The Fundamental Differences Between Vitamin K1 and K2
Vitamin K is a family of fat-soluble vitamins, primarily consisting of vitamin K1 (phylloquinone) and vitamin K2 (menaquinones). While they share some metabolic pathways, their sources, functions, and distribution within the body are quite different. Understanding these differences is crucial for appreciating why they are often best taken in combination.
Vitamin K1 is mainly found in green leafy vegetables such as kale, spinach, and broccoli. Its primary function is in the liver, where it acts as a cofactor for the synthesis of coagulation proteins that are essential for blood clotting. However, the body's absorption of vitamin K1 from plant sources can be relatively low, and it is rapidly metabolized and cleared from the bloodstream.
Vitamin K2 encompasses a group of subtypes known as menaquinones (MKs), with MK-4 and MK-7 being the most common. K2 is found in fermented foods like natto, certain cheeses, and some animal products, including egg yolks and organ meats. K2's primary roles are in extra-hepatic tissues, such as bones and blood vessels. The MK-7 form of K2 has a significantly longer half-life than K1, allowing it to remain in circulation for longer and reach these peripheral tissues more effectively.
Synergistic Benefits: Why Taking K1 and K2 Together Works
Because K1 and K2 have different primary target tissues and functions, consuming both can lead to more comprehensive health benefits. This is especially true for bone and cardiovascular health, where K2 appears to have a more significant impact.
Bone Health: Both forms are involved in activating proteins that support bone mineralization. However, research suggests K2 may be more effective. K2, particularly MK-7, has been shown to reduce age-related bone loss and fracture risk, especially when combined with vitamin D and calcium. A balanced intake ensures that proteins involved in both coagulation and proper calcium regulation are fully activated.
Cardiovascular Health: Vitamin K helps prevent arterial calcification by activating Matrix Gla Protein (MGP), which inhibits calcium from depositing in soft tissues like arteries. Several studies suggest that higher vitamin K2 intake, but not necessarily K1, is associated with a lower risk of coronary heart disease. Combining K1 and K2 provides benefits for both blood vessel elasticity and overall clotting function.
The Role of Vitamin D and K2
For optimal bone and cardiovascular health, vitamin D and vitamin K2 work in tandem. Vitamin D promotes calcium absorption, while vitamin K2 directs that calcium to where it's needed—the bones—and away from places it shouldn't be, like the arteries. Many supplements on the market now combine vitamins D3 and K2 for this reason.
Is It Safe to Take Vitamin K1 and K2 Together?
For most healthy individuals, taking vitamin K1 and K2 together from both dietary sources and supplements is safe. There is currently no known toxicity level for oral intake of K1 or K2, and a tolerable upper intake level (UL) has not been established.
However, there is a critical contraindication for individuals taking blood-thinning medications, such as warfarin (Coumadin). Vitamin K directly counteracts these drugs, so a consistent intake must be maintained under strict medical supervision. Any change in vitamin K intake, whether from diet or supplements, must be discussed with a healthcare provider. Some individuals may also experience mild digestive issues or rare allergic reactions.
Comparison of Vitamin K1 and K2
| Feature | Vitamin K1 (Phylloquinone) | Vitamin K2 (Menaquinones) |
|---|---|---|
| Primary Sources | Green leafy vegetables (spinach, kale), some vegetable oils | Fermented foods (natto, cheese), egg yolks, animal products, gut bacteria |
| Main Function | Activation of blood clotting factors in the liver | Regulation of calcium in extra-hepatic tissues (bones, arteries) |
| Absorption | Less efficiently absorbed from plant sources, though improved with dietary fat | Generally better absorbed, especially when paired with fat |
| Bioavailability/Half-life | Relatively short half-life (hours); less available to peripheral tissues | Longer half-life (days for MK-7); more available for extra-hepatic tissues |
| Supplement Form | Found alone or in combination products | Available as MK-4, MK-7, or combined; MK-7 is often preferred |
How to Get Both K1 and K2 in Your Diet
To ensure a comprehensive intake of both vitamin K forms, focus on a varied diet rich in both plant-based and fermented foods.
Food Sources for Vitamin K1:
- Kale
- Spinach
- Broccoli
- Brussels sprouts
- Collard greens
Food Sources for Vitamin K2:
- Natto: Japanese fermented soybeans, exceptionally rich in MK-7.
- Cheese: Hard and soft cheeses contain varying amounts of MKs.
- Egg Yolks: A good source of MK-4.
- Meat: Chicken and beef liver are notable sources.
- Sauerkraut: Another source of bacterially-derived K2.
K1 and K2 in Supplement Form
For those who have difficulty obtaining adequate K1 and K2 from their diet, supplements offer a convenient solution. Many high-quality supplements combine K1, K2 (often MK-7), and vitamin D3 to provide a comprehensive formula for bone and cardiovascular health. When choosing a supplement, look for reputable brands and consider the inclusion of fat to enhance absorption, as vitamin K is fat-soluble.
Thorne's Vitamin K, for example, includes K1 and both MK-4 and MK-7 forms of K2 in a single capsule, highlighting the benefits of combined supplementation.
Conclusion: A Holistic Approach to Vitamin K Intake
There is no need to choose between vitamin K1 and K2; the evidence shows they work together to support overall health. While K1 is the immediate go-to for blood clotting, K2 offers longer-term systemic benefits for bone and cardiovascular systems. For most people, a balanced diet rich in both plant and fermented or animal foods is the ideal approach. When diet falls short, combined K1 and K2 supplements can help fill the gap and provide comprehensive support for your blood, bones, and heart. Always consult a healthcare professional before starting any new supplement regimen, especially if you are taking medications like blood thinners.
