Researchers at Brigham and Women’s Hospital (BWH) have found that drinking certain types of tea containing high concentrations of an amino acid called L-theanine may help strengthen the body’s immune system response when fighting off infection. The findings were first discovered in laboratory cell cultures and then verified in a small human investigation.

“The health benefits of tea have been touted for centuries but no human research has demonstrated an association between tea drinking and immunology,” said lead author Jack Bukowski, MD. “Now we have a new explanation for the medicinal effect of tea. Our data suggest that the amino acid L-theanine may specifically boost the capacity of gamma delta T cells – the body’s first line of defense against infection.”

In the lab, human gamma delta T cells exposed to L-theanine were then mixed with bacteria to simulate an infection. They multiplied up to 10-fold and thus produced high levels of disease-fighting chemicals. In contrast, those cells without L-theanine produced no immune response to the bacterial infection.

Researchers then compared the immune system strength of men and women before and after they started to drink tea. A control group drank coffee instead. The study showed that those people who drank five to six small cups (about 20 ounces) of black tea per day were better equipped to prevent infection.

“Our research suggests that when tea drinkers become exposed germs, some, but not all, may be protected from getting sick,” explained Bukowski. “And, importantly, those who do become ill, may develop a milder infection or disease compared to non-tea drinkers, although further research will be needed to confirm these predicted outcomes.”

L-theanine is found in black, green, oolong and pekoe teas and is also available in supplement form.

Brigham and Women’s Hospital, Apr 21, 2003