Experimental studies have revealed that green tea catechins and theanine prevent influenza infection, while the clinical evidence has been inconclusive. Keiji Matsumoto, of the Department of Drug Evaluation & Informatics at the University of Shizuoka in Japan, and colleagues undertook a study to determine whether taking green tea catechins and theanine can clinically prevent influenza infection.
The researchers conducted a randomized, double-blind, placebo-controlled trial of 200 healthcare workers for five months from Nov. 9, 2009 through April 8, 2010 in three healthcare facilities for the elderly in Higashimurayama, Japan. The catechin/theanine group received capsules including green tea catechins (378 mg/day) and theanine (210 mg/day). The control group received placebo. The primary outcome was the incidence of clinically defined influenza infection. Secondary outcomes were laboratory-confirmed influenza with viral antigen measured by immunochromatographic assay and the time for which the patient was free from clinically defined influenza infection, meaning the period between the start of intervention and the first diagnosis of influenza infection, based on clinically defined influenza infection.
Matsumoto, et al. report that 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 (five 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).
The researchers conclude that among healthcare workers for the elderly, taking green tea catechins and theanine may be effective prophylaxis for influenza infection. Their research was published in BMC Complementary and Alternative Medicine.
Reference: Matsumoto K, Yamada H, Takuma N, Niino H and Sagesaka YM. Effects of Green Tea Catechins and Theanine on Preventing Influenza Infection among Healthcare Workers: A Randomized Controlled Trial. BMC Complementary and Alternative Medicine 2011, 11:15doi:10.1186/1472-6882-11-15