The hazards of brussels sprouts consumption at Christmas

A man in Scotland with chronic heart failure and severe left ventricular systolic dysfunction caused by coronary artery disease received a HeartMate II (Thoratec) left ventricular assist device (LVAD) as a bridge to transplantation. In line with standard practice, he was anticoagulated with warfarin. The target international normalised ratio (INR) was 2.0 (reference interval, 1.8–2.2). Stable anticoagulation was achieved with a daily dose of 7 mg.

Four months later, in the weeks before Christmas, his INR was persistently subtherapeutic despite escalating doses of warfarin (Box). He was counselled about the importance of concordance with drug therapy and told to avoid green leafy vegetables, specifically brussels sprouts, which he admitted to enjoying over the festive season. The problems with anticoagulation did not resolve and he was readmitted to hospital 3 days after Christmas for parenteral anticoagulation with low molecular weight heparin and assessment of his response to directly observed warfarin therapy. His INR rose to 2.8 within 3 days of readmission, but there were no bleeding complications. He consumed a standard hospital diet during this readmission. On specific questioning, he admitted to consumption of 15–20 brussels sprouts on 3–4 occasions per week in the period before readmission. His warfarin requirement returned to baseline once this dietary indiscretion was corrected.

Warfarin inhibits the enzyme vitamin K1 epoxide reductase, decreasing the amount of reduced vitamin K1 that is available for carboxylation of coagulation factors II, VII, IX and X. The action of warfarin may be antagonised by ingestion of foods rich in vitamin K1. Brussels sprouts (Brassica oleracea) have a vitamin K1 content of 140.3 μg per 100 g after preparation by boiling.1 The mass of a typical brussels sprout is 10–15 g. We estimated that our patient consumed 0.6 to 1.7 mg of vitamin K1 per week, depending on sprout mass, portion size and ingestion frequency. This is a relatively small amount of vitamin K1 compared with the recommended 2.5–5 mg oral dose of vitamin K1 for reversal of a high INR without spontaneous bleeding. However, brussels sprouts have additional effects on warfarin pharmacokinetics. In a trial involving 10 healthy subjects, a diet including 400 g of brussels sprouts per day for 2 weeks stimulated warfarin metabolism, with a 29% increase in mean elimination rate constant.2

A previous report showed that a patient maintained on high-dose warfarin developed bleeding complications due to a high INR during a hospital admission because her usual vitamin K1-rich diet was unavailable in hospital.3 Patients have also experienced thrombotic complications due to a low INR because of consumption of other vitamin-K1-rich foods, including broccoli, lettuce and wild turnip greens.4,5 We believe this is the first description of a festive-season hospital admission caused directly by the consumption of brussels sprouts.

Finally, a detailed dietary history from our patient was notable for an absence of cranberry sauce over the festive period. Widely recognised as a traditional Christmas “trimming”, its well described potentiating effects on warfarin via inhibition of the cytochrome P450 system might have served to offset the procoagulant action of the sprouts.6 However, this strategy has not been subjected to a rigourous clinical trial and, while cranberry juice has attained popularity as a urinary deodoriser, its ability to counteract the malodorous sequelae of excessive sprout ingestion has not, to our knowledge, been demonstrated. We were therefore compelled to advocate a policy of strict abstinence (“nowt sprout”) pending further investigation of alternative approaches.

Excessive consumption of brussels sprouts can antagonise the action of warfarin and may precipitate admission to hospital. Doctors and patients should be aware of this possibility. Doctors should consider counselling patients who must remain anticoagulated at all times, such as those with LVADs or mechanical valve replacements, against excessive consumption of this traditional Christmas fare.

International normalised ratio (INR) and warfarin dose* before the patient’s readmission

* The warfarin dose is the mean of five daily doses, taken around each INR measurement.