What is Vitamin K2 and How Does It Work?
Vitamin K is a family of fat-soluble vitamins, primarily found in two forms: K1 and K2. While vitamin K1 (phylloquinone) is heavily involved in blood clotting and found in leafy greens, vitamin K2 (menaquinone) plays a more significant role in regulating calcium metabolism. K2 achieves this by activating specific proteins that direct calcium to where it's needed, such as the bones and teeth, and prevents it from depositing in soft tissues like arteries and kidneys. This function is crucial for bone mineralization and maintaining healthy, flexible blood vessels.
There are several subtypes of K2, known as menaquinones (MK-n), but the two most notable for supplementation are MK-4 and MK-7.
- MK-4: Found primarily in animal products like egg yolks and meat from grass-fed animals. It has a very short half-life, meaning it is cleared from the blood quickly and requires frequent, higher doses to maintain active levels.
- MK-7: Produced during bacterial fermentation, with natto (fermented soybeans) being the richest source. MK-7 boasts a much longer half-life, allowing for consistent blood levels with a single daily dose, making it more effective for extrahepatic tissues like bones and blood vessels.
The Health Benefits of K2 Supplements
Research has highlighted several potential benefits of vitamin K2, with supplements often proving effective in addressing deficiencies common in Western diets.
Bone Health
Vitamin K2 is a crucial partner for calcium and vitamin D, as it helps activate osteocalcin, a protein that binds calcium to the bone matrix. Supplementing with K2 may significantly benefit bone quality, particularly for older adults and postmenopausal women.
- One systematic review found that K2 supplementation could reduce vertebral fractures by up to 60% and hip fractures by 77% in specific patient groups.
- Studies show that combining vitamins D, K2, and calcium can maintain or improve bone mineral density and reduce fracture risk more effectively than calcium alone.
Cardiovascular Health
K2 activates matrix Gla-protein (MGP), which helps prevent calcium from depositing in arterial walls, a major factor in heart disease. By keeping arteries flexible and clear, K2 supports healthy circulation and may lower the risk of cardiovascular events.
- A large-scale prospective study found that a higher intake of K2 was linked to a significant reduction in severe aortic calcification and coronary heart disease mortality.
- K1 intake did not show a similar benefit, reinforcing the distinct role of K2 in arterial health.
Other Emerging Benefits
Preliminary studies suggest K2's potential in other areas, although more research is needed.
- Dental Health: Research suggests K2's activation of osteocalcin may also promote the formation of dentin, supporting stronger teeth.
- Brain Health: K2 plays a role in synthesizing important brain lipids, and some studies show an association between higher K levels and better cognitive function.
Comparison of K2 Supplement Forms (MK-4 vs. MK-7)
When choosing a K2 supplement, the form matters due to differences in bioavailability and half-life.
| Feature | MK-4 (Menaquinone-4) | MK-7 (Menaquinone-7) |
|---|---|---|
| Half-Life | Short (cleared in hours). | Long (stays in blood for days). |
| Absorption | Poorly absorbed at nutritional doses. | Well-absorbed and accumulates in the body. |
| Source | Animal products (organ meats, egg yolks). | Fermented foods (natto) and some cheeses. |
| Dosage | Requires larger, multiple daily doses for effect. | Effective with smaller, single daily doses. |
| Primary Role | Known to have some specific tissue functions. | Best for consistent long-term support of bone and heart health. |
Potential Risks and Safety Considerations
K2 supplements are generally safe for most healthy individuals and have a very low potential for toxicity, with no established Tolerable Upper Intake Level. However, there are important considerations.
Interaction with Blood Thinners
Individuals taking blood-thinning medications like warfarin should consult a healthcare provider before taking K2 supplements. Vitamin K can counteract the effects of these medications, and changes in K intake must be carefully monitored. Newer anticoagulants are often not vitamin K-dependent, offering more flexibility.
Combining with Vitamin D
K2 is often combined with vitamin D3 because they work synergistically. Vitamin D enhances calcium absorption, and K2 ensures that calcium is directed to the bones and not the arteries.
Rare Side Effects
Some people may experience mild digestive upset, though this is not common.
How to Get Enough Vitamin K2
While supplements offer a direct way to increase K2 levels, prioritizing dietary intake is the best first step. The amount needed can vary, but experts suggest a daily intake of 100-300 mcg for adults is beneficial for bone and heart health.
Foods Rich in K2
- Natto: The best source, rich in MK-7.
- Hard and Soft Cheeses: Gouda, Brie, and other fermented cheeses contain MK-8 and MK-9.
- Organ Meats: Beef and chicken liver provide MK-4.
- Egg Yolks: Especially from grass-fed hens.
- Grass-Fed Butter: A good source of MK-4.
- Sauerkraut: Offers smaller amounts of K2 from fermentation.
The Role of Supplements For those unable to get sufficient K2 from diet alone, supplementation can be a practical option. Choosing an MK-7 supplement is often recommended due to its higher bioavailability and longer half-life, ensuring consistent levels in the body. Always opt for a high-quality, third-party tested product.
Conclusion: Are K2 supplements right for you?
While a healthy diet should always be the priority, the scientific evidence suggests that K2 supplements can be a powerful tool for supporting long-term health, particularly for bones and the cardiovascular system. As Western diets are typically low in K2-rich foods, supplementation offers a reliable way to address potential deficiencies. Individuals at higher risk, such as postmenopausal women or those with a history of heart disease, may benefit most from supplementation. As with any supplement, consulting a healthcare provider is essential, especially for those on blood thinners, to determine the right dosage and approach for your individual needs. By ensuring adequate K2 levels, you can support your body's ability to direct calcium to the right places, contributing to stronger bones and a healthier heart.
Vitamin K: Fact sheet for health professionals, NIH Office of Dietary Supplements
