To quantify glycyrrhizin's effect on the humoral response, Raphael and Kuttan measured the number of anti-body producing cells and production of antibodies in the spleen, which increased in response to treatment with glycyrrhizin.

The effect of glycyrrhizic acid on the humoral immune response in mice

It was found that white blood cell count  increased in mice treated with glycyrrhizic acid. 

The impact of glycyrrhizic acid on the white blood cells of mice

Taking licorice for a prolonged period of time can result in harmful effects, and those considering taking licorice to strengthen their immune system should consult their doctors first. Less side effects have been reported with licorice that is taken orally compared to intravenously or intraperitoneally. For certain groups of people, even a small amount of licorice can be harmful. 

Harmful side effects of licorice  

In a clinical trial by Cinatl et al., glycyrrhizin was tested on patients in a hospital in Germany who were infected with SARS-CoV. Glycyrrhizin was he most effective compound tested that inhibited SARS-CoV replication. Glycyrrhizin had a selectivity index of 67. It inhibited replication, adsorption and penetration of the virus.

Glycyrrhizin’s effect on vero cells that were  infected with SARS-CoV

Similar to SARS-CoV-2, influenza A virus (H5N1) is a viral respiratory disease that affects the lungs. Glycyrrhizin can reduce H5N1’s ability to affect IL-6 and chemokine production, and it also blocked DNA binding of the virus. For this reason, glycyrrrhizin could be a very powerful antiviral agent that should be considered for the prevention of SARS-CoV-2 infection.

Glycyrrhizin’s effect on the influenza A virus (H5N1)

Licorice contains a saponin callled glycyrrhizin, which has antiviral and immunomodulatory responsibilities. 

Santa Clara University

- Licorice 
- Garlic 
- Tea
- Ethanolic leaves extracts of the common fig 
- Hexane leaves extract of mango

Yang F. et al. state that pomegranate, black pepper, papaya, soybeans, long pepper, black caraway, barberry, European plum, Chinese box thorn and white mulberry also have immunomodulatory properties that may help prevent COVID-19. Considering their cheap price compared to other measures, consumption of these functional food plants may be a cost-effective strategy to prevent cases of COVID-19. 

Examples of functional food plants with immunomodulatory and antiviral effects that may help fight against COVID-19 

Yang, F., Zhang, Y., Tariq, A., Jiang, X., Ahmed, Z., Zhihao, Z., Idrees, M., Azizullah, A., Adnan, M., & Bussmann, R. W. (2020). Food as medicine: A possible preventive measure against coronavirus disease (COVID-19). Phytotherapy research : PTR, 10.1002/ptr.6770. Advance online publication. https://doi.org/10.1002/ptr.6770

Food as medicine: A possible preventive measure against coronavirus disease (COVID-19)

The impact of licorice on the immune system

Garlic contains bioactive sulphur-containing compounds, such as sulphoxide and polyphenols, which can strengthen the immune system. 

The impact of garlic on the immune system 

The leaves of green tea and black tea contain gallic acid, epigallocatechin gallate and quercetin, which are responsible for immunomodulatory activities. 

The impact of tea on the immune system 

Ethanolic leaves extracts of the common fig have been used in the past to fight various gastrointestinal, cardiovascular, respiratory and inflammatory problems. It was found that oral administration of the extract improved the humoral and cell-mediated immune responses. 

How ethanolic leaves extracts of the common fig benefit the immune system

In vivo oral administration of hexane leaves extract of mango resulted in immunomodulatory activity in white blood cells and bone marrow hematopoietic cells, which was seen through an increased WBC count and increased size of the thymus and spleen. 

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