The Two Forms of Vitamin K: K1 and K2
Vitamin K is not a single compound but a group of fat-soluble vitamins, with the two most prominent forms being vitamin K1 (phylloquinone) and vitamin K2 (menaquinones). These two forms have different primary dietary sources, which is important for understanding how to get enough of this essential nutrient.
Vitamin K1 (Phylloquinone)
This form is the most common in the Western diet and is primarily derived from plant-based foods. Foods rich in vitamin K1 are easily accessible and include a wide range of vegetables.
- Green Leafy Vegetables: This is the most abundant source of vitamin K1. Examples include:
- Kale
- Spinach
- Collard greens
- Swiss chard
- Brussels sprouts
- Broccoli
- Vegetable Oils: Certain oils are significant sources, especially those used in salad dressings, mayonnaise, and margarine. These include:
- Soybean oil
- Canola oil
- Olive oil
Vitamin K2 (Menaquinones)
This form is created by bacteria and is predominantly found in fermented foods and animal products. It has various subtypes (MK-4 to MK-13), each with different properties and sources.
- Fermented Foods: The richest known source of K2 (specifically MK-7) is a traditional Japanese food.
- Natto (fermented soybeans)
- Some cheeses (e.g., Gouda, Brie, Blue Cheese) contain MK-8 and MK-9
- Sauerkraut
- Animal Products: These primarily provide MK-4, which some animals synthesize from K1.
- Organ meats (especially liver)
- Egg yolks
- Grass-fed dairy products
- Certain meats (e.g., chicken)
Why Your Body Needs Vitamin K
Vitamin K plays a critical role in several bodily functions that are vital for maintaining good health.
Blood Clotting
Its most famous function is enabling the blood to clot correctly. The body needs vitamin K to produce prothrombin and other coagulation factors in the liver. Without sufficient vitamin K, blood clotting is impaired, leading to excessive bruising and bleeding.
Bone Health
Vitamin K also plays a vital role in bone metabolism by helping the body produce osteocalcin, a protein needed for healthy bone tissue. Adequate vitamin K is necessary for the carboxylation of this protein, which helps bind calcium to the bone matrix. Some studies show a link between higher vitamin K intake and lower incidence of hip fractures.
Heart Health
Emerging evidence suggests that vitamin K can help prevent vascular calcification, or the hardening of arteries, by activating the matrix Gla protein (MGP). Inadequate vitamin K status is associated with increased calcification within arterial walls.
Comparison of Vitamin K Sources
| Food Type | Vitamin K Form | Primary Sources | Key Role | Absorption Factor |
|---|---|---|---|---|
| Plants | K1 (Phylloquinone) | Kale, Spinach, Broccoli, Vegetable Oils | Primarily liver function for blood clotting. | Lower absorption rate; improved with fat. |
| Animal/Fermented | K2 (Menaquinone) | Natto, Cheese, Liver, Egg Yolks | More active in extra-hepatic tissues, especially bone and soft tissues like arteries. | Higher absorption rate, longer-circulating. |
| Gut Bacteria | K2 (Menaquinone) | Gut bacteria synthesis | Contributes to overall K2 status, though less reliable than dietary intake. | Varies based on bacterial health and diet. |
Maximizing Vitamin K Absorption
As a fat-soluble vitamin, consuming vitamin K with a source of dietary fat can significantly improve its absorption. For example, drizzling olive oil on a spinach salad can help your body get more of the vitamin K1 present. Likewise, consuming K2-rich foods like egg yolks or cheese, which naturally contain fat, aids in absorption.
Conclusion: Diversify Your Vitamin K Intake
To ensure adequate levels for optimal health, it is best to include a mix of both K1 and K2 sources in your diet. While most people get enough K1 through vegetables, incorporating fermented foods, quality dairy, and meat products can help provide the longer-circulating K2 form. A balanced diet rich in a variety of these foods is the most natural way to meet your needs and support healthy blood clotting, strong bones, and cardiovascular health. For specific dietary concerns, especially if you are on medication, always consult a healthcare provider.
For more in-depth information on Vitamin K, the NIH Office of Dietary Supplements provides a comprehensive fact sheet.
Important Considerations
- Medication Interactions: Individuals on blood-thinning medication like warfarin need to be careful with their vitamin K intake, as it can interfere with the drug's effectiveness. Sudden changes in vitamin K consumption can alter the medication's effect, and regular, consistent intake is often recommended.
- Supplementation: Most healthy adults can meet their vitamin K needs through a varied diet. However, supplementation may be necessary for those with absorption issues or specific medical conditions. Always consult a doctor before starting any supplement regimen to determine the correct type and dose.
Key Takeaways
- Two Forms: Vitamin K exists as two main types: K1 (phylloquinone) from plants and K2 (menaquinones) from fermented and animal products.
- Plant-Based K1: Dark, leafy green vegetables like kale, spinach, and broccoli are the most common sources of Vitamin K1.
- Fermented and Animal K2: Natto is a potent source of K2, while other sources include cheese, egg yolks, and organ meats.
- Blood & Bone Health: Vitamin K is essential for proper blood clotting and supports healthy bone metabolism.
- Fat is Key for Absorption: As a fat-soluble vitamin, intake with dietary fat improves absorption, so pairing vegetables with oil is beneficial.
