Yuko M Sagesaka, Hiroshi Yamada, Norikata Takuma, Keiji Matsumoto, Hitoshi Niino
Journal: BMC complementary and alternative medicine 2011;11():15
PMID: 21338496
Influenza infection is the main cause of acute respiratory illnesses worldwide with limited prevention and treatment options. Pre-clinical experiments have shown that green tea catechins can prevent influenza infection in vitro, but clinical evidence has not been conclusive. The aim of this randomised, double-blind study was to evaluate the clinical efficacy of two compounds from green tea, catechins and theanine, in preventing influenza infection. 196 participants completed the 5 months study. The incidence of clinically defined influenza infections was significantly lower in the catechin/theanine group than in the placebo group. The incidence of laboratory-confirmed influenza infection was also lower in the catechin/theanine group than in the placebo group, but this difference was not statistically significant. No serious adverse events were observed in either group. The occurrence of mild symptoms, such as bloating and constipation, did not significantly differ between the two groups. The authors concluded that the effectiveness of catechin/theanine in this trial might be underestimated due to methodological limitations and that larger scale randomised trials are needed to confirm the effectiveness of catechin/theanine to prevent laboratory-confirmed influenza infection.
BACKGROUND
Experimental studies have revealed that green tea catechins and theanine prevent influenza infection, while the clinical evidence has been inconclusive. This study was conducted to determine whether taking green tea catechins and theanine can clinically prevent influenza infection.
DESIGN, SETTING, AND PARTICIPANTS
A randomized, double-blind, placebo-controlled trial of 200 healthcare workers conducted for 5 months from November 9, 2009 to April 8, 2010 in three healthcare facilities for the elderly in Higashimurayama, Japan.
INTERVENTIONS
The catechin/theanine group received capsules including green tea catechins (378 mg/day) and theanine (210 mg/day). The control group received placebo.
MAIN OUTCOME MEASURES
The primary outcome was the incidence of clinically defined influenza infection. Secondary outcomes were (1) laboratory-confirmed influenza with viral antigen measured by immunochromatographic assay and (2) the time for which the patient was free from clinically defined influenza infection, i.e., the period between the start of intervention and the first diagnosis of influenza infection, based on clinically defined influenza infection.
RESULTS
Eligible healthcare workers (n = 197) were enrolled and randomly assigned to an intervention; 98 were allocated to receive catechin/theanine capsules and 99 to placebo. The incidence of clinically defined influenza infection was significantly lower in the catechin/theanine group (4 participants; 4.1%) compared with the placebo group (13 participants; 13.1%) (adjusted OR, 0.25; 95% CI, 0.07 to 0.76, P = 0.022). The incidence of laboratory-confirmed influenza infection was also lower in the catechin/theanine group (1 participant; 1.0%) than in the placebo group (5 participants; 5.1%), but this difference was not significant (adjusted OR, 0.17; 95% CI, 0.01 to 1.10; P = 0.112). The time for which the patient was free from clinically defined influenza infection was significantly different between the two groups (adjusted HR, 0.27; 95% CI, 0.09 to 0.84; P = 0.023).
CONCLUSIONS
Among healthcare workers for the elderly, taking green tea catechins and theanine may be effective prophylaxis for influenza infection.
TRIAL REGISTRATION
ClinicalTrials (NCT): NCT01008020.
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