Why Vitamin K Matters
Vitamin K is required by the liver to produce several clotting factors (II, VII, IX, X). Deficiency causes bleeding tendency, measured indirectly through prolonged prothrombin time (PT/INR) rather than direct vitamin K blood testing, which isn't routinely available.Causes of Deficiency
- Newborns (immature gut, low placental transfer) — routine vitamin K injection given at birth
- Malabsorption conditions (coeliac disease, cystic fibrosis, bile duct obstruction)
- Long-term broad-spectrum antibiotic use (kills gut bacteria that produce vitamin K)
- Severe liver disease (impaired synthesis of clotting factors even with adequate vitamin K)
Vitamin K and Warfarin
Warfarin works by blocking vitamin K's clotting function. This is why consistent (not necessarily low) vitamin K intake matters for people on warfarin — sudden increases in vitamin K-rich foods (leafy greens) can reduce warfarin's effectiveness, while decreases can dangerously increase INR.Newborn Vitamin K InjectionThe vitamin K injection given to newborns shortly after birth prevents a rare but serious bleeding disorder (vitamin K deficiency bleeding/haemorrhagic disease of the newborn) — this is a well-established, evidence-based practice recommended by all major health authorities.
Is there a direct blood test for vitamin K levels?
Direct vitamin K level testing exists but is rarely used clinically — PT/INR is the practical, widely available test that reflects vitamin K-dependent clotting function.
Should I avoid green vegetables if I'm on warfarin?
No — you should eat a consistent amount of vitamin K-rich foods rather than avoiding them, as sudden dietary changes (either direction) are what causes INR instability.
Medical Disclaimer: This page is for general education only and does not replace professional medical advice. Always consult a qualified healthcare provider.