June 13, 2019
By Megan Brooks
NEW YORK (Reuters Health) - Increasing dietary vitamin K intake can help stabilize anticoagulation therapy in patients taking warfarin with a history of instability, according to results of a randomized controlled trial.
"Results from this study and previous supplementation trials provide reasonable evidence for thinking that warfarin-treated patients would benefit from intakes that minimally meet the daily recommend intake (90 and 120 ug/d for women and men, respectively). In our study, participants from the vitamin K intervention group consumed about three times the DRI," lead investigator Dr. Guylaine Ferland, professor of nutrition at University of Montreal and scientist at the Montreal Heart Institute Research Center, told Reuters Health by email.
Dr. Ferland presented the study findings June 11 at the American Society for Nutrition (ASN) annual meeting in Baltimore, Maryland.
The study included 46 patients who were on warfarin for more than six months, had a target international normalized ratio (INR) range of 2.0 to 3.0 or 2.5 to 3.5, and percent time in therapeutic range (%TTR) of less than 50% in the past six months.
Half were randomly allocated to a vitamin K (VK) intervention group and half to a control group. The VK group received dietary counsel to increase their VK intake by at least 150 ug/day through specific food choices, recipes and cooking strategies. The control group received general dietary information.
Warfarin therapy was monitored weekly by INR. The primary clinical outcome was anticoagulation stability as defined by %TTR ˃70% during weeks 4 through 24.
According to the authors, the %TTR over the assessment period was 67.7 for the VK group and 61.4 for the control group, a nonsignificant difference. However, increasing dietary VK intake resulted in a significantly greater proportion of patients with %TTR ˃70% over the assessment period (50% vs. 20%, P=0.026).
"Our hope is that healthcare professionals will stop advising warfarin-treated patients to avoid green vegetables," Dr. Ferland said in a conference statement.
She told Reuters Health, "Concerning changes in clinical practice, sample size for our study was somewhat small (23 patients in each group) so confirming the results in a larger size study would be optimal. That said, our diet intervention did not lead to any serious adverse events so there would not be obvious counter indication for applying it in light of current evidence."
Dr. Ferland emphasized that higher vitamin K intakes "should also be consistent one day to the next. Aiming for consistent daily vitamin K intake is what is currently recommended to patients on warfarin, however reality if often quite different."
Dr. Zhaoping Li, director of the Center for Human Nutrition at David Geffen School of Medicine at UCLA, in Los Angeles, who wasn't involved in the study, said the findings are important and will likely come as a surprise to most clinicians.
"Physicians and registered dietitians have been recommending patients to avoid green leafy vegetables so that their INR can be stable. Those are the very patients who would benefit from fruits and vegetables tremendously," Dr. Li told Reuters Health by email.
Would the same be true in patients who are already fairly stable on warfarin? "Most likely," said Dr. Li, but "the study didn't directly test those patients."
The study was funded by the Canadian Institutes of Health Research (CIHR). The authors have no relevant disclosures.
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