Science Questions with Surprising Answers
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Dr. Christopher S. Baird

Does licorice cause high blood pressure?

Category: Health      Published: September 3, 2013

Regular consumption of real licorice can cause dangerously high blood pressure. Public Domain Image, source: Christopher S. Baird.

Yes. Consumption of licorice (liquorice) can lead to dangerously high blood pressure and dangerously low potassium levels (hypokalemia). Licorice contains glycyrrhizinic acid, which sets off a well-understood chain reaction of biochemical events in the body resulting in high blood pressure.

In a healthy person, the kidney excretes excess potassium into the urine in response to the hormone aldosterone. Interestingly, the hormone cortisol is chemically similar enough to aldosterone that it can also make the kidneys get rid of potassium. But cortisol is not part of the aldosterone/potassium feedback loop, so the ability of cortisol to act on the kidneys is a bad thing that could lead to abnormally low potassium. To prevent this from happening, the body has a specific enzyme (HSD-11β) that breaks down cortisol in the kidney before it has a chance to hijack the aldosterone receptors. The key here is that the glycyrrhizinic acid in licorice deactivates the protective enzyme in the kidney. Without this enzyme present to break down cortisol, cortisol successfully signals to the kidneys to get rid of potassium. Because cortisol is outside of the normal potassium feedback loop, the cortisol continues to tell the kidneys to get rid of potassium even after body potassium levels have dropped dangerously low. Eating licorice therefore leads to lowered potassium levels.

Potassium is an element that becomes a strongly positively-charged ion when in a dry salt or dissolved in water. The human body takes advantage of this property by using potassium to regulate fluid balance and to pass electrical signals along neurons. Low potassium levels therefore lead to fluid inbalance and interruption of nerve transmission. The end results of licorice overdose are high blood pressure, muscle cramping, muscle pain, muscle weakness, heart arrhythmias, constipation, impaired breathing, and even paralysis and heart failure. If caught in time, taking potassium supplements and avoiding licorice can quickly return the body to healthy functioning.

The licorice discussed here is true, unmodified licorice from the licorice plant, which contains glycyrrhizinic acid. Many popular candies that are labeled as "licorice" these days either contain no true licorice (they contain artificial flavors instead) or have the glycyrrhizinic acid deliberately removed from the licorice. But some licorice candies do indeed still contain unmodified licorice. Furthermore, many herbal supplements and home remedies that list "licorice" or "licorice root" as an ingredient do contain the potentially dangerous glycyrrhizinic acid. Eating a small amount of authentic licorice on one day will not give you enough glycyrrhizinic acid to do much harm. Typically, you must eat a very large amount of licorice in one sitting (4 bags) or eat it every day for a couple of weeks before the glycyrrhizinic acid builds up enough to become dangerous. For someone who loves eating licorice or someone who is taking daily herbal pills with licorice, overdosing is very easy. A paper in the Journal of Human Hypertension states: "We now know that the effects of eating liquorice depends on the dose but prolongation of the consumption from 2 to 4 weeks does not influence the response. The maximal blood pressure rise is reached after the first 2 weeks. These results are in accordance with previous studies, which reveal that the liquorice-induced hormonal changes can be measured as soon as 1 week after the start of consumption of 100 g of liquorice."

The medical journals are peppered with accounts, such as this JAMA report, of patients eating too much licorice and ending up in the hospital:

The curious syndrome of pseudoaldosteronism caused by excessive licorice ingestion usually causes muscle weakness, hypertension, and paresis. The following case is unusual in that a previously healthy patient presented in fulminant congestive heart failure (CHF) after ingesting large quantities of licorice for one week. Report of a Case: 53-year-old man suffered shortness of breath, ankle edema, increasing abdominal girth, weight gain, headache, and weakness for one week. On the eve of his admission he sat in a chair all night, unable to sleep lying down. He had been in excellent health, was taking no medications, and had never been previously hospitalized. He had always been a heavy salt and water user. He had eaten 700 gm of licorice candy beginning nine days earlier, having consumed the last piece one day prior to admission... An x-ray film of the chest (Figure) showed the heart size to be at the upper limits of normal with pulmonary vascular congestion and a right basilar pleural effusion. With a 2-gm sodium diet and bed rest, but no medications, the patient lost 12 lb over the next four days by diuresis. Needless to say, further licorice was withheld. He became asymptomatic, the x-ray film of the chest improved, the T-wave changes on the ECG became normal, and the blood pressure returned to a normal of 128/ 80 mm Hg. Four days after admission he was discharged.

Christopher S. Baird is a physics professor at West Texas A&M University and author of the book, The Top 50 Science Questions with Surprising Answers.

Topics: aldosterone, blood, high blood pressure, hypertension, hypokalemia, licorice, liquorice, potassium