For Health Care Practitioners:
It was previously thought that consistent amounts of vitamin K through supplementation would not affect International Normalization Ratio (INR); however, new research proves otherwise (1). Case studies and controlled clinical trials demonstrate that even small doses of vitamin K at 25 micrograms (mcg) consumed through a multivitamin can interfere with INR (2).
Most daily multivitamins contain at least 25 mcg of vitamin K, a relatively small dose, and the CDC concludes that over half of Americans take a multivitamin (3, 4). Kurnik et al. examined the influence multivitamins with 25 mcg of vitamin K have on INR in patients taking warfarin. After 4 weeks of consuming one multivitamin with 25 mcg of vitamin K at the same time daily, study participants had subtherapeutic INR’s. This demonstrates that small changes in vitamin K intake can alter coagulation and that taking a multivitamin with vitamin K will affect INR (5). Even when vitamin K is ingested in a liquid form supplement, it still reveals alterations in INR (6-8). Thus, the addition or elimination of a multivitamin with even small amounts of vitamin K to patients on warfarin will likely affect their INR.
The research cited above was the driving force behind the development of K Free Daily. It was created by a Pharm.D. and an MS,RD (Masters of Science, Registered Dietitian), who regularly work with patients struggling to maintain a consistent INR even without vitamin supplementation. Many patients expressed a desire to take a daily multivitamin and were told it would be unwise because of the likely changes in INR that would ensue from starting, stopping, or missing even a single dose of their multivitamin. K Free Daily is formulated without vitamin K, soy or niacin, and with clinically-proven safe levels of vitamin E, vitamin C and magnesium when studied in patients taking warfarin. It is the only multivitamin that patients on warfarin can stop and start sporadically without concern for their INR. With the exception of vitamin K and niacin, K Free Daily includes all the essential vitamins and minerals found in the leading multivitamin brands.
Concerns In Elderly Patients
Along with an increase in lifespan, the number of patients prescribed warfarin is also on the rise. Nearly 10% of all patients in their 80s have atrial fibrillation (9). The hidden sources of vitamin K in over-the-counter multivitamins pose a concern for elderly individuals as it can substantially increase total daily vitamin K intake (10).
Research Supporting the Nutrients in K Free Daily
Due to the known interactions between warfarin and common nutrients found in many over-the-counter supplements including Green Tea, Soy, Fish Oil, Garlic, Niacin, and Coenzyme Q10, those nutrients are completely eliminated from K Free Daily (6, 11, 12).
Some studies indicate there may be a mild interaction between warfarin and very high doses of vitamin C and vitamin E (12-14). Therefore, K Free Daily contains moderate amounts of those nutrients at levels considered safe for patients taking warfarin based on current research (1, 2, 5). This supplement provides just enough of these nutrients to prevent a deficiency and far less than the amounts thought to pose any risks to patients on warfarin.
Studies demonstrate high doses of vitamin C (>5-10 g/day) interact with coagulation; K Free Daily contains 60 mg of vitamin C. Studies show high doses of vitamin E (≥ 1200 IU/day) may affect INR (13) while intakes of Vitamin E at 400 IU has no interaction with INR (14); K Free Daily contains 10 IU. Vitamin A supplementation in rats have shown to cause abnormal bleeding but no such results have been seen in humans and toxicity of Vitamin A has not been shown to cause abnormal bleeding in humans (12). To err on the cautious side, K Free Daily contains 2000 IU of vitamin A (50% as Beta Carotene), which is 40% of the recommended daily intake. Some studies suggest magnesium and zinc may decrease the absorption of warfarin due to the binding of the minerals to warfarin if taken within 2 hours of each other; therefore, as stated on the product label, we suggest taking K Free Daily at least 2 hours before or after administration of warfarin (15).
K Free Daily is United States Pharmacopeia (USP) grade and developed in a facility that abides by Good Manufacturing Practice (GMP) standards. USP is a governing agency that sets guidelines for dietary supplements to assure the material meets specific standards. GMP is a testing procedure that occurs in the manufacturing facility to help ensure the quality of the product.
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