The Claim and Our Verdict
- The claim: A Japanese study claims tea can significantly reduce the transmission risks of coronavirus (specifically, SARS-CoV-2 that causes COVID-19).
- The study, undertaken by the team of professor Osam Mazda at Kyoto Prefectural University in Japan, only presents the results of in vitro experiments – experiments conducted in laboratory-controlled environments. Clinical trials are still being conducted and have not finished. Therefore, the study only presents the effects of tea inactivating the coronavirus outside the human body. Preventing infection from the coronavirus inside the human body has not yet been proven.
- The papers authored by Mazda have not been peer-reviewed. Therefore, their credibility has not been widely acknowledged.
- Other research conducted by the team of professor Hisakazu Yano at Nara Medical University in Japan claims that not all kinds of teas have the same capability of inactivating the coronavirus.
- Our ruling: Therefore, we rate the claim as PARTIALLY TRUE.
A Facebook post published May 12, 2021, claims a Japanese study found that tea products, such as bottled tea and tea bags, can significantly reduce the transmission risks of coronavirus and could even kill it.
The post had been shared 29 times, and had received 9 comments and 141 likes or other reactions as of the issuance of this report.
A keyword search found a news article published April 15, 2021, related to the claim. The article claims the study was conducted by the research team of professor Osam Mazda. According to the news article, the study found catechin – a naturally occurring phenol and antioxidant – in tea can quickly and effectively inactivate the coronavirus. The article claims relevant clinical trials are still being conducted and their results will be published later. Early versions of two papers related to this study were published on the preprint server for Biology—BioRxiv. The papers claim the research findings are only based on in vitro experiments – experiments conducted in laboratory-controlled environments. Therefore, the current study findings do not show the effects of teas and their constituents on preventing a coronavirus infection inside the human body. The statement, “teas can significantly reduce the transmission risks of COVID-19 and could even kill the coronavirus,” is inaccurate.
It should be noted, a preprint version of a scholarly or scientific paper is only a manuscript that has not been peer-viewed. Meaning, it has not been evaluated and critiqued by other scholars. Therefore, the credibility of the abovementioned papers has not been widely acknowledged.
Further keyword searches found another study conducted by the research team of professor Hisakazu Yano. A press release published Nov. 25, 2020, claims that Yano’s team conducted in vitro experiments for three kinds of teas and found some of them significantly inactivated the coronavirus. This indicates that not every kind of tea has the same anti-coronavirus effects. The press release adds that the study did not test the anti-coronavirus effect when people drink the teas.
Therefore, we rate the claim as PARTIALLY TRUE.
- Facebook post, May 12, 2021.
- Shokuhin, “Teas can quickly and effectively inactivate coronavirus: professor Mazda at Kyoto Prefectural University of Medicine,” April 16, 2021.
- Kyoto Prefectural University of Medicine, introduction of professor Osam Mazda.
- BioRxiv, “Rapid inactivation in vitro of SARS-CoV-2 in saliva by black tea and green tea,” January 5, 2021.
- BioRxiv, “Significant inactivation of SARS-CoV-2 by a green tea catechin, a catechin-derivative and galloylated theaflavins in vitro,” December 6, 2020.
- ResearchMap, introduction of professor Hisakazu Yano.
- Nara Medical University, “The effect of teas on inactivating coronavirus,” November 25, 2020.
- BioRxiv, the preprint server for Biology, the website.