Re: Why should a person with hypertension not eat black licorice?

Dear J:

This is a fascinating question, and one that I was introduced to in my medical school courses. We had, as a case study, a hypertensive individual that was also a habitual licorice consumer. That is the key: habitual. Having licorice once in a while is not damaging, but over time, licorice ingestion can induce pseudoaldosteronism. Aldosterone is the adrenal hormone that acts on the kidney, telling it to retain water and sodium. This hormone also induces the loss of potassium, which is exchanged for sodium in the kidney. Licorice contains glycyrrhizin, which is absorbed as glycyrrhetinic acid. Glycyrrhizin, inhibits an enzyme called 11-beta-hydroxysteroid dehydrogenase, which converts cortisol to cortisone. Cortisol, but not cortisone, binds to the aldosterone receptor in the kidney and mimicks the effects of aldosterone, which could explain the effects of licorice - a buildup of cortisol, which is recognized by the body as aldosterone. In fact, in a study by Bernardi et al (ref 3), healthy volunteers given 814mg of glycyrrhizin/day experienced hypokalemia and increased body weight (apparently due to water retention) after 1-2 weeks.

OK, so licorice causes pseudoaldosteronism. What does pseudoaldosteronism do? Kidney retention of water and sodium lead to increased blood volume. Increased blood volume leads to increased blood pressure (think of it as turning up the tap on a water hose - the more water, the more pressure on the hose). Abnormally increased blood pressure over time is called hypertension.

As a sidelight, the hypokalemia (reduced potassium) induced by licorice due to the retention of sodium over potassium, can also be dangerous. Hypokalemia is usually tolerated well by most people and is often discovered incidentially with a blood test. If serum potassium drops too low, however, people can experience muscle weakness (due to altered resting potential of the muscle cells), polyuria (lots of urine), polydipsia (lots of thirst) and in some cases can cause cardiac arrhytmias and other EKG changes, due to altered repolarization and increased automaticity.

I hope this helps!
Have a good day-
Ingrid
MadScientist

References:
1) Rose and Renke Renal Pathophysiology - the essentials Baltimore: Williams & Wilkins, 1994.
2) Lilly, Ed. Pathophysiology of Heart Disease, 2nd Ed Baltimore: Williams & Wilkins, 1998.
3) Bernardi, M et al. "Effects of prolonged ingestion of graded doses of licorice by healthy volunteers." Life Sciences 55(11):863-872, 1994.
4) Ruschitzka et al. "Endothelin 1 type a receptor antagonism prevents vascular dysfunction and hypertention induced by 11-beta-hydroxysteroid dehydrogenase inhibition: a role of nitric oxide." Circulation 103(25):3129-3135, 2001 June 26.
5) Lozano P et al. "Upper limb ischemia induced by chronic licorice ingestion." Journal of Cardiovascular Surgery 41(4):631-632, 2000 August.
6) Shibata S. "A drug over the millennia: pharmacognosy, chemistry and pharmacology of licorice." Yakugaku zasshi- Journal of the Pharmaceutical Society of Japan 120(10):849-862, 2000 Oct.