Understanding Vitamin K2 and Its Forms
Vitamin K is a fat-soluble vitamin essential for various physiological processes, including blood clotting and calcium metabolism. It is primarily known in two natural forms: Vitamin K1 (phylloquinone) and Vitamin K2 (menaquinones). While K1 is abundant in leafy green vegetables, K2 is predominantly found in animal products and fermented foods.
Vitamin K2 itself is further divided into subtypes, designated as MK-4 through MK-13. The two most-discussed subtypes are MK-4 and MK-7, which differ significantly in their dietary sources, bioavailability, and half-life in the body. Understanding these distinctions is critical for anyone aiming to optimize their vitamin K2 intake from food.
Eggs Contain MK-4, Not MK-7
The short answer to the question "Do eggs have vitamin K2 MK-7?" is no. Research consistently shows that the vitamin K2 present in eggs is almost exclusively in the MK-4 form. Unlike MK-7, which is synthesized by bacteria, MK-4 is derived from the conversion of vitamin K1 by animals, or from supplementary synthetic vitamin K (menadione) added to feed. This conversion process makes animal products like eggs and meat primary sources of MK-4.
The Impact of Hen's Diet on Egg's MK-4 Content
The quantity of MK-4 in an egg is not fixed and is highly dependent on the chicken's diet and environment.
- Pasture-Raised Hens: Chickens that forage on grass, weeds, and insects consume more vitamin K1, which their bodies then efficiently convert to MK-4, concentrating it in the egg yolks. Eggs from pasture-raised hens can have significantly higher levels of MK-4 compared to conventional eggs.
- Conventionally-Raised Hens: Chickens raised in confinement and fed a standard grain-based diet produce eggs with substantially lower MK-4 content. While their feed may be fortified with synthetic vitamin K (K3), which is also converted to MK-4, the amount is less than what can be achieved through a natural, diverse diet.
What About Vitamin K2 MK-7? Other Sources
Since eggs are not a viable source of MK-7, individuals seeking this specific, long-chain menaquinone must turn to other dietary options. MK-7 is produced by specific bacteria during fermentation, making fermented foods its richest sources.
- Natto: This traditional Japanese dish of fermented soybeans is, by far, the richest food source of MK-7, containing hundreds of micrograms per serving. Its unique preparation with Bacillus subtilis is responsible for the incredibly high concentration.
- Cheeses: Certain types of aged and fermented cheeses contain moderate amounts of MK-7 and other longer-chain menaquinones (MK-8, MK-9). Good examples include Gouda, Brie, and Edam.
- Sauerkraut: This fermented cabbage can provide a modest amount of vitamin K2, including MK-7, through bacterial activity.
The Key Differences Between MK-4 and MK-7
While both MK-4 and MK-7 are important forms of vitamin K2 with health benefits, they have distinct properties that affect how the body utilizes them. This comparison table highlights their major differences.
| Feature | Vitamin K2 (MK-4) | Vitamin K2 (MK-7) |
|---|---|---|
| Dietary Source | Animal products (egg yolks, liver, meat, butter) | Fermented foods (natto, aged cheeses, sauerkraut) |
| Production | Primarily converted from dietary K1 in animal tissues | Produced by specific bacteria during fermentation |
| Molecular Structure | Shorter side-chain (smaller molecule) | Longer side-chain (larger molecule) |
| Bioavailability | Poorly absorbed at nutritional doses, short half-life | Well-absorbed and accumulates in the bloodstream |
| Half-Life | Eliminated from the blood within hours | Remains in the body for up to 72 hours, supplying tissues longer |
| Mechanism | Rapidly utilized or stored in the liver | Stays in circulation longer, delivering K2 to extra-hepatic tissues |
Maximizing Your Vitamin K2 Intake
For optimal health, including both MK-4 and MK-7 in your diet is recommended. Because eggs contain the MK-4 form, sourcing them from pasture-raised hens can maximize your intake of this specific variant. Combining eggs with other K2-rich foods ensures a balanced approach.
- Eat Pasture-Raised Eggs: Prioritize eggs from hens that have access to outdoor pastures, as their yolks contain substantially higher MK-4 levels. One study found eggs from pastured hens contained 20% more K2 than grain-fed hens.
- Include Fermented Foods: Add natto (if you can acquire the taste), aged cheeses like Gouda, or sauerkraut to your diet to obtain MK-7.
- Pair with Fat: As a fat-soluble vitamin, K2 absorption is enhanced when consumed with a source of dietary fat. Since eggs and certain cheeses naturally contain fat, this is an easy combination to achieve.
- Consider Supplements: For those with limited access to K2-rich foods, supplements containing both MK-4 and MK-7 can be a convenient option. Always consult a healthcare provider before starting any new supplement.
Conclusion: Do Eggs Have Vitamin K2 MK-7?
To definitively answer the question, eggs contain vitamin K2, but specifically the MK-4 subtype, not the MK-7 variant. The quantity of MK-4 is highly influenced by the hen's diet, with pasture-raised eggs being a superior source compared to conventional alternatives. For those seeking the longer-acting MK-7, fermented foods like natto and aged cheeses are the best dietary choices. By understanding the distinct roles and sources of MK-4 and MK-7, you can make more informed dietary choices to support your overall health.
One study, comparing the bioavailability of MK-4 and MK-7 supplements, found that nutritional doses of MK-7 are better absorbed and lead to a significant increase in serum levels, unlike MK-4. This further solidifies the need for a varied diet that includes both food sources.
National Institutes of Health (NIH) study on Vitamin K2 bioavailability
