Working in long-term care, I often get questions about what foods to avoid when using the medication, Warfarin, also called Coumadin. People report that they are told to stay away from foods that are high in Vitamin K. Some also have questioned whether or not they could have leafy greens and cranberry juice. According to the Academy of Nutrition and Dietetics, the target should be to have a stable Vitamin K intake.1 A brief was conducted by Leblanc and colleagues who looked at three hundred and seventeen patients, classifying them to three groups, depending on what they were told to do when placed on Warfarin. The groups were: Limit or avoid vitamin K-rich foods, aim for a stable Vitamin K intake or no Vitamin K-related advice. The results were:
- 68% were told to limit or avoid vitamin K-rich foods
- 10% reported that they were instructed to have a stable Vitamin K intake
- 22% did note recall receiving any Vitamin-K related advice
Overall, most warfarin users reported avoiding Vitamin K-rich foods, which has caused them to have a lower than usual Vitamin K intake.1 In a different study, Li et al reported that having 250 mL of cranberry juice daily did not have any significant interactions with warfarin.2 The Academy of Nutrition and Dietetics also cautions Warfarin users to avoid herbal supplements, vitamin E and fish oil supplements as not much is known about the interactions between these items and the drug.1
Many are avoiding green vegetables and cranberry juice and this has raised the question as to whether or not there is a need for better nutrition counseling. The researchers recommend that more studies be conducted, focusing on effective counseling strategies utilizing evidence-based Vitamin K recommendations.2 Until then, RDNs should recommend maintaining a stable Vitamin K intake and avoiding vitamin E, fish oil and herbal supplements.
1) Academy of Nutrition and Dietetics. Vitamin K and Coumadin. https://www.eatrightpro.org/news-center/nutrition-trends/diseases-and-conditions/vitamin-k-and-coumadin. (eatrightPro subscription required) Accessed 5/26/2019
2) Leblanc C, Dube MP, Presse N, et al. Avoidance of vitamin K-rich foods is common among warfarin users and translates into lower than usual vitamin K intakes. J Acad Nutr Diet. 2016; 116(6):1000-1007.
3) Li Z, Seeram NP, Carpenter CL, Thames G, Minutti C, Bowerman S. Cranberry does not affect prothrombin time in male subjects on warfarin. J Am Diet Assoc. 2006;106:2057-2061.