The difference between vitamin K1 and K2
Before discussing the content in eggs, it's helpful to understand the two main types of vitamin K. Vitamin K1, or phylloquinone, is primarily found in plants, particularly leafy green vegetables. Vitamin K2, or menaquinones, is mostly found in animal products and fermented foods. While both are important for blood clotting, vitamin K2 (specifically MK-4, the form in eggs) plays a more significant role in regulating calcium metabolism, which supports bone health and prevents arterial calcification.
Why egg vitamin K content is so variable
The most important factor determining the amount of vitamin K in an egg is the hen's diet. This has a profound effect on the fat-soluble vitamins, including K, which are predominantly stored in the yolk. The contrast between conventionally raised and pasture-raised hens is a primary example of this variation.
Conventional vs. pasture-raised hens
- Conventional Eggs: Chickens in large-scale commercial farming operations are typically fed grain-based diets, which contain minimal vitamin K compared to a natural diet of insects and forage. As a result, the eggs from these hens have a very low vitamin K content. Standard nutrition data for a large hard-boiled egg lists phylloquinone (K1) at just 0.15 mcg. For two eggs, this would be a negligible amount.
- Pasture-Raised Eggs: These hens spend time outdoors, where they consume grass, insects, and other natural foods. This diverse diet is rich in vitamin K, which is then passed on to the eggs. Studies have shown that pasture-raised hens produce eggs with significantly higher levels of vitamin K2, the MK-4 form. The yolks of just two pasture-raised eggs can provide around 120 mcg of vitamin K2, fulfilling a substantial portion of the recommended daily intake for adults.
Biofortified eggs
Some producers now offer biofortified eggs from hens fed a diet specifically enriched with vitamin K2. These eggs can have an even higher, more consistent level of vitamin K than pasture-raised eggs, with some studies showing content upwards of 46–51 µg per 100g of egg.
Comparison of vitamin K content in eggs
| Attribute | Conventional Large Egg | Pasture-Raised Egg (Estimated) | Biofortified Egg (per 100g) |
|---|---|---|---|
| Hen's Diet | Grain-fed indoors | Foraging on pasture | Diet enriched with vitamin K |
| Primary Form of K | Trace amounts of K1 and K2 | Higher levels of K2 (MK-4) | Very high levels of K2 (MK-4) |
| Vitamin K (per egg) | Approx. 0.25-0.3 mcg total K | Variable, but significantly higher K2 | 46-51 mcg (per 100g) |
| Two Eggs Total | Approx. 0.5-0.6 mcg total K | Can be ~120 mcg K2 | Very high K2, varies by size and fortification |
| Location in Egg | Yolk | Yolk | Yolk |
Dietary context: eggs vs. other sources
Even with their potential for high vitamin K2 content, eggs are just one piece of the puzzle. It's important to consume a variety of vitamin K-rich foods to get both K1 and K2. Here is a list of other notable food sources:
- Leafy greens: Excellent source of Vitamin K1. Examples include spinach, kale, collard greens, and Swiss chard.
- Fermented foods: Natto (fermented soybeans) is one of the highest food sources of vitamin K2 (MK-7). Cheese, like Roquefort and Emmental, also contains K2.
- Cruciferous vegetables: Broccoli and cabbage contain good amounts of vitamin K1.
- Other animal products: Some meats, like chicken, and dairy products also provide vitamin K2.
Enhancing your vitamin K intake
For those looking to boost their vitamin K intake, pairing eggs with other K-rich foods is an effective strategy. Consider making an omelet with spinach and kale, adding cheese to your eggs, or having a side salad with mixed greens and a hard-boiled egg. As a fat-soluble vitamin, vitamin K is better absorbed when consumed with dietary fat, which the egg yolk provides naturally. This makes the combination of eggs and other vitamin K sources particularly efficient for absorption.
Conclusion
In summary, the amount of vitamin K in 2 eggs is highly dependent on how the hens are raised. While conventional eggs provide only a minimal amount, eggs from pasture-raised or biofortified hens can offer a powerful dose of vitamin K2. By choosing eggs from healthier, free-roaming chickens, consumers can substantially increase their intake of this important nutrient, which plays a critical role in bone and heart health. For a more comprehensive overview of vitamin K and its functions, see this fact sheet from the National Institutes of Health.
