Vitamin D and Warfarin Interaction

Mechanism of Action and Potential Interaction

Warfarin works by inhibiting vitamin K-dependent clotting factors through inhibition of the vitamin K epoxide reductase enzyme complex, preventing the regeneration of vitamin K, according to the American College of Cardiology 1
Unlike vitamin K, vitamin D operates through different physiological pathways and does not directly interfere with warfarin's mechanism of action, as stated by the American College of Cardiology 1

Vitamin K directly counteracts warfarin's effect and can significantly reduce INR when consumed in varying amounts, as reported by the American College of Cardiology [2] [3]

Unlike vitamin K intake, vitamin D supplementation does not require the same level of dietary restriction to maintain stable anticoagulation, according to the American College of Cardiology [2] [3]

Medications that significantly interact with warfarin include antibiotics and amiodarone, which can potentiate warfarin's effect, as noted by the American College of Cardiology [4] [5]
Barbiturates, rifampicin, and carbamazepine increase hepatic clearance of warfarin, reducing its anticoagulant effect, as reported by the American College of Cardiology [4] [5]
Dietary vitamin K from green vegetables or supplements can significantly counteract warfarin's effect, according to the American College of Cardiology [2] [3]
Maintaining consistent vitamin K intake is more important for stable anticoagulation than restricting vitamin D, as stated by the American College of Cardiology [2] [3]

Patients should not be counseled to confuse vitamin D with vitamin K when discussing dietary restrictions while taking warfarin, as advised by the American College of Cardiology [2] [3]