Model T

If I reported to you on every article and study I come across that concerns one of the many health benefits of drinking tea, we could change the name of the e-Alert to the tea-Alert. Today, however, I have a new tea study to tell you about that appears to be a genuinely important breakthrough, as well as great news for daily tea drinkers.

Usually when I tell you about something good that tea does for us, the plant compound called flavanoids gets the credit. But for this e-Alert, flavanoids will give up the spotlight to another healthy tea component: an amino acid called L-theanine.



Chain reaction

The current issue of the Proceedings of the National Academy of Sciences carries a study from Harvard Medical School and Brigham and Women’s Hospital in which researchers isolated L-theanine from black tea. (L-theanine is also found in green and oolong tea.)

The researchers hypothesized this brief biology lesson: When L-theanine enters the liver it’s converted to a molecule called ethylamine that helps facilitate the work of gamma-delta T cells. These cells promote the secretion of interferon – an important compound that helps the body fight an assortment of infections: viral, parasitic, fungal, and bacteria. The key word in this paragraph (as we’ll see in a moment) is “interferon.”

Using a group of 21 subjects, researchers took blood samples from all, then had 10 of them drink five cups of coffee each day for four weeks, while 11 drank five cups of black tea each day for the same period. At the end of the test period more blood was drawn from each subject. All of the blood samples were then exposed to E-coli bacteria. In response to the bacteria, the blood cells from the tea drinkers secreted five times the amount of interferon as blood samples taken from the same subjects before the test period. The amount of interferon secreted by the blood samples of the coffee drinkers was the same, both before and after the test.

Larger trials are needed to thoroughly confirm these results, but the Harvard researchers believe that their study offers a reliable indication that a daily intake of five cups of tea each day can significantly help the immune system fight infection.

Chilled out 

This new research is a welcome addition to what we already know about L-theanine. In an HSI Members Alert that we sent you in January 2002 we described L-theanine as a neurologically active amino acid capable of inducing chemical changes in the brain that leave a person feeling alert but relaxed.

Japanese research using human subjects has revealed that L-theanine crosses the blood-brain barrier and induces several distinct chemical changes in the brain that can reduce feelings of stress. Approximately 30 minutes after it’s ingested, L-theanine stimulates production of alpha waves, which can create a feeling of being both alert and deeply relaxed. L-Theanine also stimulates production of gamma aminobutryic acid (GABA), a neurotransmitter that limits nerve cell activity in those areas of the brain associated with anxiety.

At the Laboratory of Nutritional Biochemistry at the University of Shizuoka in Japan, researchers found that L-theanine also “significantly increased” tryptophan, an amino acid that is the basis of serotonin. As most HSI members I’m sure will know, serotonin is a mood-altering brain chemical, essential in creating a feeling of well-being and relaxation, and may help alleviate symptoms of clinical depression.

Don’t go there

But amazingly, after fighting infection, reducing anxiety and relieving depression, L-theanine is still not done providing health benefits.

In another study conducted at the University of Shizuoka (this one in the School of Pharmaceutical Sciences), researchers found that L-theanine may increase the capabilities of a mainstream anticancer drug called Doxorubicin (DOX), which is used to treat tumors. Doctors found that adding L-theanine to the treatment boosted the potency of DOX by preventing the drug from flowing out of the tumor cells. This allowed DOX to be active longer and potentially destroy more cancer cells. This study was conducted with lab animals, so more research is needed, but it provides a very promising indication that the full benefits of L-theanine are still being uncovered.

The authors of the Harvard study on the immune system strengths of L-theanine said they hope their research might lead to the development of a L-theanine based pharmaceutical. And if they’re determined to go down that road, I’m sure we can’t stop them. But in the meantime, they’ve already given away their secret: five cups of tea daily may provide immeasurable benefits throughout your body.

I’ll pass on the drugs, thanks, but I think I would like another cup of tea.

To Your Good Health,

Jenny Thompson
Health Sciences Institute

“Antigens in Tea-Beverage Prime Human (note: greek characters are in the name of this description of T cells – but they don’t translate into HTML so you can’t see them) T Cells In Vitro and In Vivo for Memory and Nonmemory Antibacterial Cytokine Responses” Proceedings of the National Academy of Sciences, V. 100, No. 10, 6009-6014, 5/13/03,
“A Cup of Tea May Be Germs’ New Enemy – Study Finds Tea Sharpens Body’s Defense Against Infection” Associated Press, 4/22/03,
“Tea is Good for You” Health 24, 5/15/03,