Licorice Root for Tooth Decay, Gum Disease, and Oral Health
The Licorice Plant
Licorice is a perennial herb in the legume family—the same family to which peas and beans belong. The root of the plant is edible and is both sweet and flavorful. In addition to being eaten whole and chopped, it can be boiled in water to make an extract. This extract can be concentrated and added to foods and drinks or used to make candy, sometimes in combination with other substances. The word "licorice" is used to refer to the plant, the extract, or the candy. In the UK, the word is spelled "liquorice".
Licorice has been a popular food additive since ancient times. It's also had a long use in traditional medicine. Today it's claimed to have many health benefits. There is preliminary evidence supporting some of these claims, but for others the evidence is mixed. Research suggests that licorice may be very beneficial for oral health, however. It appears to inhibit the activity of bacteria that cause tooth decay and gum disease.
Although the future role of licorice in oral hygiene looks promising, there are potential dangers to ingesting the root or extract, especially for some people. Anyone who eats or drinks the products or who uses them in the hope of improving dental hygiene needs to be very aware of these dangers.
The scientific name of the licorice plant is Glycyrrhiza glabra. It's a member of the family Fabaceae, which is also known as the Leguminosae or the Legume family. Peas, beans, lentils, and peanuts also belong to this family. The members of the family have compound leaves and a fruit in the form of a legume or a pod.
Two Antibacterial Compounds in Licorice Root
Two antibacterial chemicals in licorice root are licoricidin and licorisoflavan A. In 2012, an international research team made some interesting discoveries that linked these chemicals to oral health. The results were published by the American Chemical Society.
The researchers found that each chemical strongly inhibited two major tooth decay bacteria—Streptococcus mutans, which is the most important bacterium involved in human tooth decay, and Streptococcus sobrinus. The chemicals also had a major inhibitory effect on two common gum disease bacteria—Porphyromonas gingivalis and Prevotella intermedia. In addition, the licoricidin moderately inhibited a third bacterium, Fusobacterium nucleatum, which is often associated with periodontal disease.
The scientists used an extract made from licorice root and tested it on bacteria that were placed in lab containers. Hopefully the chemicals obtained from the root will have the same effect in our mouths as they did in the lab. If they do, we'll need to find out how much licorice needs to be used and how long it will have to stay in contact with oral bacteria to inhibit their growth.
Trans-Chalcone and Oral Bacteria
In 2015, researchers at the University of Edinburgh examined another antibacterial compound in licorice. The researchers tested the effect of a chemical called trans-chalcone on oral bacteria. The news release from the university refers to the potential benefit of natural products for oral health, but it also says that the trans-chalcone was "related" to chemicals in licorice root. This presumably means that a natural substance was slightly altered. Even before the experiment was performed, scientists knew that licorice root contains chemicals called chalcones and that these have antibacterial properties.
The researchers found that trans-chalcone blocks an enzyme needed by Streptococcus mutans when it forms biofilms. A biofilm is a collection of bacteria embedded in a protective polysaccharide layer. Biofilms in the mouth are known as plaque. Bacteria in biofilms are much harder to attack than those outside biofilms.
The research is very interesting, but once again it was performed in lab equipment instead of in the human mouth. Lab results are sometimes the same as the results in humans, but not always. Two problems with the use of licorice products for oral health are that materials in the mouth are diluted by saliva and they are quickly swallowed. Researchers at the University of Michigan may have a solution to this problem. They used a licorice lollipop in their research project. Since the lollipop was repeatedly sucked, potentially beneficial compounds were continually added to the mouth.
Licorice Lollipops and Oral Bacteria
In a pilot study, researchers at the University of Michigan gave a small group of children sugar-free lollipops that contained a licorice extract. They found that when children at high risk for cavities sucked two lollipops a day for three weeks, the level of Streptocococcus mutans in their saliva was greatly decreased. The bacterial population stayed at a decreased level for twenty-two days after the last lollipop was sucked and then began to increase again.
In another pilot study using lollipops, the licorice extract in the candy was rich in a substance called glycyrrhizol A. In this study, people of different ages sucked two lollipops a day for ten days. Many of the people (but not all of them) showed a big decrease in Streptococcus mutans in their saliva after the treatment.
Other research suggests that licorice root extracts can reduce the inflammation involved in periodontal disease and even inhibit the bone loss that occurs in the disease. They could be very helpful for improving oral health.
The amount of licorice root that can be safely tolerated depends on body weight as well as pre-existing health conditions and life stage. Pregnant and nursing women and people with estrogen-sensitive diseases shouldn’t eat licorice.
