Vitamin K consumption and anticoagulation stability in outpatients with atrial fibrillation under vitamin K antagonists

Resumo

Objective: To evaluate vitamin K intake and anticoagulation stability in outpatients with atrial fibrillation (AF) using vitamin K antagonists (VKA) in a regional Brazilian population, in which data on this association are still scarce. Methods: This was a prospective cohort study including 37 adult outpatients with nonvalvular AF on stable VKA therapy, followed at a university hospital in southern Brazil. Vitamin K intake was assessed at baseline, 30 days, and 60 days using 24-hour dietary recalls, and prothrombin time was measured and expressed as the international normalized ratio (INR). Anticoagulation stability was evaluated by time in therapeutic range (TTR) calculated with the Rosendaal linear interpolation method; TTR ≥60% was considered adequate. Continuous variables were compared using Student’s t test or the Mann-Whitney test, and categorical variables using Pearson’s chi-square or Fisher’s exact test; correlations were assessed with Spearman’s coefficient, and repeated measures were analyzed with generalized estimating equations. A P value <0.05 was considered significant. The study was approved by the Research Ethics Committee of the Federal University of Santa Maria (protocol no. 4.490.085, CAEE 40530620.4.0000) and all participants provided written informed consent. Results: The mean age was 69.0±9.9 years, and 78.4% were male. Overall, mean vitamin K intake across the three evaluations was 34.4 μg/day; only 5.4% of participants met current Dietary Reference Intake recommendations. At baseline, patients with adequate TTR (≥60%) had higher vitamin K intake than those with inadequate TTR (<60%) (median 34.8 vs. 13.9 μg/day; P=0.033). However, no significant association between vitamin K intake and TTR was observed at 30 days (median 34.3 vs. 29.8 μg/day; P=0.877) or 60 days (median 16.1 vs. 24.0 μg/day; P=0.307), nor when considering the mean intake across all three visits (median 35.9 vs. 30.4 μg/day; P=0.458). Conclusion: In this regional Brazilian cohort of AF outpatients on VKA therapy, average dietary vitamin K intake was substantially lower than recommended, and short-term vitamin K intake was not associated with anticoagulation stability as measured by TTR. These findings address a relevant knowledge gap by providing populationspecific data on vitamin K consumption and its relationship with anticoagulation control in Brazilian patients using VKA.