Understanding Vitamin K2: The MK-4 and MK-7 Distinction
Vitamin K is a fat-soluble vitamin with two main forms: K1 (phylloquinone) and K2 (menaquinone). While K1 is primarily found in leafy green vegetables, K2 is present in certain animal and fermented foods. K2 itself has several subtypes, with the most relevant being MK-4 and MK-7.
- MK-4: This subtype of K2 is found almost exclusively in animal products, including egg yolks, liver, and grass-fed butter. In animals, K1 from the diet (like grass) is converted into MK-4 and stored in fatty tissues and organs.
- MK-7: This form is produced by bacteria and is abundant in fermented foods like nattō, a traditional Japanese fermented soybean dish. MK-7 has a longer half-life in the body compared to MK-4.
Eggs are a valuable dietary source of the MK-4 subtype, but not all eggs are created equal. The nutritional profile of an egg, especially its K2 content, is directly influenced by the chicken's environment and feed.
The Pasture-Raised vs. Conventional Egg Difference
Research shows a dramatic difference in the vitamin K2 content of eggs based on the hen's diet. Conventional eggs, laid by chickens fed primarily industrial grains, contain a modest amount of K2. Pasture-raised eggs, however, come from hens that are free to roam and forage on grass and insects, which are rich in vitamin K1. The chickens' bodies convert this K1 into the highly bioavailable MK-4 form of K2, which is then passed into their eggs.
- Conventional Eggs: Chickens are fed grain-based diets, resulting in lower K2 levels. For example, some data shows conventional eggs having approximately 15.5 mcg of MK-4 per 100g of yolk.
- Pasture-Raised Eggs: Hens have a more natural diet, leading to significantly higher K2 levels. The yolks from pasture-raised hens can have K2 levels several times greater than conventional eggs.
Choosing pasture-raised eggs is therefore a simple and effective way to substantially boost your dietary intake of MK-4. The difference is a testament to the importance of sustainable farming practices not just for animal welfare, but also for human nutrition.
Health Benefits of Vitamin K2 (MK-4) from Eggs
The MK-4 found in egg yolks is crucial for several physiological processes that support long-term health.
Supporting Bone and Dental Health
Vitamin K2 plays a key role in calcium metabolism, activating two important proteins: osteocalcin and matrix GLA protein (MGP). Osteocalcin is responsible for binding calcium and integrating it into bone tissue, strengthening the skeletal structure. This process also helps strengthen dental tissue, making teeth more resistant to decay. Japanese studies have shown that K2 supplementation can significantly reduce the risk of fractures.
Promoting Heart and Cardiovascular Health
While directing calcium into bones, K2 also prevents it from being deposited in soft tissues like arteries and blood vessels. This is critical for cardiovascular health, as arterial calcification is a major risk factor for heart disease. Studies have found that higher K2 intake is associated with a lower risk of severe arterial calcification and heart disease.
Vitamin K2 Food Source Comparison
To put the K2 content of eggs into perspective, let's compare it with other sources. The MK-4 found in eggs has different characteristics than the MK-7 found in fermented foods like nattō.
| Food Source | Primary K2 Subtype | Typical K2 Content (per 100g) | Notes |
|---|---|---|---|
| Pasture-Raised Egg Yolk | MK-4 | 37-60 mcg | Excellent and bioavailable source of MK-4. |
| Nattō (Fermented Soybeans) | MK-7 | 800-1100 mcg | Richest known source of K2, but has a different taste. |
| Hard Cheeses (e.g., Gouda) | MK-8, MK-9 | 76.3 mcg | Good source, but concentrations vary. |
| Goose Liver Pâté | MK-4 | 369 mcg | A concentrated source, though less common in many diets. |
| Grass-Fed Butter | MK-4 | 15 mcg | Useful addition, contains other fat-soluble vitamins. |
| Conventional Egg Yolk | MK-4 | 15.5 mcg | Lower K2 levels compared to pasture-raised options. |
Maximizing Vitamin K2 Intake from Eggs
To ensure you are getting the most vitamin K2 from your eggs, here are a few tips:
- Choose Pasture-Raised: This is the most important factor. Look for labels like "pasture-raised" or "grass-fed" at farmers' markets or health food stores.
- Eat the Yolk: The yolk is where the vitamin K2 and other fat-soluble vitamins are concentrated. Skipping the yolk means missing out on this vital nutrient.
- Combine with Other K-Rich Foods: Pairing eggs with leafy greens (rich in Vitamin K1) or other K2 sources like grass-fed butter can create a synergistic nutritional effect.
Conclusion
In summary, eggs are a valuable source of vitamin K2, specifically the MK-4 menaquinone, but their concentration is heavily influenced by the hen's diet. Opting for eggs from pasture-raised chickens is the best way to ensure you are consuming a high amount of this crucial nutrient. A diet that includes high-quality eggs can contribute significantly to bone and cardiovascular health. While fermented foods like nattō provide far higher amounts of the MK-7 subtype, eggs offer a reliable and accessible source of MK-4, making them an excellent dietary staple for nutrient-conscious consumers.
A Final Word on K2
For those interested in delving deeper into the history and importance of vitamin K2, consider exploring the research of Dr. Weston A. Price, who identified a powerful fat-soluble nutrient, dubbed “Activator X,” which modern science has identified as vitamin K2. His work highlights the value of traditional diets rich in high-quality animal fats. Learn more at the Weston A. Price Foundation website.
Further Reading
For more in-depth scientific analysis on the role of vitamin K2 and its health benefits, research studies published in journals like Nutrients and Food & Nutrition Research offer valuable insights. These resources underscore the growing body of evidence supporting K2's importance beyond simple coagulation.
