People around the world have been drinking tea for thousands of years. Today, scientific research is showing what ancient cultures may have already known - that tea may have several health benefits. Among these is the ability to help the immune system fight infection. Results from a recent study in the Proceedings of the National Academy of Sciences strengthen scientist's understanding of how tea may enhance immunity.

Comparing tea drinkers with coffee drinkers

Researchers from Harvard University in Boston compared specific aspects of immune function in tea drinkers with those in non-tea drinkers. All of the study participants were healthy adults who were non-tea drinkers prior to the study. Eleven participants were asked to drink five to six cups of black tea (steeped for five minutes) per day for either 2 or 4 weeks; ten other participants were asked to drink five to six cups of instant coffee per day.

The participants' blood was drawn before the study's start and then every week during the test period. The blood samples were analyzed for activity of specific cells related to immune function. Two weeks into the study, 7 of the 11 tea drinkers showed an enhanced immune response, whereas only 1 of 10 coffee drinkers showed the same response.

How it may work

The researchers theorize that a substance in brewed tea called L-theanine may be involved in tea's ability to affect immune function.

How does this affect you?

It must be remembered that the scientists were examining chemical reactions in blood samples; the volunteers did not report fewer illnesses or colds. And, while the results of this study are interesting and will likely spur further research, they are preliminary, particularly because the number of subjects studied was so small. Also remember that the subjects drank five to six cups of tea per day, and it's not known if just one or two cups a day would have a similar effect. Finally, the results of this study apply to black tea only, and cannot be extended to green tea or herbal tea.

The bottom line: Enjoy tea as part of an overall healthful diet. But if you if you think you have an infection, don't forego a trip to the doctor for a pot of tea.