Role of dietary vitamin K intake in chronic oral anticoagulation: prospective evidence from observational and randomized protocols.
OBJECTIVE
The potential association between vitamin K intake and coagulation instability has been explored primarily in case reports and small, retrospective, uncontrolled studies. We prospectively evaluated the effects of dietary vitamin K intake on anticoagulation parameters.


METHODS
In an observational protocol, clinical characteristics and vitamin K intake, assessed semiquantitatively, were evaluated in 39 outpatients who made 230 visits to our anticoagulation clinic. In a randomized crossover protocol, 12 patients with stable anticoagulation underwent 4-day in-hospital dietary interventions, 1 to 2 weeks apart, providing a 500% increase and an 80% decrease in vitamin K intake relative to the baseline level.


RESULTS
Univariate analysis of the observational data demonstrated a progressive, statistically significant inverse association between the vitamin K intake score and different levels of anticoagulation. Multivariate logistic regression analysis showed that vitamin K intake was independently associated with both overcoagulation and undercoagulation. In the randomized protocol, the international normalized ratio increased from 2.6 +/- 0.5 at baseline to 3.3 +/- 0.9 at day 7 (P = 0.005) in subjects on the vitamin K-depleted diet and decreased from 3.1 +/- 0.8 at baseline to 2.8 +/- 0.6 at day 4 (P = 0.04) in those on the vitamin K-enriched diet.


CONCLUSIONS
Our prospective data strengthen the concept that the interaction between vitamin K and coumarin is a clinically relevant, major independent factor that interferes with anticoagulation stability.
Franco
Viviane
V
Cardiovascular Division, Hospital de Clínicas de Porto Alegre and Cardiovascular Post-Graduation Program, School of Medicine, Rio Grande do Sul Federal University, Porto Alegre, RS, Brazil.
Polanczyk
Carisi A
CA
Clausell
Nadine
N
Rohde
Luis E
LE
D000284:Administration, Oral; D000925:Anticoagulants / Q000494:pharmacology*; D001777:Blood Coagulation / Q000187:drug effects*; D016022:Case-Control Studies; D018592:Cross-Over Studies; D004032:Diet; D016903:Drug Monitoring; D005260:Female; D018565:Food-Drug Interactions; D006801:Humans; D016015:Logistic Models; D008297:Male; D008875:Middle Aged; D015999:Multivariate Analysis; D019370:Observation; D010644:Phenprocoumon / Q000494:pharmacology; D011446:Prospective Studies; D014812:Vitamin K / Q000494:pharmacology*; D014859:Warfarin / Q000494:pharmacology
D000925:Anticoagulants; D014812:Vitamin K; D014859:Warfarin; D010644:Phenprocoumon