What is Vitamin K?
Vitamin K is a family of fat-soluble vitamins, with the two main natural forms being vitamin K1 (phylloquinone) and vitamin K2 (menaquinone). These forms are found in different foods and have distinct roles in the body.
Vitamin K's Primary Functions in the Body
Blood Clotting
Vitamin K is essential for blood coagulation as it helps the liver synthesize vital clotting factors. A deficiency impairs blood clotting, leading to excessive bleeding and bruising. Newborns receive a vitamin K injection to prevent Vitamin K deficiency bleeding (VKDB).
Bone Health
Vitamin K is crucial for activating osteocalcin, a protein that regulates calcium and its integration into bone, supporting bone strength. Low intake is linked to reduced bone density and a higher risk of fractures. High-dose vitamin K2 supplements have been studied for osteoporosis treatment.
Cardiovascular Health
Vitamin K, particularly K2, may benefit heart health by activating matrix Gla protein (MGP), which inhibits arterial calcification. This action is thought to help prevent plaque buildup and reduce the risk of heart disease. Adequate intake, especially of K2, is associated with a lower risk of coronary heart disease.
The Difference Between Vitamin K1 and Vitamin K2
| Feature | Vitamin K1 (Phylloquinone) | Vitamin K2 (Menaquinone) |
|---|---|---|
| Primary Source | Plant-based foods (green leafy vegetables, vegetable oils) | Animal products, fermented foods, and gut bacteria |
| Main Function | Primarily involved in liver-based synthesis of blood-clotting factors | Affects extra-hepatic tissues like bones and arteries |
| Best Food Sources | Kale, spinach, broccoli, collard greens, soybean oil | Natto (fermented soybeans), cheese, egg yolks, some meats |
| Bioavailability | Tightly bound within plant matrices, absorption is improved when consumed with fat | Generally considered more bioavailable for extra-hepatic tissues |
Sources of Vitamin K
Diet is the main source of vitamin K.
Vitamin K1 (Phylloquinone):
- Green leafy vegetables: Kale, spinach, Swiss chard, collard greens, mustard greens.
- Vegetables: Broccoli, Brussels sprouts, cabbage.
- Oils: Soybean oil, canola oil, olive oil.
Vitamin K2 (Menaquinone):
- Fermented foods: Natto, sauerkraut.
- Dairy products: Hard and soft cheeses.
- Animal products: Egg yolks, chicken meat, beef liver.
Potential Risks and Interactions
Vitamin K Deficiency
Deficiency is uncommon in healthy adults but can occur with conditions affecting fat absorption or from prolonged antibiotic use. Symptoms include easy bruising and excessive bleeding.
Drug Interactions
- Warfarin (Coumadin): Warfarin interferes with vitamin K's action to prevent blood clots. Consistent daily intake of vitamin K is crucial for individuals taking warfarin to maintain the medication's effectiveness.
- Antibiotics: Broad-spectrum antibiotics can reduce gut bacteria that produce vitamin K.
- Other drugs: Some cholesterol-lowering drugs and weight-loss medications can also decrease vitamin K absorption.
Toxicity
Natural forms of vitamin K (K1 and K2) are not known to be toxic, and no upper intake limit is set. The synthetic form (K3) is toxic and not used in human supplements in the US.
Conclusion
Consuming vitamin K through a balanced diet is vital for several bodily functions, including blood clotting, bone mineralization, and preventing arterial calcification. The two primary forms, K1 and K2, highlight the value of a diverse diet. Most healthy adults get enough vitamin K from food, and supplements are generally not needed unless recommended by a healthcare provider, especially for those on anticoagulant therapy like warfarin. Maintaining a consistent intake supports proper coagulation and long-term bone and heart health.
