Which vitamin should be avoided by patients who take warfarin?

Vitamin K should be avoided by patients who take warfarin because it plays a crucial role in the synthesis of clotting factors in the liver. Warfarin works by inhibiting the action of vitamin K, thereby reducing the blood's ability to clot. When patients consume foods or supplements high in vitamin K, it can counteract the anticoagulant effect of warfarin, leading to potential complications such as an increased risk of thrombosis (blood clots). Therefore, consistent intake of vitamin K is essential for patients on warfarin to maintain stable INR (International Normalized Ratio) levels and achieve effective anticoagulation therapy.

In contrast, the other vitamins listed—A, D, and folic acid—do not have this direct interaction with warfarin and do not significantly affect its efficacy. This is why they are generally considered safe for patients who are on this medication.