Liquorice: could get you in to all sorts of trouble

Liquorice-lovers beware: the active ingredient in granny's favourite gums may raise your blood pressure. Even a few chews a day can increase blood-pressure levels, research from Iceland now shows.

It has been known for some time that liquorice raises blood pressure. But researchers believed that "liquorice consumption has to be almost heroic to have an effect", according to Helga Sigurjonsdottir and her colleagues of Sahlgrenska University Hospital in Goteborg, Sweden.

Not so: just a handful of sweets a day can bring about a change, the group has shown. "Liquorice-induced hypertension is underestimated and could be misunderstood," they suggest.

Munching a mere 50g of liquorice daily for 2 to 4 weeks - approximately a small tube of liquorice sweets - caused a significant rise1.

Affecting up to 20% of the UK and 25% of the North and South American population, hypertension - blood pressure over 140/90 - increases risk of a heart attack or stroke. Complex genetic and lifestyle factors play a part too, so weight loss, increased exercise, good diet and reduced salt are key steps to cutting risk.

Though on the list, liquorice's role is not always looked into. "Maybe it should be part of our routine enquiry," suggests kidney specialist Robert Unwin at Middlesex Hospital in London, recalling a hypertensive case resulting from over-indulgence in the liquorice sweets called Pontefract cakes. "The concept that you have to be eating vast quantities of Liquorice Allsorts is not necessarily true," he agrees.

Besides sweets, liquorice is added in varying quantities to chewing tobacco, gum, teas, infusions and oils. As any greedy school kid knows, "as soon as you eat too much, it's not good for you," says Daniel Henke of UK liquorice confectionery manufacturer Haribo.

A long-standing staple of Chinese medicine, raw liquorice is extracted from the plant Glycyrrhiza glabra. Its actions on the steroid system are traditionally exploited to treat conditions from inflammation to bronchitis.

Sweet and low

Liquorice excess is a well-known evil. In the late 1960s, the side effects of liquorice-derived peptic ulcer drugs revealed a whole new pathway of blood-pressure control, recalls hypertension researcher Paul Stewart of the University of Birmingham, UK.

The active ingredient, glycyrrhetinic acid, blocks breakdown of the hormone cortisol, making the kidney retain water and salt. Cortisol's role in blood pressure was previously unsuspected: "Liquorice was quite pivotal," says Stewart, who uncovered the cortisol-breakdown enzyme that it targets.

Currently, only rare cases hint at the enzyme's importance in blood pressure control: patients who have mutations in the enzyme or who eat liquorice by the sackload. Whether its activity is a common susceptibility factor in hypertension is now under investigation. "It's going to be more important than we thought," predicts Stewart.