Potential Dangers of Licorice Root Products
Black and red licorice candy rarely contain real licorice extract. They’re generally flavored with anise oil and/or artificial flavors instead of licorice. They contain a lot of sugar too, which is bad for oral health. Both licorice and anise seeds get much of their flavor from a chemical called anethole.
Real licorice candy and products are available, but caution is needed before a person starts eating or drinking these. Licorice affects blood pressure by increasing the amount of a hormone called aldosterone in the blood. Aldosterone stimulates water and sodium reabsorption in the kidneys and also stimulates potassium excretion. An excessive amount of aldosterone raises blood pressure and may lead to heart problems. It may also cause muscle weakness.
Licorice contains isoflavones, which are phytoestrogens, so it may affect the function of hormones in the body. Some evidence suggests that it lowers the testosterone level in men. Another potential problem with ingesting the substance is that it may interfere with the action of certain medications.
The European Scientific Committee on Food advises that regular glycyrrhizin doses of 100 mg/day present a risk to health, and advocate a safe average daily intake of no more than 10 mg/person/day. This is an amount equivalent to less than half a cup of liquorice tea or just 6 g of liquorice confectionary daily.— Allcock, E. and Cowdery, J, British Medical Journal
The consensus of health experts seems to be that for most people licorice is safe when used occasionally and in moderate amounts to flavor foods or drinks or to eat as a treat. The maximum amount that is safe depends on an individual's state of health. As mentioned above, some people shouldn't eat the substance at all.
People over forty who have heart disease seem to be most susceptible to health problems caused by the root or extract. Even children may be adversely affected by licorice, however, as the video below shows.
Several researchers say that up to five or six grams of licorice a day is probably safe for healthy adults. They also say that five grams a day may be too much for people who have heart disease or kidney problems, however. It seems advisable to use considerably less than this amount when using licorice for oral health, even when a product is being used as a mouthwash.
Healthy people should follow the recommended limits above and should also look at the WHO recommendations below, which are slightly different. People who have health problems such as heart or kidney problems or high blood pressure should ask their doctor about the advisability of eating, drinking, or using licorice products.
The World Health Organization (WHO) recommends a maximum intake of 2 mg glycyrrhizic acid per kg of body weight per day. The organization says this intake is unlikely to cause adverse effects, although negative effects are still possible in sensitive people. Licorice is assumed to contain 0.2% glycyrrhizic acid by weight.
Glycyrrhizin (or glycyrrhizic acid) is the main chemical responsible for the sweetness of licorice. It also seems to be responsible for many of the potentially dangerous effects of the substance. The boy described in the video above had eaten twenty licorice candies a day for four months before his seizures. This gave him a daily dose of 2.88 mg of glycyrrhizic acid per kg of body weight, which is significantly higher than the upper limit recommended by the World Health Organization.
Deglycyrrhizinated licorice products (DGL products) are available in stores. These products have had their glycyrrhizin removed and may therefore be safe. It's not known if ingesting DGL instead of whole licorice eliminates every dangerous effect or has all of the health benefits that are attributed to the whole substance.
A Licorice Poll
Do you eat licorice?
Oral Health Now and in the Future
Anything that decreases tooth decay and gum disease and is also safe to use would be a great addition to an oral hygiene routine. Oral hygiene products that are flavored with licorice root or extract already exist, but it’s unknown if they contain enough of the helpful chemicals to affect bacteria in the mouth.
Perhaps in the future we’ll be able to buy mouthwashes containing effective amounts of the antibacterial chemicals from licorice root (assuming their ability to fight oral bacteria is confirmed by more research). We may also be able to buy toothpaste and chewing gum that contain useful amounts of the chemicals. Until then, we need to be careful when eating or drinking products containing them. It would be a good idea to keep track of the amount of licorice that we’re ingesting or using in order to prevent any health problems from developing.
Dried licorice root fights oral bacteria from the American Chemical Society
Trans-chalcone and oral bacteria from the University of Edinburgh
Licorice lollipops and oral health from the European Archives of Paediatric Dentistry (abstract and preview)
Black licorice warning from the FDA (Food and Drug Administration)
Elsevier. (2015, March 2). Licorice manufacturers encouraged to state daily limit of consumption. ScienceDaily. Retrieved September 23, 2018 from www.sciencedaily.com/releases/2015/03/150302081147.htm
Licorice side effects and safety from WebMD
Allcock, E., & Cowdery, J. (2015). Hypertension induced by liquorice tea. BMJ Case Reports, 2015, bcr2015209926. http://doi.org/10.1136/bcr-2015-209926
Safe level of glycyrrhizic acid from WHO (World Health Organization)
Questions & Answers
© 2012 Linda Crampton