was ist k3 vitamin — which blood markers matter?

Vitamin K3 (menadione) is a synthetic form of vitamin K not recommended for human consumption due to potential toxicity (oxidative stress, hemolysis). Unlike natural K1 (phylloquinone) and K2 (menaquinone), K3 is used mainly in animal feed. Blood markers relevant to vitamin K status include undercarboxylated osteocalcin (ucOC) for bone health and PIVKA-II (des-gamma-carboxy prothrombin) for hepatic function. These markers reflect overall vitamin K activity, not specifically K3. There is no established biomarker for K3 intake because it is not normally present in human circulation. For suspected vitamin K deficiency, measuring K1 and K2 levels, along with coagulation markers (prothrombin time/INR), is appropriate. Evidence for K3 in humans is weak and based on mechanistic studies. Safety note: K3 can cause hemolytic anemia in newborns and is banned for human use in several countries. Consumers should avoid self-supplementation with K3.