About two hundred health care workers in three different healthcare facilities in Japan were randomized to receive either a placebo or a combination of green tea catechins and theanine that contained 378 mg/day of catechins and 210 mg/day of theanine, both constituents found in green tea.
Of these eligible health care workers, 98 received the green tea and 99 received the placebo. The incidence of clinical signs and symptoms of influenza infection was significantly lower in the green tea (4.1%) group compared with the placebo group (13.1%).
The catechins and theanine in green tea have shown previous promise as a strategy for preventing influenza infections. In the laboratory, experiments have shown that green tea catechins can prevent influenza infection. A small study was then done that reported that gargling with tea catechins extracts was effective in preventing influenza infection in the elderly individuals in nursing homes. Green tea extracts have also been shown to enhance systemic immunity and prevent upper respiratory infections and influenza symptoms in adults. Based on this preliminary research, the more substantial randomized, double-blind study was done on the effectiveness of green tea catechins and theanine in preventing influenza infections. This is an extremely useful, simple, safe method of reducing the incidence of influenza. I will be advising my patients to take a standardized extract of green tea capsule regularly and/or drinking green tea liberally, especially during flu season.
Matsumoto K, Yamada H, Takuma N, et al. Effects of green tea catechins and theanine on preventing influenza infection among healthcare workers: a randomized controlled trial. BMC Complementary and Alternative Medicine 2011; 11:15