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Japanese researchers set out to explore various foods and ingredients that may inactivate the strain of SARS-CoV-2 responsible for COVID-19.
By Ellen Wan
As COVID-19 mutates over time, variants and sub-variants different from the original SARS-CoV-2 virus emerge. A recent study, conducted in Japan, found that green tea (Japanese sencha), matcha, and black tea can effectively inactivate certain Omicron subvariants. In addition, saliva produced after consuming candy containing green tea or black tea exhibited virus-inactivating properties in vitro, rendering the virus less contagious.
The COVID-19 virus 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. A previous study they conducted found that polyphenols found in green tea or black tea reduced the infectivity of the virus in human saliva in vitro, demonstrating virus-inactivating properties. The polyphenols in tea can bind to the spike protein of the virus, preventing it from infecting cells.
The research team published their 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 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 non-infected 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 decreased to less than one 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 were not 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 μM 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, and when used to treat cells, it does not induce anti-virus effects in the cells.
The research team had previously suggested that holding tea in the mouth for 10 seconds before swallowing it while dining in a restaurant could temporarily inactivate the virus in saliva, potentially reducing the risk of droplet transmission and group infections. However, the research team also pointed out that despite the high levels of catechins in tea leaves, it is challenging for them to enter the bloodstream and exert their effects throughout the entire body.
Catechins Inhibit Virus Replication
In addition to binding to the virus’s spike protein and rendering it non-infectious, 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, potentiate adaptive immunity, and improve acute lung injuries.
Chiang-Ting Chien, the founding dean and a distinguished professor of the School of Life Science at National Taiwan Normal University, along with the research team, noted that when the catechins concentration reaches over 195 micrograms per milliliter, it can inhibit an enzyme associated with virus replication and infection. Data from human consumption of catechins also showed that immune-related CD8+ T cells can maintain peak levels for 4 to 5 hours. For an adult weighing 50 kilograms, daily intake of a total of 2.5 grams of the catechins, divided into 2 to 3 doses, can produce sufficient concentration in the bloodstream, potentially inhibiting coronavirus replication in the human body.
Mr. Chien also pointed out that while drinking green tea can provide catechin intake, the dosage might not be sufficient to inhibit the virus. 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 the technical supervisor at Taiwan’s Ministry of Health and Welfare, stated that during the SARS-CoV-2 pandemic, there have been many confirmed cases despite receiving two vaccine doses. They hope that consuming catechins can enhance immunity and resistance against the COVID-19 virus.
Additionally, EGCG exhibits inhibitory effects on various viruses. The British Journal of Pharmacology has compiled a list of viruses that EGCG can inhibit, including HIV, hepatitis B, and influenza viruses, among others.
Enhance Immunity With Tea Leaves Rich in Vitamins and Minerals
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 in vitro 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.
Lin pointed out that tea leaves contain key immune-boosting nutrients. Vitamin A protects respiratory mucous membranes and prevents infections. Vitamin C stimulates the production of antibodies and immune cells. Vitamin D regulates proteins that combat pathogens and possesses anti-inflammatory properties. Vitamin E helps maintain cell membrane integrity. Iron supports the production of enzymes that enhance immune cells, while zinc plays a role in supporting the immune response. During a pandemic, supplementing these nutrients appropriately can enhance immune function.
Choosing Between Black Tea and Green Tea
Black tea and green tea contain different types of tea polyphenols, all of which possess antiviral properties. So which one 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.
Ms. Lin explained that individuals with a “heaty” body constitution, such as those who often experience dry mouth, mouth bitterness, constipation, and are prone to acne, are well-suited for consuming green tea. Conversely, those with a cool body constitution, like those who frequently have cold extremities, are sensitive to cold winds, and experience loose stools, are better suited for drinking black tea. It is important to note that women should avoid excessive consumption of green tea during their menstrual period.
Vietnamese American Conservative Alliance (VACA)
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