In Shizuoka prefecture in Japan, JA group has started an interesting practice which promotes its staff to gargle with green tea as one of the countermeasures against COVID-19. Now, the threat of COVID-19 requires the most of organizations with more strict management for public health and hygiene. For example, hospitality industry and restaurants wash various places and apparatus with alcohol more frequently. Many companies recommend their workers to wash their hands with soap more carefully. As such kind of practice, the JA group in Shizuoka recommends their staff to gargle with green tea frequently as an preventive care.
*Note : The word “tea” in this post means the tea made from shoots of tea plant Camellia Sinensis, which includes
At the present time, there are no evidences to prove the effect of tea gargling for the inhibition of COVID-19 infection, and the JA group in Shizuoka know the fact. However, the JA group seems to intend to do all they can do as far as possible. Of course, there are many reports implying that tea polyphenols might have antiviral effects against influenza[312, 751], herpes[308], calicivirus[309], HIV[310, 313] etc. based on the wide levels of evidence from in-vitro to meta-analysis. Some clinical studies indicate that tea gargling might reduce the risk of influenza. So the JA group in Shizuoka seems to expect tea gargling could have the similar effects for prevention of COVID-19.
I think their action has a high option value in this situation, where there are a few choices for us to do actually against the viral threat. The amount of vaccine for the new coronavirus is limited. The medicine specific to the viral disease has not been developed yet. Some research institutes has developed vaccine for the inhibition of novel coronavirus infection but there are little countermeasures sufficiently efficient for remediation of the new viral disease. Fortunately, Shizuoka prefecture is the biggest tea production and consumption area, which means many families have green tea in their house. Thus we can try the countermeasure of gargling with green tea with less additional cost. Even if the tea gargling will not be effective for inhibition of COVID-19, we can get the other beneficial effects from the practice, such as preventive care for flu and common cold, improvement of oral health and so on. Thus I think the less expensive treatment has a high option value in terms of real option.
In addition, Shizuoka prefectural government has been recommended gargling with green tea for students in elementary and junior high schools. The prefectural government has delivered each school the pamphlet, which describes health benefits of green tea and recommend children to gargle with green tea for preventive care against influenza and common cold, as shown below.
The pamphlet describes some beneficial effects of tea. One is daily intake of green tea can reduce the hazard ratio of death and increment in nursing care level, based on the report of the hygiene division of the Shizuoka prefectural government. Second one is richness of functional compounds such as vitamin C and catechins. The third one is the anti-viral effect of tea gargling against influenza and common cold, expressed by the cartoon at the bottom. The prefectural committee of education delivered this pamphlet with the surveillance report about dietary situation of students in their home to every education committee in each city on the late February, I’ve heard.
The cartoon of tea gargling in the pamphlet is describe in a great book “Small Encyclopedia of Tea For Children” (written in only Japanese), published in 2012 by the Shizuoka prefectural government as one of the tea education, on which the prefectural government has put a great significance.
As for the scientific aspect of the tea gargling, a series of investigation including clinical study conducted by Prof. Yamada indicate that gargling with green tea might decline the risk of influenza in wide range of age groups, as mentioned in the previous post. However the results of these research could not conclude that tea gargling can prevent influenza. For example, a randomized controlled trial of high school students resulted in the low hazard ratio 0.71 in the protocol group of tea gargling, however, the confidential interval ranged over 1 and p-value was 0.16, which indicates the difference in the risk of influenza between tea gargling group and non-protocol group is not significant [753].
Recently Ide et al.(2016) performed the meta-analysis of these investigations about tea gargling[766]. The meta-analysis based on the reports of 2 cohort researches and 3 randomized controlled trials imply that the relative risk of influenza is 0.70 at the fixed effects model with CI range between 0.54 and 0.89, and the relative risk is 0.71 at the random effects model with CI range between 0.56 and 0.91, which means the relative risk of influenza significantly declines in the group of tea gargling. Of course, we cannot absolutely conclude “tea gargling can prevent influenza infection” as the authors mentioned that they cannot avoid publication bias and additional studies are required.
At the present time, there are no clinical studies tested the effect of tea gargling against the novel coronavirus disease. Thus nobody cannot guarantee the anti-viral effect of tea gargling against COVID-19. On the other hand, as reported by China Daily, tea polyphenols might inactivate the novel coronavirus in-vitro, as conducted in Zhejian Provincial Center of Disease Control and Prevention. Although this in-vitro experimental result also cannot conclude “drinking tea or oral administration of tea polyphenols are effective as preventive care against COVID-19”, I hope this result could accelerate the further investigations testing the effects of tea constituents for the prevention of COVID-19.
Anyway tea has various health benefits including the activation of immune system as posted before, thus trying tea gargling might expect high option value as long as the additional cost is less expensive. It could be worth to try gargling with tea, I think.
At the end, I’d like to mention the extra question. Why tea drinking cannot inhibit the infection of COVID-19 in Wuhan city in Hubei province? On the next time, I’d like to consider the efficient way to inhibit viral infection using tea in terms of mucoadhesion.
< References >
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[310] Taylor-Robinson A.W. (2016) : Tea Polyphenol Extracts as a Natural Dietary Supplement to Current Treatment of HIV/AIDS, Journal of Traditional Medicine & Clinical Naturopathy, 5(2).188
[312] Nakayama M., Suzuki K., Toda M., Okubo S., Hara Y., Shimamura T. (1993) : Inhibition of the Infectivity of Influena Virus by Tea Polyphenols, Antiviral Res. 21(4):289-299.
[313] Liu S., Lu H., Zhao Q., He Y., Niu J., Debnath A.K., Wu S., Jiang S. (2005) : Theaflavin derivatives in black tea and catechin derivatives in green tea inhibit HIV-1 entry by targeting gp41, Biochim. Biophys. Acta 1723(1-3):270-281.
[750] Furushima D., Ide K., Yamada H. (2018) : Effect of Tea Catechins on Influenza Infection and the Common Cold with a Focus on Epidemiological/Clinical Studies, Molecules 23(7):1795.
[751] Yamada H., Takuma N., Diamon T., Hara Y. (2006) : Gargling with Tea Catechin Extracts for the Prevention of Influenza Infection in Elderly Nursing Home Residents: A prospective clinical study, The Journal of Alternative and Complementary Medicine, 12(7):669-672.
[753] Toyoizumi K., Yamada H., Matsumoto K., Sameshima Y. (2013) : Gargling with Green Tea or Influenza Prophylaxis: A Pilot Clinical Study
[754] Ide K., Yamada H., Matsushita K., Ito M., Nojiri K., Toyoizumi K., Matsumoto K., Sameshima Y. (2014) : Effects of Green Tea Gargling on the Prevention of Influenza Infection in High School Student: A Randomized Controlled Study, PLOS One 9(5):e96373.
[766] Ide K., Yamada H., Kawasaki Y. (2016) : Effect of gargling with tea and ingredients of tea on the prevention of influena infection: a meta-analysis, BMC Public Health 16:396.