Effects of green tea gargling on the prevention of influenza infection in high school students: a randomized controlled study

PLoS One. 2014 May 16;9(5):e96373. doi: 10.1371/journal.pone.0096373. eCollection 2014.


Background: The anti-influenza virus activity of green tea catechins has been demonstrated in experimental studies, but clinical evidence has been inconclusive. School-aged children play an important role in the infection and spread of influenza in the form of school-based outbreaks. Preventing influenza infection among students is essential for reducing the frequency of epidemics and pandemics. As a non-pharmaceutical intervention against infection, gargling is also commonly performed in Asian countries but has not yet been extensively studied.

Methods and findings: A randomized, open label, 2-group parallel study of 757 high school students (15 to 17 years of age) was conducted for 90 days during the influenza epidemic season from December 1st, 2011 to February 28th, 2012, in 6 high schools in Shizuoka Prefecture, Japan. The green tea gargling group gargled 3 times a day with bottled green tea, and the water gargling group did the same with tap water. The water group was restricted from gargling with green tea. The primary outcome measure was the incidence of laboratory-confirmed influenza using immunochromatographic assay for antigen detection. 757 participants were enrolled and 747 participants completed the study (384 in the green tea group and 363 in the water group). Multivariate logistic regression indicated no significant difference in the incidence of laboratory-confirmed influenza between the green tea group (19 participants; 4.9%) and the water group (25 participants; 6.9%) (adjusted OR, 0.69; 95%CI, 0.37 to 1.28; P = 0.24). The main limitation of the study is the adherence rate among high school students was lower than expected.

Conclusions: Among high school students, gargling with green tea three times a day was not significantly more efficacious than gargling with water for the prevention of influenza infection. In order to adequately assess the effectiveness of such gargling, additional large-scale randomized studies are needed.

Trial registration: ClinicalTrials.gov NCT01225770.

Publication types

  • Randomized Controlled Trial
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adolescent
  • Catechin / analysis
  • Catechin / pharmacology*
  • Chromatography, Affinity
  • Humans
  • Influenza, Human / prevention & control*
  • Japan
  • Logistic Models
  • Mouthwashes / pharmacology*
  • Mouthwashes / therapeutic use
  • Odds Ratio
  • Patient Compliance / statistics & numerical data
  • Tea / chemistry*


  • Mouthwashes
  • Tea
  • Catechin

Associated data

  • ClinicalTrials.gov/NCT01225770

Grant support

This work was supported by Grants-in-Aid for Scientific Research (KAKENHI) Grant Number 23590887. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.