Randomised controlled trialindependent cross-checkabstract checked★ key study I-VEG-104 in-depth review

Steady vitamin K can stabilise warfarin

Vitamin K supplementation can improve stability of anticoagulation for patients with unexplained variability in response to warfarin.

Overview

Sconce E et al.. Blood 2007 · PMID 17110451 · DOI 10.1182/blood-2006-09-049262

A daily 150 microgram vitamin K supplement more than doubled the share of unstable patients who reached stable control (19 of 35 vs 7 of 33).

Does the study support the specific claim? No · Methodological quality: moderate

Study explained simply

What did the researchers want to find out?: Test whether low-dose vitamin K stabilises warfarin control.
How was the study done?: Double-blind RCT, 6 months.
How many people, animals or samples were studied?: 70 patients with unstable INR.
What was actually found?: Vitamin K improved stability and time in range.
How large was the observed effect?: Time in range +28% vs +15%.
What do the results mean in everyday life?: A constant intake of vitamin K is not the enemy of warfarin; big swings are.
What are the study's limitations?: Small, supplement not food.
What does it say about Elawady's specific claim?: Contradicts the idea that vitamin K-containing greens in themselves destabilise therapy.
Do the results apply to Germany and Europe?: Universal.
What can explicitly not be concluded from this study?: Cannot prove that eating more greens has the same effect.

Does daily oral vitamin K (150 ug) improve stability of anticoagulation in patients with unstable warfarin control?

Study design: Randomised controlled trial – Double-blind placebo-controlled randomized trial, 6 months
Population: Warfarin-treated patients with unexplained unstable anticoagulation control
Country: United Kingdom (Newcastle; from author affiliation)
Period: not stated in abstract
Sample size: 70
Inclusion and exclusion criteria: not stated in abstract

Results: Greater decrease in SD of INR with vitamin K (-0.24 +/- 0.14 vs -0.11 +/- 0.18; P < .001) and greater increase in time in target range (28% +/- 20% vs 15% +/- 20%; P < .01). Improvement in 33/35 vs 24/33; stable control achieved in 19 vs 7 patients.
Absolute risks: not reported
Authors' conclusion: Concomitant vitamin K supplementation, perhaps by reducing relative day-to-day variability in dietary vitamin K, can significantly improve anticoagulation control in patients with unexplained instability.

Recalculated from reported counts: stable control 54.3% vs 21.2%, RR 2.56 (95% CI 1.24-5.28), NNT 3 (stats/C-VEG-12_warfarin.py).

Limits the claim: a steady, higher vitamin K intake improved rather than destabilised control; low intake is linked to instability.

Cochrane review (Mahtani 2014, not added) found insufficient overall evidence for supplementation.

Universal.

Shows that consistent vitamin K intake is compatible with stable warfarin therapy; the problem is variability, not presence of vitamin K.

Multidimensional assessment
Multidimensional assessment
Authenticity of the source	verified
Methodological quality	moderate
Risk of bias	low
Precision of results	low
Directness	indirect
Reproducibility	partly replicated
Consistency with the overall evidence	mixed
Regional transferability	high
Adequacy of the interpretation (by the archive)	not applicable

Whether consistent dietary greens give the same benefit as supplements.