Vitamin K2 is a fat-soluble nutrient that manages calcium within the body. While Vitamin K is often associated with blood clotting, K2—specifically the menaquinones—activates proteins that direct calcium to necessary areas, such as the bones. Understanding where to find this nutrient is important for maintaining proper bone and cardiovascular health.
Dietary Sources of Vitamin K2: MK-4 versus MK-7
Vitamin K2 is not a single compound but a group of menaquinones, with the most common and well-studied forms being menaquinone-4 (MK-4) and menaquinone-7 (MK-7). These two forms differ significantly in their food origins and how the body handles them. MK-4 is primarily found in animal products, while MK-7 is a product of bacterial fermentation.
MK-4 is present in foods like high-fat dairy, egg yolks, and organ meats, particularly liver and goose liver pâté. The amount of MK-4 in these animal sources can vary widely depending on the animal’s diet, with products from grass-fed animals often containing higher levels. However, the MK-4 found in food is generally present in smaller, less consistent amounts compared to the MK-7 levels in its primary source.
MK-7 is a long-chain menaquinone produced by certain bacteria during fermentation. The richest known dietary source is natto, a traditional Japanese food made from fermented soybeans, which contains exceptionally high concentrations of MK-7. Other fermented foods and cheeses, such as Gouda and Jarlsberg, also contain MK-7 and other longer-chain menaquinones like MK-8 and MK-9, but at much lower levels than natto.
Supplementing K2: Choosing the Right Formulation
Many people turn to supplements because obtaining consistent, meaningful amounts of K2 from diet alone can be difficult, especially for MK-7 if natto is not a regular part of their meals. Supplements offer a concentrated and convenient source, making it easier to ensure a reliable daily intake. Both MK-4 and MK-7 are available in supplement form, but they function differently once consumed.
Supplemental MK-7 is often favored because it possesses a longer half-life in the bloodstream, circulating for approximately 72 hours. This sustained presence allows for consistent activation of K2-dependent proteins with a once-daily microgram dose, typically ranging from 90 to 200 micrograms (mcg). MK-7’s stability makes it bioavailable.
In contrast, supplemental MK-4 has a short half-life, cleared from the bloodstream within six to eight hours. Because of this rapid clearance, MK-4 generally requires larger, milligram-level doses (often 45,000 mcg or 45 milligrams) taken multiple times a day to maintain steady levels. For most consumers, the convenience and bioavailability of the MK-7 form make it the more practical choice.
Maximizing K2 Intake: Absorption and Synergy
To ensure K2 is utilized, consider its fat-soluble nature. Like other fat-soluble vitamins, K2 must be consumed alongside dietary fat for absorption in the small intestine. Pairing K2-rich foods or supplements with a source of fat, such as olive oil, nuts, or full-fat dairy, enhances the nutrient’s uptake.
The effectiveness of K2 is closely linked to its relationship with Vitamin D3. Vitamin D3’s primary role is to promote the absorption of calcium from the gut, making it available in the bloodstream. Vitamin K2 then acts as a traffic controller, activating proteins that direct this absorbed calcium into the bones and away from soft tissues, such as the arteries.
Taking Vitamin D3, especially in higher doses, without sufficient K2 can increase the body’s need for K2, as more calcium is absorbed and requires management. Combining these two nutrients is a common strategy to ensure that calcium is absorbed efficiently and utilized for bone health, rather than contributing to soft tissue calcification.