Drinking Tea May Boost Immune System

Study provides new theory on health benefits of tea - a cup a day may keep illness away-- by Brigham and Women's Hospital

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. Results from the research appear in the April 21 issue of the Proceedings of the National Academy of Sciences.

"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, PhD of BWH. "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."

A core component of the immune system - gamma delta T cells - have been shown to prevent and minimize the severity of disease. It has also been shown that once introduced to a natural form of L-theanine (commonly found in bacteria, vegetables, wine and tea), the disease-fighting capabilities of gamma delta T cells are enhanced.

Arati Kamath, PhD, study co-author, tested the specific immunologic effect of L-theanine by exposing cultures of human gamma delta T cells to a substance called ethylamine - the body's natural form of the L-theanine. The researchers then stimulated an infection by mixing the cells with bacteria. Once infected, the exposed cells mounted a significantly stronger immune response. The gamma delta T cells with ethylamine multiplied up to 10-fold and thus produced high levels of disease-fighting chemicals. In contrast, those cultures without ethylamime produced no immune response to the bacterial infection. The second step was to replicate this laboratory finding in human subjects.

Because L-theanine is found in black, green, oolong and pekoe teas, the researchers 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. At two weeks, the halfway point of the study, the gamma delta T cells from the tea drinkers, but not the coffee drinkers, showed an enhanced ability to produce disease-fighting chemicals after exposure to bacteria. Specifically, when blood samples were analyzed, the researchers found that the tea drinkers made up to five-fold higher amounts of anti-bacterial proteins - an indicator of a stronger immune response.

"Our research suggests that when tea drinkers become exposed germs, some, but not all, may be protected from getting sick," explained Bukowski, also of Harvard Medical School. "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."

The data were collected from 11 healthy tea drinkers and 10 coffee drinkers who consumed about 600 mL per day of a beverage prepared to their taste. Blood samples were drawn at the onset and at weekly intervals throughout the four-week study.

"This study is an exciting first step in showing that natural substances in common foods like tea, vegetables and fruits can help our body's defense against many types of infection," Bukowski concluded.

BWH is a 725-bed nonprofit teaching affiliate of Harvard Medical School and a founding member of Partners HealthCare System, an integrated health care delivery network. Internationally recognized as a leading academic health care institution, BWH is committed to excellence in patient care, medical research, and the training and education of health care professionals. The hospital's preeminence in all aspects of clinical care is coupled with its strength in medical research. A leading recipient of research grants from the National Institutes of Health, BWH conducts internationally acclaimed clinical, basic and epidemiological studies.


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