Effects of green tea gargling on the prevention of influenza infection in high school students: A randomized-controlled study Kazuki Ide1, Hiroshi Yamada1, Miki Ito1, Kumi Matsushita2, Kei Nojiri1, Kiichiro Toyoizumi1, Keiji Matsumoto1, and Yoichi Sameshima3 1: Grad. Sch. Pharm. Sci., Univ. Shizuoka, 52-1 Yada, Suruga-ku, Shizuoka 422-8526, Japan 2: Kikugawa General Hospital, 1632 Higashiyokoji, Kikugawa, 439-0022, Japan 3: Omaezaki Municipal Hospital, 2060 Ikeshinden, Omaezaki, 437-1696, Japan Correspondent email: [email protected] Summary A randomized-controlled study among high school students was carried out during the influenza epidemic season form December 1st, 2011 to February 28th, 2012. The incidence of clinically-defined influenza was lower in the green tea gargling group (13.5%) in the Full analysis set (FAS) population, 13.8% in the Per protocol set (PPS) population based on adherence rate >75%) than in the water group (16.8% in the FAS population, and 18.4% in the PPS population). However this difference was not significant in multivariate logistic regression analysis, and Cox proportional hazards regression. Additional large-scale randomized-controlled studies with high adherence rate are needed to evaluate the effects of green tea gargling as a preventive measure for influenza infection. Introduction Non-pharmaceutical interventions have an essential role to prevent epidemics and pandemics of influenza added to the pharmaceutical interventions as vaccination and neuraminidase inhibitors. Gargling is one of the common preventive measures in Asian countries, and several experimental studies have shown that anti influenza virus activities of green tea components in vitro (Nakayama, et al. 1993; Steinmann, et al. 2013). However, the effect of green tea gargling on the prevention of influenza infection has been inconclusive. Based on this background, we conducted a randomized-controlled study to evaluate the clinical efficacy of green tea gargling on the prevention of influenza infection among high school students in Japan. Materials and methods A randomized, open label, 2-group parallel study was conducted to evaluate the efficacy of green tea gargling for 90 days during an epidemic season, from December 1st, 2011 to February 28th, 2012. We recruited 2,838 students who attended 6 high schools in Kakegawa and Ogasa district of Shizuoka. Written informed consent was obtained from the participants and their guardians. Participants in the green tea gargling group were provided bottled green tea (500 mL) containing approximately 37 mg/dL total catechins, including 18% of (-)-epigallocatechin gallate (EGCG) manufactured by Kakegawa Tea Merchants Association. Participants in the water gargling group were asked to gargle with tap water and not to gargle with green tea during the study. Participants in both green tea and water group also asked to gargle 3 times a day (after arriving at school, after lunch, and after school). The primary outcome was incidence of the laboratory-confirmed influenza infection with viral antigen detected by immunochromatographic assay. The secondary outcomes were (1) incidence of clinically-defined influenza infection specified as fever (≥ 37.8 ºC) and any 2 of following additional symptoms: cough, sore throat, headache, or myalgia, and (2) the time for which the participants was free from clinically defined influenza infection. The FAS and PPS population were used for all efficacy analysis, and safety analysis was performed for the FAS population. The comparison of overall incidence and cumulative incidence rate of influenza infection between the two groups were determined by Kaplan-Meier method, and Cox proportional hazards regression model was also 1 used. P < 0.05 was considered statistically significant. All statistical analysis was performed using SPSS for Windows, version 21.0 (IBM Corp., Armonk, NY). Results and discussion Among 6 high schools, 757 students gave written informed consent and assessed for eligibility. All of them were enrolled and randomly assigned to an intervention; 387 were allocated to the green tea group and 370 were allocated to the water gargling group. After assignment, 10 of them were withdrawn from the study. The baseline characteristics of the participants were well balanced, except for type of clubs (sport- or culture-related). Therefore, type of club was considered as a confounding variable in multivariate analysis. In addition, vaccination was also considered as an independent variable because of its medical implications. In the FAS and PPS population, there was no difference between the green tea and water gargling groups in the incidence of laboratory-confirmed influenza infection. The incidence of clinically-defined influenza infection was lower in the green tea gargling group (13.5% in the FAS population, 13.8% in the PPS population) than in the water group (16.8% in the FAS population, and 18.4% in the PPS population). However this difference was not significant in multiple logistic regression analysis and Cox proportional hazards regression. No adverse events were observed in the participants of either group during the study. This randomized-controlled study was conducted to evaluate the efficacy of green tea gargling in preventing influenza infection. While several experimental and clinical studies (Yamada, et al. 2006) had shown the effects of green tea components on the prevention of influenza infection, this study of a 90-day green tea gargling intervention among high school students did not show a significant effect compared with water gargling. There are several limitations to this study. One limitation is baseline green tea consumption. Over 70% of the participants in both groups drink green tea on a daily basis (≥ 200 mL/day). Based on our previous observational study among elementary school students (Park, et al. 2011), regular green tea consumption might affect the rate of influenza infection. Adherence rate may also have affected the results of this study. The non-adherence in the FAS population was 29%, and if the study could be made larger, it may be possible to detect a significant efficacy of green tea gargling. Additional large-scale randomized-controlled studies with high adherence rate are needed to evaluate the effects of green tea gargling as a preventive measure for influenza infection. Acknowledgements We gratefully acknowledge the students who participated in the study, and teaching staffs at the Kakegawa Nishi High School, Kakegawa Higashi High School, Kakegawa Technical High School, Yokosuka High School, Ogasa High School, and Ikeshinden High School for their dedicated cooperation. This work was supported by Grants-in-Aid for Scientific Research (KAKENHI) Grant Number 23590887. References Nakayama, M., Suzuki, K., Toda, M., Okubo, S., Hara, Y., Shimamura, T. (1993) Inhibition of the infectivity of influenza virus by tea polyphenols. Antiviral Res. 21: 289-299. Steinmann, J.B., Buer, J., Pietschmann, T., Steinmann, E. (2013) Anti-infective properties of epigallocatechin-3-gallate (EGCG), a component of green tea. Br. J. Pharmacol. 168: 1059-1073. Yamada, H., Takuma, N., Daimon, T., Hara, Y. (2006) Gargling with tea catechin extracts for the prevention of influenza infection in elderly nursing home residents. J. Altern. Complement. Med. 12: 669-672. Park, M., Yamada, H., Matsushita, K., Kaji, S., Goto, T., Okada, Y., Kosuge, K., Kitagawa, T. (2011) Green tea consumption is inversely associated with the incidence of influenza infection among schoolchildren in a tea plantation area in Japan. J. Nutr. 141: 1862-1870. 2 .