A black treat made from the dried root of a Mediterranean plant, liquorice can be sweet, salty or slightly bitter. Its characteristic flavour comes from the chemical compound glycyrrhizin, which is much sweeter than table sugar.
As tasty as it may be (many people can't stand it though), overconsumption of liquorice can cause health problems. So can ingesting too much sal ammoniac (ammonium chloride), which is used in salty liquorice.
What are the possible adverse effects of liquorice? Who's especially at risk? And how much is safe to eat?
"To answer the question of liquorice's harmfulness, you've first got to distinguish between children's and adult liquorice," says Dr Christian Schulze, a professor of pharmaceutical biology at the University of Greifswald in Germany.
"Children's liquorice hardly contains any of the potentially harmful substance glycyrrhizin," he says, explaining that under European Union law, the maximum permissible amount of glycyrrhizin in a 100 g liquorice product is 200 mg.
While the exact amount doesn't have to be stated on the package, he points out, eating normal quantities of children's liquorice isn't seen to be harmful. But this doesn't mean that it's OK for kids to eat as much of it as they want.
"As to the ingredients of children's liquorice, what I find much more concerning - and which is always overlooked - is the high sugar content," says Dr Martin Smollich, head of the Institute for Nutritional Medicine's working group on pharmaconutrition at the Lübeck campus of Schleswig-Holstein University Hospital in Germany.
Sugar is the main ingredient in liquorice products. "In addition are sugar syrup and often sal ammoniac - ammonium chloride, in other words. Mainly for this reason, children as well as adult risk groups shouldn't overindulge in liquorice," Smollich says.
Sal ammoniac, also known as salmiac salt, is what gives salty liquorice its salty, astringent taste - chiefly in adult liquorice. Schulze warns that it can upset children's mineral balance and trigger symptoms such as nausea or vomiting.
Adult liquorice contains more glycyrrhizin than children's liquorice does, and it can also cause health problems in both adults and children. "Elevated doses of glycyrrhizin and sal ammoniac in adults can set off a chain of side effects," Schulze says.
Glycyrrhizin is broken down after ingestion into glycyrrhetinic acid, which can cause cortisol levels in the kidneys to rise. This affects mineral metabolism: Sodium accumulates and potassium is lost.
As a result, says Smollich, "blood pressure can rise, and there may be fluid retention in the joints and face. What's more, muscle weakness can occur and the concentration of potassium in the blood may be disrupted."
People with congestive heart failure should therefore consume adult and salty liquorice with caution. The same goes for anyone who takes a cortisol preparation, has high blood pressure or must keep an eye on their fluid and mineral/salt balance, perhaps because they take a diuretic.
"For all of these people, consuming a normal amount of liquorice can be dangerous," Schulze warns. The precise amount at which glycyrrhizin becomes toxic varies from person to person and depends, among other things, on height and weight along with eating and exercise habits.
Germany's Federal Institute for Risk Assessment (BfR), whose stated mission is the protection of human health, recommends consuming no more than 100mg of glycyrrhizin daily.
According to Smollich, "no health effects can be expected unless you habitually ingest more than 200 mg of glycyrrhizin daily. To reach this amount, you'd have to eat 200 g of customary liquorice or 25-100 g of adult liquorice daily" - quite a lot even for true liquorice lovers.
Only for the aforementioned risk groups can even small amounts of liquorice cause health problems, he says. To be on the safe side, he advises eating no more than several pieces at a time and not, say, half the package in one sitting.
Does liquorice contain any substances beneficial to health? Schulze answers in the affirmative: "Liquorice juice contains flavonoids, which can have positive effects on health." Flavonoids are secondary plant metabolites, and research has shown them to have anti-inflammatory properties, for example.
"However," he adds, "in order to get the positive effects, you'd have to eat so much liquorice that they'd be outweighed by the harmful effect of glycyrrhizin."
