was ist vitamin k3 — when to see a doctor?

Vitamin K3 (menadione) is a synthetic form of vitamin K not approved for human supplementation due to toxicity risks (hemolytic anemia, liver damage). It is used in animal feed and as a precursor for other K vitamins. You should see a doctor if you have accidentally ingested K3 or experience symptoms such as jaundice, anemia, or unusual bleeding. Also consult a physician if you suspect vitamin K deficiency (e.g., due to blood thinners or liver disease) – but then use natural K1 or K2, not K3. Evidence for K3 in humans is weak and based on mechanistic and animal studies. Consumer DNA/nutrition tests (e.g., MyBody-X) typically cover K1/K2, not K3. Be cautious of marketing claims promoting K3.