What is Vitamin K2?
Vitamin K is a fat-soluble vitamin essential for several physiological processes, and it exists in two primary forms: K1 (phylloquinone) and K2 (menaquinone). While vitamin K1 is abundant in leafy green vegetables and is vital for blood clotting, vitamin K2 is a less common but increasingly recognized nutrient for its roles in bone mineralization and cardiovascular health. Unlike K1, which is primarily plant-derived, vitamin K2 is found in animal products and fermented foods. It is further categorized into subtypes called menaquinones (MK-4, MK-7, etc.), which differ in their bioavailability and function.
The King of K2: Natto
Without a doubt, the highest concentration of vitamin K2 in any food is found in natto, a traditional Japanese dish made from fermented soybeans. Natto contains extremely high levels of the highly bioavailable MK-7 form of vitamin K2, with over 1,000 mcg per 100 grams. The potent fermentation process using Bacillus subtilis natto bacteria is responsible for this remarkable production. However, many people find natto's strong, pungent smell and slimy texture challenging to palate. For those who enjoy it, including just a tablespoon in a meal can significantly boost K2 intake. For others, exploring alternative sources is necessary.
Significant Sources of K2 from Animal Products
Animal products are a primary source of the MK-4 form of vitamin K2. The concentration of this nutrient can be highly dependent on the animal's diet, with pasture-raised or grass-fed animals often yielding higher amounts.
Goose and Other Organ Meats
Goose liver pate is an exceptionally rich source of MK-4, containing hundreds of micrograms per 100-gram serving. Beef liver and chicken liver also provide significant amounts, making organ meats a powerful addition to a K2-rich diet for those who consume them.
Egg Yolks
The humble egg yolk is a solid source of MK-4, particularly from chickens that are pasture-raised. Studies show that egg yolks from pasture-fed hens have higher K2 content than those from conventionally raised, grain-fed hens. The K2 is primarily concentrated in the yolk, not the egg white.
Dairy Products
Different types of cheese offer varying but notable levels of vitamin K2, mainly as longer-chain menaquinones like MK-8 and MK-9. Hard, aged cheeses tend to have higher concentrations than soft or fresh cheeses due to the bacterial cultures used in fermentation and the aging process. Good options include:
- Gouda and Edam
- Cheddar
- Brie and Munster
Full-fat dairy, such as butter and whole milk from grass-fed cows, also contains respectable amounts of the MK-4 form. The fat content is key, as K2 is fat-soluble, and reduced-fat dairy products have significantly lower levels.
The Role of Fermented Foods Beyond Natto
Beyond natto, other fermented foods contribute to K2 intake, though typically in much lower concentrations. Kefir, a fermented milk drink, can provide some K2 depending on the culture and process. Sauerkraut, made from fermented cabbage, also offers a small amount of K2. While these foods may not be as potent as natto, they can still contribute beneficially to overall intake as part of a varied diet.
Dietary Comparison of Vitamin K2 Sources
| Food (per 100g) | Primary K2 Type | Approx. K2 Content (mcg) | Notes |
|---|---|---|---|
| Natto | MK-7 | >1000 | Highest known concentration |
| Goose Liver Pâté | MK-4 | ~369 | Potent MK-4 source |
| Hard Cheeses (e.g., Gouda) | MK-8, MK-9 | ~76 | Content varies by type and age |
| Soft Cheeses (e.g., Brie) | MK-8, MK-9 | ~56 | Content varies by type and age |
| Egg Yolk (pasture-raised) | MK-4 | ~32-60 | Content is diet-dependent |
| Butter (grass-fed) | MK-4 | ~15 | Fat content is key |
| Chicken Liver | MK-4 | ~12 | Organ meat source |
| Sauerkraut | MK-4 to MK-9 | ~5 | Much lower than natto |
Maximizing Vitamin K2 Absorption
To get the most out of vitamin K2-rich foods, it's beneficial to consume them alongside a source of dietary fat, as K2 is a fat-soluble vitamin. For example, cooking vegetables high in K1 with butter or oil can enhance absorption, and the K2 in dairy is already packaged with fat. The synergistic relationship with Vitamin D is also important, as adequate levels of both are needed for optimal calcium metabolism and distribution.
Conclusion
For those seeking to find what food has the most vitamin K2 in it, the answer is unequivocally natto, with an incredibly high concentration of the MK-7 subtype. However, a balanced approach to nutrition is often more practical than relying on a single food item. Fortunately, many other delicious and accessible foods are rich in various K2 forms, including aged cheeses, pasture-raised egg yolks, and organ meats like goose liver. By incorporating a variety of these fermented and animal-based foods into your diet, you can support robust bone and cardiovascular health. It's also important to consume K2 with healthy fats to ensure proper absorption and to maintain adequate vitamin D levels, as these nutrients work together for maximum benefit.
To learn more about the scientific differences between vitamin K1 and K2 and their respective impacts on health, you can consult authoritative sources such as the NIH's Office of Dietary Supplements.
