What is Vitamin K2 and why is it important?
Vitamin K is a fat-soluble vitamin found in two primary forms: K1 (phylloquinone) and K2 (menaquinone). While K1 is primarily involved in blood clotting, K2 plays a more significant and lasting role in directing calcium to its proper place in the body. K2 activates key proteins, such as osteocalcin and matrix Gla protein (MGP), that ensure calcium is deposited into bones and teeth while preventing its accumulation in soft tissues like arteries and kidneys. The subtypes of vitamin K2, such as MK-4 and MK-7, differ in their absorption and half-life, with MK-7 being particularly bioavailable and having a longer half-life in the blood.
The lack of a uniform RDA for vitamin K2
Despite its crucial functions, there is currently no universally established Recommended Dietary Allowance (RDA) specifically for vitamin K2. The current vitamin K recommendations from bodies like the U.S. National Academy of Medicine are based mainly on vitamin K1's role in blood clotting and do not account for K2's distinct functions in extrahepatic tissues. However, emerging research and expert consensus point toward the importance of adequate intake, especially for specific health outcomes.
General considerations for vitamin K2 intake
Experts suggest focusing on obtaining adequate vitamin K2 based on research into its extra-hepatic benefits for bone and heart health. The appropriate amount can vary depending on individual needs and health goals.
- General Adult Health: Ensuring sufficient daily intake for healthy adults is important for activating K2-dependent proteins.
- Targeted Support: For individuals with risk factors for cardiovascular disease or osteoporosis, higher levels of intake may be considered, often in conjunction with vitamin D3.
- Special Circumstances: Patients taking anticoagulant medications like warfarin need to consult a doctor before considering K2 supplements, as it can affect medication effectiveness. A doctor can provide guidance that does not interfere with blood thinners.
Food sources of vitamin K2
Unlike vitamin K1, which is abundant in leafy greens, vitamin K2 is less common in the typical Western diet. It is primarily found in animal products and fermented foods. The K2 content can vary significantly based on how the food is produced. For example, animal products from grass-fed animals typically have higher K2 levels than those from grain-fed livestock.
- Natto: This Japanese fermented soybean dish is the richest dietary source of vitamin K2 (MK-7).
- Cheeses: Fermented hard and soft cheeses, such as Gouda, Brie, and Münster, are good sources of various menaquinones (MK-7, MK-8, MK-9).
- Meat and Organ Meats: Goose liver pate, chicken liver, and fatty meats from grass-fed animals contain notable amounts of K2, particularly MK-4.
- Eggs: The yolk of eggs, especially from pasture-raised hens, is a good source of MK-4.
- Sauerkraut: Fermented cabbage can provide some K2, though it is a less potent source than natto.
Vitamin K1 vs. Vitamin K2 intake
Both forms of vitamin K are important, but they behave differently in the body. While K1 is absorbed and utilized quickly by the liver for blood clotting, K2 has a longer half-life, allowing it to circulate more widely and support extra-hepatic functions. A healthy diet should ideally include both, but given the relative scarcity of K2 in many modern diets, supplementation might be beneficial for certain individuals.
| Feature | Vitamin K1 (Phylloquinone) | Vitamin K2 (Menaquinone) |
|---|---|---|
| Primary Function | Blood clotting | Directs calcium to bones and arteries |
| Best Food Sources | Leafy greens (kale, spinach), broccoli, soybeans | Fermented foods (natto), animal fats (grass-fed dairy, egg yolks) |
| Bioavailability | Poorly absorbed, with less than 10% absorbed from plants | Better absorbed, especially when consumed with fats |
| Circulation Time | Short half-life, cleared from blood in hours | Long half-life (especially MK-7), can remain in blood for days |
| Storage Site | Primarily in the liver | Redistributes to extra-hepatic tissues like bones and arteries |
| Supplementation | Usually not necessary for healthy adults from diet alone | Often advised due to low dietary intake |
Conclusion
While an official RDA for vitamin K2 does not yet exist, a consensus among experts and research indicates that adequate daily intake, particularly of the MK-7 subtype, can support optimal bone and heart health. Since the modern diet often lacks sufficient sources of K2, increasing your consumption of fermented foods like natto and high-fat grass-fed dairy products is beneficial. For those with specific health goals or dietary restrictions, discussing supplementation with a healthcare professional is the best way to determine the appropriate approach. Proper intake of vitamin K2, in conjunction with other crucial nutrients like vitamin D, helps ensure that calcium is used effectively by the body, bolstering long-term health.
An authoritative outbound link
For more detailed information on vitamin K and its different forms, you can refer to the National Institutes of Health (NIH) Office of Dietary Supplements: https://ods.od.nih.gov/factsheets/VitaminK-HealthProfessional/
