was ist vitamin k3 — what are common causes?

Vitamin K3 (menadione) is a synthetic form of vitamin K not found in nature. It was formerly used in supplements and for vitamin K deficiency prophylaxis, but was banned for human use in many countries due to significant toxicity (hemolytic anemia, liver damage, oxidative stress). It is still used in animal feed. The question 'what are common causes?' is ambiguous: if it refers to vitamin K3 deficiency, there is no natural deficiency because K3 is not a dietary nutrient. Possibly the intended meaning is vitamin K deficiency (K1/K2), which can be caused by malabsorption, medications (e.g., antibiotics, anticoagulants), or liver disease. Evidence for K3 toxicity in humans is strong (hemolytic crises in infants, hepatotoxicity). The provided context does not contain information on vitamin K3; this answer is based on established medical knowledge.