No need to restrict dietary vitamin K intake in patients on warfarin, say researchers

Increasing dietary vitamin K intake may be beneficial in patients taking warfarin, according to new research.

Vitamin K is found in green leafy vegetables, including broccoli, spinach and lettuce. | GETTY IMAGES
Vitamin K is found in green leafy vegetables, including broccoli, spinach and lettuce. | GETTY IMAGES

In a randomised controlled trial examining the effect of dietary intervention in patients on warfarin, increasing intake of vitamin K-rich foods resulted in more stable anticoagulation.

The Canadian trial, presented at the 2019 meeting of the American Society for Nutrition in Baltimore on 11 June, recruited patients treated with warfarin for at least 6 months who had a history of anticoagulation instability.

Approximately half of the patients were randomised to receive general dietary counselling and cooking lessons, and the other half were randomised to receive counselling and cooking lessons specifically aimed at increasing their dietary intake of vitamin K by ≥150 microgram per day.

The primary endpoint, stable anticoagulation, was defined as more than 70% of time spent in the therapeutic INR range from weeks 4 to 24.

A total of 49 participants completed the study. After 6 months, 14 of the 28 patients (50%) counselled to increase their vitamin K intake had stable anticoagulation levels, compared with 4 of the 21 patients (19%) who received general nutritional advice (p=0.026).

'I think all warfarin-treated patients would benefit from increasing their daily vitamin K intake,' said lead study author Guylaine Ferland, professor of nutrition at the University of Montreal. 'That said, given the direct interaction between dietary vitamin K and the action of the drug, it is important that (higher) daily vitamin K intakes be as consistent as possible.'

Ferland added: 'Our hope is that healthcare professionals will stop advising warfarin-treated patients to avoid green vegetables.'

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