Blood clotting, or hemostasis, seals damaged blood vessels to prevent blood loss. This complex process involves various proteins synthesized by the liver. The single nutrient required for the functional activation of these proteins is Vitamin K. Without this fat-soluble vitamin, the body cannot produce the active components necessary to form a stable blood clot.
Vitamin K: The Clotting Catalyst
Vitamin K is a group of fat-soluble compounds, with the two most common natural forms being K1 and K2. Vitamin K1 is predominantly found in plant-based sources and is primarily utilized by the liver for blood coagulation. Vitamin K2 is found in animal products and fermented foods, and gut bacteria also produce it. While K1 is the main form involved in clotting, K2 focuses more on bone and cardiovascular health. Both forms function as cofactors for the same enzyme needed to activate clotting proteins.
How Vitamin K Activates Clotting Factors
The function of Vitamin K is to act as a necessary cofactor for an enzyme called gamma-glutamyl carboxylase (GGCX). This enzyme performs a specific post-translational modification known as gamma-carboxylation on certain proteins. This chemical reaction adds a carboxyl group to specific glutamic acid residues on the protein structure. This modification converts inactive protein forms, synthesized in the liver, into their active, functional counterparts.
The Vitamin K-dependent proteins include clotting Factors II (Prothrombin), VII, IX, and X. Once carboxylated, these factors gain the ability to bind calcium ions, which is required for them to attach to the site of injury and participate in the coagulation cascade.
If Vitamin K is unavailable, the liver still synthesizes the clotting factors, but they remain in an inactive state. This failure to activate the clotting factors directly leads to impaired blood coagulation and an increased risk of bleeding. The anticoagulant medication Warfarin works by inhibiting the enzyme that recycles Vitamin K back into its active form, effectively blocking this carboxylation process.
Where to Find Vitamin K
The primary source of Vitamin K1 in the diet is dark, leafy green vegetables, including:
- Kale
- Spinach
- Collard greens
- Broccoli
Since Vitamin K is fat-soluble, consuming these vegetables with a source of fat, like olive oil or avocado, can improve absorption.
Vitamin K2 is found in animal-sourced foods and fermented products. Fermented foods, such as the Japanese soybean dish natto, are particularly rich sources of K2. Smaller amounts are also present in cheeses, egg yolks, and meat. For adults, the Adequate Intake (AI) for total Vitamin K is approximately 120 micrograms (mcg) per day for men and 90 mcg per day for women.
Signs of Insufficient Vitamin K
Vitamin K deficiency is rare in healthy adults because it is widely available in food and produced by gut bacteria. However, health conditions and medications can interfere with its absorption or metabolism. Conditions that impair fat absorption, such as celiac disease or cystic fibrosis, are common causes since Vitamin K is fat-soluble. Long-term use of antibiotics can also disrupt the gut bacteria that synthesize Vitamin K2, lowering levels.
The most recognizable sign of a deficiency is excessive bleeding, which may manifest as easy bruising, nosebleeds, or blood in the stool. A severe concern is Vitamin K Deficiency Bleeding (VKDB). Because Vitamin K transfer across the placenta is poor, newborns are at high risk, and preventative administration is standard practice to avoid life-threatening bleeding.