This blog post examines the scientific basis for how vitamin K plays a crucial role in the blood clotting process and why deficiency can lead to bleeding that doesn’t stop easily, even from small wounds.
Most people have experienced falling and getting hurt while playing on the playground as children. If the wound isn’t severe, they often don’t think much of the bleeding and continue playing. This is because, surprisingly, the blood doesn’t keep flowing but quickly clots and hardens. Our bodies activate a sophisticated mechanism called blood coagulation to prevent excessive bleeding, and the key substance that promotes this reaction is vitamin K. So, what kind of substance is vitamin K, and through what chemical reactions does it aid blood coagulation?
Vitamin K (chemical formula: C31H46O2) is a fat-soluble vitamin, generally classified into three types: K1, K2, and synthetic vitamin K. Here, “K” stands for the Danish word “Koagulation” (coagulation), originating from the naming convention of the scientist who first identified the link between vitamin K and blood clotting. Vitamin K is an essential nutrient for the human body, deeply involved in blood clotting and bone formation, despite requiring only a very small daily intake. Since K1 and K2 are found in plant and animal foods or synthesized by gut bacteria, vitamin K deficiency is rare in healthy adults. However, because vitamin K primarily acts in the liver, individuals with impaired liver function may experience difficulties with blood clotting. Meanwhile, synthetic vitamins K3, K4, and K5 exhibit toxicity when taken in excess. Their current use is limited to applications such as pet food additives, mold inhibitors, or food freshness preservation. Notably, K3 is banned for medical use due to human toxicity concerns, a fact repeatedly confirmed by recent research and regulatory standards.
Vitamin K’s function in the blood coagulation process involves a complex series of reactions, primarily participating in the liver’s production of prothrombin (Factor II), an essential coagulation factor. The most fundamental role of vitamin K is to convert glutamic acid residues. Glutamic acid is one of the amino acids that make up proteins. Vitamin K adds a carboxyl group (-COO-) to it, converting it into gamma-carboxyglutamic acid. Gamma-carboxyglutamic acid possesses two carboxyl groups on its gamma carbon, which carry a negative charge and stably bind calcium ions (Ca²⁺) like a clamp. Gamma-carboxyglutamic acid bound to Ca²⁺ helps coagulation proteins attach to and function on the inner walls of blood vessels, enabling rapid and efficient blood clotting.
Most people believe platelets directly perform hemostasis, but in reality, when an injury occurs and platelets are destroyed, a protein called fibrin is produced. This fibrin envelops the platelets, forming a gel-like coagulation mesh that suppresses bleeding. Fibrin forms a network as small units gradually assemble, firmly anchoring platelets and suturing the vascular wound like sealing it with stone. The enzyme producing this fibrin is thrombin, which is prothrombin activated through a phosphorylation process. Thrombin generation occurs through a cascade of catalytic actions performed by coagulation factors such as Xa, IXa, XIa, and XIIa, amplifying the blood clotting signal.
A key point in this cascade reaction is that gamma-carboxyglutamic acid (GCA) plays an essential role at each stage. For coagulation factors like XIIa, XIa, IXa, Xa, and thrombin to activate, they absolutely require gamma-carboxyglutamic acid and Ca²⁺ ions as catalysts. Therefore, without gamma-carboxyglutamic acid, coagulation factors cannot exist either. Consequently, prothrombin, thrombin, and fibrin are not produced, preventing the blood coagulation process itself from occurring. Vitamin K is the substance that plays a crucial role in the production of this vital gamma-carboxyglutamic acid.
Vitamin K deficiency can impair blood clotting ability, leading to internal bleeding or a tendency to bleed. Even minor impacts can easily cause bruising, bleeding may not stop readily, or bone density may decrease, increasing the risk of fractures. As mentioned earlier, deficiency cases in healthy adults are rare. However, individuals with impaired liver function due to alcoholism, fetuses with restricted nutrient supply, or newborns with disrupted gut microbiota balance are at high risk of vitamin K deficiency. Newborns, in particular, have insufficiently developed gut microbiota. Consequently, many countries routinely administer a vitamin K injection immediately after birth. This practice has become an established international medical guideline for preventing neonatal hemorrhagic disease.
To address such risks, the biochemistry field has synthesized and purified vitamin K, leading to the development and production of vitamin K supplements and ointments. Furthermore, recent research indicates that vitamin K is gaining attention not only for its blood clotting function but also for its potential to inhibit Alzheimer’s disease progression, regulate insulin action, and provide antioxidant effects. Research on this essential substance for the human body continues to expand, and its outcomes will continue to make significant contributions to enhancing human health.
