Researchers reviewed six random control trials (RCTs) and four prospective cohort studies to evaluate the evidence supporting the effectiveness of tea gargling and tea catechin consumption in preventing viral respiratory infections.
They explain that catechins (or flavanols) present in green tea inhibit the proliferation of viruses in the upper respiratory tract (URT) by forming a protective barrier in the pharynx.
On flavanol in particular, epigallocatechin gallate (EGCg), has a direct anti-viral effect and physically binds to and flushes out viruses in the URT.
“EGCg and epigallocatechin (EGC) bind to the hemagglutinin spike on the viral surface and neuraminidase to inhibit attachment of the virus to the cell surface, thereby preventing influenza infection,” the research team states.
“Given the evidence that EGCg, a main component of tea catechins, provides effective protection against influenza virus and adenovirus, it may also protect against respiratory infections caused by other viruses.”
Natural interventions
Interest in non-pharmaceutical interventions (NPIs) that may slow or prevent the spread of infectious disease has increased due to recent pandemics involving influenza, severe acute respiratory syndrome-coronavirus (SARS-CoV), and COVID-19.
Measures that can reduce their impact and severity in the early stages is deemed key in the fight against infection.
There is considerable research on the efficacy of NPIs, such as hand washing, wearing masks and physical distancing, in reducing the transmission of respiratory infections have been performed, but limited documentary proof supporting the effectiveness of tea gargling and tea catechin, therefore the efficacy of the intervention is “not well accepted”.
One study reviewed by the team demonstrated consumption of catechin capsules reduced the incidence of influenza-like symptoms by 32.1%, and another noted “strong effects” following consumption of large amounts of catechins per day.
Study protocol
Review literature was sourced from PubMed, Cochrane Library, Web of Science, and Ichushi Web databases. Study material was evaluated for risk of bias and the quality assessed independently.
The cohorts from the four studies were selected from populations with a custom of gurgling black tea and green tea, consumption of black tea and green tea, and those who consumed Goishi tea, a local type of green tea produced in the Kochi prefecture in Japan.
Interventions in the RCTs included data from 3,748 subjections and consumption of either green tea extracts (catechin solution for two RCTs, and catechin-containing capsules for two RCTs) or bottled green tea (two RCTs), with placebo (four RCTs) or water (two RCTs) as the control group.
Five of the RCTs were conducted in Japan and one in the US.
Review findings
Preventive effects identified in the present study likely derive from the effects of tea or tea catechins, the authors say. Furthermore, some of the studies provided clear descriptions regarding the amounts of tea catechin consumed, which allowed them to conduct a meta-analysis on the dose-dependency of the catechin effect. This revealed a significant correlation between the risk ratio and the total daily amount of catechins consumed.
“Specifically, the larger the amount of daily catechin consumption, the stronger the preventive effect against the spread of viral respiratory infection. Furthermore, as reported by Furushima et al., drinking a tea catechin-containing drink three times a day (high-catechin group) had a stronger preventive effect than drinking it once a day.”
Review findings are consistent with previous meta-analysis and confirm the robustness of the study. They suggest tea gargling and tea catechin consumption presents a relatively easy and effective way to inhibit the spread of viral respiratory infections.
The authors conclude that: “Incorporating tea catechin consumption and/or tea gargling into the daily routine may be effective NPIs for preventing viral respiratory infections”.
Source: European Journal of Nutrition
Published online: doi.org/10.1007/s00394-021-02681-2
‘Preventive effects of tea and tea catechins against influenza and acute upper respiratory tract infections: a systematic review and meta‑analysis’
Mai Umeda, Takeichiro Tominaga, Kazuya Kozuma, Hidefumi Kitazawa, Daisuke Furushima, Masanobu Hibi, Hiroshi Yamada