Cranberry juice is used as both a refreshing drink and as a traditional method to prevent urinary tract infections. If you enjoy cranberry juice, or use it for medicinal purposes, know that it does contain a fair amount of vitamin K and may interact with certain medications.
Vitamin K Content
Vitamin K's primary role in the body is to facilitate the proper clotting of blood and without it a simple cut could cause a life-threatening loss of blood. If you have blood that clots easily you may need to be on blood thinning medications. In this case, you need to be aware of the vitamin K content of foods, as too much dietary K may interfere with your medication's ability to work properly. The USDA National Nutrient Database reports that a one cup serving of cranberry juice contains 12.9 mcg of vitamin K, which is 16 percent of the recommended daily intake.
Vitamin K and Cranberry Interaction
Cranberry juice has been reported to interact with blood thinning medications such as warfarin or coumadin. The March 2011 issue of "The Annals of Pharmacotherapy" reports a case in which consuming cranberry juice actually enhanced the effects of warfarin, a popular blood thinner. While you may assume that since cranberry juice contains a fair amount of vitamin K it would inhibit the blood thinner's ability to work properly, various studies report that cranberry juice actually increases vitamin K's effects. A May 18, 2009 report in The New York Times explains that one theory of this heightened effect may be the fact that cranberries contain compounds that deactivate enzymes that give the body the ability to break down warfarin. If you enjoy cranberry juice but are also on blood thinning medication, speak to your doctor before consuming the juice.
How Much Vitamin K Is Safe To Consume?
If you are on warfarin therapy, or taking other blood thinners, the National Institutes of Health recommends that you limit your daily consumption of foods that contain more than 60 percent of the RDI of vitamin K per serving. For example, brussel sprouts should be limited because a 1/2 cup serving contains 190 percent of the RDI for vitamin K. While cranberry juice only contains 16 percent and would not need to be limited, the fact that it may actually enhance the effects of a blood thinner make it an exception.
Other Vitamins in Cranberry Juice
While cranberry juice contains a fair amount of vitamin K, it is also high in vitamin C, with 23.5 mg or 39 percent of the RDI in a 1 cup serving. It also offers 3.0 mg of vitamin E. Both C and E are antioxidant vitamins that help protect the body from free radicals that can damage your DNA and lead to chronic disease. Vitamin A, the B vitamins and several necessary minerals round out cranberry juice's nutritional benefits.