Vitamin K is an essential fat-soluble vitamin crucial for adult health, stored in the liver and fatty tissues. While most adults in the US get enough from their diet, certain conditions or medications can lead to deficiency. Beyond blood clotting, its importance for bone and cardiovascular health is increasingly recognized. This guide explores vitamin K's roles, forms, and how to ensure sufficient intake.
The Dual Nature of Vitamin K: K1 vs. K2
Naturally occurring vitamin K comes in two main forms with different sources and functions.
- Vitamin K1 (Phylloquinone): Found mainly in leafy greens and essential for activating clotting factors in the liver. It has lower absorption and is used quickly.
- Vitamin K2 (Menaquinones): Present in fermented foods and animal products, and produced by bacteria. K2, particularly MK-7, is more bioavailable with a longer half-life, benefiting tissues like bones and arteries.
Primary Roles: How Vitamin K Helps Adults
Blood Coagulation
Vitamin K is vital for activating liver-synthesized proteins (factors II, VII, IX, X) necessary for blood clotting. Deficiency impairs clotting, causing excessive bleeding. This function is why patients on warfarin need consistent vitamin K intake.
Bone Health
Essential for bone strength, especially with age, vitamin K activates proteins like osteocalcin, which helps bind calcium to bone, improving density. Low vitamin K is linked to lower bone density and increased fracture risk. Vitamin D works synergistically with vitamin K for bone health, and high-dose K2 is used for osteoporosis in Japan.
Cardiovascular Health
Vitamin K supports heart health by preventing arterial calcification. It activates matrix Gla protein (MGP), which inhibits calcium buildup in blood vessels. Arterial calcification is a major heart disease risk. Studies, like the Rotterdam Study, suggest higher K2 intake lowers heart disease risk. K2 is considered more effective than K1 for preventing arterial calcification.
Signs of Subclinical Deficiency in Adults
While severe deficiency is rare, suboptimal intake can lead to subclinical deficiency, affecting bone and cardiovascular health. Risk factors include malabsorption disorders, long-term antibiotic use, or warfarin therapy. Signs may include easy bruising, excessive bleeding, heavy periods, low bone density, or arterial stiffness.
Table: Comparing K1 and K2 for Adult Health
| Feature | Vitamin K1 (Phylloquinone) | Vitamin K2 (Menaquinone) |
|---|---|---|
| Primary Sources | Leafy green vegetables (kale, spinach, broccoli) | Fermented foods (natto, cheese), animal products (egg yolks, liver) |
| Main Function | Activates liver proteins for blood clotting | Activates proteins in extrahepatic tissues (bones, arteries) |
| Bioavailability | Lower absorption, shorter half-life | Higher bioavailability, longer half-life (especially MK-7) |
| Focus in Research | Primarily on coagulation function | Stronger focus on bone and heart health |
| Long-Term Storage | Less widely distributed and stored | More widely distributed in extrahepatic tissues |
How to Ensure Adequate Vitamin K Intake
A balanced diet usually provides enough vitamin K. Consuming K-rich foods with some fat improves absorption.
Excellent sources of Vitamin K1 include:
- Kale
- Spinach
- Broccoli
- Brussels sprouts
- Cabbage
Good sources of Vitamin K2 include:
- Natto (fermented soybeans)
- Hard and soft cheeses
- Egg yolks
- Chicken and pork
Supplements are available for those with dietary restrictions or absorption issues but should be discussed with a healthcare provider, especially if taking anticoagulants.
Conclusion
Vitamin K's benefits for adults are extensive, supporting blood clotting, strong bones, and cardiovascular health. Both K1 and K2 are important, but K2's higher bioavailability makes it particularly beneficial for bone and artery health. A diverse diet of leafy greens, fermented foods, and some animal products provides both forms, activating vital vitamin K-dependent proteins. For optimal health, a balanced diet and professional consultation are recommended.
NIH Office of Dietary Supplements fact sheet on Vitamin K
Potential Interactions
Vitamin K can interact with medications like warfarin. Consistent intake is crucial for those on these medications, and any changes should be discussed with a doctor. High doses of vitamin E can also interfere with clotting. While a balanced diet is usually sufficient, medical advice is necessary for specific health conditions or supplementation.
Considerations for Older Adults
Age can affect vitamin K levels, and its role in bone and vascular health increases with age. While the recommended intake increases slightly, older adults, especially postmenopausal women, might benefit from higher K2 intake for bone and heart health, though more research is needed.
Beyond Bone and Blood
Research is exploring new roles for vitamin K in areas like brain health, cognitive function, and immunity. The widespread presence of vitamin K-dependent proteins highlights its broad importance for overall health.
