it away from where it can cause harm, like the arteries. The menaquinones (MK) that comprise K2 come in various subtypes, with MK-4 found in animal products and MK-7 largely concentrated in fermented foods. Understanding the distinction between K1 and K2 is crucial for building a diet that supports overall bone and heart health.
Top Dietary Sources of Vitamin K2
For those asking, Can K2 be found in food?, the answer is a resounding yes, but the sources are specific and often differ from common fruit and vegetable lists. Incorporating a variety of these foods is the most effective way to ensure adequate intake of both MK-4 and MK-7 forms.
The Fermented Food Powerhouse: Natto
One of the most potent and concentrated sources of vitamin K2 is natto, a traditional Japanese dish made from fermented soybeans. Natto is exceptionally rich in the MK-7 subtype of K2, with a single tablespoon containing a substantial amount. Its potent fermentation process is responsible for its high K2 content, and its distinct flavor makes it a unique addition to the diet.
Animal Products and MK-4
Animal products are a primary source of the MK-4 subtype of vitamin K2. The concentration of this vitamin can vary significantly based on the animal's diet, with products from grass-fed animals generally having higher levels. Key sources include:
- Egg Yolks: Eggs from free-range or grass-fed hens are good sources of MK-4.
- Liver and Organ Meats: Chicken liver and goose liver pate are particularly rich.
- Butter: Specifically, butter made from the milk of grass-fed cows contains notable levels of K2.
Cheeses: Aged for K2
Certain cheeses contain vitamin K2, with aged, hard cheeses typically providing higher amounts than younger, soft varieties. The K2 is produced by the bacteria involved in the cheese-making and aging process. Excellent options include:
- Gouda
- Brie
- Edam
- Cheddar
Other Fermented and Animal-Based Sources
Other foods that contribute to K2 intake include:
- Sauerkraut: Fermented cabbage contains smaller but still notable amounts of K2.
- Salami and Cured Meats: Processed meats like salami can contain both MK-4 and MK-7.
- Chicken: Dark poultry meat contains higher amounts of K2 than other meats.
Comparison of Vitamin K Forms
To help differentiate the sources and functions of the two main types of vitamin K, here is a comparison table:
| Feature | Vitamin K1 (Phylloquinone) | Vitamin K2 (Menaquinones) |
|---|---|---|
| Primary Sources | Leafy green vegetables (spinach, kale, broccoli) | Fermented foods (natto), animal products (egg yolks, liver, grass-fed dairy) |
| Main Function | Blood clotting | Calcium metabolism (directs calcium to bones, removes from arteries) |
| Bioavailability | Lower absorption, especially from raw sources | Higher bioavailability, especially the MK-7 subtype |
| Key Health Impact | Ensures proper blood coagulation | Supports bone health and cardiovascular wellness |
The Benefits of a K2-Rich Diet
Beyond its role in blood clotting, vitamin K2 provides significant benefits for long-term health, primarily due to its regulation of calcium. K2 activates a protein called matrix GLA protein (MGP), which helps prevent calcium from accumulating in blood vessel walls, a major risk factor for heart disease. It also activates osteocalcin, a protein that binds calcium to bones, thereby improving bone mineral density and strength. Studies, particularly those from Japan where natto consumption is higher, have shown promising results linking higher K2 intake with reduced risk of coronary heart disease.
Conclusion
In summary, the answer to 'Can K2 be found in food?' is that it can, but a specific dietary approach is needed. Unlike the widespread availability of K1 in plant foods, vitamin K2 requires intentional consumption of animal products like grass-fed dairy, eggs, and organ meats, as well as fermented foods such as natto and aged cheeses. For optimal health, focusing on a diverse diet that includes these sources is crucial for supporting robust bone health and protecting cardiovascular function. While some people may consider supplements, integrating these nutrient-dense foods into your meals is the most natural and effective way to boost your K2 intake.
Reference
For more information on the types of vitamin K and their sources, see the National Institutes of Health's article on the subject: Vitamin K Fact Sheet for Health Professionals
