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Q1: I'm on warfarin, following a stroke and being warned not to eat green-leaved vegetables or anything that contributes vitamin K. I understand the ban on cranberries, liver and grapefruit but surely, greens are vital to our well being. Do we have any alternatives? John Benn.

A1: The introduction of warfarin and of anticoagulants revolutionised the outlook in patients who had blood that had the potential to clot more readily than that of the majority of other people. Giving warfarin to patients who had had ischaemic strokes, strokes that have been caused by a clot, or who had suffered a TIA (transient ischaemic attack are the small, fleeting strokes caused by wandering small clots whose symptoms pass off within 24 hours) has enormously improved the chances of long-term survival. Around 80 per cent of all strokes are caused by clots, either thrombi or emboli.

The downside of warfarin is that it increases the risk of haemorrhage from practically any part of the body. Obviously in patients who have suffered from a stroke caused by a bleed - a haemorrhagic stroke - warfarin and anticoagulation is contra indicated as it would increase the chance of bleeding. Warfarin is also not given to patients who have any other bleeding tendency or open sores, including those hidden from the eye in the stomach or intestines.

Any patient taking warfarin attends an anticoagulant clinic where their blood is regularly tested so that the correct dose can be given so as to achieve the ideal degree of, as patients say, thinning of the blood.

The anticoagulant factor, as you suggest, is indeed affected by food and drink. The most important household commodity that is liable to affect coagulation is alcohol. The golden rule, and a rule that may be lifesaving, is that patients on warfarin must drink the same amount of alcohol every day. This is the same amount come rain or shine, misery or happiness, rejoicing or mourning. If a patient settles for two tots of whisky a day he, or she, must take two tots, or its alcoholic equivalent, daily - neither more nor less.

About ten years ago I was asked to see a distinguished consultant who had obviously had a haemorrhagic stroke. He was on warfarin. I asked him if anyone had ever told him, cardiology wasn't his speciality, that he was never allowed to vary his intake of alcohol. He replied that he knew that he should take the same amount of alcohol daily but could make an exception on this occasion as it was his son's wedding. He nor you, nor any patient taking warfarin, can forget this rule whether there is a wedding, funeral, college reunion, office party or even a christening. If someone is a heavier, social drinker they could perhaps manage half a bottle of wine a day, but this must be programmed into their warfarin regime, and once programmed into it and their dose of warfarin they must drink their half bottle a day even if it is a cold, miserable lonely day.

Food is a more difficult problem. It is true that anticoagulants are vitamin K antagonists and therefore upset the clinic's calculations and the size of the dose. For this reason patients are not asked to do without all green-leafed vegetables as you suggest, for they are as you say excellent for your health. Rather patients are asked to have more or less the same amount of green vegetables daily. To a lesser extent the same advice applies to other foods. Having a menu that doesn't vary much in its nature helps to maintain regular control of your anticoagulation. Your diet doesn't have to be boring but it should be similar, as similar say as army food, boarding school food or even old-style country cooking. It can be delicious even if the surprises of gourmet cooking are removed.

Cranberries can be a problem, some authorities think the problem is exaggerated, but I recommend that my patients shouldn't take cranberries if they have been prescribed warfarin. Nor should patients take gingko biloba, ginger, appreciable amounts of garlic or ginseng. All these substances can increase the effect of warfarin and could cause a haemorrhage.

Livers could occasionally be important in patients taking warfarin, but not as you suppose the liver on your plate but to the liver in your abdomen. There have been a few very occasional instances where warfarin has upset liver function tests. For many years I have done routine liver function tests on my patients taking warfarin but have never come across any troubles. If there are changes in the liver function the good news is that once the warfarin is stopped they revert to normal.

Grapefruit is not in itself dangerous but it may interfere with the metabolism of a great many drugs as it blocks the metabolic pathway that also deals with the medication. It would be as well to change grapefruit juice for orange juice in your breakfast menu. There are a host of other drugs that are incompatible with warfarin but your doctor and anticoagulant clinic will know about these when you talk to them and check any treatment you are taking or are later prescribed to make certain that there is no clash.