Understanding Vitamin K2: More than just K1
Vitamin K is a family of fat-soluble vitamins, most commonly known in two forms: vitamin K1 (phylloquinone) and vitamin K2 (menaquinones). While vitamin K1 is abundant in leafy green vegetables and plays a critical role in blood clotting, vitamin K2 is primarily associated with promoting bone and cardiovascular health. Menaquinones, abbreviated as MKs, are the different subtypes of K2, with the most common being MK-4 and MK-7. Unlike K1, which is found in plants, K2 is predominantly found in fermented foods and animal products, and is also produced by our gut bacteria.
Fermented foods rich in MK-7
Bacterial synthesis is the primary method for producing long-chain menaquinones like MK-7, making fermented foods key sources.
- Natto: This Japanese dish made from fermented soybeans is the most potent food source of vitamin K2, with extremely high levels of MK-7. Its high concentration and high bioavailability make it a superstar source, though its slimy texture and strong flavor can be an acquired taste for some.
- Cheeses: The K2 content in cheese varies widely depending on the type, fat content, and fermentation process. Hard and aged cheeses often contain significant levels of K2, including MK-8 and MK-9.
- High K2 cheeses: Gouda, Edam, and Munster are consistently cited as excellent sources.
- Moderately high K2 cheeses: Blue cheese and cheddar also contribute notable amounts of K2.
- Kefir and Fermented Milk: Fermented milk products contain K2, with content linked to the fat content and specific bacterial cultures used in production. Full-fat versions contain significantly more K2.
- Sauerkraut: This fermented cabbage, especially when traditionally prepared with a long fermentation time, is another source of bacterially-produced K2.
Animal products providing MK-4
Animal products contain the MK-4 form of vitamin K2, which is synthesized in animal tissues. Since K2 is fat-soluble, higher fat content in animal foods generally translates to higher K2 levels.
- Organ Meats: Liver, particularly goose liver pate and beef liver, is exceptionally high in the MK-4 variant.
- Egg Yolks: Eggs from pasture-raised chickens offer more K2 in their yolks compared to conventionally raised eggs, as the hens' diet influences the nutrient profile.
- Fatty Meats: Fatty cuts of meat, including chicken thighs with skin, pork chops, and certain salami products, contribute valuable amounts of K2.
- Butter: Butter made from the milk of grass-fed cows contains a higher concentration of K2 (MK-4).
Comparing Vitamin K1 and Vitamin K2
Understanding the differences between the two main forms of vitamin K can help clarify their respective dietary sources and health functions.
| Feature | Vitamin K1 (Phylloquinone) | Vitamin K2 (Menaquinone) |
|---|---|---|
| Primary Sources | Dark, leafy green vegetables (kale, spinach, broccoli), some vegetable oils. | Fermented foods (natto, cheese) and animal products (liver, egg yolks). |
| Key Functions | Primarily involved in blood clotting processes. | Important for bone metabolism and cardiovascular health by directing calcium. |
| Bioavailability | The body has difficulty absorbing K1 from plants. | Often absorbed more readily by the body, especially the MK-7 subtype. |
| Main Subtypes | Single subtype, Phylloquinone. | Multiple subtypes (MK-4, MK-7, MK-8, etc.), based on bacteria and animal source. |
| Role with Calcium | Less direct involvement with calcium metabolism and deposition in soft tissues. | Activates proteins (like osteocalcin) to bind calcium to bone and prevent arterial calcification. |
Optimizing your K2 intake
For those looking to increase their intake of vitamin K2, incorporating a mix of these foods is beneficial. For example, vegetarians can focus on fermented options like natto, kefir, and aged cheeses, while those who eat meat can incorporate grass-fed dairy, egg yolks, and organ meats. Since K2 is fat-soluble, consuming these foods with a source of fat can enhance absorption.
Some K2-rich foods like hard cheeses and fatty meats should be consumed in moderation due to potential high saturated fat or sodium content. For Western diets where these foods may not be regular staples, supplements containing MK-4 or MK-7 are a viable option, though dietary sources are generally preferred. Individuals on anticoagulant medication, such as warfarin, must maintain a consistent vitamin K intake and should consult a doctor before making significant dietary changes.
Conclusion
Vitamin K2 is a crucial, yet often underappreciated, nutrient with distinct functions from its more common cousin, vitamin K1. Its ability to regulate calcium metabolism is vital for strong bones and a healthy cardiovascular system. While the Western diet typically offers limited K2, a variety of potent sources exist. By strategically incorporating foods like natto, aged cheeses, kefir, egg yolks, and liver into your diet, you can ensure a sufficient intake of this essential vitamin for long-term health.
Key takeaways
- Natto is the richest natural source: The Japanese fermented soybean dish provides the highest concentration of vitamin K2 (MK-7) of any food.
- Fermented dairy is significant: Aged, hard cheeses like Gouda, and full-fat products such as kefir and butter, are excellent sources of different K2 variants.
- Animal foods contain MK-4: Meat, especially organ meats like liver, and egg yolks from pasture-raised chickens are primary sources of the MK-4 form.
- Fat enhances absorption: As K2 is fat-soluble, consuming K2-rich foods alongside fats, such as cooking with butter or oil, can improve bioavailability.
- K1 and K2 have different roles: While K1 focuses on blood clotting, K2 is key for bone and heart health by directing calcium.
- Dietary choices impact K2 levels: The K2 content in animal products is influenced by the animal's diet, with grass-fed animals and pasture-raised chickens producing higher levels.
- Consider supplements if needed: For individuals with low dietary intake, particularly vegetarians avoiding natto or those who consume limited animal products, K2 supplements are an option.
FAQs
Question: Which food has the most vitamin K2? Answer: Natto, a traditional Japanese dish of fermented soybeans, is the most concentrated food source of vitamin K2, specifically the MK-7 subtype.
Question: Is vitamin K2 found in vegetables? Answer: Unlike vitamin K1, which is abundant in leafy greens, vitamin K2 is found primarily in fermented foods and animal products. Vegetables are not a reliable source.
Question: Do all cheeses have K2? Answer: No, K2 content varies significantly. Hard and aged cheeses like Gouda, Edam, and Munster tend to be higher in K2 than softer or processed cheeses.
Question: Is there K2 in eggs? Answer: Yes, vitamin K2 (MK-4) is present in the egg yolk. Eggs from pasture-raised chickens often have higher K2 levels compared to conventional eggs.
Question: Does sauerkraut contain K2? Answer: Yes, sauerkraut, a fermented cabbage dish, contains vitamin K2 produced during the fermentation process by bacteria, but levels can be lower than in natto or certain cheeses.
Question: What is the difference between Vitamin K1 and K2? Answer: Vitamin K1 is mainly found in green leafy vegetables and is crucial for blood clotting. Vitamin K2, found in fermented and animal foods, plays a key role in bone and heart health.
Question: Do lean meats contain vitamin K2? Answer: Since K2 is fat-soluble, it is primarily found in fatty cuts of meat and organ meats, not lean cuts.
Question: Can gut bacteria produce K2? Answer: Yes, certain bacteria in the human gut can synthesize some vitamin K2, but dietary intake from fermented and animal foods is the major source of functionally available K2.
Question: Should people on blood thinners watch their K2 intake? Answer: Yes, anyone on anticoagulant medication like warfarin must maintain a consistent intake of vitamin K, including K2, as sudden changes can affect the medication's effectiveness. Consult a doctor before making significant dietary changes.
