The virus that causes COVID-19 primarily spreads through the saliva of infected individuals, including asymptomatic carriers. Saliva containing the virus is released when talking, sneezing, or coughing, forming droplets and aerosols that disperse into the air.
Professor Osam Mazda and his research team at Kyoto Prefectural University of Medicine in Japan believe that inactivating the virus in saliva is crucial for preventing COVID-19. Therefore, they explored various foods and ingredients that may inactivate the strain of SARS-CoV-2 responsible for COVID-19.
The research team published the new study on Oct. 3 in Scientific Reports, indicating that green tea, matcha, and black tea rapidly and effectively inactivated some Omicron subvariants.
One of the experiments in the study involved seven healthy volunteers who consumed candies containing green tea, black tea, or no tea components, and had their saliva subsequently collected. Researchers found that saliva collected immediately after consuming candies containing green or black tea had high concentrations of tea polyphenols, including epigallocatechin gallate (EGCG) and theaflavin digallate. When researchers mixed saliva samples with the early Omicron virus strain BA.1 for 10 seconds, they observed rapid inactivation of the virus by saliva containing tea polyphenols. However, the virus-inactivating effect gradually diminished between 5 and 15 minutes after the cessation of the candy.
The research team believes that if infected individuals consume candies containing green tea or black tea, it may be useful in inactivating the virus, decreasing the virus load in the oral and gastrointestinal tracts, and preventing the virus from spreading to nearby noninfected individuals.
Another experiment involved steeping black tea, green tea, or matcha in hot water and subsequently mixing the virus suspension with the tea beverages for 10 seconds, followed by assessing the virus’s virulence. The results revealed that the infectivity of the BA.1 and other Omicron subvariants—meaning their ability to establish an infection—decreased to less than 1 percent.
Not only does freshly brewed tea have virus-inactivating effects, but bottled green tea beverages purchased from grocery stores also significantly reduced the infectivity of Omicron subvariants BA.1, BA.5, and BQ.1.1, although they weren’t effective against BA.2.75.
The study also found that different Omicron subvariants have varying sensitivity to tea polyphenols. For instance, EGCG at a concentration of 1000 micromolars can inactivate more than 99 percent of the BA.1 and BA.5 viruses. However, the BA.2, BA.2.75, XBB.1, and BQ.1.1 viruses remained infectious at the same EGCG concentration.
Black tea, produced by oxidizing green tea leaves, exhibits a vibrant reddish-orange color due to the transformation of tea polyphenols into theaflavins in the tea leaves. The researchers treated various Omicron viruses with theaflavin concentrations similar to those found in black tea and observed a significant reduction in the virulence of BA.1, XE, BA.5, XBB.1, and BQ.1.1 viruses. However, the same theaflavin concentration had little effect on BA.2 and BA.2.75.
The research also found that the antiviral mechanism of EGCG is to render the virus inactive, so when used to treat cells, it doesn’t induce antivirus effects in the cells.
Catechins Inhibit Virus Replication
In addition to binding to the virus’s spike protein and rendering it noninfectious, previous research has revealed other antiviral properties of tea polyphenols. Researchers at National Taiwan Normal University discovered through animal studies that catechins can inhibit coronavirus replication, increase the potential of adaptive immunity, and improve acute lung injuries.While drinking green tea can provide catechin intake, the dosage might not be sufficient to inhibit the virus, Mr. Chien noted. Furthermore, the catechins used in the experiment were extracted using professional techniques and are caffeine-free, which are different from the catechins found in commercially available green tea.
Chih-Ching Yang, the lead author of the paper and a technical supervisor at Taiwan’s Ministry of Health and Welfare, stated that there have been many confirmed cases of COVID-19 despite the affected individuals having received two vaccine doses. The hope is that consuming catechins can enhance immunity and resistance against the SARS-CoV-2 virus.
Tea Leaves Rich in Vitamins and Minerals Enhance Immunity
Sean Lin, an American virology expert and former director of the Virology Department at the U.S. Army Research Institute, mentioned on the Health 1+1 program that findings from laboratory experiments involving tea leaves may not necessarily reflect the actual effects of drinking tea. Nevertheless, tea leaves are rich in nutrients and offer substantial support for everyday health and immune enhancement.Choosing Between Black Tea, Green Tea
Black tea and green tea contain different types of tea polyphenols, all of which possess antiviral properties. So which type should you opt for? Lin Gui, a traditional Chinese medicine practitioner from Taiwan, said in an article that according to traditional Chinese medicine, tea leaves are considered to have cooling properties. However, the tea-making process, which includes roasting and oxidation, can alter their nature. Green tea, having not undergone oxidation, tends to have a cooling nature, whereas black tea, having undergone oxidation, exhibits a warmer nature.Individuals with a “hot” body constitution, such as those who often experience dry mouth, mouth bitterness, and constipation, and are prone to acne, are well-suited for consuming green tea, Ms. Lin said. Conversely, those with a cool body constitution, such as those who frequently have cold extremities, are sensitive to cold winds, and experience loose stools, are better suited for drinking black tea. It’s important to note that women should avoid excessive consumption of green tea during their menstrual period.
